CALIFORNIA DIPT, OF PUBLIC HEALTH 
TRICHINOSIS PROBLEM IN CALIFORNIA Trichinosis Problem 
IN CALIFORNIA 
Report of a Survey 
1940-1941 
K. B. Kerr, Sc. D., 
Zoologist 
STATE OF CALIFORNIA 
DEPARTMENT OF PUBLIC HEALTH 
IN COOPERATION WITH THE 
U. S. PUBLIC HEALTH SERVICE 
10687 
printed in California state printing office 
SACRAMENTO. 1042 GEORGE H. MOORE, STATE PRINTER TABLE OF CONTENTS 
Scope of Survey 7 
Causative Organism 8 
Symptoms 9 
Incidence in California 11 
Laboratory Methods 11 
Incidence of Infection in Swine 13 
Garbage Feeding 14 
Slaughter-house Sampling 15 
Classification of Specimens 16 
Incidence of Infection in Slaughtered Swine 17 
Incidence in Swine of the United States 18 
Classification of Swine Specimens to Intensity of Infection and Type of Food 19 
Incidence in Swine at Institutions 20 
Grain and Raw Garbage Feeding 23 
Trichina Infection in Market Pork Products 25 
Types of Pork Products Infected 27 
Distribution of Infected Pork Products By Areas 28 
Trichina Infection in Man 29 
Distribution of Cases 1930 to 1940 30 
Distribution by Counties 1930 to 1940 31 
Classification by Sources 1930 to 1940 32 
General Discussion 33 
Summary 35 
Bibliography 36 
Page 
MAPS 
Map Showing Sources of Swine Slaughtered in California 13 
Map Showing Distribution by Counties of Trichinosis, Case Rate Per 100,000, 
1930 Through 1940 Based on Estimated 1935 Population 31 
TABLES 
Table I Showing the Proportion in Which Swine Diaphragms Were Taken 
Prom a Single Lot of Hogs Traceable to One Ranch 15 
Table II Showing the Incidence of Trichina Infection in Swine Slaughtered in 
California 17 
Table 111 Showing the Number of Ranches from Which Swine Specimens Were 
Secured and the Number of These That Produced Trichinous Swine 18 
Table IV Classification of the Infected Swine Specimens According to the Inten- 
sity of Infection and the Type of Food the Swine Received 19 
Table V Showing the Incidence of Trichina Infection in Various Pork Products 
Purchased on the Retail Market 26 
Table VI Showing the Types of Pork Products Infected and the Degree of 
Infection in Each Type 27 
Table VII Showing the Distribution of the Pork Products According to Area 
and the Incidence Found in Each Area 28 
Table VIII Showing the Proportion of Pork Products Produced in the Region 
in Which They Were Purchased and the Proportion Produced in Other 
Regions 28 
Table IX Showing the Number and Per Cent Positive of Human Diaphragms 
in Relation to the Type of Population 29 
Table X Showing the Trichinosis Case Rate in California and in the Three 
Subdivisions for the Eleven Year Period, 1930 Through 1940 30 
Table XI Showing the Broad Classification of the Reported Sources of Infec- 
tion of Cases of Trichinosis in California According to the Year in Which 
They Occurred 32 FOREWORD 
The author wishes to express his appreciation to Surgeon L. B. 
Byington and Medical Director N. E. Wayson, Medical Officers in 
Charge, Plague Suppressive Measures Laboratory, U. S. P. 11. S., for 
their cooperation in providing office and laboratory space for conduct- 
ing this work. Thanks are also due to the staff of the survey, who, 
through their cooperation, made it possible for the work to be carried 
out smoothly. Mention should also be made of the cooperation of the 
meat packing industry of the State which willingly supplied ns with 
data and assisted us in procuring specimens. 
The epidemiological data were supplied by Miss I. M. Stevens, 
Supervising Morbidity Statistician. Her generous cooperation in this 
and other matters is much appreciated. 
Several other members of the State Department of Public Ilealtli 
have assisted in the preparation of the manuscript. Their able assist- 
ance has greatly facilitated its preparation and thanks are due them. Trichinosis Problem in California 
Health authorities in California have been aware for a number of 
years that trichinosis is relatively more common in the State than in a 
number of other States. Since there is no known treatment, drug or 
otherwise, which will destroy the parasite causing the disease, it is 
imperative that methods be developed to prevent its occurrence. In 
order to have available the factual data basic to the development of 
such methods, the State Board of Public Health directed the institution 
of a survey of the problem. The survey was specifically charged with 
determining the role of the garbage fed hog in the problem, the impor- 
tance of rodents as agents of infection in the hog, the frequency with 
which the parasite occurs in pork products, the study of the epidemio- 
logical aspects of the disease, and to cooperate with the medical pro- 
fession with regard to the use of the trichina intradermal and precipitin 
reaction in diagnosing infections with the parasite. The results of this 
work are herein reported. 
A discussion of the organism which causes trichinosis and its life 
cycle is basic to understanding the problem and the methods by which 
it might be controlled. The disease is caused by a small parasitic 
nematode or round worm known as Trichinella spiralis. The adult 
worms are most commonly found in the small intestine. Their size 
depends on their sex; female worms are 3-4 mm. in length and about 
100 microns in diameter; male worms are 1.4-1.6 mm. in length and 
40-50 microns in diameter. The infective larvae are found in the stri- 
ated or voluntary muscle of the same host in which adults occur. These 
larvae are about 1 mm. in length. 
Natural infections with the parasite have been found in many car- 
nivorous and omnivorous mammals. Chickens and other birds have never 
been found infected under natural conditions; however, certain birds have 
been experimentally infected. The larvae do not always develop in a 
normal manner in these. No infections of cold-blooded animals have 
ever been reported. Therefore, as far as man is concerned, trichinous 
meat from mammals, and in particular, pork, is the source of infection. 
The life cycle of Trichinella spiralis, or trichina as the worm is 
commonly known, is as follows. Upon the ingestion of meat containing 
infective larvae, the capsule surrounding the larva is digested off by 
the action of gastric juice and the young worm is liberated. These 
then pass into the small intestine where they undergo further develop- 
ment. In this location the sexes develop to maturity, usually within 72 8 
TRICHINOSIS PROBLEM IN CALIFORNIA 
hours, and mate promptly. The female Avorras then burrow into the 
mucosa or lining of the intestine and start to discharge living young 
Avithin six to seven days after infection. Larval production may con- 
tinue for six or more weeks. 
At birth the young larvae are about 100 microns in length and 6 
microns in diameter. They migrate from the female worm into the 
lymph spaces and are carried passively by the lymph fIoAV, through 
the thoracic duct, into the venous circulation and thence to the right 
heart. After attaining the arterial circulation by way of the pulmo- 
nary capillaries, the larvae are carried to the voluntary muscles. 
Larvae are most numerous in the blood stream from the eighth to 
twenty-fifth day after infection. They may begin to penetrate the 
muscles as early as the ninth to tenth day after infection, but are 
extremely difficult to find before the fifteenth day. This is due to their 
small size and to the fact that relatively few worms have reached the 
muscles prior to this time. 
In the voluntary muscles the larvae penetrate the fibers and 
undergo rapid growth in the substance of the fibers. Ten days to two 
weeks after penetration of the fibers, the larvae reach a length of 
approximately 1 mm. and become spirally coiled, at which time they 
have reached the infective stage. This stage may be reached as early as 
21 days after infection. The presence of the worms in the muscle 
fibers causes marked degenerative changes resulting in the formation 
of a membranous capsule or cyst about the larva, so that typical REPORT OF 1940-1941 SURVEY 
9 
encysted larvae are found about six weeks after infection. The cysts 
usually contain a single larva, but two or more larvae have been seen 
within a cyst. The deposition of calcium about the cyst wall begins in 
eight to 10 months. Complete calcification may not occur for several 
years. The larvae may remain alive for several years. When they die 
they may disintegrate or they may become calcified. 
Wright and Brady (1) give a concise description of the symptoma- 
tology of trichinosis. This description is quoted below. 
“The symptoms of trichinosis are very diverse and may affect any 
system of the body with the possible exception of the reproductive 
system. The intensity of the disease is extremely variable and is 
dependent for the most part on the degree of infection and the resist- 
ance of the individual. Thus, one may encounter all gradations of 
symptoms ranging from a mild, almost subclinical syndrome to those 
characterizing a severe fulminating fatal infection. Because of this, 
it is not surprising that all cases of the diseases are not readily recog- 
nized and the symptoms are sometimes confused with those of half a 
hundred other diseases which they may simulate. 
“In some cases, the initial response to infection is referable to the 
gastro-intestinal tract and is manifested by nausea, vomiting and 
diarrhea. These symptoms may be noted as early as 24 to 48 hours 
after the ingestion of trichinons meat. Occasionally, they appear later. 
Many cases of trichinosis show no gastro-intestinal symptoms; such 
symptoms are most likely to be encountered in severe infections. The 
fever in most cases is irregular with a peak of about 103° F. However, 
there are recorded cases in which the temperature has gone higher with 
a plateau typhoid-like curve or with the intermittent septic type of 
temperature. The fever usually subsides by lysis during convalescence. 
“A persistent edema of the face may appear about the ninth or 
tenth day of illness. This edema is most apparent in the suborbital 
tissue and may also involve the conjunetivae with bulbar chemosis. 
The patient may complain of photophobia. Edema in other parts of 
the body, particularly the dependent portions, may occur later in the 
course of the disease. 
“Muscle tenderness and soreness are frequently present. Pain is 
evidenced mostly on movement of the muscles. The myalgia is fre- 
quently most pronounced in the larger muscle masses such as those 
of the thighs, calves, shoulders and back. However, mastication and 
deglutition may be painful and marked involvement of the diaphragm 
and intercostals may lead to respiratory difficulties. The tenderness 
and pain usually reach their height four to six weeks after onset and 
may not completely subside until a year or two after acute illness. 
“Petechiae and ecchymoses may occur subcutaneously in various 
parts of the body. Subungual splinter hemorrhages are said to be a 10 
TRICHINOSIS PROBLEM IN CALIFORNIA 
diagnostic feature but occur only in a relatively small proportion of 
the cases. There may be an annoying pruritis with or without skin 
lesions. 
“Electrocardiograph studies indicate that myocardial damage 
may occur during the acute phase of illness due to the passage of large 
numbers of larvae through the heart muscle. Not infrequently there 
is involvement of the central nervous system due to the invasion of the 
larvae with a resulting clinical syndrome which may simulate closely 
that of encephalitis, meningitis, or myelitis. The passage of the larvae 
through the lungs may result in severe congestion which may be fol- 
lowed by bronchopneumonia with fatal termination in the fifth or sixth 
week of illness. The urine may show a slight amount of albumin and 
contain casts. 
“The acute phase of the disease usually subsides in about six to 
eight weeks. However, symptoms of muscle pain and tenderness and 
inordinate fatigue may incapacitate the patient for months and persist 
for a year or more. ’ ’ 
SYMPTOMATOLOGY 
cy. Time of onset 
S after infection 
Location of 
parasites 
Symptoms which 
may he exhibited 
Sometimes 
tentatively 
diagnosed as: 
(Typhoid Fever 
Food Poisoning 
Intestinal Influenza 
Colitis 
Appendicitis 
Larvae and 
Adults in 
Intestinal 
Lumen and 
Villi 
I Nausea 
Vomiting 
Diarrhea 
Constipation 
Abdominal Pain 
Enteral 24 to 72 hours 
Bosinophilia 
Irregular 
Hyperpyrexia 
Edema (Especially 
Suhorbital) 
Conjunctivitis 
(Photophobia 
Myalgia 
Sore Throat 
i Dyspnoea 
'Cough 
Scarlatiniform Rash 
Rose Spots 
Urticaria 
Pleurisy 
Pneumonia 
Arthritis 
Rheumatism 
Upper Respiratory 
Infection 
Laryngitis 
I Conjunctivitis 
Influenza 
Intercostal Neuritis 
Measles 
Frontal Sinusitis 
Asthma 
Pleurisy 
Pneumonia 
Larvae in 
Blood Stream 
and Muscles 
Parenteral after 
4 to 5 days 
( Chest Pain 
) Tachycardia 
\ Apical Murmurs 
I Dicrotic Pulse 
! Myocarditis 
Endocarditis 
[ Larvae Passing 
I Through Heart 
Larvae in 
Brain and 
Meninges 
I Severe Headache 
Malaise , 
Marked Hyperpyrexia 
Disorientation 
Delirium 
Coma 
I Encephalitis 
1 Meningitis 
I Poliomyelitis REPORT OF 1940-1941 SURVEY 
11 
The above discussion, which is illustrated by chart 1, shows clearly 
the complex picture of trichinosis. It is understandable from this how 
the 50 or more other diseases listed by Hall (2) have been confused 
with trichinosis. It also indicates that the cases reported in the regis- 
tration area are probably not a true index of the extent of the occur- 
rence of the disease. 
The records of the California State Health Department show that 
722 cases of trichinosis have been reported during the past eleven years 
(1930 through 1940), 715 of which originated within the State. This 
is an average annual case rate of 11.3 per 100,000 population (based 
on the estimated 1935 population). Undoubtedly most of these cases 
represent frank, fully developed trichinosis. That a well organized 
health department, upon investigation of reported cases, frequently 
finds more cases is well illustrated by the report of Yener (3) which 
pointed out that the epidemiological investigation of several suspected 
cases revealed 25 cases. However, there is no way of tracing unrecog- 
nized cases or determining the number of these. Therefore, the 
number of reported cases does not represent a true index of the 
prevalence of the disease. Further evidence that infection with 
trichinae is much more common than indicated by the number of 
reported cases is provided by the surveys of necropsy material. 
McNaught and Anderson (4) reported finding an incidence of 24.0 
per cent in 200 human diaphragms from residents of San Francisco. 
Butt & Lapeyre (5) reported an incidence of 18.2 per cent in 170 
human diaphragms from residents of the vicinity of Los Angeles. 
The degree of infection in some of these diaphragms would indicate 
possible clinical trichinosis although no history of such an illness was 
obtainable on any of the infected patients. 
According to the figures presented by Sawitz (6) California 
ranked first in the average annual case rate per million population 
for the seven years, 1930-1936. Sawitz takes care to point out the 
factors which might influence the veracity of his figures, such as, the 
efficiency of the reporting of cases and the consciousness of trichinosis 
on the part of the medical profession in an area. It therefore seems 
justifiable to believe that the disease may be several times more 
prevalent than the number of reported cases would indicate. 
Laboratory Methods 
Various types of specimens were collected for examination for 
trichinae. They were examined by the digestion-Baermann method as 
described by Kerr, Jacobs and Cuvillier (7). This is a standard 
method and is essentially a digestion of the specimen in artificial 
gastric juice consisting of 5 grams pepsin, 7 cc. concentrated HCI 
in a liter of water, screening off the larger particles, pouring into 12 
TRICHINOSIS PROBLEM IN CALIFORNIA 
settling funnels and examining the sediment for trichinae. In exam- 
ining human diaphragms, the digestion-Baermann method was supple- 
mented by a direct microscopic examination using a press as described 
by Nolan and Bozicevich (8). 
The digestion-Baermann method is very dependable for the detec- 
tion of all infections with living trichinae. Since most swine are 
slaughtered when less than a year old, it was not necessary to use the 
direct microscopic examination which is particularly valuable in the 
detection of infections with dead trichinae. Thus, the data given 
below are not an absolute incidence of infection, but only relative to 
the capabilities of infecting man. 
With regard to the examination of human diaphragms, it was 
desirable to determine as far as possible the absolute incidence oh 
infection. The direct microscopic method was therefore used on these 
specimens as a supplementary method. It was also used on any meat 
specimens suspected of causing a case of trichinosis or on any specimens 
suspected of being subjected to preservatives other than boric acid. 
Specimens which were several days in transit to the laboratory 
were shipped in powdered boric acid. This retarded bacterial decom- 
position but had no effect on the viability of any trichinae contained 
in them. Such specimens were washed thoroughly in running tap 
water to remove all of the boric acid before they were digested. 
In presenting the data the State has been divided into three areas 
which provide a better analysis of the problem. These areas are (1) 
Southern, including Imperial, Kern, Los Angeles, Orange, Riverside, 
San Bernardino, San Diego, San Luis Obispo, Santa Barbara, and 
Ventura counties; (2) Central, including Alameda, Butte, Colusa, 
Contra Costa, Fresno, Glenn, Kings, Lake, Madera, Marin, Mendocino, 
Merced, Monterey, Napa, Sacramento, San Benito, San Francisco, San 
Joaquin, San Mateo, Santa Clara, Santa Cruz, Solano, Sonoma, 
Stanislaus, Sutter, Tehama, Tulare, Yolo, and Yuba counties; (3) 
Northern and Sierra Nevada, including Alpine, Amador, Calaveras, 
Del Norte, El Dorado, Humboldt, Inyo, Lassen, Mariposa, Modoc, 
Mono, Nevada, Placer, Plumas, Shasta, Sierra, Siskiyou, Trinity, and 
Tuolumne counties. 
The first, or southern group of counties, represents that portion 
of the State containing the largest population, mostly urban. It also 
contains a large proportion of arid desert country as well as large 
orchard districts. The second, or central group of counties, is the 
next in population, slightly less than half of which is urban population. 
It also contains the great valley agricultural area. The third, or 
northern and Sierra Nevada group of counties, has the smallest popu- 
lation which is largely rural. This area is predominately mountainous 
although certain portions of it are valuable agricultural districts. REPORT OF 1940-1941 SURVEY 
13 
Incidence of Trichina Infection in Swine 
The well established fact that man most frequently acquires 
infection with trichinae through the consumption of raw or insufficiently 
cooked pork makes necessary a study of pork production and the 
methods whereby swine might acquire an infection. It also requires 
an analysis of the sources of pork marketed in California. 
Insufficient swine are raised in California to supply the demand, 
therefore many head are shipped in from other States for immediate 
slaughter. Map 1 shows the sources of swine slaughtered in California. 
MAP SHOWING SOURCES OF SWINE SLAUGHTERED 
IN CALIFORNIA 
States Supplying Hogs To California 
Listed In Order Of Their Importance~ 
NEBRASKA 
TEXAS 
I DAHO 
COLORADO 
OKLAHOMA 
lOWA 
NEW MEXICO 
UTAH 
MISSOURI 
OREGON 
SOUTH DAKOTA 
KANSAS 
NEVADA 
ARIZONA 
MISCELLANEOUS 14 
TRICHINOSIS PROBLEM IN CALIFORNIA 
The average number of swine slaughtered here for the past 20 years 
is about 1,650,000 of which number only about 650,000 were raised 
within the State. The 1,000,000 imported head are from the following 
States listed in the order of their importance: Nebraska, Texas, Idaho, 
Colorado, Oklahoma, lowa, New Mexico, Utah, Missouri, Oregon, South 
Dakota, Kansas, Nevada, Arizona, and minor shipments from a few 
other States. These shipments are affected by the large middle western 
hog markets, price controlling whether the hogs travel east or west 
for slaughter. Thus, 60 per cent of the swine slaughter in California 
is made up from animals whose history it would be impossible for us 
to obtain except the approximate area from which they originated. 
Interstate shipment being involved, the control of trichinosis in these 
swine should be a Federal problem. This survey, therefore, concerned 
itself primarily with the infection in swine raised in California. It is 
these data which are presented in this section. The diaphragm was 
the muscle used throughout this work. The average size of the speci- 
mens following the removal of the fascia and surplus fat was about 
50 grams. Usually one-half of the diaphragm, including one pillar, 
was taken. 
In order to obtain a representative sample of specimens, a quota 
was set up for the three regions of the State. The proportion of swine 
raised in an area was calculated from the data given by Scott (9) 
and the average number of California swine slaughtered over a period 
of 20 years. A quota of 5,750 specimens from swine which could be 
traced from the slaughterhouse to the ranch on which they were 
raised was arbitrarily set up. This was divided proportionately into 
quotas for the three areas, 1,680 for the southern group of counties, 
8,540 for the central group of counties and 530 for the northern and 
Sierra Nevada group of counties. An attempt was made to rigidly 
adhere to these quotas. However, in the case of the northern and 
Sierra Nevada region, the quota was not attained by 31 specimens. 
More than the quota was obtained for the other regions. 
Garbage feeding of swine is very prevalent in California. The 
survey by Updegraff showed that at least 85 per cent of the cities of 
5,000 or more population in the State dispose of their garbage in whole 
or in part by feeding it to swine. Mr. C. G. Gillespie, Chief of the 
Bureau of Sanitary Engineering of the State Health Department has 
expressed the opinion that garbage feeding of swine could be found 
in California wherever there was sufficient garbage to make it practical 
to feed it. The Federal Bureau of Agricultural Economics in dis- 
cussing the extent of garbage feeding of hogs showed that 246,325 
garbage fed hogs were marketed annually from the 42 California 
counties from which they had received reports. It also showed that REPORT OF 1940-1941 SURVEY 
15 
it was a growing industry in 10 counties, declining in five, and station- 
ary in 29. Judging from these data and those provided by the Federal 
live stock census, it would appear that at least one-third of California 
swine are raised on garbage. Thus a representative yet conservative 
portion of our quota of 5,750 specimens would be 1,900 specimens from 
garbage fed swine. 
The swine specimens were collected by visiting the slaughter- 
houses and determining whether the hogs they purchased could be 
traced from the lot number of the establishment to the farm from 
which they originated. In the case of many of the smaller slaughter- 
houses this was a practical procedure. However, it was not practical 
in the larger establishments since they received many of their hogs 
through stockyards, independent buyers and auction sales so that a 
single lot number represented numerous ranches. The problem of 
tracing hogs from these sources was solved by using tattooing outfits 
and marking each hog at the place it was sold and before it was 
mixed with stock sold by other ranches. It was thus possible to obtain 
a random sample of identifiable specimens. Care was taken to avoid 
repeated sampling from a ranch unless it was a large producer of hogs. 
With regard to the garbage fed hogs, repeated samples were taken more 
frequently because they came from larger ranches and formed a larger 
proportion of the hog production in that particular area. 
Older hogs such as sows, stags, and boars may not be adequately 
represented in our series. Frequently these animals would be killed 
at an entirely different time and perhaps in a different locality than 
the more choice animals. Special trips to slaughterhouses to secure 
specimens from such animals were never made. 
Table 1 shows the proportion in which swine diaphragms were 
taken from lots of various sizes which were traceable to the farm from 
which they originated. Thus, representative samples were secured in 
proportion to the number of swine from a given lot from a given ranch. 
TABLE I 
Showing the Proportion in Which Swine Diaphragms Were Taken From 
a Single Lot of Hogs Traceable to One Ranch 
Number of 
Proportion of 
Maximum number 
hogs in lot 
specimens taken 
specimens taken 
1- 5 
all 
5 
6- 10 
1/2 
5 
11- 25 
1/3 
8 
26- 50 
1/4 
12 
51- 75 
1/5 
15 
76-100 
1/7 
14 
101-150 
1/8 
18 
151-200 
1/9 
22 
over 200 
1/10 
20 plus 16 
TRICHINOSIS PROBLEM IN CALIFORNIA 
The classification of the specimens depended on the inspection of 
the ranch. Inspection of the ranch consisted of interviewing the 
rancher and inspecting the hog pens and food given to the hogs. 
Information relative to the type and abundance of rodents about the 
ranch and vicinity was also obtained. From all of this information 
the specimens were classified in the following feed categories: 
1) Grain, including cull fruits and vegetables from packing houses and 
canneries, forage, tankage, but excluding any possibility of raw meat 
scraps in the diet; 
2) Grain, bought as feeders, the same as (1) except that the farmer 
previously had purchased the hogs from other ranches, whom we were 
unable to trace; 
3) Grain and ranch kitchen scraps, that is, the small amount of gar- 
bage produced at any one of the ranches was fed to the hogs in addition 
to (1) ; 
4) Raw garbage, garbage fed in the condition collected from restau- 
rants, resorts, camps, and households, grain may or may not have been 
fed as a supplementary feed; 
5) Cooked garbage, the same as (3) except that the garbage was sub- 
jected to sufficient cooking to kill trichinae; 
6) histitutional, raw garbage from State, county or city institutions 
which was fed by the personnel of the institution to swine, slaughtered 
by or for the institution, and the resultant pork consumed by the 
inmates of the institution; 
7) Raw offal, offal from farm slaughtered animals fed to swine that 
would otherwise fall into categories (1), (2), or (3) ; 
8) Cooked offal, offal from rural slaughterhouses cooked (frequently 
under State inspection) in open pots or vats and fed to swine. 
The results of the examination of the swine diaphragms are pre- 
sented in table 2. In all, 7,034 specimens were examined, 5,934 of 
which came from swine which were traceable to the ranch on which 
they were last fed. The figures in the grain, grain and ranch kitchen 
scraps and raw garbage groups are the significant figures in this table. 
They show that the frequency of infection in the raw garbage fed hog 
is 12 times that of the grain fed hog. Apparently the small amount of 
garbage originating in the ranch kitchen is a minor factor as a source 
of infection for swine, there being no appreciable difference in the 
incidence for this group and for the grain group. 17 
Geographic divisions 
Southern California 
(10 counties) 
Central California 
(29 counties) 
Northern and Sierra 
Nevada area of California 
(19 counties) 
Total 
Quota of specimens for division 
1,680 
3,540 
530 
5,750 
Type of food received by hog 
Number 
specimens 
examined 
Number 
specimens 
trichinous 
Per cent 
specimens 
trichinous 
Number 
specimens 
examined 
Number 
specimens 
trichinous 
Per cent 
specimens 
trichinous 
Number 
specimens 
examined 
Number 
specimens 
trichinous 
Per cent 
specimens 
trichinous 
Number 
specimens 
examined 
Number 
specimens 
trichinous 
Per cent 
specimens 
trichinous 
Grain _ ... 
485 
6 
11.2 
1,762 
5 
4 0.3 
189 
0 
0.0 
2,436 
11 
9 0.5 
Grain, bought as feeders 
64 
4 
6.3 
195 
0 
0.0 
17 
0 
0.0 
276 
4 
1.4 
Grain and ranch kitchen scraps 
187 
0 
0.0 
758 
2 
0.3 
164 
5 
3.0 
1,109 
7 
0.6 
Raw garbage . . . _ 
1,012 
22 
2 2.2 
616 
78 
612.7 
73 
9 
712.3 
1,701 
109 
10 6.4 
Cooked garbage . . ... 
18 
0 
0.0 
16 
0 
0.0 
2 
0 
0.0 
36 
0 
0.0 
Institutional 
48 
1 
2.1 
152 
0 
0.0 
29 
0 
0.0 
229 
1 
0.4 
Raw offal ..... 
15 
0 
0.0 
21 
3 
14.3 
0 
0 
0.0 
36 
3 
8.3 
Cooked offal.. ... 
3 
0 
0.0 
83 
5 
6.0 
25 
1 
4.0 
111 
6 
5.4 
Totals . _ . 
1,832 
33 
31.8 
3,603 
93 
62.6 
499 
15 
83.0 
5,934 
141 
11 2.4 
B. Specimens not traceable to ranch 
554 
9 
12 0.4 
States other than California _ _ _ ... 
546 
2 
13 0.4 
Grand totals.. .. . . . _ ... 
7,034 
145 
14 2.1 
1 Standard deviation of 1.2% is 0.5 
« 
Standard deviation of 2.6% 
is 0.3 
11 Standard deviation of 2.4% is 0.2 
2 Standard deviation of 2.2% 
is 0.5 
7 
Standard deviation of 12.3% 
is 3.8 
12 Standard deviation of 0.4% is 0.3 
3 Standard deviation of 1.8% is 0.3 
3 
Standard deviation of 3.0% is 0.8 
13 Standard deviation of 0.4% is 0.3 
4 Standard deviation of 0.3% is 0.1 
3 
Standard deviation of 0.5% 
is 0.1 
14 Standard deviation of 2.1% is 0.2 
5 Standard deviation of 12.7% 
is 1.3 
10 
Standard deviation of 6.4% is 0.6 
REPORT OF 1940-1941 SURVEY 
Showing the Incidence of Trichina Infection in Swine Slaughtered in California 
TABLE II 
A. Specimens traceable to ranch 18 
TRICHINOSIS PROBLEM IN CALIFORNIA 
Tlie 5,934 specimens from swine which were traced back to the 
ranch came from 897 ranches. The distribution of these ranches in the 
various feed categories is shown in table 3. It will be noted that 
trichinous specimens were secured from 59 ranches. 
TABLE 111 
Showing the Number of Ranches from Which Swine Specimens Were Secured 
and the Number of These That Produced Trichinous Swine 
Classification 
Number of 
Number of ranches with 
of ranch 
ranches 
trichinous swine 
Grain 
419 
7 
Grain, bought as feeders 
48 
2 
Grain and ranch kitchen 
scrap 240 
O 
Raw garbage 
118 
43 
Cooked garbage _ 
7 
0 
Institutional 
12 
1 
Raw offal 
4 
1 
Cooked offal 
20 
2 
Total 
897 
59 
The only figures available showing the general incidence in swine 
in the United States are those given by Schwartz (12), who found 
an incidence of 0.95 per cent in 13,000 so-called grain fed hogs, and 
5.7 per cent in 10,500 garbage fed hogs. There is no indication in this 
report of the method used in determining the type of food on which 
these hogs were fed. It is stated that the 13,000 specimens were 
obtained from swine “that had been raised on farms and fed forage, 
grain and other feeds, including, in some cases, more or less garbage.” 
It is probable that this group is comparable to our nongarbage fed 
groups, that is, the grain, grain bought as feeders, grain and ranch 
kitchen scraps, raw offal and cooked offal groups. If so, then 3,968 of 
our specimens would be comparable to the so-called grain fed group of 
Schwartz. In these specimens there were found 31 positive specimens, 
an incidence of 0.8 per cent. This figure is not materially different 
from that of Schwartz. Likewise, there is no significant difference 
between the incidences found in the garbage fed hogs. In other words, 
the data presented here indicate that the average situation in California 
is no worse than the average situation in the United States. This is 
also represented in our figures for swine which originated in states 
other than California and California swine which were not traceable 
to the farms, the incidence in these two groups being the same. 
The annual report of the Director, Bureau of Animal Industry to 
the Secretary of Agriculture for 1937 (13) gives an incidence of 3.4 
per cent in 3,876 raw garbage fed swine which came mostly from two 
Pacific Coast States. The difference between this incidence and that REPORT OF I 940-1941 SURVEY 
19 
reported herein is 3.0. The computation of the standard deviation of 
this difference by the formula 4. where•« is the per cent 
\nl'n2 
positive, q the per cent negative, and n the number examined, gives 0.6. 
It therefore appears likely that the difference is statistically significant. 
However, the samples are not entirely comparable because our sample 
originated in only part of the area from which the other sample was 
taken, and therefore the incidence of 3.4 per cent should not be taken 
as being indicative of the situation in California. 
TABLE IV 
Classification of the Infected Swine Specimens According to the Intensity of 
Infection and the Type of Food the Swine Received 
Intensity 
0.0- 
0.09 
0.1- 
0.99 
1.0- 
9.9 
10.0- 
49.9 
50.0- 
99.9 
100.0 
and over 
Total 
Grain 
5 
2 
O 
0 
1 
0 
.11 
Grain, bought as feeders 
0 
2 
0 
1 
1 
0 
4 
Grain and kitchen scraps 
1 
0 
Q 
o 
1 
0 
2 
7 
Raw garbage 
31 
41 
1!) 
5 
4 
9 
109 
Institutional 
1 
0 
0 
0 
0 
0 
1 
Raw offal 
0 
3 
0 
0 
0 
0 
3 
Cooked offal 
0 
1 
2 
1 
2 
0 
0 
California not traced 
o 
0 
0 
0 
0 
0 
2 
Out of State 
0 
1 
0 
0 
0 
1 
2 
— 
— 
— 
— 
— 
— 
— 
Total 
40 
50 
27 
8 
8 
12 
145 
Per cent of total 
27.0 
34.5 
18.6 
5.5 
5.5 
8.3 
100.0 
The classification of the trichinons swine specimens according to 
the type of food the hog received and according to the intensity of the 
infection is shown in table 4. The majority of the infections were light, 
the lightest being one larva in 79 grams of diaphragm muscle. How- 
ever, the intensity of infection ranged up to 2,234 larvae per gram of 
diaphragm muscle. Twenty-seven and six-tenths per cent of the speci- 
mens had fewer than one larva per 10 grams of muscle, and 34.5 per 
cent had more than one larva per 10 grams but fewer than one larva 
per gram of muscle. Thus, 62.1 per cent of the specimens had an 
infection of less than one larva per gram of diaphragm muscle. 
Schwartz found that 70 to 80 per cent of their infected specimens were 
in this same category. We have therefore found a somewhat greater 
proportion of more heavily infected specimens. It is recognized that 
the diaphragm is one of the preferred sites for these parasites and it 
is probable that the rest of the carcass was more lightly infected. This, 
however, does not materially lessen the value of the data as an index 
of the potential hazards of man acquiring an infection from the 
resultant pork. 
A discussion of the source of infection of the swine in the various 
food categories would be helpful in explaining some of the incidences 
found. As a matter of convenience, the grain and raw garbage groups 
will be discussed last. 20 
TRICHINOSIS PROBLEM IN CALIFORNIA 
It is not possible to offer an entirely satisfactory explanation of the 
possible sources of infection in the grain bought as feeders group. 
Although the ranch from which these specimens came fed only grain to 
their swine and therefore the latter remarks about grain fed swine are 
applicable here, the history of these swine previous to the time they 
were moved on to the ranch to which we traced them is not obtainable. 
However, it is improbable that many of these swine were born on 
garbage feeding ranches, since it is more common for the garbage 
ranches to buy feeder pigs than to sell them. 
The grain and ranch kitchen scrap category represents a group of 
swine that get a relatively small amount of garbage, namely that origi- 
nating in the ranch kitchen. The amount of kitchen scraps these swine 
might get would depend on two factors, the number of people eating 
on the ranch, which would determine the amount of garbage available, 
and the number of swine on the ranch. In most cases there would be a 
very small amount of garbage per hog. Furthermore, meat scraps in 
such garbage are frequently separated from the rest of the scraps and 
fed to the dogs and cats on the place. Thus, in our experience it would 
be the exception rather than the rule that hogs in this category would 
have access to meat scraps. This does not eliminate the possibility of 
infection occurring in this manner, but rather indicates that the factors 
affecting the grain fed swine are chiefly operative here. 
It Avas rather difficult to e\Taluate the hazard in the institutional 
group. The most constant factor was that in the institutions established 
for a longer period of time, the entire supply of fresh pork Avas derived 
from their oaaui herds. With one exception, the institutions raised all 
of their own hogs and Avith one exception they fed only garbage from 
their oavu institution. About one-third of the institutions supplemented 
their fresh pork supply by purchasing ham and bacon in the open 
market. In handling the meat it was the general practice to trim it 
for cooking in the institution’s butcher shop. The meat scraps from 
the shop were all rendered for grease. In no case was offal from the 
kill fed to the hogs. Therefore the opportunities for infection of the 
herds A\7ould come almost entirely from inadequate cooking of the pork 
in the institution’s kitchens, such scraps reaching the hogs in the 
garbage from the tables. It would appear that this occurs, since one 
trichinous specimen AA7as found. This specimen came from the institu- 
tion AArhich Avas feeding its oaaoi as Avell as garbage from another insti- 
tution. The second institution purchased its entire pork supply on the 
open market. 
The feeding of raw offal from a slaughterhouse is illegal in Cali- 
fornia. therefore, the specimens in this category only received offal 
from the occasionally slaughtered farm animal. The three trichinous REPORT OF 1940-1941 SURVEY 
21 
specimens in this group came from one ranch which was concerned in 
an outbreak of trichinosis and the findings served to conclusively point 
to the source of the outbreak. 
The positive specimens in the cooked offal group came from two 
establishments. One was a slaughterhouse under State inspection and 
therefore the offal should have been cooked under inspection. Appar- 
ently the process was not properly watched in this case. The other 
establishment had been a slaughterhouse, but it is now only a meat 
wholesaling establishment. Trimmings from meat cut for distribution 
are cooked and fed to hogs. These hogs in turn are slaughtered and 
the pork is sold through the establishment. No inspection of cooking 
occurs at this plant. 
With regard to garbage as a source of swine infection, an attempt 
was made to find trichinae in meat scraps gathered from garbage which 
was to be fed to hogs. They were found once in 37,400 grams of pork 
scraps, but these trichinae were not viable. In a personal communi- 
cation, Dr. W. IT. Wright, of the National Institute of Health, has 
informed us about the examination of 555 composite 100-gram samples 
of pork scraps from residential garbage of Washington, D. C. Of these 
composite samples, 1.6 per cent were positive for trichinae. One-third 
of the positives contained viable larvae even though the pork had 
apparently been partially cooked. Thus it is logical for us to assume 
that the primary source of infection for the garbage fed hog is the 
pork in the garbage rather than some extraneous factor. 
An insufficient number of specimens was gathered in this work to 
show what effect the cooking of the garbage would have on the inci- 
dence. However, the literature contains several references of value. 
In the annual report of the Director of the Bureau of Animal Industry 
for 1937, the results of the examination of 1,860 swine fed on cooked 
garbage in two Pacific Coast States were reported. Only 0.6 per cent 
of the specimens was positive. As mentioned earlier, the same report 
showed 3.4 per cent of 3,876 swine fed on raw garbage in the same area 
was positive. In the similar report for 1939, no infected specimens 
were found among 1,000 specimens from swine fed on cooked garbage. 
Cameron (14) in reporting on the examination of garbage fed swine in 
Canada, where cooking of garbage prior to feeding it to hogs is required 
by law, found only 0.2 per cent of the swine infected. The report of 
the New York State Trichinosis Commission (15) contains the follow- 
ing: “The Commission is informed that England has long required the 
cooking of garbage fed to hogs. According to information received 
here, less than 25 cases of trichinosis were reported in England from 
1900 to 1941.” It would thus appear that the cooking of garbage is an 
effective method of controlling the infection in garbage fed swine. 22 
TRICHINOSIS PROBLEM IN CALIFORNIA 
The question of where grain fed swine might acquire an infection 
arises. There are three possible explanations which occur to us; (1) 
that Ave failed to determine all of the ranches that feed offal from the 
occasional hog that might have been slaughtered on the premises; (2) 
that some of these swine did receive scraps from the ranch kitchen, a 
fact that was denied by some of the ranchers, but later admitted when 
the evidence of such scraps was pointed out to them in their hog pens; 
and (3) that the hog might have eaten an infected rodent. Proof of 
such an occurrence is exceedingly hard to obtain. Rodents were col- 
lected from each of the seven grain ranches from which trichinous 
specimens were secured and from one of the grain and ranch kitchen 
scrap feeding ranches. None of tbe field mice, ground squirrels, 
gophers or wood rats were found infected although 101 specimens were 
examined. Prom one ranch where a history had been obtained that 
the swine husbandman had seen some bogs eating dead rats that tbe 
dogs and cats bad killed, we found infected tbe one rat caught imme- 
diately adjacent to the bog pens. None of the 14 rats trapped in the 
vicinity of the main buildings 500 or more feet away and across a 
highway were found infected. 
On four of the grain ranches having positive specimens it is the 
practice to irrigate at regular intervals the alfalfa fields in which tbe 
bogs foraged. This practice drowned any rodents which might be 
present in the fields. It would be possible for hogs to eat such rodents 
when they were turned back into the fields after the water bad soaked 
into the ground. In the area from which these specimens came, gophers 
and field mice were the most common rodents. 
It is presumed that rodents would acquire their infection from 
eating infected pork scraps thrown to the chickens in the barn yard 
with the kitchen scraps. Tbe parasite might be maintained and spread 
through a colony by one or several rodents eating a dead infected 
rodent. 
Examination of rats collected about garbage feeding establish- 
ments, most of which gave us trichinous swine specimens, showed that 
nine of 154 specimens taken were infected with trichinae, an incidence 
of 5.4 per cent, which approximates tbe incidence found in the garbage 
fed hog. 
An attempt was made to obtain opinions from the farmers as to 
whether bogs eat rats or other rodents. Amongst the 795 which were 
questioned, 80 stated that they had seen hogs eat rats, 104 stated that 
hogs would probably eat rats but that they had never seen it, 15 stated 
that bogs would eat rats after they bad been killed, one stated that bogs 
would kill rats but not eat them. 111 stated that hogs would not eat 
rats, and tbe remainder, 447 bad no opinion on tbe subject. We can 23 
REPORT OF I 940-1 941 SURVEY 
conclude from this that hogs will eat rats and other rodents but that it 
is not a common occurrence. Therefore, the possibility of a hog acquir- 
ing an infection from rats or other rodents is probably rather 
uncommon. 
The incidences of infection in the three areas, as shown in table 2 
and graph, are interesting because of their divergence. As far as 
can be determined the number of specimens in the important categories 
is in the proper proportion to the total. For instance, there are more 
garbage fed hogs in the southern region than there are grain fed hogs 
and hence more specimens from garbage fed swine were obtained. 
Although the difference in per cent positive for grain fed hogs in the 
southern and central areas is 0.9, the difference does not appear to be 
statistically significant. With regard to the garbage fed hog, the 
difference in the incidence in the two areas is 10.5 and it appears likely 
that this difference is statistically significant. 
Relative Importance of Grain and Raw Garbage Fed Swine as Sources of 
Human Trichinosis in California 
The reasons for the low incidence in the garbage fed hog of the 
southern area are not immediately apparent. Possible factors which 
would affect this figure are (1) the amount and character of meat scraps 
in the garbage, (2) the type of garbage, (3) the ratio of the amount of 24 
TRICHINOSIS PROBLEM IN CALIFORNIA 
garbage to the amount of supplementary food fed, and (4) the presence 
of rodents even though it is known they play only a minor role. There 
is no way of determining factual data on the first point; however, some 
indirect evidence is available from the examination of pork products 
as reported and discussed in the next section. With regard to the 
second point, it is our impression that the bay area, which has the 
largest urban population in the central region, disposes of most of its 
household garbage by other methods; thus it is chiefly the “swill” or 
wet restaurant garbage which is being fed to hogs. In the southern 
region it is the common practice to dispose of household and restaurant 
garbage by feeding it to hogs (see also Updegraff, 1.c.). Third, the 
amount of supplementary food given depends on the individual feeder 
and the quantity and quality of the garbage he is feeding. It must be 
granted that a higher incidence would be expected in hogs fed a small 
amount or no supplementary nongarbage food. It is not known whether 
our figures for the southern area largely represent ranches using con- 
siderable quantities of supplementary food. Concerning the fourth 
point, we can say that there are very few rodents about the ranches in 
the southern area while they are relatively common about the ranches in 
the central area. The rodents might account for a slight difference in 
the per cent positive, but not for the extent found. 
Hobmaier and Geiger (16) examined 93 garbage fed swine from 
the vicinity of San Francisco and found 34 infected, an incidence of 15 
per cent. These specimens came from seven ranches. Recently, 
McNaught and Zapata (17) reported finding only 20 positive specimens 
in 495 examinations of specimens from garbage fed swine from the same 
area, an incidence of 4 per cent. The incidence found by us for the 
central area, 12.7 per cent, agrees fairly well with that of Hobmaier 
and Geiger. The majority of the 616 specimens came from the same 
area, that is, the swine were fed on garbage originating in or near San 
Francisco. Following the survey of Hobmaier and Geiger a rodent 
control program was instituted on the ranches. McNaught and Zapata 
suggested that the lower incidence found by them might be due in part 
to this program. Since our incidence is in closer agreement with 
that found by the first survey, it does not appear likely to us that the 
rodent control program materially reduced the incidence. Other factors 
which might account for the low figure found by McNaught and Zapata 
are not apparent at this time. 
The evidence presented in this portion of this report indicates that 
by abolishing the practice of feeding raw garbage to swine the incidence 
of swine infection with trichinae would be materially reduced. Thus, 
there would be less trichinous pork sold in the markets of California. REPORT OF 1940-1941 SURVEY 
25 
Trichina Infection in Market Pork Products 
Studies of pork products showing the extent of their infection with 
trichinae are few in number. Hobmaier and Geiger (he.) examined 
pork sausages from 20 agencies, and found sausage from five of these 
infected. They do not state how many samples were examined to find 
the trichinous specimens. McNaught and Anderson (1.c.) reported 
finding two of 10 specimens of pork sausage infected with trichinae. 
The New York State Trichinosis Commission (1.c.) reported the most 
extensive survey to date. In their work 471 samples of pork meat 
products were collected from retail shops in New York State in such a 
manner that they were representative in area and type of product for 
sale. Of these, 294 were products to be cooked after sale and 177 were 
products which were to be eaten without further cooking on the part 
of the consumer. Eighteen of the 471 specimens, or 3.8 per cent were 
found infected. Of these 18, four contained living trichinae presum- 
ably capable of infecting man. Seven of the 18 were products to be 
eaten without further cooking on the part of the consumer. However, 
only one of these contained living trichinae and it was not a federally 
inspected product. Thus, no live trichinae were found in products of 
this type passing through federal inspection. 
California is unique among other States of the Union because it is 
the only State which has a meat inspection system which compares very 
favorably to the Federal meat inspection. The California regulations 
regarding meat inspection are patterned after the Federal regulations 
and are well enforced. These regulations apply to all slaughterhouses 
and meat processors in counties of 27,000 or more population. These 
establishments do not necessarily have to use the State meat inspection 
service, for they may use a local service provided that service is 
approved by the State. Slaughterhouses and meat processors in coun- 
ties with populations of less than 27,000, but marketing their products 
in surrounding counties must also he inspected. Thus, most of the meat 
sold in California is inspected. 
The samples of pork meat products examined hy the survey were 
purchased in the retail markets. Therefore the data derived from 
these samples represent the pork reaching the consumer. In order to 
obtain representative samples from all sections of the State, the number 
of samples purchased in a given section depended on the population of 
that section. One sample for a given area was purchased for each 
3,000 population of that area. Since the populace commonly believes 
that trichinosis is frequently acquired through the consumption of pork 
products such as salami, the survey is weighted. One-fourth of the 
samples consisted of products which were presumably processed so 
that any trichinae contained in them were rendered nonviable. 26 
TRICHINOSIS PROBLEM IN CALIFORNIA 
TABLE V 
Showing the Incidence of Trichina Infection in Various Pork Products 
Purchased on the Retail Market 
Products Not Processed to Kill Trichinae 
Number of 
Number of 
Per cent of 
specimens 
specimens 
specimens 
Type of product 
examined 
positive 
positive 
Fresh link sausage 
436 
16 
3.7 
Fresh bulk sausage 
620 
5 
0.8 
Fresh pork chops 
586 
1 
0.2 
Miscellaneous 
20 
0 
0.0 
Ham—cured 
34 
0 
0.0 
Bacon—cured 
45 
0 
0.0 
Total 
1.750 
22 
1.3 
Products Processed to Kill Trichinae 
Chorizos 
9 
0 
0.0 
Salami 
ICO 
0 
0.0 
Cervelat 
7 
0 
0.0 
Mettwurst _ 
12 
0 
0.0 
Headcheese 
13 
0 
0.0 
Garlic sausage 
10 
0 
0.0 
Blood and tongue sausage 
6 
0 
0.0 
Linguisa 
8 
0 
0.0 
Liver sausage 
18 
0 
0.0 
Bologna 
40 
0 
0.0 
Wieners 
17 
0 
0.0 
Various loaves 
26 
0 
0.0 
Thuringer 
17 
0 
0.0 
Ham loaves 
222 
0 
0.0 
Canadian bacon 
21 
0 
0.0 
Miscellaneous 
23 
0 
0.0 
— 
— 
— 
Total 
Grand total 
609 
2,359 
0 
0.0 
Table 5 shows the incidence of infection with trichinae found in 
the various pork products. There were 2,359 specimens examined. 
Of these, 1,750 were fresh products which should have been cooked 
after purchase and 609 were products the further cooking of which 
after purchase should not have been necessary. Twenty-two of the 
1,750 fresh products were infected witli trichinae, as incidence of 1.3 
per cent. All of these products came from meat packers located in 
California. The standard deviation of 1.3 is 0.3 when computed by 
the formula used in the previous section. Further analysis of 
the data shows that the pork product most commonly found infected 
was the fresh link sausage, and the next most commonly infected prod- 
uct was the hulk sausage. There are, of course, similar products. The 
mean weight of the fresh products examined was 130 grams with a 
range from 22 to 775 grams. 
A possible explanation for this distribution of infected material 
among the types of pork products lies in the fact that the sausages 
are made up of trimmings from general pork cuts, pork which would REPORT OF 1940-1941 SURVEY 
27 
not look well on the counter of the butcher shop, and that from old 
sows, boars and stags. The Jink sausages are largely made up by the 
packing house and therefore would be more apt to contain the poorer 
grade of pork than would the bulk sausage which was frequently 
prepared and ground by the retail butcher. 
Showing the Types of Pork Products Infected and the Degree of Infection 
In Each Type 
TABLE VI 
Positive 
number 
Type of product 
Weight of 
product 
(grams) 
Number of trichinae 
recovered 
Number 
per gram of 
product 
Live 
Dead 
Total 
1 
Link 
Sausage 
__ 161 
36 
2 
38 
0.2 
2 
Bulk 
Sausage 
__ 775 
25 
0 
25 
0.3 
8 
Bulk 
Sausage 
__ 150 
402 
83 
485 
3.2 
4 
Bulk 
Sausage 
__ 115 
0 
3 
3 
0.03 
5 
Link 
Sausage 
__ 183 
15 
1 
16 
0.0!) 
0 
Link 
Sausage 
__ 211 
125 
6 
131 
0.6 
7 
Pork 
Chops 
152 
85 
0 
85 
0.6 
8 
Link 
Sausage 
__ 128 
3 
1 
4 
0.03 
9 
Link 
Sausage 
__ 116 
4 
4 
8 
0.07 
10 
Link 
Sausage, 
__ 230 
21 
7 
28 
0.1 
11 
Link 
Sausage 
__ 166 
3 
0 
3 
0.02 
12 
Link 
Sausage 
— 140 
8 
0 
8 
0.06 
13 
Link 
Sausage 
150 
0 
1 
1 
0.01 
14 
Bulk 
Sausage 
__ 289 
0 
6 
6 
0.02 
15 
Link 
Sausage 
__ 146 
16 
0 
16 
0.1 
16 
Bulk 
Sausage 
__ 171 
38 
0 
38 
0.2 
17 
Link 
Sausage 
162 
0 
1 
1 
0.01 
18 
Link 
Sausage 
__ 144 
2 
0 
2 
0.01 
19 
Link 
Sausage 
__ .134 
254 
1 
255 
1.9 
20 
Link 
Sausage 
145 
• > 
0 
3 
0.02 
21 
Link 
Sausage 
222 
Q 
O 
0 
3 
0.01 
22 
Link 
Sausage 
173 
24 
5 
29 
0.2 
Table 6 shows the degree of infection in the pork products. 
Twelve, or more than half of the infected specimens, contained fewer 
than one larva per 10 grams of sample, eight contained fewer than one 
larva per gram of sample, but more than one larva per 10 grams of 
sample. The remaining two infected specimens contained more than 
one larva per gram of sample. The table also shows that 18 of the 
specimens contained viable trichinae and three contained only nonviable 
larvae. Whenever possible the viability of the trichinae was checked 
by feeding the larvae to a guinea pig. All infections showing 50 or 
more larvae were so checked; that is, four of the 22 samples. In each 
case an infection was established in a guinea pig, thus proving the 
viability of the larvae. 
None of the 609 products processed to kill trichinae before being 
retailed contained either living or dead larvae. The mean weight of 
these samples was 134 grams with a range from 31 to 460 grams. 
These products were divided into 16 types as shown in table 5. All 
but one of these products were inspected by either Federal, State or 28 
TRICHINOSIS PROBLEM IN CALIFORNIA 
State approved local inspection. The one uninspected product was 
probably produced illegally. These results show the advantage of an 
inspection system, since inspection of this type of product is conducted 
particularly against trichinosis. It operates on the assumption that 
all pork being used in such products may contain trichinae and there- 
fore must be processed either by (1) freezing at a specified temperature 
over a specified period of time; (2) salting at the required concen- 
tration and storing under lock and key over a specified period of time; 
or (3) by heating to a specified temperature for a specified period of 
time. The efficiency of these methods as enforced under Federal 
inspection is continually being checked. The annual reports (1.c.) 
show that the laboratory examination of more than 8,000 samples of 
such inspected pork revealed that none of the products contained 
living trichinae, although dead trichinae were found a number of times. 
Showing the Distribution of the Pork Products According to Area and the 
Incidence Found in Each Area 
TABLE VII 
Fresh Products 
Processed Products 
Number 
Number 
Per cent 
Number 
Per cent 
Area examined 
trichinous 
trichinous 
examined 
trichinous 
Southern 903 
5 
0.0 
365 
0 
Central 775 
17 
2.2 
231 
0 
Northern and Sierra Nevada 72 
0 
0.0 
13 
0 
Total 1750 
22 
1.3 
609 
0 
Table 7 shows the breakdown of the data into the three regions 
being considered. It will be noted that five of the 903 samples of 
fresh products from the southern region were trichinous, an incidence 
of 0.6 per cent; 17 of the 775 specimens from the central region 
contained trichinae, an incidence of 2.2 per cent; and none of the 72 
specimens from the northern and Sierra Nevada region was trichinous. 
The difference in the per cent trichinous in the southern and central 
regions is 1.6, and the standard deviation of this figure is 0.6. Since 
twice the standard deviation is less than the difference, it would appear 
likely that the difference is statistically significant. 
TABLE VIII 
Showing the Proportion of Pork Products Produced in the Region in Which 
They Were Purchased and the Proportion Produced in Other Regions 
Region in which 
product was retailed 
Southern 
Region in Which Product 
Rorthern 
and Sierra 
Central Nevada 
teas Packed 
Other 
States 
Unknown 
Southern 
91 
0 
0 
7 
2 
Central 
3.2 
90.1 
0.3 
5.1 
1.3 
Northern and Sierra 
Nevada 
2 
52 
37 
8 
1 
Total 
92 
G 
2 REPORT OF 1940-1941 SURVEY 
29 
It is interesting to note the origin of the products with regard 
to the area in which packed. As pointed out in the previous section, 
this does not necessarily mean that the pork originated from swine 
raised in the region. Table 8 shows that 90 per cent of the products 
purchased in the southern and central regions was packed in the region. 
The most lightly populated region received 52 per cent of its products 
from the central region, 2 per cent from the southern, and 37 per cent 
of the products were packed within the area. In our experience, 92 
per cent of all the products purchased was produced by meat packers 
in California and 6 per cent supplied from packers located in other 
States. The remaining 2 per cent was not sufficiently identified to 
allocate it to the point of origin. Most of the products supplied by 
out-of-State sources were processed so that trichinae should have been 
killed, and all of them came from Federally inspected plants. 
Referring to the incidence in the garbage fed swine of the 
areas under consideration (table 2), it will be noted that in the 
southern region where the incidence in the market products was 
significantly lower than that in the other regions, the incidence in 
the garbage fed swine in the area was also significantly lower. The 
data therefore indicate a marked correlation between the two inci- 
dences, the incidence in the garbage fed swine reflecting the incidence 
in the market pork products. They also indicate that the elimination 
of the practice of feeding raw garbage to swine would be reflected in 
the amount of trichinous market pork products. 
Trichina Infection in Man 
An extensive survey of the incidence of infection in human 
necropsy material was not undertaken because of the work of McNaught 
and Anderson, Butt and Lapeyre and the National Institute of Health, 
U. S. Public Health Service, the latter survey still being under way. 
These surveys were largely made on diaphragm material from an urban 
population. We therefore endeavored to obtain supplementary data 
on the rural population and in particular from the area north of San 
Francisco. The results of the examination are expressed in table 9. 
Showing the Number and Per Cent Positive of Human Diaphragms in Relation 
to the Type of Population 
TABLE IX 
Number 
Number 
Per cent 
Type of 
specimens 
specimens 
specimens 
population 
examin ed 
trichinous 
trichinous 
Rural 
11 
0 
0.0 
Urban 
49 
5 
10.2 
Unknown 
S 
0 
0.0 
Rural (sent to USPHS) 
7 
0 
0.0 
Total 
70 
5 
7.1 30 
TRICHINOSIS PROBLEM IN CALIFORNIA 
A total of 70 specimens was received. Of these, seven came from an 
area having a population of 1,000 or less and were forwarded to the 
National Institute of Health for their survey. A negative report was 
received on these specimens. Eleven of the remaining 63 specimens 
which were examined by us came from areas which are sometimes 
termed rural, that is, the population was 2,500 or less, 49 came from 
urban areas and inadequate data were received on three specimens. 
Thirty-eight of the specimens came from State institutions and all of the 
positives were among these specimens. The positive specimens con- 
tained 1, 4, 7 and 14 calcified cysts with dead larvae in the gram of 
tissue examined miscroscopically. The fifth positive specimen con- 
tained one live and one dead larvae in the 42 grams of material digested. 
TABLE x 
Showing the Trichinosis Case Rate in California and in the Three Subdivisions 
for the Eleven Year Period, 1930 Through 1940 
No. reported 
Population 
Pate per 
Area 
cases 
(estimated 1935) 
100,000 
Southern 
112 
3,462,753 
3.2 
Central 
484 
2,631,987 
18.4 
Northern and Sierra Nevada 
119 
228,338 
52.1 
Total 
715* 
6,323,074 
11.3 
* Six additional cases are 
another State. 
charged to California, but the disease was acquired in 
The distribution of reported cases of trichinosis is rather uneven 
as shown in map 2. This distribution is based only on the cases 
reported during the past 11 years. This period is used because the 
efficiency of the reporting has been much better than during the 
preceding years. The case rates for the three areas which we are con- 
sidering are expressed in table 10. Although these data are not an 
absolute index of cases, as mentioned previously, they indicate the 
general distribution of cases. Thus, we find that in the largest popu- 
lation group, the southern area, the lowest case rate occurs; in the 
intermediate population group, the central area has the next highest 
case rate; and the smallest population group, the northern and Sierra 
Nevada area, has the highest case rate. The number of cases charged 
to the various counties is unevenly distributed over the 11-year period. 
Most of the cases charged to the northern and Sierra Nevada counties 
represent outbreaks of from five to 44 cases. In the other two groups 
of counties the proportion of cases occurring in outbreaks is not so high. 
These data include 25 cases, the reported source for which was bear 
meat. REPORT OF 1940-1941 SURVEY 
31 
Distribution by Counties of Trichinosis, Case Rate Per 100,000 
1930 Through 1940 Based on Estimated 1935 Population 
Comparing the incidence in the swine diaphragms and market pork 
products with the case rate shows a striking parallelism, particularly 
for the central and southern groups of counties (tables 2, 7 and 10), 
It would appear that the case rates in these two groups of counties 
reflect the incidence of infection found in market pork products. The 
association between the incidence in the market pork products and that 32 
TRICHINOSIS PROBLEM IN CALIFORNIA 
in garbage fed swine lias already been pointed out. Thus, it would 
appear that the number of cases of trichinosis in an area would be a 
direct reflection of the incidence in the garbage fed swine of the area. 
TABLE XI 
Showing the Broad Classification of the Reported Sources of Infection of Cases 
of Trichinosis in California According to the Year in Which They Occurred 
Commercial 
Fresh pork processed 
Year products products 
Home 
processed 
products 
Bear 
meat 
Unknown 
'Total 
A. Before the institution of 
39?,0 58 
the State Meat Inspection 
50 38 
5 
151 
1931 
19 
3 
18 
40 
1932 
18 
4 
62 
84 
1933 
32 
21 
7 
4 
64 
1934 
20 
23 
8 
51 
1935 
38 
26 
2 
5 
71 
1936 
29 
9 
2 
40 
1937 
31 
29 
i 
2 
— 
63 
— 
— 
— 
— 
— 
— 
Total 
245 
166 
118 
22 
14 
564 
Per cent of total 
43.4 
29.8 
20.9 
3.9 
2.5 
100.0 
B. Following the institution 
1938 39 
of the State 
10 
Meat Inspect 
12 
ion 
4 
65 
1939 
29 
7 
o 
o 
2 
41 
1940 
32 
4 
12 
— 
3 
51 
— 
— 
— 
— 
— 
— 
Total 
100 
21 
24 
3 
9 
157 
Per cent of total 
63.7 
13.4 
15.3 
1.9 
5.7 
100.0 
Grand total 
345 
187 
142 
25 
23 
721 
Per cent of total 
47.8 
25.8 
19.7 
3.5 
3.2 
100.0 
Table 11 shows a general classification of the types of products 
which have been reported as sources of infection for cases of trichi- 
nosis. The table has been divided into two sections because of the 
institution of the State meat inspection in 1937. Following the insti- 
tution of this inspection, there was a falling off in the number of cases 
of trichinosis resulting from the consumption of commercially processed 
products. This is in accordance with the examination of the 609 
processed products (table 5), none of which was found to contain 
viable trichinae. The results of the examination of the processed 
market pork products indicate that all reports attributing trichinosis 
to one of these products should be questioned and investigated further. 
General Discussion 
The data collected by the survey show that as far as California 
raised swine are concerned, the chief problem in the control of trichi- 
nosis lies in the practice of disposing of raw garbage by feeding it to 
swine. Elimination of this practice would not eliminate the problem REPORT OF 1940-1941 SURVEY 
33 
of trichinosis, but it would materially reduce the amount of infected 
pork products sold in this State. 
It was pointed out earlier that there were 1,650,000 head of swine 
slaughtered annually in California, and that 650,000 of these were 
raised in the State. All data indicate that there are 250,000 garbage 
fed swine in California. The incidence for these swine, 6.4 per cent, 
indicates that there would be 16,000 head infected with trichinae. An 
incidence of 0.8 per cent was found in nongarbage fed swine, therefore 
3,200 head of the 400,000 nongarbage fed swine would be infected. 
Schwartz (1.e.) in discussing the role of garbage fed swine in trichinosis 
assumes that 10 per cent of the swine raised in the United States are 
fed in part or entirely on garbage. He found 5.7 per cent of the 
garbage fed swine infected. Based on Schwartz’s assumption and 
incidence, 100,000 of the 1,000,000 head of non-California swine would 
be garbage fed, or 5,700 infected head. Again, Schwartz found that 
1.0 per cent of the nongarbage fed swine infected. Thus, 9,000 of the 
900.000 head of non-California grain fed swine would be infected. 
This would indicate a total of 33,900 head of infected swine slaughtered 
annually in California. At least 47 per cent of this total would have 
been raised on garbage in California. It would seem, therefore, that 
the elimination of this practice in California would reduce the amount 
of trichinous pork sold by nearly 50 per cent. 
To state the matter in another way, if we assume that the average 
dressed hog carcass weighs 150 pounds, then about 5,000,000 of the 
247,000,000 pounds of pork produced annually in California would he 
infected. The removal of infection from California garbage fed swine 
would almost cut this amount in half. Such a procedure would be a 
considerable advance in the control of trichinosis. 
A good deal of thought and effort have been expended on ways 
and means of determining the trichina infected hog carcass in 
the slaughterhouse. To date, all methods developed have been uneco- 
nomical or impractical because they are not sufficiently accurate. The 
microscopic inspection of each carcass is too expensive and does not 
detect all infections. The skin testing of hogs with trichina intra- 
dermal antigen is not only laborious but also not sufficiently accurate 
according to the report of Spindler, Cross and Avery (18). It has been 
suggested that each hog carcass might be rendered safe by freezing. 
This would not be practical from the standpoint of economics. 
The question of the methods of disposing of garbage arises. In 
addition to the practice of feeding it to swine, the following methods 
are in use: fill and cover, dumping at sea, grinding and discharging 
into sewers, incineration, reduction, and cooking the garbage before 
feeding it to swine. All of these methods except reduction and feeding 34 
TRICHINOSIS PROBLEM IN CALIFORNIA 
the garbage to swine treat the material as a valueless product. It must 
be recognized that garbage has value. 
The fill and cover method is practical particularly where waste 
lands are conveniently available. Even where waste lands were not 
available, the City of Fresno has worked out a very satisfactory method 
at a nominal cost for disposing of household noncombustible refuse 
which is mixed with garbage. 
Dumping at sea is not particularly practical on the California 
coast because the prevailing currents sweep a great deal of the refuse 
back on the beaches, thus creating a nuisance. The method is used by 
certain cities for disposing of household garbage and noneombustible 
refuse. 
The grinding and discharge of garbage into sewers effectively 
disposes of garbage, but its general use would cause the overhauling and 
rebuilding of many sewage plants. The increased amount of bulk in 
the sewage would call for increased sewage plant capacity. 
Incineration is in use in various places. To handle restaurant or 
so-called wet garbage in these plants is an expensive process because 
of the fuel required to dispose of the water in the garbage. 
Reduction of the garbage for grease recovers some of the value of 
the garbage. The use of the process is frequently affected by the price 
of grease, for when the price of that product falls below the operating 
costs of the plant there is a temptation to dispose of the garbage by 
other means. 
Judging from the experience in England, Canada, and several 
sections of the United States, the cooking of garbage before feeding it 
to hogs is a practical and economical means of disposing of this refuse. 
Unfortunately, many of the California hog feeders are prejudiced 
against cooking of the garbage because of an experience of the largest 
of them. This experience involved an attempt to save several days 
accumulation of garbage from a large urban center during a period of 
interruption of transportation facilities. In this case the garbage was 
thoroughly cooked on gondola cars before being transported. It 
remained in these cars for 48 or more hours and was still warm when 
unloaded. Under such circumstances, most of the food value would 
have been destroyed by the long cooking period. 
It would be desirable to have available plans and costs of operating 
garbage cookers. However, such information is almost nonexistent. 
The Canadian Department of Agriculture furnishes hog raisers a plan 
for building a type of cooker which is both economical and effective for 
small amounts of garbage. Information concerning methods of handling 
and cooking the tonnage of garbage originating in such cities as Los 
Angeles and San Francisco does not seem to be available. REPORT OF 1940-194 I SURVEY 
35 
From the standpoint of agriculture and swine sanitation the feed- 
ing of raw garbage is not considered good practice. The losses of swine 
on such ranches are greater than they are on grain feeding ranches due 
to the diseases which are transmitted through the garbage. In Califor- 
nia, the most important of these diseases are vesicular exanthema and 
hog cholera. The attitude of the State Department of Agriculture is 
reflected in a mimeographed release (19) which indicates that the 
cooperation of the department is available for any efforts to eliminate 
the practice. 
In conclusion, it appears that the least disruption of present 
methods of garbage disposal would be to require the cooking of the 
garbage before it is fed to swine. In most cases this would not require 
a large capital on the part of the rancher nor would it materially 
increase the cost to the municipality for disposing of its garbage. 
Municipalities could not then be accused of contributing to this public 
health problem. 
Summary 
The problem of trichinosis in California is no different from that 
in any other State. By and large it is due to the practice of disposing 
of garbage from cities, towns, resorts, and camps by feeding it to hogs 
in the condition in which it is collected. An incidence of 6.4 per cent 
was found in the 1,701 garbage fed swine examined for trichinae. Such 
swine provide almost 50 per cent of the trichinous pork sold in Cali- 
fornia. 
The examination of market pork products shows that fresh sausage 
is the most commonly infected product. A study of the distribution of 
such products revealed the fact that infected products were more 
common in areas where the incidence was highest in the garbage fed 
swine. It would thus appear that the two incidences are related. 
The case rate distribution apparently reflects the incidence found 
in market pork products, which, in turn, is related to the incidence 
among the garbage fed swine. It thus appears that the number of 
cases of trichinosis in an area may be a direct reflection of the incidence 
in garbage fed swine. 
The practice of cooking garbage from municipalities before feeding 
it to swine is being successfully carried out in England, Canada and 
certain parts of the United States. Since this practice under proper 
supervision would eliminate nearly 50 per cent of the trichinous pork 
sold annually on the California markets, it appears that its institution 
would materially lessen the trichinosis problem without seriously dis- 
rupting the present methods of garbage disposal. 36 
TRICHINOSIS PROBLEM IN CALIFORNIA 
Bibliography 
(1) Wright, W. 11., and F. J. Brady. The medical and public health 
aspects of trichinosis. Federal Security Agency, United States 
Public Health Service, National Institute of Health, Washington, 
D. C. 14 pp. August 1940. 
(2) Hall, M. C. Studies on Trichinosis 111. The complex clinical 
picture of trichinosis and the diagnosis of the disease. Public 
Health Reports, 52 (18) 539-551. April 30, 1937. 
(3) Yener, 11. I. Trichiniasis Report of an outbreak of 25 eases. Los 
Angeles City Board of Health Commissioners. Bull. No. 33. 17 
pp. January 11, 1938. 
(4) McNaught, J. 8., and E. Y. Anderson. The incidence of Trichi- 
nosis in San Francisco. Jour. Amer. Med. Assoc. 107, 1446-1448. 
October 31, 1936. 
(5) Butt, E. M., and J. L. Lapeyre. Trichina spiralis: Its Incidence 
in Necropsy Material. Calif, and Western Med., 50, 361-363. 
1939. 
(6) Sawitz, W. Prevalence of Trichinosis in the United States. 
Public Health Reports 53, 365-383. March 11, 1938. 
(7) Kerr, K. 8., L. Jacobs and E. Cuvillier. Studies on Trichinosis 
XIII. The incidence of human infection with trichinae as indi- 
cated by post-mortem examination of 3,000 diaphragms from 
Washington, D. C. and five Eastern seaboard cities. Pub. Health 
Repts. 56, 836-855. April 18, 1941. 
(8) Nolan, M. O. and J. Bozicevich. Studies on Trichinosis V. The 
incidence of trichinosis as indicated by post-mortem examinations 
of 1,000 diaphragms. Pub. Health Repts. 53, 652-673. April 
29, 1938. 
(9) Scott, G. A. California Livestock statistics with special reference 
to shipments into and out of the State, slaughter within the State 
and marketings. United States Department of Agriculture, 
Bureau of Agricultural Economics in cooperation with California 
Department of Agriculture. 45 pp. October, 1937. 
(10) Updegraff, W. R. How Western Cities Collect and Dispose of 
Refuse. Western City, 16, 13-21, May, 1940; 16-25, June, 1940; 
13-21, July, 1940. 
(11) Anonymous. Extent of Garbage Feeding of Hogs. U. S. Depart- 
ment of Agriculture, Bureau of Agricultural Economics. Wash- 
ington, D. C. June, 1940. (Mimeographed release) 2 pp, 7 tables. 
(12) Schwartz, B. The Trichinosis Situation in the United States. 
11. S. Department of Agriculture, Bureau of Animal Industry. 
7 pp. February, 1940. Also Sclent. Monthly. 5 (3) 241-247. 
September, 1940. 
(13) Annual Reports of the Chief of the Bureau of Animal Industry 
to the Secretary of Agriculture for 1934, 1935, 1936, 1937, 1938 
and 1939. REPORT OF 1940-1941 SURVEY 
37 
(14) Cameron, T. W. M. Investigations on Trichinosis, 11. A further 
survey of the incidence of Trichinella spiralis in hogs in Eastern 
Canada. Canadian Jour., Res., 17 (D), 151-153. July, 1939. 
(15) “Meat for Millions.” Report of the New York State Trichinosis 
Commission. Legislative Document (1941) No. 52. 282 pp. 
1941. 
(16) Hobmaier, M. and J. C. Geiger. Trichinelliasis in San Francisco. 
American Journal Public Health. 28, 1203-1211. October, 1938. 
(17) McNaught, J. 8., and E. M. Zapata. Incidence of Trichinella 
spiralis in garbage fed hogs in San Francisco. Proe. Soc. Exp. 
Biol, and Med. 45, 701-704. 1940. 
(18) Spindler, L. A., S. X. Cross and J. L. Avery. Results of Intra- 
cutaneous Tests for the Detection of Trichina Infection in Swine. 
Proc. Helminthol. Soc. Washington 8, 1-6. 1941. 
(19) Duckworth, C. U. Diseases of Animals from Garbage Feeding. 
Division of Animal Industry, California Department of Agricul- 
ture. 7 pp. December 18, 1940. (Mimeographed release) 
10687 4-42 5M