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Chapter 18 - Salmonellal Infections

Contents

CHAPTER XVIII

Salmonellal Infections

Dwight M. Kuhns, M. D.1

HISTORICAL NOTE

The early history of salmonella food poisoning is not directly related to the military; however, it is briefly presented here to orient the reader as to the status of the problem in past years. In 1888, an epidemic of food poisoning occurred in Frankenhausen, Germany, that was traced to contaminated meat.2 From the feces of a fatal case of the disease, Gärtner isolated an organism which he called Bacillus enteritidis, because of the enteritis produced. The organism was renamed Salmonella, to honor Dr. Daniel E. Salmon in recognition of his research on hog cholera. Dr. Salmon was the first to describe a member of this group. In 1885, Dr. Salmon and Dr. Theobald Smith isolated Bacillus choleraesuis from cases of hog cholera (Salmonella choleraesuis in modern terminology). 3 Although it was excellent work, Dorset and de Schweinitz, in 1903, demonstrated that hog cholera is actually caused by a filterable virus, the bacteria being secondary invaders and not always present.

The rod-shaped motile bacterium (implicated at Frankenhausen) was subsequently discovered in other cases of food poisoning, although many other types of food poisoning were not found to be caused by Salmonella organisms nor were all the newly discovered related species first found in food-poisoning cases. Staphylococci were implicated in cases of food poisoning several years before the discovery of the genus Salmonella. Furthermore, many of the Salmonella species were not first discovered in connection with food poisoning. Thus, Salmonella aertrycke, today known as Salmonella typhimurium, was first isolated from mice by Lofller in 1890, while Sal. choleraesuis, as has already been noted, was first found in swine. Still others, such as Salmonella oranienburg, were first isolated from the feces of healthy humans.

Numerous cases of food poisoning are mentioned in the older literature such as those described by van Ermengem in which sausages were suspected of having caused illness .4 A Belgian inspector of meat, reputed to have been an expert in his field, examined the meat and declared the sausages to be fit for human consumption. The inspector developed severe diarrhea 10 hours

1 Acknowledgment is hereby made to Martin Roth, M. A., for his faithful assistance. in the research for historical material for this section and in the final preparation of the manuscript.

2 Gartner, A.: Ueber die Fleischvergiftung in Frankenhausen a. k. and den Erreger derselben. Cor.-Bl. d. allg. ärztl. Ver. v. Thüringen, Weimar, 1888, xvii, 573-600.
3 Salmon, D. E.: Investigations in Swine Plague. U. S. Bur. Anim. Indus. 2d Ann. Report, 1885, pp. 184-246.

4 Dack, G. M.: Food Poisoning. Chicago: The University of Chicago Press, 1949.


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later, on 26 October 1895. This was followed by fever, high pulse, and abdominal distress. Six days later, he died. Necropsy revealed viscera laden with Salmonella enteritidis. This account is mentioned here not to cite the fact that some inspectors may lack competence but rather to point out that food, highly contaminated with pathogenic organisms, can appear quite satisfactory in gross appearance as well as in smell and taste.

Many organisms similar to Sal. enteritidis were discovered even before the First World War. However, up to and including the period of World War 1, there is no substantial literature on either Salmonella or food poisoning. Scattered reports are available on what were then designated as the paratyphoid fevers. This group consisted of a variety of gastroenteric conditions similar, though not identical, to typhoid fever. It is generally believed that the paratyphoid fevers were by no means a major problem to the United States Army during World War I but what might be more accurately described as a nuisance. During 1916 and 1917, there were sporadic and epidemic occurrences of the disease in United States Army personnel along the Texas-Mexico border and in Mexico itself. Soon after, it was learned that outbreaks were occurring in France among British and French troops. In July 1917, the United States Army incorporated paratyphoid A and paratyphoid B organisms in its regular typhoid vaccine.

Table 71 shows the incidence and deaths for paratyphoid fever, most of which resulted from contaminated food or water, among officers and enlisted personnel from 1 April 1917 to 31 December 1919, inclusive. It is necessary to view the statistics with caution. First, a wide variety of conditions in the World War I period were consigned to the ill-defined categories paratyphoid A and paratyphoid B. They were milder than classical typhoid fever, with diarrhea a more characteristic feature. Secondly, an individual who died in an Army hospital was listed as a paratyphoid (or typhoid) death if that was the condition for which he had been admitted. It was the practice of the Surgeon General's Office, at the time, to list for statistical purposes the disease for which a patient was initially admitted to the hospital as the cause of death if the patient died.5 Thus, while many paratyphoid deaths were, in fact, ascribed to paratyphoid fever, others were not. Further, the concept of food poisoning had not yet been clearly defined, many cases being considered examples of ptomaine poisoning, a meaningless classification. 6

During the interval between World War I and World War II, little of note occurred in the history of salmonellal food poisoning, at least insofar as the Army was concerned. One development of great significance, however, was the classification schemata that were gradually devised through biochemical

5 (1) The Medical Department of the United States Army in the World War. Communicable and Other Diseases. Washington: U. S. Government Printing Office, 1928, vol. IX. p. 15. (2) The Medical Department of the United States Army in the World War. Statistics. Washington: Government Printing Office, 1925, vol. XV, pt. 2, p. 12. (3) Annual Reports of The Surgeon General, U. S. Army, to the Secretary of War. Washington: Government Printing Office, 1921. pp. 20-21; 1934, pp. 5-6; 1936, p. 7.

6 (1) Morgan, 11. R.: The Salmonella. In Bacterial and Mycotic Infections of 6an.2d ed. Philadelphia: J. B. Lippincott Co., 1952, ch. 17, pp. 420-436. (2) Savage, W. G.: Bacterial Food Poisoning. In A System of Bacteriology in Relation to Medicine. London: II. M. Stationery Office, 1929. vol. III, ch. 12, pp. 407-413.


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TABLE 71.–Occurrence of paratyphoid A and paratyphoid B in World War I (absolute numbers and annual rates)

study of the organisms, not only as relating to the cultural characteristics but also their antigenic composition. Progress in this area was largely due to the excellent work of Kauffmann (1937) and White (1926) who first studied the Salmonella species in great detail and showed how they could be classified on the basis of their antigenic structure.

TYPING AND CLASSIFICATION

At the beginning of World War II, there was at Copenhagen, Denmark, an international Salmonella typing center of which Dr. Fritz Kauffmann was director. In the United States, there were two large Salmonella centers, one at Beth Israel Hospital, New York, N. Y., under the supervision of Dr. E. Seligmann and one at the Kentucky Agricultural Experiment Station, Lexington, Ky., supervised by Dr. P. R. Edwards. Some of the work at Lexington was, as a result of the war, sponsored and paid for by the Army Medical Service Graduate School, then known as the Medical Department Professional Service School, Army Medical Center, Washington, D. C.

The main role of the Army Medical Service Graduate School was that of preparing and supplying typing serums for Army laboratories, Army service command medical laboratories, medical general laboratories, other general hospital laboratories, and station hospital laboratories. A great part of the Army's knowledge of the species of Salmonella causing food poisoning is due to the fine work of such laboratories as the 15th Medical General Laboratory, which was located at Naples, Italy, from 21 November 1943 to 25 October 1945. Salmonella typing and identification had become a new field, with new skills for the bacteriologist and technician to learn and master.7 Military and

7(1) Edwards, P. R., and Bruner, D. W.: Serological Identification of Salmonella Cultures. Kentucky Agr. Exp Sta. Cir. 54: 3-35,1942. (2) Kauffmann, Fritz: Enterobacteriaceae: Collected Studies on Salmonella, Arizona, Ballerup-Bethesda, Escherichia, Alkalescens-Dispar, Klebsiella, Shigella, Providence and Proteus. Copenhagen: Ejnar Munksgaard, 1951.


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civilian bacteriologists distinguished themselves in that field. Never before in the history of medicine and bacteriology had so much concentrated attention been centered upon the species of one bacterial genus. It should be noted that during this period of intensive research, two schools of thought on Salmonela classification arose. Some believed that the division of this genus into species and strains had been carried to hair-splitting extremes, where minute, differences were deemed sufficient reason for such subdivision. Others maintained that the differences, regardless of how minute they might be, had taxonomic and epidemiologic significance, if they remained constant.

The following is a list of those Salmonella species discovered during the World War II period and is included here for reference purposes: 8

Species:

Source

Species:

Source

Sal. kaposvar

Human

Sal. heves

Human

Sal. kaapstad

Do

Sal. florida

Do

Sal. hartford

Rat .

Sal. madelia

Human, chick.

Sal. manhattan

Human, turkey, chick, reptile, hog

Sal. sundsvall

Human

Sal. szentes

Do.

Sal. narashino

Human

Sal. schwarzengrund

Do.

Sal. sendai

Do.

Sal. concord

Human, turkey, chick

Sal. durban

Do.

Sal. orientalis

Human

Sal. vejle

Do.

Sal. gorgia

Human

Sal. meleagridis

Human, reptile

Sal. claibornei

Do.

Sal. illinois

Human, hog, turkey, partridge

Sal. loma linda

Do.

Sal. mississippi

Human, hog

Sal. New York

Do.

Sal. oregon

Human, turkey, chick, hog, reptile

Sal. butantan

Human, (child)

Sal. pretoria

Hog

Sal. grumpensis

Guinea pig

Sal. havana

Human

Sal. adelaide

Do.

Sal. urbana

Human, hog, chick

Sal. inverness

Do.

Sal. salinatis

Human, rat

Sal. papauna

Do.

Sal. tennessee

Human, turkey, fowl, egg

Sal. cardiff

Do.

Sal. bonariensis

Human, hog

Sal. virginia

Do.

Sal. amherstiana

Chicken

Sal. pensacola

Do.

Sal. javiana

Human

Sal. miami

Human, chimpanzee

Sal. weltevreden

Do.

Sal. canastel

Human

Sal. simsbury

Human, turkey

Sal. italiana

Do

Sal. kohn

Human

Sal. napoli

Do.

Sal. infantalis

Human, (child)

Sal. orion

Do.

Sal. pueros

Human

Sal. veneziana

Do.

Sal. taksony

Do.

Sal. pamona

Human, fowl

Sal. solt

Do.

Sal. champaign

Chicken


8 Breed, Robert S., Murray, E. G. D., and Hitchens, A. Parker: Bergey's Manual of Determinative Bacteriology. 6th ed. Baltimore. The Williams & Wilkins Co., 1948.


421

The names of the species indicate, in some instances, where they, were first isolated.Chickens became an important source, and rodents and hogs were often found to be infected. Spray-dried egg powder was the source of a number of Salmonella strains. They, were found in 10 percent of over 6,000 samples of spray-dried egg powder. The commonest types were Sal. oranienbury, Sal. montevidio, Sal. meleagridis, Sal. bareilly, and Sal. anatum, but several others were encountered. One of the outstanding epidemiologic contributions of this experiment of infected egg powder was that it revealed the cause of a cluster of outbreaks around holiday seasons. Although dogs are not mentioned as an original source in this group, they were found to have a significant carrier role.

Table 72 is a brief summary of the outstanding salmonellal food-poisoning outbreaks during World War II. Most of the recorded outbreaks are those of the European and the Mediterranean Theaters of Operations. Salmonellal infections in these two theaters were the subject of special field study. The data which appear in table 72 represent only those cases of food poisoning which were reported on individual medical records and will grossly understate the total experience with this disease group. Several facts become apparent from a study of this table. Very often it was possible to trace the outbreak to the food responsible for it. Sometimes this was not possible as the foods had been discarded before being suspected of contamination. Certain types of foods seem to be responsible for salmonellal food-poisoning outbreaks more frequently than do others, in particular, desserts (especially puddings) and meats (especially poultry). Of the various types of poultry, turkey seems often to be responsible for outbreaks. This may be significant since turkey is not frequently served. In most outbreaks, the cause was traced to a single Salmonella species; however, two or three species were found to be simultaneously involved in some cases. 9 Most of the cases ran the typical course for food poisoning with nausea, diarrhea, vomiting, and cramps as the salient symptoms, and these lasted only a few days.

An analysis of national statistics made by Dr. Milton Feig, a district health officer in Wisconsin, revealed that meat and meat products were involved in 27.8 percent of salmonellal food-poisoning cases; poultry, 18.5 percent; bakery products, 14.8 percent; milk and milk products, 14.8 percent; vegetables, 13 percent; and other and unknown foods, 29.6 percent. These add to approximately 119 percent because more than one food item was responsible in some of the outbreaks.10

9 (1) Bruner, D. W., and Joyce, B. J.: Salmonella Types Encountered by the 15th Medical General Laboratory. Am. J. Hyg. 45:19-24, January 1947. (2) Anderson, D. T., Johnson, L. M., Wetherbee, D. G., and Kuhns, D. M.: Isolation of Three Salmonella Species of Group C in One Case of Salmonellosis. U. S. Armed Forces M. J. 1: 1511-1515, December 1950. (3) Edwards, P. R., and Bruner, D. W.: The Occurrence of Multiple Types of Paratyphoid Bacilli in Infections of Fowls; With Special Reference to Two New Salmonella Species. J. Infect. Dis. 66: 218-221, May-June 1940. (4) Randall, C. C., and Marks, L. M.: A Salmonella Outbreak Involving Three Types of Genus. Mil. Surgeon 97:144-146, August 1945.

10 Feig, M.: Diarrhea, Dysentery, Food Poisoning, and Gastroenteritis; A Study of 926 Outbreaks and 49,879 Cases Reported to the United States Public Health Service (1945-1947). Am. J. Pub. Health 40: 1372-1394, November 1950.


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TABLE 72.–Chronological list of salmonellal outbreaks in World War II


423

TABLE 72.–Chronological list of salmonellal outbreaks in World War II -continued


424

CONTROL OF SALMONELLOSIS

During World War 11, the approach taken to the problem of salmonellosis was largely preventive. Most of the methods employed were not new, as they had been used, though not with the same thoroughness, in previous wars.11 Troops were thoroughly indoctrinated in the fundamentals of hygiene, with emphasis on personal cleanliness as well as cleanliness of the messgear that a soldier carries in the field.

At those installations where dishes were used, the dishes were air dried following washing and sterilization; no dish towels were used. Frequent dish culturing was carried out to determine the thoroughness of washing and sterilization.12 Dish culturing was introduced in the Fourth Service Command early in the war and was found invaluable in maintaining good mess sanitation for a million and a half troops in training.

High standards were maintained in the processing of foods. Milk samples were sent to laboratories to determine how well pasteurization had been carried out. For meat products, cattle and poultry were inspected before being sent to slaughter as well as after slaughter, for determining fitness for consumption. Since the epidemiology of salmonellal food poisoning in animals and birds is essentially the same as for humans, the possibility of chlorinating water to be used for animals and poultry was considered. However, such measures are largely out of the control of the Army. Foods were carefully refrigerated to prevent bacterial growth during storage and in the preparation of meats; no meats were to be used for consumption if undercooked.

The need for control of fly breeding and prevention of flies from contacting excreta (for example, by screening latrines) and contacting food supplies was on the whole appreciated. Rodents, stray dogs, and stray cats were also recognized as a potential danger and were not permitted to come in contact with food supplies and human excreta.

One of the great achievements of military medicine in World War II was the accommodation of all Army installations throughout the world with laboratory facilities. Specimens of milk, foods, and feces were forwarded to the appropriate laboratories for bacteriologic examination. The fecal specimens were often those of permanent foodhandlers, and when a carrier was discovered his unit commander was to be notified and instrusted that carriers were not permitted to be permanent handlers of food.

In addition to these procedures, TAB (typhoid, paratyphoid A, and paratyphoid B) vaccine continued to be routinely administered to all Army personnel.

11 Dunham, George C.: Military Preventive Medicine. 3d ed. Harrisburg: Military Service. Publishing Co., 1940.

12 War Department Field Manual 21-10, Military Sanitation. Washington: U. S. Government Printing Office, July 1945.


425

RESEARCH

In the United States, pioneer work in the development of agglutination serums for Salmonella identification was done by Edwards, of the University of Kentucky, Lexington, Ky. This work, as already noted, was adopted by the Army Medical Service Graduate School where the production of typing serums was expanded for Army-wide usage (p.419). The purpose of this was to carry out applied research and investigation whenever an outbreak of salmonellosis occurred; thus, a considerable amount of information was obtained concerning the species of Salmonella involved in an outbreak. Many epidemiologic investigations were carried out, and very often it was possible to trace the origins of an epidemic. If an outbreak was traceable to a sample of powdered dehydrated eggs, it was necessary to trace that egg powder to determine where and flow it had become contaminated originally: whether it lead become contaminated from the poultry or the foodhandlers, whether flies had contaminated it, or whether it was the fault of improperly cleaned mess equipment. Many outbreaks were never successfully traced, and often the causative Salmonella was not found.

EPIDEMIOLOGIC ASPECTS OF SALMONELLOSIS

Under wartime conditions, the diarrheal diseases are especially important, and many factors contribute to their occurrence.13 For example, early in World War II, as the Armed Forces increased in size and large numbers of men from all parts of the Nation were required to live together in centers of basic military training, the various proposed methods of prevention and control were due for the acid test. The men lived together in maneuver areas and in close quarters, often at hastily constructed camps and bivouacs in which it is impossible to achieve the highest sanitary standards.Active immunity, developed from exposure to the common Salmonella organisms, had not as yet been established, and a fertile field was afforded for outbreaks of salmonellosis. There was epidemiologic significance in the fact that the Army consisted of men who had been quickly brought together from all walks of life, from all parts of the country, and from all levels of sanitary habits and education.

Among other factors of epidemiologic importance is the fact that animals and birds as well as human beings furnish an ever-present reservoir of the Salmonella organisms. Among the possible carriers of Salmonellae are rats, mice, rooks, turkeys, pigs, ducks, and chickens. Rats, flies, mosquitoes, and even ticks have been shown to be capable of acting as vectors.14 The matter is further complicated by the fact that carriers play a vital role in the spread of

13 Rubenstein, A. D., Feemster, R. F., and Smith, H. M.: Salmonellosis as a Public Health Problem in Wartime. Am. J. Pub. Health 34: 841-853, August 1944.

14 (1) Ostrolenk, AL; and Welch, H.: The House Fly as a Vector of Food Poisoning Organisms in Food Producing Establishments. Am. J. Pub. Health 32: 487-494, May 1942. (2) Smith, H. W., and Buxton, A.: An Outbreak of Salmonella schwartzengrund Infection in Poultry. J. Path. & Baet. 63: 459-463, July 1951. (3) Weleh, H., Ostrolenk, and Bartram, M. T.: Role of Rats in the Spread of Food Poisoning Bacteria of the Salmonella Group.Am. J. Pub. Health 31: 332-340, April 1941.


426

salmonellosis. Some of these carriers are of the convalescent type since they continue to excrete the bacteria during the time they are recovering from their illness.Others are asymptomatic and therefore represent a far greater danger than those exhibiting symptoms, since the former may be the origin of many an outbreak of undetermined origin before being apprehended. Some Salmonella carriers are intermittent since periods of time during which Salmonella organisms are excreted alternate with periods of time in which they are apparently absent. Most individuals continue to be carriers for relatively short periods of time, while a few retain the organisms for longer periods. In civilian life, the laws and facilities in some areas are inadequate for dealing with the carrier problem, while in the Army close followups are maintained on known carriers.

A Typical Outbreak

Greifinger and Silberstein describe a completely investigated outbreak of Salmonella food infection in military personnel.15 The places of occurrence perhaps for reasons of military security are not mentioned.The outbreak was first recognized on 25 July 1943 when 28 individuals, all males, between 21 and 50 years of age were hospitalized mainly for the symptoms of nausea and abdominal cramps. These symptoms subsided in 24 to 48 hours. Bowel movements numbered 8 to 15 per day and were loose, watery, and brownish green in color. Fourteen of the patients had occult blood in their stools, ten had pus, and three showed pus and mucus. Temperatures ranged from 1010 to 104 0 F. Fried fish, tartar sauce, and rice pudding had been served at the evening mess.The fish was suspected, since it was noticed that the ice, refrigerating it, had melted.More individuals developed the usual symptoms until a total of 115 persons were incapacitated; 93 percent had diarrhea, 72.2 percent had cramps, and only 21.7 percent complained of nausea.

An interesting followup study was conducted to determine how long the individuals would continue to harbor the organisms. This is one of the greatest contributions to historical literature on salmonellosis. The results are summarized in table 73.

From the figures in table 73, it is apparent that as long as 3 months after the initial infection one may remain a carrier of Salmonella. Of the 115 individuals who were infected, 5.2 percent continued to harbor Sal. oranienburg into the 13th week. The patients were retained in the hospital until three consecutive stools were negative. The differential media employed were desoxycholate citrate, eosine methylene blue, and S.-S. (Shigella-Salmonella thiosulfatecitrate-bile) agar. Of these differential media, S.-S. agar was found to yield the largest incidence of positives. If the 5.2 percent infected individuals were carriers rather than reinfected individuals, it would indicate that individuals who have had salmonellosis should be potential carriers for that period of time.

15Greifinger, W., and Silberstein, J. K.: Salmonella Food Infection in Military Personnel; An Outbreak Caused by S. oranienburg, S. typhimurium, S. anatum. J. Lab. & Clin. Med. 29: 1042-1053, October 1944.


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TABLE 73.-Persistence of salmonellal infectionas determined by positive fecal cultures in 115 patients

RELATIVE INCIDENCE OF SALMONELLA SPECIES

Several Salmonella species were cited as the one most frequently occurring. Thus, according to Seligmann, in 1946, Salmonella schottmülleri was the most common Salmonella in the United States. Dack, in 1949, considered Sal. typhimurium as the Salmonella species found in more outbreaks of food poisoning than any other type. Edwards and Bruner 16 studied 225 cultures isolated from the feces of patients who had gastroenteritis.In order of frequency, the first nine species were: Sal. typhimurium, Sal. newport, Sal. paratyphi B. var. java, Sal. panama, Sal. oranienbury, Sal. san diego, Sal. bareilly, Sal. montevideo, and Sal. enteritidis. Undoubtedly, the original source of some of these species was eggs. During World War II, dried eggs were shipped to United States troops in all theaters of operations. According to Dack, of 7,584 amples that were sent from the United States, Canada, and Argentina, 754 (9.9 percent) were found to contain Salmonella. In all, 33 species were found.

A thorough study on the relative occurrence of Salmonella species was made by Brunet in the Mediterranean theater during World War II.17 It is

16 Edwards. P. R., and Bruner, D. W.: The Occurrence and Distribution of Salmonella Types in the United States. J. Infect. Dis. 72: 58-67, January-February 1943.

17 Bruner, D. W.: Salmonella Infections of World War II,[Official record.]


428

probably the most comprehensive analysis as to species and group occurrence on Salmonella conducted in any theater of operations. The study not only covers the incidence among United States Army troops in the Mediterranean theater but also includes valuable data on incidence among civilians, prisoners of war, French Army personnel, and carriers. The group C Salmonellae apparently were the most frequent cause of salmonellal food poisoning. Salmonella sp. (Type Oranienburg) was the most common Salmonella species causing gastroenteritis in United States Army personnel in the Mediterranean. Also, there were more carriers of Salmonella sp. (Type Oranienburg) in the United States Army than any other Salmonella species. Salmonella sp. (Type Montevideo) remained a close second. The increased number of carriers in each species were in proportion to the number of cases of gastroenteritis reported and cultured.

The occurrence of salmonellosis in the Pacific area was recorded by the 19th Medical General Laboratory, the laboratory research center for New Guinea and the Philippines.The species of Salmonella that were isolated on New Guinea in order of the number of bacteriologic isolations is shown in table 74. On New Guinea, as in other areas of the Pacific, the Salmonellae were not as common a cause of food poisoning as the Shigellae.

TABLE 74.-Salmonellosis outbreaks and isolations of Salmonella species and types in New Guinea, September 1944 to July 1945

It is to be noted that while Sal. enteritidis was the number one disease in occurrence, Salmonella typhosa was responsible for the greatest number of outbreaks. The distinction made here is of epidemiologic significance particularly in food-poisoning outbreaks. Eventually, it is presumed that bacteriologists will no longer refer to infections with Salmonella contracted through food as food poisoning but simply as Salmonella infections.

The species of Salmonella that were isolated in the Philippines, in descending number of isolations, is shown in table 75. The outstanding causes of salmonellal food poisoning in the Philippines were, according to these data, Sal. enteritidis and Sal. paratyphi.


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TABLE 75.-Salmonellosis outbreaks and isolations of Salmonella species and types in the Philippines, July 1945 to December 1946

LABORATORY ADVANCES IN DIAGNOSIS OF SALMONELLOSIS

The laboratory diagnosis of salmonellal food poisoning is basically not different from what it has always been. It depends upon the recovery of the organism, usually from the stools, based on a principle dating back to Koch's postulates. Yet, considering the incidence of salmonellal food poisoning, it is a fact that in many cases the organism is never demonstrated. In the field, it was often impossible to transport biological specimens under proper conditions. Another and perhaps more important point is the fact that Salmonellae will often be present only during the brief period of acute symptoms. According to Verder and Sutton,18 there is an inverse relationship between the number of ingested organisms and the incubation period. The smaller the number of organisms taken in, the more prolonged will be the period of incubation. Thus, there is a strong lilkelihood that a stool specimen taken even 1 day following the subsidence of symptoms will be void of Salmonellae. As for the contaminated food, it is often. discarded before an examination can be conducted.

There are several differential media in use, including Shigella-Salmonella medium, tetrathionate broth base, and selinite-F enrichment medium. Occasionally, one encounters a Salmonella species that will not grow on S.-S. agar.For this reason it is a prudent policy to use a less inhibiting medium in addition. Most often in salmonella. outbreaks, only one species is found. Occasionally, two or even three species are present simultaneously, and it would be a moot question to inquire as to which species is producing which symptoms.19 A procedure of great value in diagnosing salmonella. food

18 Verder, E., and Sutton, C.: Is Salmonella Food Poisoning Caused by Living Bacilli or by Thermostabile Toxic Product?. J. Infect. Dis. 53: 262-271, September-October 1933.

19 See footnote 9 (2), p. 421,


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poisoning was the anal-swab technique introduced by Hardy. Its main advantage lay in the fact that it was not necessary to wait until stool specimens were collected from those who were to be tested. Anal swabs could be taken from a number of individuals in a very short time and cultures made on a large scale.

EVALUATION OF THE ARMY'S EXPERIENCE

Carriers.-In evaluating the Army's experience with salmonellosis, several conclusions can be elicited. First, it was never among the most serious of the medicomilitary problems. The history of salmonellal food poisoning shows that the preventive aspects have always been given more attention than the therapeutic aspects. In typical cases, the symptoms are striking and soon disappear completely leaving the victim little cause for alarm. As a result, many of the patients recover, only to become carriers for a greater or shorter period of time. Although the Army's treatment of the carrier problem compares favorably with that of the best civilian health departments, it is also true that the Army especially during the time of war places major stress on returning to duty as many men as possible as soon as they appear capable of resuming work. However, in cases of salmonellal infection, it is not safe to return a man to duty in the mess merely because of the subsidence of acute symptoms. In connection with the carrier problem, it should be noted that surprisingly few outbreaks during World War II were found traceable to a carrier origin.

Foodhandlers.-The most important military consideration in the carrier problem is that of the career foodhandler as developed during World War II..20 A foodhandler may without his or anyone else's knowledge dispense Salmonellae systematically to large numbers of troops throughout his career. Of lesser significance is the temporary foodhandler, especially in basic training units where it is accepted procedure to utilize kitchen police in the handling and distribution of food.

Vectors and reservoirs of salmonellal infection.-The role of vectors and reservoirs in salmonellal food poisoning has already been mentioned in the literature.Flies are of prime importance.The problem is more than one of using insecticides; also required is the rigorous application of the basic well-known principles of hygiene and the execution of such measures as the screening of messhalls and latrines whenever possible. Even then, there exists the problem of animal and bird reservoirs, perhaps more challenging than the flies and surely a far more difficult problem under field conditions. It must be stressed, however, that even though hygienic principles were sometimes abandoned during World War II field conditions, the sanitary level achieved in the field during the war was higher than that of any previous war.

The military problem.-Salmonellosis is of special interest to the Army for more than the theoretic reasons that have been discussed. Although it

_

20 Stone, W. S.: Food Handlers in the Army and Their Relationship to Salmonella Food Poisoning.Am. J. Pub. Health 33: 706-708, June 1943.


431

rarely caused serious infection, it can with dramatic suddenness temporarily incapacitate large numbers of troops. In time of war, this can lead to catastrophic results. During World War II, as in World War I, most of the Army's outbreaks were sporadic, and real epidemics were the exception rather than the rule. There are two explanations for this. The first explanation is that over a period of half a century the Army had attained and on the whole maintained a high standard of sanitation. The second explanation is the preventive role of the Army's TAB vaccine which is routinely administered to all military personnel. The validity of the first point is generally accepted. There is, however, divided opinion as to the value of the vaccine. While some consider it effective in preventing salmonellal infection, many believe it has little value. The truth may be between the two extremes, and while TAB vaccine might not be effective in preventing salmonellosis it may have some effect on mitigating the symptoms, thereby modifying the course of the disease.