Food Poisoning Part 4

CHAPTER V

FOOD-BORNE PATHOGENIC BACTERIA

Many cases of so-called food poisoning are due to the presence of pathogenic bacteria in the food. In some instances, as in the typical meat poisoning epidemics, symptoms develop so soon after eating that the particular food involved is immediately suspected and laid hands on. In other cases the guilty article of food is difficult to trace. Certain cases of tuberculosis are undoubtedly caused by swallowing tubercle bacilli in the food, but the precise source and date of infection can be rarely, if ever, certainly established.

The presence of pathogenic bacteria in food is usually due either to the contamination of the food by infected human beings during the process of preparation or serving, or to an infection of the animal from which the food is derived. The relative importance of these two factors is quite different in the various infections.

TYPHOID FOOD INFECTION

The typhoid bacillus does not attack any of the domestic animals; consequently all food-borne typhoid is caused more or less directly by human contamination. A remarkable instance of typhoid infection due to food was reported in 1914 in Hanford, California, where ninety-three typhoid cases were caused by eating Spanish spaghetti served at a public dinner.[49] Investigation showed that this dish was prepared by a woman typhoid-carrier who was harboring living typhoid bacilli at the time she mixed the sauce for the spaghetti before baking. Further laboratory experiments indicated that the ordinary baking temperature at which the spaghetti was cooked was not only not sufficient to sterilize the food, but afforded a favorable opportunity for the bacteria in the interior of the ma.s.s to multiply. The infection of the food was consequently heavy and involved a very large proportion (57 per cent) of those present at the dinner.

Merited celebrity attaches to the exploits of the typhoid-carrier, Mary Malloy, who, in pursuing her career as cook in and about New York City, is known to have caused at least seven typhoid outbreaks in various families in which she worked and one extensive hospital epidemic.

Similar cases of typhoid food infection by employees in restaurants and public inst.i.tutions are by no means uncommon, and show the necessity of protecting food from contamination during the whole process of preparation and serving. Acting on this principle, the Department of Health of New York City has inaugurated a comprehensive examination of the cooks and waiters (approximately 90,000) employed in the public restaurants and dining-rooms in that city. Results have been obtained in the discovery of typhoid-carriers and of cases of communicable disease that amply justify this procedure as an important measure for protecting the community against the dissemination of infection.

Some foods by their origin are exposed more than others to typhoid contamination. Such vegetables as lettuce, celery, radishes, and watercress, which are commonly eaten without cooking, are more likely to convey typhoid than peas, beans, and potatoes. A typhoid outbreak apparently due to watercress has been reported from Philadelphia.[50] At a wedding breakfast to forty-three guests on June 24, 1913, watercress sandwiches were served, and subsequent inquiry showed that nineteen of the guests partook of these sandwiches. Eighteen of this number became ill with typhoid fever within a month, the illness developing in most cases after the guests had scattered to their summer homes. Those who did not eat watercress sandwiches were not affected. Typhoid infection by uncooked celery has also been reported.[51]

The practice of using human excreta as fertilizer in truck gardens is sometimes responsible for a dangerous contamination of the soil, which is communicated to the growing plants and persists for a long time.[52]

Even scrupulous was.h.i.+ng of vegetables is not sufficient to render them bacterially clean. In the future the danger to the community from this source is likely to become increasingly serious unless the growing use of this method of soil enrichment is definitely checked.

In 1915 an increasing number of typhoid cases in South Philadelphia led to an investigation by the state health department.[53] This disclosed the fact that the majority of the cases were cl.u.s.tered in and about three public markets.

These are all curb markets--fruits, vegetables, pastry, clothing, and miscellaneous merchandise of every description are dumped on push-carts and pavements without regard for any sanitary precautions. The patrons of these markets handle and pick over the exposed foodstuffs, thus giving every opportunity for the transmission of disease....

The greatest number of cases occurred in the immediate vicinity of the Christian Street Market. This market is largely patronized by the inhabitants of the section known as "Little Italy." The patrons of the South Street Market are princ.i.p.ally Hebrews, while the Seventh Street Market is patronized in the main by Hebrews and Poles.

The following conclusion was reached regarding the particularly large number of cases among persons of one nationality:

Our inspectors have found that the different methods used by the Italians and Hebrews in the preparation of their food are responsible for the larger number of cases being found in the vicinity of the Christian Street Market in Little Italy. It is the custom of the Italians to eat many of the fruits and vegetables raw, while the Hebrews cook the greater portion of their food. It is presumably due to this custom that the members of the Italian colony have suffered to a greater extent than the other residents of the district.

A bacterial examination of various kinds of vegetables obtained from push-carts and curb markets led to the finding of the typhoid bacillus upon some of the celery. It would naturally be difficult to determine in such cases whether the typhoid bacilli were derived from infected soil in which the celery was grown or whether the contamination occurred through improper handling.

Bread, when marketed unwrapped, is subject to contamination from flies and from uncleanly handling. Katherine Howell[54] has shown that unwrapped loaves of bread sold in Chicago were more or less thickly smeared with bacteria and were coated on the average with a much larger number than wrapped loaves. In some cases typhoid fever has been directly traced to bread. Hinton[55] has recorded the occurrence of seven typhoid cases in the Elgin (Illinois) State Hospital, which were apparently due to a typhoid-carrier whose duty it was as attendant to slice the bread before serving. When this typhoid-bearing attendant was transferred to another department where she handled no uncooked food, cases of typhoid ceased to appear.[56]

Food such as milk that is not only eaten customarily without cooking, but is also suitable for the growth of typhoid bacilli, needs to be particularly safeguarded. It is noteworthy that the compulsory pasteurization of milk in New York, Chicago, and other large American cities has been accompanied by a great diminution in the prevalence of typhoid fever. Until recent years milk-borne typhoid in the United States has been common and hundreds of typhoid epidemics have been traced to this source.

[Ill.u.s.tration: FIG. 5.--Bacteria left by fly pa.s.sing over gelatin plate.

(By courtesy of Doubleday, Page & Company.)]

One food animal, the oyster, frequently eaten raw, has been connected on good evidence with certain typhoid outbreaks.[57] The number of well-established oyster typhoid epidemics is not great, however, and the danger from this source has sometimes been exaggerated. The source of oyster contamination is in sewage pollution either of the sh.e.l.lfish beds or of the brackish water in which the oyster is sometimes placed to "fatten" before it is marketed. State and federal supervision of the oyster industry in the United States in recent years has largely done away with the taking of oysters from infected waters, and although oysters--and clams and mussels as well--must be steadily safeguarded against sewage contamination, the actual occurrence of oyster infection at the present time is believed to be relatively rare.

Probably the most effective method of preventing typhoid food infection is to investigate every case of typhoid fever and trace it, so far as practicable, to its origin. In this way typhoid-carriers may be discovered and other foci of infection brought to light. Carriers, once found, may be given proper advice and warned that they const.i.tute a danger to others; the complete control of typhoid-carriers who are not disposed to act as advised is a difficult problem and one not yet solved by public health authorities.

ASIATIC CHOLERA

With Asiatic cholera, just as with typhoid fever, domestic animals are not susceptible to the disease, all cases of infection having a direct human origin. Drinking-water is the usual vehicle of cholera infection, and even in countries where the disease is endemic, food-borne outbreaks of this disease are far less common than those of typhoid fever.

Occasional instances of Asiatic cholera due to milk supply and to contaminated fruits or lettuce are on record, but these are exceptional and cannot be regarded as exemplifying a common mode of spread of this disease. The extent, however, to which dwellers in tropical countries--and indeed in all lands--are at the mercy of their household helpers is ill.u.s.trated by the following experience of the English bacteriologist, Hankin. "I have seen," he says, "a cook cooling a jelly by standing it in a small irrigation ditch that ran in front of his cookhouse. The water running in this drain came from a well in which I had detected the cholera microbe. He cleaned a spoon by dipping it in the drain and rubbing it with his fingers; then he used it to stir the jelly."[58]

TUBERCULOSIS

Animal experiments have shown that both meat and milk derived from tuberculous cattle are capable of conveying infection. The precise degree of danger to human beings from the use of these foods under modern conditions is still in dispute. Since the tubercle bacillus of bovine origin differs from the tubercle bacillus of human origin in certain well-defined particulars, it is possible by careful study to distinguish the human infections caused by the bovine bacillus from those caused by the so-called human tubercle bacillus. Additional comparative investigations are needed in this field, and these may enable us to estimate eventually more fully than is possible at present the extent of human tuberculous infection derived from bovine sources.

Meat is a less likely source of infection than milk, chiefly because it is rarely eaten without cooking. Opinion regarding the actual frequency of the transmission of tuberculosis by means of the meat of tuberculous cattle has been widely at variance in the past, and must even now be based on indirect evidence. There is no well-established instance of human infection from the use of the flesh of tuberculous cattle. The significance of this fact, however, is diminished by the observation that tubercle bacilli can pa.s.s through the intestinal wall without leaving any trace of their pa.s.sage and can make their way to the lungs or to other distant organs where they find opportunity for growth. This, together with the long period which usually elapses between the actual occurrence of infection and the discovery of the existence of infection, makes the difficulty of securing valid evidence peculiarly great.

Opposed to any very frequent occurrence of meat-borne tuberculosis are the facts that the tubercle bacillus is not commonly or abundantly present in the ma.s.ses of muscle usually marketed as "meat," that the tubercle germ itself is not a spore-bearer and is killed by ordinary cooking, and that the reported cases of the finding of tubercle bacilli of bovine origin in adults over sixteen years of age are extremely rare.

This latter fact is perhaps the strongest evidence indicating that tuberculous meat infection, although theoretically possible, is at least not of common occurrence.

Most of the commissions and official agencies that have considered the precautions to be taken against possible tuberculous meat infection are agreed that the entire carca.s.s of an animal should be condemned when the tuberculous lesions are generalized or when the lesions are extensive in one or both body cavities as well as when the lesions are "multiple, acute, and actively progressive." Any organ showing evidence of tuberculous lesions is obviously not to be pa.s.sed as food. On the other hand, it is considered that portions of properly inspected animals may be put on the market if the tuberculous lesion is local and limited and the main part of the body is unaffected; in such cases contamination of the meat in dressing must be avoided. It is the general belief that when such precautionary measures are taken the danger of tuberculous infection through properly cooked meat is so slight as to be negligible.

Milk is a much more likely vehicle than meat for the transmission of tuberculosis. Freshly drawn raw milk from tuberculous cattle may contain enormous numbers of tubercle bacilli, especially if the udder is diseased. Contamination of milk by the manure of tuberculous cows can also occur. Observers in England, Germany, France, and the United States have found tubercle bacilli in varying numbers in market milk, and have proved that such milk is infectious for laboratory animals. Although, as pointed out with reference to meat infection, the difficulties of tracing any particular case of tuberculosis to its source are very great, there are a number of instances on record in which the circ.u.mstantial evidence strongly indicates that milk was the vehicle of infection. Especially convincing are the observations on the relative frequency of infection with bovine and human tubercle bacilli at different ages as shown in the following tabulation:[59]

==================================================================== |Adults Sixteen|Children Five to|Children under | Years Old | Sixteen Years | Five Years | and Over | Old | --------------------+--------------+----------------+-------------- Human tubercle | 677 | 99 | 161 bacilli found | | | Bovine tubercle | 9 | 33 | 59 bacilli found | | | -------------------------------------------------------------------

The large proportion of bovine tubercle bacillus infections in children stands in all probability in causal relation to the relatively extensive use of raw milk in the child's dietary.

The proper pasteurization of milk affords a safe and reasonably satisfactory means of preventing tuberculous infection from this source.

The general introduction of the pasteurizing process in most American cities has ample justification from the standpoint of the prevention of infection.

VARIOUS MILK-BORNE INFECTIONS

The facts related in the foregoing pages indicate that of all foods milk is the most likely to convey disease germs into the human body. This is partly due to the fact that milk is sometimes obtained from diseased animals, and partly to the fact that unless great care is taken it may readily become contaminated during the process of collection and transportation; if milk is once seeded with dangerous bacteria these can multiply in the excellent culture medium it affords. It is also partly because milk is commonly taken into the alimentary tract without being cooked. For these reasons the amount of illness traceable to raw milk far exceeds that ascribable to any other food.

There are several infections that may be communicated by milk, but are rarely if ever due to other foodstuffs. Diphtheria and scarlet fever are perhaps the best known of these. Both diseases have been repeatedly traced to the use of particular milk supplies, although various forms of individual contact also play a large role in their dissemination.

Milk-borne scarlet fever and diphtheria seem to be generally, if not always, due to the direct contamination of the milk from human sources.

It is considered possible, however, by some investigators that the cow may sometimes become infected from human sources with the virus of scarlet fever or diphtheria and may herself occasionally contribute directly to the infection of the milk.

A serious milk-borne disease, which has lately been conspicuous in Boston, Chicago, Baltimore, and other American cities under the name of "septic sore throat" or "streptococcus sore throat," originates apparently in some cases from infection of the udder of the cow by an infected milker; in other cases the milk has seemingly been directly infected by a human "carrier." The specific germ is thought to have been isolated and its connection with the disease demonstrated in the laboratory. This disease, like diphtheria and scarlet fever, is sometimes due to contact. It is not known to be caused by any food except milk.

Foot-and-mouth disease of cattle is transmissible to man through the milk of infected cattle, but this infection in man is not very common or as a rule very serious. So far as known, it is not communicated to man in any other way except through the use of uncooked milk.

Such cases of infection or "poisoning" by milk may be prevented, as already stated, by the exclusive use of heated milk. The possible occurrence of nutritional disturbances (e.g., scurvy) in a small proportion of the children fed on pasteurized or boiled milk is considered by many physicians to be easily remedied and to possess much less practical importance than the avoidance of infection.

POSSIBLE INFECTION WITH B. PROTEUS

One widely distributed organism known as _Bacillus proteus_ has been several times held responsible for food poisoning outbreaks, but it is not yet certain how far this accusation is justified. _B. proteus_ is related to _B. coli_, but most varieties do not ferment lactose and are much more actively proteolytic than the latter organism, as shown by their ability to liquefy gelatin and casein. Like _B. coli_, they form indol and ferment dextrose with gas production. Varieties of _B.

proteus_ are found widely distributed in decomposing organic matter of all sorts.

The evidence upon which this bacillus is regarded as the cause of food poisoning is not altogether convincing. The outbreak described by Pfuhl[60] is typical. Eighty-one soldiers in a garrison at Hanover were suddenly attacked with acute gastro-enteritis four to twelve hours after eating sausage meat. The meat was found to contain _B. proteus_ in large numbers, although it was prepared with ordinary care and was entirely normal in appearance, taste, and smell. Rats and mice fed with the sausage became ill and _B. proteus_ was isolated from the blood and internal organs. But these animals sometimes die when fed with quite normal meat, and _B. proteus_ and other common intestinal bacteria are often isolated from the body after death. _B. proteus_, in fact, is found in many animal foods and in the apparently normal human intestine.

Like _B. coli_, it frequently invades the internal organs after or shortly before death. Finding _B. proteus_ in food or in the internal organs does not therefore const.i.tute definite proof of any causal relations.h.i.+p. The evidence attributing other outbreaks to infection with _B. proteus_ is similarly inconclusive.

It is equally uncertain whether the production of a poison in food by this species can in any degree be held responsible for meat poisoning.

_B. proteus_ is common enough in decomposing food material and under certain circ.u.mstances is known to generate substances that are toxic for man. It is possibly true that toxic substances are produced in the early stages of decomposition by this organism. In the opinion of Mandel[61]