Bainbridge and Dudfield[86] describe an outbreak of acute gastro-enteritis occurring in a boarding-house; it was found that no one article of food had been eaten by all the persons affected, and there were other reasons for supposing the outbreak to be due to miscellaneous food contamination by a servant who was a carrier.
There is, therefore, ground for believing that occasional contamination of food may be brought about by bacteria of this group derived from human sources. It is not clear, however, how frequent this source of infection is, compared to infection originating in diseased animals. It must be admitted, too, that English investigators are disposed to look upon outbreaks similar to those just described as infections with B. paratyphosus B, an organism which they would distinguish from the "true" food poisoning bacilli, B. enteritidis and B. suipestifer.
3. Miscellaneous contaminations: Some investigators, especially certain German writers, regard the bacilli of the paratyphoid group as so widely distributed in nature that any attempt to control the spread of infection is like fighting windmills. According to this view the bacilli occur commonly in our everyday surroundings and thence make their way rather frequently into a variety of foodstuffs. Various German investigators have reported the presence of paratyphoid bacilli in the intestinal contents of apparently normal swine, cattle, rats, and mice and more rarely of other animals, in water and ice, in German sausage and chopped meat, and in the bodies of apparently healthy men. To what extent their alleged ubiquity is due to mistaken bacterial identification, as claimed by some English investigators, remains to be proved. There is no doubt that in some quarters exaggerated notions have prevailed respecting a wide distribution of the true paratyphoid bacteria. Savage and others believe that the hypothesis that food poisoning outbreaks are derived from ordinary fecal infection of food is quite unfounded. It is pointed out that there is good evidence of the frequent occurrence of intestinal bacteria in such food as sausages and chopped meat, and that consequently, if paratyphoid infections could occur through ordinary contamination with intestinal bacteria not connected with any specific animal infection, food poisoning outbreaks should be exceedingly common instead of—as is the case—comparatively rare.
At the present time even those who maintain that these bacilli are of common occurrence admit that their abundance is more marked in some regions than in others. Southwest Germany, for example, seems to harbor paratyphoid bacilli in relatively large numbers. Possibly local differences in distribution may account for the discrepancies in the published findings of German and British investigators.
A special case is presented by the relation of these bacilli to rats and mice. Among the large number of bacteria of the paratyphoid group is the so-called Danysz bacillus, an organism quite pathogenic for rodents, and now and again used in various forms as a "rat virus" for purposes of rodent extermination. Several outbreaks of food poisoning in man have been attributed on more or less cogent evidence to food contamination by one of these viruses either directly by accident, as in the case described by Shibayama,[87] in which cakes prepared for rats were eaten by men, or indirectly through food contaminated by mice or rats that had been infected with the virus.[88] The use of such viruses has not proved of very great practical value in the destruction of rodents, and is open to serious sanitary objections, since the animals after apparent recovery can continue to carry the bacilli of the virus and to distribute them on or near food substances.
It seems possible that rats and mice may become infected with certain bacteria of this group without human intervention, and that these infected animals may be the means of contaminating foodstuffs and so causing outbreaks of food poisoning. Proof of the frequency with which this actually occurs is naturally difficult to obtain.
There is no escape from the conclusion that in any given case of food poisoning the exact source of infection is often largely conjectural. Even when suspicion falls strongly on a particular article of food, it may not be possible to establish beyond a reasonable doubt whether the material (meat or milk) came from a diseased animal or whether it was infected from other sources (man or other animals) at some stage during the process of preparation and serving. The most definitely attested cases yet put on record are those in which it is possible to trace the infection to food derived from an ailing animal.
Means of prevention.—The most obvious and probably the most important method of preventing infection with paratyphoid bacilli is the adoption of a system of inspection which will exclude from the market as far as possible material from infected animals. To be most effective such inspection must be directed to examination of the living animal. The milk or the meat from diseased animals may give no visible sign of abnormality. In the Ghent outbreak of 1895 the slaughter-house inspector, a veterinary surgeon, was so firmly convinced that the meat which he had passed could have had no connection with the outbreak, that he ate several pieces to demonstrate its wholesomeness. The experiment had a tragic ending, as the inspector was shortly attacked with severe choleraic symptoms and died five days later, paratyphoid bacilli being found at the autopsy. Müller[89] also has described a case in which paratyphoid bacilli were found in meat that had given rise to a meat poisoning outbreak although the meat was normal in appearance and the organs of the animal showed no evidence of disease to the naked eye. It is evident that inspection of the live animal will often reveal evidence of disease which might be missed in the ordinary examination of slaughter-house products.
Although inspection of cows used for milking and of food animals before slaughter is highly important, it does not constitute an absolute protection. Emphasis must be repeatedly laid on the fact that meat, and especially milk that is derived from seemingly healthy animals, may nevertheless contain paratyphoid bacilli. To meet this difficulty in part the direct bacterial examination of the carcasses of slaughtered food animals has been proposed, but this seems hardly practicable as a general measure. In spite of all precautions taken at the time of slaughtering it seems probable that occasionally paratyphoid-infected meat will pass the first line of defense and be placed on the market.
This danger, which is probably not a very grave one under a reasonably good system of inspection of live animals, may be met by thoroughly cooking all foods of animal origin. It is worth noting that some of the internal organs, as the liver and kidneys, are more likely to contain bacteria than the masses of muscle commonly eaten as "meat." Sausages, from their composition and mode of preparation, and chopped meat ("hamburger steak") are also to be treated with especial care. Consumption of such foods as raw sausage or diseased goose liver (paté de foie gras) involves a relatively high risk. It is true of paratyphoid infection as of most other forms of food poisoning that thorough cooking of food greatly diminishes the likelihood of trouble.