THE MILK SUPPLY OF CITIES IN RELATION TO THE

EPIDEMIOLOGY OF TYPHOID FEVER.

By LESLIE L. LUMSDEN.

Passed Assistant Surgeon, Public Health and Marine-Hospital Service.

Milk is a favorable culture medium for the Bacillus typhosus. Therefore, if a small particle of matter containing this organism is introduced into milk the organism may undergo rapid multiplication and become disseminated throughout the bulk of the milk. The temperature at which the milk is kept and the number and kind of the other bacteria present affect the rate at which the multiplication of the B. typhosus takes place, and in some instances, no doubt, the bacilli, after gaining access to a body of milk, die out before that milk is drunk. In the majority of instances, however, it is probable that the bacillus will survive and so endanger all susceptible persons into whose alimentary canals such milk is taken.

Considering the tremendous multiplication which the bacillus can undergo within twenty-four hours in milk it is easy to appreciate how one can or bottle of infected milk taken into a dairy and there mixed with a large volume of milk may be responsible for exposure to infection of several thousand persons.

Dairy products such as ice cream, buttermilk, butter and cheese, etc., made from infected milk have to be kept in mind as possible factors in the spread of typhoid fever.

Ice cream. It has been proven experimentally that the process of freezing does not at once destroy all typhoid bacilli, and outbreaks of typhoid fever have been traced quite definitely to infected ice

cream.

a

Butter and cheese.-Bruck has shown that butter made from milk experimentally infected with B. typhosus may retain the bacillus for as long as twenty-seven days. Under ordinary conditions, however, it would seem that the presence of many vigorous saprophytes, the washing out of large numbers of bacteria in the buttermilk, and the

"Bruck, Deutsche Med. Woch., 1903, XXIX, p. 460, Milk.

salting, would lessen the chances of the B. typhosus remaining in the butter, and it is improbable that butter frequently plays much part in the spread of typhoid fever. (McCrae, in Osler's Modern Medicine, Vol. II, 1907.)

Buttermilk would, of course, be fully as dangerous as the cream from which it was derived.

Cheese. The time required for the ripening of cheese makes the chances of infection from this dairy product certainly very slight.

Butter and cheese from a given source are usually so widely distributed that should an outbreak of typhoid fever in a large city be caused by them it would be very difficult to trace unless the outbreak were very extensive and pronounced or other factors could be excluded so that attention would be directed to these dairy products.

WAYS IN WHICH THE TYPHOID BACILLUS MAY GET INTO MILK.

At the dairy farm.-The milk supply for the average American city is obtained from a large number of dairy farms and the liability of cases of typhoid fever developing every year among persons living on these farms can be readily appreciated. The city of Washington, for example, obtains its milk supply from about 1,000 dairy farms. Estimating the average number of persons living at a dairy farm at about 7, and considering the fact that every year, in the United States, about one person in every 300 has typhoid fever, some 25 cases per year may be expected to occur on the dairy farms supplying Washington with milk.

When cases exist on the dairy farms the chances of the infection being conveyed from the patients to the milk, in the majority of instances, must be great. Frequently the cases are not recognized as typhoid until the second or third week of illness, during which period no precautions are taken. In many instances there are mild cases unattended by a physician and cases following an irregular course, which go through the attack without being recognized. Too frequently when the cases are correctly diagnosed in the comparatively early stages of the disease the disinfection of the patient's stools and urine and the other precautions necessary to prevent the spread of the infection are found to be woefully inefficient.

When the infection is not destroyed as it leaves the body of the patient, there are many ways in which the typhoid bacilli may be carried from a patient on a dairy farm to the milk. Thus, those caring for the sick or handling the soiled bedding or excreta of the patient may convey the infection on their hands or clothing. Persons who have recovered from the symptoms of the disease but are still discharging the bacilli in their stools or urine may directly contaminate the milk in handling it. Some persons after passing through an attack of ty

phoid fever continue to discharge the bacilli in their stools or urine for years. One of these so-called bacillus carriers working in milk at a dairy farm or dairy may contaminate a can of milk from time to time and be the source of infection for a number of cases. It is easy to appreciate how much infection might be spread from a bacillus carrier, such as the one so admirably discovered by Soper," if working at a dairy farm or dairy.

It is possible for persons in the early stage of the disease, and even before becoming ill enough to take to bed, to contaminate milk. The spread of infection from cases in the early stage has generally been considered of infrequent occurrence on the ground that the bacilli rarely appear in the urine before the end of the third week of illness and that few if any are discharged in the feces during the first week or two. On the contrary, H. Conradi," who has made extensive studies on the conveyance of typhoid infection in Germany, states that he has reached the conviction that not only is the infection transmitted most often during the earliest stages of the disease, before its true nature has been recognized, but that it also frequently takes place during the incubation period. He bases this opinion on the observation that of 89 cases which he attributed to infection by contact, some 58 per cent of the secondary cases had onset of illness in the first week of the illness of the primary case, indicating that more or less of the secondary cases must have received the infection during the incubation period of the primary cases.

Flies passing from the infected excreta to the milk or the milk cans may readily convey the infection.

The excreta of patients thrown into the privy or in the yard or field nearby may be carried by drainage, seepage, on the feet of persons, etc., to the well, spring, or stream from which water is used for washing cans and so be conveyed to the milk.

In country places there are frequent instances where chickens and other fowls have free access to the privy contents and may readily carry infection on their feet to the well. The excreta of patients, carelessly handled, may become dried and carried as dust into exposed milk or more frequently into exposed milk vessels.

Bottles or cans in some way contaminated at the house or dairy in the city and without previous disinfection are again filled with milk at the dairy farm may be the means of conveying infection from the dairy farm back to the city.

At the dairy.-Milk after it reaches the city dairy is not only exposed to the danger of becoming contaminated by persons handling

"The Work of a Chronic Typhoid Germ Distributor." Jour. Am. Med. Assn., Vol. XLVIII, No. 24, p. 2019.

Deut. Med. Woch., Oct. 10, 1907.

the milk, as at the farms, but also is exposed to chances of becoming contaminated indirectly by flies, dust, etc. In some American cities many of the diaries are located in the most unhygienic sections, and frequently cases of typhoid fever are cared for in houses adjoining the dairy or even in the same building, but on the floor above. In these instances it is easy to understand how flies may pass from the dejecta of a patient to a can or bottle of milk and so be the means of conveying the infection. Cans or bottles returned from houses in which there are typhoid patients and which have been handled by persons caring for the sick and not disinfected before being refilled may be the means of disseminating the infection in the

milk.

From the water used for washing the bottles or cans, etc., at the city dairy, the B. typhosus may reach the milk. Considering the immense dilution in which the typhoid bacillus must usually exist in water taken from a large volume such as a river or lake for supplying a city, it may be that persons are rarely infected directly by the organism in the water; but it can be understood how the occasional B. typhosus in the water upon being introduced into the milk and there multiplying, may infect persons drinking that milk.

At the grocery.-In the studies of Rosenau, Lumsden, and Kastle. on the prevalence of typhoid fever in the District of Columbia there were found a number of instances in which the typhoid patients were being cared for in a room above or to the rear of the small grocery stores. In these stores milk was sold in small quantities, often as little as a cent's worth at a time, so that a quart bottle would be divided among several customers. The same hands that nursed the patient. purveyed the milk. In such instances not only is there a likelihood of infection being sent out in the milk directly from the store, but these much-handled bottles may do damage when returned to the dairy.

At the home.-Milk after being delivered to the house may become contaminated by the hands of those caring for the sick or by flies, etc., and be the medium of conveyance of infection to other members of the household.

DETERMINATION OF AN OUTBREAK OF TYPHOID FEVER DUE TO INFECTED MILK.

In the epidemiological studies of typhoid fever in a city a card should be kept for each milk dealer and on this card should be noted all cases of typhoid fever in persons who within thirty days prior to the onset of illness have used milk supplied by that dealer. Thus, as

Hygienic Laboratory Bulletin No. 35, Report on the Origin and Prevalence of Typhoid Fever in the District of Columbia, 1907.