CHARACTER OF MILK-BORNE DISEASE 379 



3. A third and probably very important source of infection comes 

 from carriers who work on the farms, in dairies, or other places 

 where milk is handled. 



Indirect human infection comes largely from the use of infected 

 water which is used in the washing of buckets, bottles, and other 

 milking utensils. Cows often have access to polluted water and 

 infection from this source may find its way into the milk from being 

 on the body of the animal. 



Character of Milk-borne Diseases. Milk-borne diseases have 

 characteristics which greatly assist the epidemiologist in his work. 

 The most important are the following: 



1. The cases usually follow the route of the milkman and it is 

 often possible to plot his route from the cases of the specific disease. 

 There would thus be the inhabitants of homes where the infected 

 milk is used suffering with the disease, while neighbors who use 

 other milk escape. There may be many purchasers of the infected 

 milk who may escape, but when careful inquiry is made it is found 

 consumers of the implicated supply furnish a much higher percentage 

 of cases than does the rest of the community. The smallest per- 

 centage invasion of households is met with in scarlet fever outbreaks. 

 But this is easily explained when one considers the number of missed 

 cases in this disease. 



2. The outbreaks from infected milk are usually explosive. 

 Sometimes the majority of the cases occur within a few days of each 

 other. Usually there is little secondary infection and the decline is 

 rapid on removal of the source of infection. The epidemic at Stam- 

 ford, Connecticut, in 1895, is a good example. There were 386 

 cases of typhoid fever and 22 deaths in the period from April 15 to 

 May 28. There were 176 persons stricken during the first week. 



Although the explosive type of epidemic is usually characteristic 

 of milk-borne outbreaks, yet Parker points out that the smoldering 

 kind may be very commonly due to infected milk. He cites as an 

 example the experience of Hill of North Branch, Minnesota, where 

 one of the physicians pointed out that in his seventeen years of 

 practice during the first twelve there was no typhoid fever, but in the 

 last five years native cases of unknown origin had been frequent. 

 Acting on this information, a list of 21 cases of typhoid fever that 

 had appeared in the town in the last five years was made, and 

 inquiry showed that seventeen of the patients were regular custo- 

 mers of a dairyman who came to town five years before, two others 

 were irregular customers, and two others may have used milk from 

 his dairy. It was learned that the wife of the dairyman, who washed 

 the cans, had suffered with typhoid fever twenty-two years before 

 and gave a positive Widal reaction, but typhoid bacilli were not 

 isolated from her stools. She was forbidden to have anything more 

 to do with the dairy and the proprietor was told that if another 



