MILK-BORNE INFECTIONS 433 



Furthermore, the infectious material may not be evenly dis- 

 tributed through the milk, and, as a matter of fact, it has happened 

 that but one out of a number of milk cans was actually infected. 

 Infectious material may gain access to a relatively small number 

 of bottles, thus carrying disease to a limited group of families. 



2. Susceptibility to the disease: Individual susceptibility to 

 a disease naturally plays an important role in the number of 

 persons coming down with a milk-fcorne infection. If, for example, 

 a milk-supply is contaminated with typhoid bacilli the percentage 

 of persons taking the infection will be smaller in a community in 

 which typhoid fever has been more or less prevalent than in a 

 community relatively free from the disease. Furthermore, since 

 typhoid fever is a disease chiefly confined to certain age limits, 

 those within these limits are more liable to suffer than others. 



3. The manner in which milk is used: If milk is used chiefly 

 on cereals, fruit, etc., it is consumed in relatively small amount, 

 and when taken in hot tea or coffee the incidence may be quite 

 small, since these beverages are taken at a temperature which 

 destroys a large number of bacteria. 



4. The virulence of the organism : The well-known variability 

 in virulence of pathogenic bacteria may be the cause of affecting 

 a small or large percentage of milk consumers. 



The facts stated show clearly that a milk-supply may be re- 

 sponsible for an epidemic even if only a small number of persons 

 is affected. On the other hand, it may happen that persons who 

 do not regularly use the incriminated supply are affected. These 

 persons may have visited friends or relatives in the stricken 

 district; or may have taken milk at a public eating house where 

 the particular milk was served; or, finally, they may have con- 

 tracted the disease by contact with those originally affected by 

 the milk. 



Pathogenic bacteria may gain access to milk in various ways, 

 namely: 1, from the personnel employed in handling the milk and 

 from the clothes of employees; 2, from contaminated bottles and 

 utensils; 3, from flies; 4, from dust in the air; 5, from domestic 

 animals; 6, from the cows. 



1. From the Personnel Employed in Handling the Milk and 

 from their Clothes. There are several possible ways in which 

 milk may become infected from employees. During the milking 

 process a carrier may be responsible for the entrance of pathogenic 

 germs. Diseases of the respiratory tract are communicated by 

 coughing, sneezing, or from the hands the germs of intestinal 

 diseases may adhere to the hands of the milkers and enter the 

 milk. Cleanliness is, unfortunately, not as widely practised as 

 is desirable, and some typhoid fever epidemics have been traced 



28 



