52 EPIDEMIC DISEASES TRANSMITTED BY MILK. 



the recognized clinical case. During convalescence, the viru- 

 lent bacilli may persist in the nose or throat for months after 

 the patient has been discharged as cured, unless the culture 

 method has been used to determine the time for release from 

 quarantine. The condition is quite parallel to the typhoid 

 bacilli carriers. Likewise, diphtheria bacilli may be isolated 

 from the nose or throat in advance of the appearance of clin- 

 ical symptoms. 



The worst of the matter is the fact that diphtheria exhibits 

 all degrees of severity down to examples of healthy persons 

 harboring virulent diphtheria bacilli. These may be quite as 

 dangerous as the recognized clinical cases. The appearance 

 of clinical diphtheria in an individual is governed in part by 

 the state of the resistance of the individual exposed to infection. 



The significance of these so-called germ cases is attracting 

 careful attention in the study of the spread of diphtheria. 

 They amount to not over 4% of the community in the absence 

 of an epidemic, but in infected households the percentage of 

 germ cases rises to 507^ of the individuals exposed. Some 

 cases are practically always found in families where infection 

 exists. This class of unrecognized carriers of infection, rather 

 than the recognized cases under treatment, is regarded as the 

 chief source for the dissemination of diphtheria in a commu- 

 nity (16, 36, 37). 



In a dairy, a convalescent or germ case may be a milker. 

 A cough or a sneeze, or any means by which saliva may get 

 on the hands, and hence to the milk, results in its contamin- 

 ation with diphtheria. Moore (19) has reported an epidemic 

 in Ithaca, N. Y., traceable to a convalescent. 



Observations tending to implicate the cow as a source of 

 diphtheria, are not supported by convincing facts (3). 



Recognition of milk-borne diphtheria epidemics. Reported 

 cases must be promptly investigated with reference to the milk 

 supply, and investigation of the dairy should be made in case 

 of suspicion. Bacteriological examinations of milk rarely 

 result in the discovery of Bacillus diphtheriae (2, 7, 20). At 

 the dairy, inquiry and physical examination of throats should 

 not be relied upon to the exclusion of taking cultures from both 



