382 PATHOGENIC MICROORGANISMS 



their onsets and courses will be characteristic to a degree which 

 makes it possible for an experienced epidemiologist to suspect the 

 water simply by a study of the incidence of cases in time and place. 

 To some extent, of course, this depends upon whether the water 

 is polluted by a single introduction of large quantities of sewage or 

 whether contamination is continuous over a longer period. In both 

 cases, however, a large number of the people living in the area 

 of the water supply will be infected during a relatively short period 

 of time. The rise of the curve which can be constructed from the 

 cases, therefore, will be steep and rapidly reach a peak. Classical 

 instances of this are the cholera epidemic in Hamburg and an 

 epidemic of typhoid fever in an American city which is described 

 in the section on typhoid fever. The incidence of the cases in places 

 will be sharply limited by the distribution of the water supply and 

 examination of the water will reveal colon bacilli. 



In milk epidemics, a still more explosive rise of the cases will 

 appear and in such cases as the Stamford epidemic described by 

 Trask, a definite connection between the milk route and the dis- 

 tribution of cases may be traced. On the basis of such suspicion, 

 the bacteriologist can investigate the milk and attempt a determina- 

 tion of recent intestinal disease or the carrier state in milk handlers. 

 Also, it is stated by many who have studied these epidemics that 

 milk epidemics are apt to claim the largest numbers of victims 

 among women and children. 



Contact epidemics will proceed by a more insidious course. In 

 such epidemics it is extremely important to gather together careful 

 data concerning the earliest cases observed and to attempt to trace 

 the cases to some association at a common meal, a restaurant or at 

 some other common source of food. Sawyer traced a "contact 

 epidemic to the carrier state in a ship's cook by a simple 

 epidemiological study of the individual cases which all led by 

 separate trails to the same ship 's galley. We have, ourselves, traced 

 cases in this way to company kitchens in military units. In large 

 communities contact epidemics may trail along for long periods of 

 time and when association is indiscriminate it may be necessarily 

 impossible to establish accurate relationships. In some contact 

 epidemics, such as those occurring in the Allied Armies in France 

 when intestinal diseases appeared in large numbers, the rise of the 

 curve simulated that of a water epidemic very largely because the 

 indiscriminate distribution of unprotected dejecta over large areas 



