TYPHOID 355 



Water still remains the most important single channel by which 

 the typhoid bacilli reach the human body. Estimates vary as to 

 the actual percentage of typhoid cases which are referable to water 

 infection. It is placed by various authors at from 10 to 40 per 

 cent. According to Gay, Schuder found that of 640 typhoid 

 epidemics 22 per cent, were due to water. Schegehdahl found 

 that of 682 cases about 33 per cent, were w r ater-borne. Typhoid 

 is, therefore, the most important water-borne disease. 



The proof that a typhoid epidemic is due to water infection 

 is usually indirect, for the actual isolation of the offending organ- 

 ism is effected with considerable difficulty and has been accom- 

 plished in only seven or eight cases. How r ever, in those cases 

 where it is found it is not always possible to prove that it was 

 present at the time the infection occurred. Strong presumptive 

 evidence is given whenever waters are proved through the presence 

 of colon bacillus to have been infected by sewage. 



The best evidence, however, obtainable that a specific typhoid 

 outbreak is due to polluted water is that obtained by the epidemi- 

 ologist. He knows that the important characteristics of water- 

 borne epidemics are: 



1 . They may be preceded by a period of dysentery. 



2. The epidemic usually has a sharp onset, the curve rising to a 

 peak and the decline being rapid. 



3. The cases are quite evenly divided over the city, that is, 

 provided the city is served by a municipal supply. 



4. They nearly always occur in the spring, fall, or winter. 



5. The pollution is usually nearby and the epidemic is of short 

 duration unless there be a continuous source of new infecting 

 material. 



The work of the epidemiologist is vividly portrayed by Hill 

 as follows: 



'To illustrate the general principles, let us suppose notification 

 be received that a typhoid fever outbreak exists in a far-off com- 

 munity. The public health detective packs his grip and goes. 

 He knows no details; he has never heard of this particular com- 

 munity before; he has not even any general information about the 

 character of the country; he enters the community with no pre- 

 conceived ideas. But he does know how typhoid fever originates 

 and how it spreads. Water, milk, food, flies and fingers are the 

 routes typhoid cases or typhoid carriers, the source. His duties 

 are to find both; and to find them, not as a scientific amusement, 

 or as a matter of record; not to furnish food for speculation above 

 all not to make a show of doing something but to stop the outbreak, 

 and then to advise measures to prevent recurrence. 



'The public health detective on entering the community affected 

 by typhoid fever does not first examine the water-supply, the 



