BACTERIA AND RURAL WATER SUPPLIES 5 



Dangers From Polluted Water 



The reason for making bacteriological examinations of water supplies needs 

 little explanation, because almost everyone knows that the purpose is to prevent 

 the spread by water of bacteria that cause infectious diseases. The public, how- 

 ever, is not so well informed as to the diseases one may contract by drinking 

 polluted water, so it may be well to digress for a brief statement on that point. 



It is not uncommon for persons bringing water samples to our laboratory to 

 ask for bacteriological examinations because they fear that such diseases as 

 tuberculosis, scarlet fever, or infantile paralysis may be spread by water. The 

 answer to such inquiries is that dangerous bacterial pollution of water comes 

 from the human sewage which is from human intestines, and consequently the 

 diseases one risks when he drinks polluted water are intestinal diseases. In the 

 United States, and particularly in the North Atlantic seaboard states, typhoid 

 fever and dysentery are the only bacterial diseases one need be much concerned 

 about from contaminated water supplies. Some health authorities believe that 

 virus from cases of infantile paralysis may be found in sewage when there are 

 cases about, and that there is some danger of water supplies being contaminated 

 with the virus. Present evidence, however, does not indicate that one need 

 greatly fear getting this disease from water. 



One usually thinks of typhoid-fever germs as coming only from persons ill with 

 the disease; but another source of danger is the typhoid carrier, a person who has 

 recovered from his illness but who may continue to excrete typhoid bacilli in his 

 stools for months or even years. In fact, carriers may be people who have had 

 cases of typhoid fever so mild that they were never recognized as such. One of 

 the most widely publicized typhoid carriers was "Typhoid Mary" Mallon, who 

 was reliably said to have been responsible for more than 50 cases of typhoid 

 fever in homes where she worked as a cook, and who was strongly suspected of 

 having been responsible for a water-borne epidemic of more than 1,300 cases of 

 the disease. Many other instances of typhoid carriers have been proved and the 

 carrier condition is well understood. 



The possibility that dysentery may be spread by carriers is not so well known, 

 but reference to standard books on bacteriology and public health indicates that 

 such carriers undoubtedly exist. 



What is a Bacteriological Examination of Water? 



Bacteriology is a highly specialized science, and unless one has studied the 

 subject he is not expected to know much about bacteria except that they are 

 "germs" that cause diseases. Consequently, it is natural for the layman to 

 assume that the bacteriologist examines water directly for the presence of typhoid 

 or dysentery bacteria. That procedure is not practicable for several reasons. 

 These bacteria are not constantly present in a water supply, even though it 

 may be considered dangerous, and it is easily possible to miss them in a laboratory 

 examination of a w'ater that may contain enough of them to start an epidemic. 

 Another important factor is that in polluted water other bacteria are usually 

 present in such numbers that their growth in culture media prevents or masks 

 the growth of the relatively few tj'phoid or dysentery bacteria that may be 

 present. 



Since direct examination of water for typhoid and dysentery bacteria is not 

 practicable, the logical procedure is to look for evidences of sewage pollution 

 which is the most likely source of these bacteria. Consequently, the bacteriologi- 



