Water Transmission.—There are two types of outbreaks of cholera according as the general water supply is contaminated or when such contamination is localized to certain wells, cisterns or other nongeneral supplies. In the former the onset is explosive and cases occur almost simultaneously and with equal distribution in all parts of the city, to disappear with almost equal suddenness.
In the latter mode of infection, cases will appear from day to day and often peculiarly localized to certain definite districts of a city or to certain definite users of a particular water supply.
Fig. 73.—An instructive contrast between Altona and Hamburg before the latter filtered its water, having learnt its lesson from a sharp outbreak of cholera. (After G. E. Armstrong.)
As an example of the first type of outbreak the Hamburg epidemic of 1892 is most instructive.
During a period of only about two months cholera attacked about 17,000 persons causing 8605 deaths in a city with a population of 600,000. This outbreak was attributed to the washing of clothes in the water of the Elbe River by Russian immigrants. These immigrants had come from cholera-infected districts and among them there undoubtedly were cholera carriers.
The water supply of Hamburg was taken directly from the river. The adjoining city of Altona, with a population of 140,000, is further down the river but filtered its water by a slow sand process. Although the water as taken from the river contained the sewage of Hamburg yet there were only 328 deaths or 2.1 per thousand as against 13.4 per thousand for Hamburg. There were many interesting points in connection with the exemption of certain places in Hamburg, of which may be noted the instance of the entire freedom from cholera of a group of houses (Hamburg Hof), with 345 occupants. This was the only section of Hamburg which was supplied with Altona water. As Hamburg and Altona are only separated by the width of a street and hence practically form a single city, the factor of food and contact transmission could easily explain the cases in Altona.
To illustrate the second type of water transmission we have the well-known incident of the Broad Street pump.
This was about the first definitely proven connection between water and cholera. In 1854 it was noted that cholera was about 10 times as prevalent in Golden Square as in other adjacent parts of London. Various factors, such as previous droughts, stagnation of lower strata of the atmosphere, sewerage defects and subsoil drainage were found to be the same in Golden Square as elsewhere. It was noted that the number of cases increased in the neighborhood of the Broad Street well. The employees of a cartridge factory where this well water was used gave a large number of cases while an adjoining brewery, which had a well of its own and served out beer to its employees, did not furnish a single case. Very striking was the case of a lady living at Hampstead, a section of London which was then free from cholera, who had acquired a liking for the water of this well and had brought out to her regularly bottles of water from the well. This lady drank some of the water on August 31 and was seized with cholera the next day. A niece drank of the same water and died of cholera as well as the aunt. A servant also contracted the disease but recovered.
Macnamara has noted the circumstance of a vessel of water, which became contaminated with cholera stools, but which at the time it was drunk by 19 persons did not show anything suspicious in odor, color or taste. One person was stricken one day afterward, two on the third day and two others came down with cholera on the fourth day. It will be noted that only 5 of the 19 were attacked. A similar lack of susceptibility of a certain proportion of people, equally exposed, has been noted in all cholera outbreaks. It is probable that of those of the 19 who did not contract cholera there were developed a certain number of cholera carriers.