"Cholera and the water supply"

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To the Editor of the Times

Sir,--I shall be obliged if you will allow me to make a few remarks on the report of Mr. Simon to the Board of Health which forms the subject of a leading article [editorial] in the Times of to-day. This report, although valuable in some respects, contains, from the nature of it, only an approximation to the truth. The population supplied with the impure water of the Southwark and Vauxhall company suffered a mortality from cholera in the late epidemic not merely three and a half times as great as that supplied by the Lambeth Company, but six times as great; and even this fact expresses the influence of the impure water in an inadequate manner, unless the different periods of the epidemic are considered separately. The inquiry which supplies the matter for Mr. Simon’s report was not an original one undertaken during the epidemic, but an additional investigation made under very disadvantageous circumstances after the epidemic was over. Early in the epidemic of 1854 I commenced a personal inquiry respecting every death from cholera which occurred in the districts in which the water supply of the above companies is intermixed. For the first four weeks of the epidemic I was furnished with the list of deaths published in the weekly returns of the Registrar-General, and for the next three weeks I was permitted to copy the addresses at the General Register-office. During the succeeding ten weeks which [while?] the epidemic continued the Registrar-General obtained from the district registrars a return of the water supply in which fatal attacks of cholera took place. The results were as follows:--In the first four weeks of the epidemic the deaths from cholera were 14 times as numerous among the population supplied with the impure water of the Southwark and Vauxhall company as among that supplied with the better water of the Lambeth Company, taking into account the respective number of these populations. In the next three weeks the mortality was 7 ½ times as great, and in the last ten weeks of the epidemic nearly five times as great in one population as the other, or, taking the whole epidemic, the difference was as 6 to 1. The relative mortality increased during the progress of the epidemic among the customers of the Lambeth Company just as it increased in the north and central districts of London, which were supplied with water which did not contain any of those impurities which take part in the propagation of cholera. This circumstance can be explained when the other causes which assist in the propagation of the disease are taken into account as well as the water. The inquiry conducted by Dr. Farr, of the General Registrar-office, and myself referred to the houses in which the fatal attacks took place; that of Mr. Simon refers to the houses in which the deaths occurred: but, as many persons fatally attacked in houses supplied by the Southwark company were removed before death to Lambeth Workhouse and other buildings supplied with water by the Lambeth Company, the latter mode of inquiry does not accord a correct result of the influence of the water. The results of my inquiry were published briefly in the Medical Times of September the 2d and October the 7th, 1854, and those of the General Registrar-office in the weekly returns of October and November, 1854. Both of these sets of results can be shown to harmonize with the amount of mortality in the respective sub-districts, while those of Mr. Simon’s inquiry do not. The mortality from cholera in the autumn of 1853 is included in the tables of Mr. Simon’s report, but that ought not to affect the result, for the deaths at that time were few, and took place, like those in the commencement of 1849, almost exclusively among the population supplied with water by the Southwark and Vauxhall Company.

I should like to say, in conclusion, that many other diseases, beside cholera, can be shown to be aggravated by water containing sewage, and that since the Southwark Water Company has obtained a supply almost equal in purity to that of the Lambeth Company the mortality of the south districts of London has greatly diminished.

I am, Sir, your obedient servant,

John Snow, M.D.

18, Sackville-street, June 25