The Snow series is an educational course. We hope you will recognise our efforts by donating to TTE or becoming a paying subscriber, as writing the series took a lot of time and effort.

Last week we discussed some more objections to Snow’s theories as he sought to exclude alternative explanations to the facts.  In today’s post, after all his work, we’ll let Snow have his say on how we can prevent waterborne diseases, as stated on page 133 of On the Mode of Communication of Cholera. 2nd edition (MCC2). On Thursday, and then finally, we will examine the aftermath of Snow’s work, his premature death, his legacy and the other official investigations on the cholera problem.

“The measures which are required for the prevention of cholera, and all diseases which are communicated in the same way as cholera, are of a very simple kind. They may be divided into those which may be carried out in the presence of an epidemic, and those which, as they require time, should be taken beforehand.”

The measures which should be adopted during the presence of cholera may be enumerated as follows:

1st. The strictest cleanliness should be observed by those about the sick. 

There should be a hand basin, water, and towel, in every room where there is a cholera patient, and care should be taken that they are frequently used by the nurse and other attendants, more particularly before touching any food.

2nd. The patient's soiled bed linen and body linen should be immersed in water as soon as they are removed until they can be washed, lest the evacuations become dry and be wafted about as fine dust. 

Articles of bedding and clothing which cannot be washed should be exposed for some time to a temperature of 212 degrees [Authors’ note: Fahrenheit] or upwards. 

3rd. Care should be taken that the water employed for drinking and preparing food (whether it comes from a pump-well or is conveyed in pipes) is not contaminated with the contents of cesspools, house drains, or sewers. In the event that water free from suspicion cannot be obtained, it should be well boiled and, if possible, also filtered.

Works are in progress for supplying a great part of London with water from the Thames, obtained, like that of the Lambeth Company, above Teddington Lock. Although this is not the best possible source for supplying a large town, it is a great improvement on the practice of many of the water companies, and the water, owing to filtration, and especially to its detention in large reservoirs, will probably be quite salubrious: at all events, it will be much safer than that of the shallow pump-wells of London, which are fed from very polluted sources. It is very desirable that the handles of nearly all the street pumps of London and other large towns should be fastened up, and the water used only for such purposes as watering the streets. A proper supply of water for shipping in the Thames is much wanted. Water acquires a flat taste by being boiled, but if it is filtered after it becomes cold, it gets re-aerated, and the flat or vapid taste is entirely removed.

4th. When cholera prevails very much in the neighbourhood, all the provisions which are brought into the house should be well washed with clean water and exposed to a temperature of 212 degrees Fahrenheit, or at least they should undergo one of these processes, and be purified either by water or by fire. 

By washing hands carefully and taking due precautions regarding food, a person may spend time among cholera patients without exposing himself to any danger.

5th. When a case of cholera or other communicable disease appears among persons living in a crowded room, the healthy should be removed to another apartment, where it is practicable, leaving only those who are useful to wait on the sick.

6th. As it would be impossible to clean out coal pits and establish privies and lavatories in them, or even to provide the means of eating a meal with anything like common decency, the time of working should be divided into periods of four hours instead of eight, so that the pit-men might go home to their meals, and be prevented from taking food into the mines.

7th. The communicability of cholera ought not to be disguised from the people, under the idea that the knowledge of it would cause panic or occasion the sick to be deserted.

British people would not desert their friends or relatives in illness, though they should incur danger by attending to them; but the truth is that to look on cholera as a "catching" disease, which one may avoid by a few simple precautions, is a much less discouraging doctrine than that which supposes it to depend on some mysterious state of the atmosphere in which we are all of us immersed and obliged to breathe.

The measures which can be taken beforehand to provide against cholera and other epidemic diseases, which are communicated in a similar way, are --

8th. To effect good and perfect drainage.

9th. To provide an ample supply of water quite free from contamination with the contents of sewers, cesspools, house drains, or the refuse of people who navigate the rivers.

10th. To provide model lodging-houses for the vagrant class and sufficient house room for the poor generally.

The great benefit of the model lodging houses arises from the circumstance that the apartments for cooking, eating, and sleeping are distinct and that all the proper offices that cleanliness and decency require are provided. The very poor who choose to avail themselves of these institutions. suffer a rate of mortality as low as that of the most opulent classes. The public wash-houses, which enable poor persons to wash the soiled linen of the sick or the healthy without doing it in the midst of the plates and dishes and provisions of the family, are well calculated to prevent the spread of disease.

11th. To inculcate habits of personal and domestic cleanliness among the people everywhere.

12th. Some attention should undoubtedly be directed to persons, and especially ships, arriving from infected places in order to segregate the sick from the healthy.  “In the instance of cholera, the supervision would generally not require to be of long duration.”

CONTEMPORARY THEMES

Some of the measures are specific to cholera or waterborne transmission, but whatever measures are proposed, they should be tested before any application. Following the precautionary principle, the risks and benefits of each course of action should be studied, not invented overnight.

A systematic review of randomised controlled trials is the highest-quality evidence for determining the effect of interventions. However, while RCTs are not always possible, systematic reviews of other study designs are, which prevent cherry-picking of the evidence.

In 1753, James Lind published what is considered the first systematic review, which aimed to provide an unbiased summary of evidence on scurvy. From about the 1980s onward, Systematic reviews became essential for informing decision-making in healthcare. 

Readings

Jefferson T et al. Physical interventions to interrupt or reduce the spread of respiratory viruses. Cochrane Library 2023. https://doi.org/10.1002/14651858.CD006207.pub6

Wolfe M, et al. A Systematic Review and Meta-Analysis of the Association between Water, Sanitation, and Hygiene Exposures and Cholera in Case-Control Studies. Am J Trop Med Hyg. 2018 Aug;99(2):534-545. doi: 10.4269/ajtmh.17-0897. 

D'Mello-Guyett L, et al. Prevention and control of cholera with household and community water, sanitation and hygiene (WASH) interventions: A scoping review of current international guidelines. PLoS One. 2020 Jan 8;15(1):e0226549. doi: 10.1371/journal.pone.0226549. 

Clarke M, Chalmers I. Reflections on the history of systematic reviews. BMJ Evidence-Based Medicine 2018;23:121-122.

The James Lind Library. Illustrating the development of fair tests of treatments in health care.

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