(this one is for Jemma, with our thanks)

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 the aftermath of the publication Snow’s work and death. In today’s final post of the series, we will discuss the two other investigations in the cholera outbreaks and what we learned from them. 

Two official investigations were carried out simultaneously as Snow’s investigation of the Golden Square outbreak. In today’s post, we will wrap up some of the loose ends of the story: the re-excavation of the pump well and most of all the two official inquiries in the the Broad Street outbreak that were contemporaneous with Snow’s. 

The first investigation was by the General Health Board (GHB) in 1854. This body was made up of famous miasmatists and gathered a mass of data without the focus that Snow brought. 

The Board Inquiry collected data on the following:

• Atmospheric pressure;

• The temperature of the air; 

• The temperature of the Thames water; 

• The humidity of the air;

• The direction of the wind; 

• The force of the wind;

• The velocity of the air;

• Electricity;

• Ozone;

• Rain and clouds;

It then conducted a series of detailed comparisons of these variables across London,  England and Scotland and described atmospheric phenomena in 1832, 1848-49 and 1853. 

The mass of data accumulated was reported and analysed in the Appendix to the report, which is 352 pages long. Section 4 contains another very detailed and interesting report.

In September 1854, Dr Fraser and colleagues examined over 800 dwellings in the area of Golden Square; they also looked at drains, the condition of streets, water provision, waste disposal and any other variables that could have caused the outbreak. However, the tone of the following example (from page 142 of the Appendix to the GHB report)  gives some idea of the bias they introduced in their work: 

The description is more thorough than Snow’s as they examined conditions in all the houses in Broad Street and its environs, but their focus was on miasmata. Fraser and colleagues were aware of the significance of the widow, the brewery and all the other cases in which the absence of exposure to the water meant the absence of disease. However, the results of the “negative” first excavation of the pump well in the autumn of 1854 helped them to dismiss the water contamination theory (see page 188).

The following extract from page 161 of the report sums up the conclusion reached by Dr Frazer and colleagues after visiting 800 homes in the area:

The report also contains slides by the famous microscopist Hassal. Dr Thomson and his colleague Rainey looked at air and water samples in the “atmosphere” and hospital wards with cholera patients.

This slide from page 147 shows a sample of air from a cholera ward taken in October 1854. “Vibriones” are marked with a G.

Other air samples taken from the empty ward or half of the beds occupied by cholera patients failed to show any vibrios. The investigators visualised vibrios, perhaps subconsciously understanding their significance but associating them with airborne transmission given the “certainty” of miasma theory at the time.

The second investigation was carried out by the Vestry of the Parish of St James, of which Snow was a member. The sub-committee visited 316 houses in the area. The Committee confirmed most of the facts of Snow’s and the GHB investigations. It located the 200-year-old plague pits, which were remote from Golden Square, thus confirming Snow’s exclusion of pervading soil poison as an explanation of the cholera epidemic.

The 1665-66 plague grave pit is hatched in the top left-hand corner of the map. As far as we can make out, it is situated between Great Marlborough Street and Maddox Street, somewhere under the modern Liberty Store. The box hatching indicates the Earl of Craven’s estate “plague fields” - a lazarette and not a burial ground. As the text states, the map was a reworking of the one produced by the GHB Inquiry. 

In MCC2 Snow locates the plague burial pit from the 1665-6 epidemic around Little Marlborough St. At pages 54-5 of MCC2 he writes:

 Whilst the presumed contamination of the water of the Broad Street pump with the evacuations of cholera patients affords an exact explanation of the fearful outbreak of cholera in St. James's parish, there is no other circumstance which offers any explanation at all, whatever hypothesis of the nature and cause of the malady be adopted. Many persons were inclined to attribute the severity of the malady in this locality to the very circumstance to which some people attribute the comparative immunity of the city of London from the same disease, viz., to the drains in the neighborhood having been disturbed and put in order about half a year previously.  Mr. Bazalgette, however, pointed out, in a report to the commissioners, that the streets in which the new sewers had been made suffered less than the others; and a reference to the map will show that this is correct, for I recollect that the streets in which the sewers were repaired about February last, were Brewer Street, Little Pulteney Street, and Dean Street, Soho. Many of the non-medical public were disposed to attribute the outbreak of cholera to the supposed existence of a pit in which persons dying of the plague had been buried about two centuries ago; and, if the alleged plague-pit had been nearer to Broad Street, they would no doubt still cling to the idea. The situation of the supposed pit is, however, said to be Little Marlborough Street, just out of the area in which the chief mortality occurred. With regard to effluvia from the sewers passing into the streets and houses, that is a fault common to most parts of London and other towns. There is nothing peculiar in the sewers or drainage of the limited spot in which this outbreak occurred; and Saffron Hill and other localities, which suffer much more from ill odors, have been very lightly visited by cholera.    

The idea that noxious vapours from decomposition of centuries-old bodies could cause cholera is pure miasmatism, but when we checked the Vestry Inquiry report we interpreted the location of the pit as being the hatched circle top left of the map (based on the GHB Inquiry map and probably annotated by Snow himself) and the plague fields on the Earl of Craven's estate as a lazarette (see the map in this Lecture).

But the cartographaer Tom Koch (who is an expert in epidemic polygons and maps) contradicted ourunderstanding of the location of the pit. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7108616/pdf/dyt194.pdf

The Vestry Inquiry text is unclear (available here), so do you agree with Koch's or our interpretation?

Look at the Vestry report from pdf page 42. The map is at pdf page 97. The blue & pink lines corresponding to the sewers being dug just before the outbreak in 1851 which supposedly disturbed the rotting remains and released miasma (considered very unlikely by the Inquiry) see pdf page 46 are faintly visible in this reproduction.

 Learning point:

Check and re check your facts and sources.

The significance is that if the oval pit according to the Vestry is not the pest field but is the rectangle corresponding to the Craven Estate “pest fields”, it's much nearer Broad Street, but there was no "nuisance" reported when they dug the sewers up.

So Snow’s map was only one of three made of the outbreak but the only one plotting the position of pumps.

Perhaps more important was the report by Jeosaphat Yorke’s re-excavation of the environs of the pump well in front of number 40 Broad Street. Yorke was the Inspector of pavements and secretary to the Parish Inquiry sub-committee. In his own words:

As one can appreciate from the section of Mr York’s map (on the right), the vault of the cesspool and the well with the pump on top were contiguous, and the two walls leaked like “a sieve”. In the planimetry (on the left), the well is shown as a circle. The outlined building above the vault is number 40 Broad Street.

Dr Frazer and colleagues disregarded Snow’s theory because the first excavation had not shown the decayed brickwork and because of the many instances in which people exposed to the water had no symptoms. This shows Frazer’s disregard or ignorance of the role of susceptibility and other factors influencing transmission and symptoms - which is odd for a miasmatist. 

The Vestry report also contained a case summary by Doctor Rodgers of Berners Street, who attended and identified the index case. She was a 5-month-old baby living at number 40 and died on the 2nd of September. Her mother washed her diapers in cold water over the cesspool, so the “poison” contaminated the Broad Street well. It was the Reverend Whitehead who identified Sarah Lewis’s baby as the index case, the portal of entry through her diapers’ washings for the “poison into the cess pool and hence the well.

The Reverend Henry Whitehead and Snow, whose reports form part of the Vestry inquiry documentation, had independently reached the same conclusions as to the role of contaminated water in the outbreak. 

However, their views were disregarded here, too “The Committee refrains, however, from expressing an opinion in favour of any hypothesis of its mode of action.”

CONTEMPORARY THEMES

There is some irony in the facts. Mr York supervised the parish-sponsored re-excavation of the pump well and cesspool in the spring of 1855, which showed leakage between the two. The cesspool was only inches away from the pump well. Dr Rodgers also probably identified the index case that Snow missed as it was a 6-month-old child with diarrhoea and not rice water faeces. This is an example of a specific sign in a baby overlooked by other physicians.

This last point is key in today’s environment as it shows the clinical difference between a syndrome and a disease, especially one characteristic of cholera.

A syndrome has multiple causes, known and unknown, which may act in a synchronous manner, but it has non-specific symptoms: think of the nonspecific diarrhoea of the child at number 40 Broad Street who did not have rice water faeces and compare it with the ease of diagnosis of a classic cholera case.

Today, influenza-like illness (ILI) is a syndrome with countless possible causes, infectious and unknown. ILI caused by agent B cannot be distinguished from the one caused by agent A (that is, if the A and B are known). Fever, fatigue, cough, aches and pains are not pathognomonic of any particular agent symptoms (see Lecture 3). If you want to identify the agent(s), you need a laboratory test. However, in the case of respiratory viruses, a test is of limited use if the condition is fleeting, or there are no licensed interventions, or there are a very high number of cases overwhelming any attempt at identification and isolation of symptomatics individuals as happened in Lombardy in March 2020 (see Lecture 6).

The second ironic fact is that Snow credits Dr Fraser (see Lecture 14) as providing him with news of the death of the Hampstead widow, her niece and the visitor from Brighton, the two cases worked on by Snow. They did not fit with Snow’s theory, but when properly analysed, they confirmed the link between exposure and outcome.

This is the nth demonstration of how box thinking can distort your perceptions. Snow does not remark on Dr Fraser’s information other than thanking him in his usual courteous manner. However, the miasmatist, Dr Fraser, may have provided the information to prove Snow wrong. In fact, he involuntarily provided Snow with one of the most famous instances of the story. Professor Geoffrey Rose used to caution his epidemiology students with the phrase, “remember the widow of Hamsptead, never forget the importance of the outlier”. The outlier, if properly investigated, can shed light on the nature of the disease and its mode of communication. However, as always, you need to keep an open mind and not jump to conclusions as Victorian miasmatists and their modern counterparts still do. 

References 

Great Britain. General Board of Health. Medical Council. Appendix to Report of the Committee for Scientific Inquiries in Relation to the Cholera-epidemic of 1854. England: Printed by George E. Eyre and William Spottiswoode, 1855, 1855. (Link)

"Report of the Committee for Scientific Inquiries in Relation to the Cholera Epidemic of 1854, Presented to Both Houses of Parliament by Command of Her Majesty." Glasgow Medical Journal 3.12 (1856): 469-73. Web.

Westminster St. James, Cholera Inquiry Comm. Report on the Cholera Outbreak in the Parish of St. James, Westminster, during the Autumn of 1854. Lond, 1855. Available here.

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