Tuesday, September 5

—————

ALL SMELL IS DISEASEEDWIN CHADWICK

The first solid cause for home began to filter through the neighborhood Tuesday morning. For the first time in four days, Henry Whitehead let himself believe that this terrible visitation might finally be passing. The wife of Mr. G, the tailor, had died that morning, but for every new death, Whitehead could point to another dramatic recovery. The servant woman he had been tending to since Friday had risen from what she had assumed would be her deathbed, her pallor much improved. Two adolescents—a boy and girl—had also turned the corner, much to the delight of their remaining family. All three of them attributed their recovery to one thing: they had consumed large quantities of water from the Broad Street pump since falling ill. The speed and intensity of their recovery made an impression on Whitehead that would linger in his mind through the coming weeks.

b) The Exemption Proves the Rule

2. Broad Street Pump

Evidence that Cholera was waterborne from the 1854 Cholera Epidemic

Distance from the Broad Street Pump

Cholera Cases per 10,000 residents

“Snow knew that the case would be made in the exceptions to the rule.” (The Ghost Map, p. 140)

“Pockets of life where you would expect death…

…pockets of death where you would expect life.”

Distance from the Broad Street Pump

Cholera Cases per 10,000 residents

“Pockets of life where you would expect death…

…pockets of death where you would expect life.”

“Pockets of life where you would expect death…

…pockets of death where you would expect life.”

Distance from Broad Street Pump (miles)

Cholera Cases per 10,000 residents

“Pockets of life where you would expect death…

…pockets of death where you would expect life.”

“Pockets of life where you would expect death… …pockets of death where you would expect life.”

St. James Workhouse—93 deaths per 10,000 residents (5/535) because water supplied by Grand Junction Waterworks

Susannah Eley—93 deaths per 10,000 residents (5/535) because water supplied by Grand Junction Waterworks

Lion Brewery—no deaths among 70 workers because private pipeline and beer drinkers

5 deaths

no deaths

Eley Brothers Factory—18 deaths

Eley Factory

Work House

Brewery 1 2

Susannah lived in Hempstead

Evidence that Cholera was waterborne from the 1854 Cholera Epidemic

1. John Snow’s Grand Experiment

Was it a natural experiment or a difference-in-difference analysis?

“London was without cholera from the latter part of 1849 to August 1853. During this interval an important change had taken place in the water supply of several of the south districts of London. The Lambeth Company removed their water works, in 1852, from [the heart of London] to [upriver]; thus obtaining a supply of water quite free from the sewage of London” (Snow, On the Mode of Communication of Cholera, 1855, p. 68).

John Snow

Battersea Bridge

NThe Thames runs from West to East

Southwark Bridge

London Bridge

moved≈1845

Moved in 1852

Seething Wells Intake

Seething Wells was beyond the tidal reach of the Thames

Southwark & Vauxhall Water Company (S&V)

Lambeth Waterworks

“The experiment ...was on the grandest scale. No fewer than three hundred thousand people of both sexes, of every age and occupation, and of every rank and station, from gentle folks down to the very poor, were divided into two groups without their choice, and, in most cases, without their knowledge; one group being supplied with water containing the sewage of London [S&V], and the other group having water quite free from such impurity [Lambeth Company]”

31 subdistricts

12 served by S&V only

3 served by Lambeth only

Not random

100 cholera cases per 10,000 residents

≈ 0 cases

“relatively well-to-do suburbs”

“smog-bound

industrial zones”

16 served by both companies

≈ random via natural experiment

pipes—promiscuously interlinked households—assigned w/o knowledge

S&V households

Lambeth households

315 cases per 10,000 residents

37 cases per 10,000 residents

Same income & elevation

Table. Cholera Deaths in 16 Sub-Districts Served by 2 Water Companies, 1854

Households Deaths

(#) (#) (# per 10,000)

S&V (intake in heart of London)

40,046 1,263 315

Lambeth (intake upriver)

26,107 98 37

Rest of London 256,423 1,422 59

“In 1849 when cholera was last present in London, mortality due to cholera was similar among persons supplied by the Lambeth Company and the Southwark and Vauxhall Company.”

Epidemiologist Ralph Frerichs

0 1 2 3 40

50

100

150

200

250

300

350

400

450

500

550

600

650

700

S&VLambeth

1849 1852 1854

Lambeth moved its intake pipe from downriver to upriver.

37

Deaths per 10,000 households

315

If the subdistricts that Lambeth served exclusively were “relatively well-to-do suburbs” then it seems plausible that it might have served relatively well-off households in the areas served by both companies (i.e., the households on the border)…

Increased risk due to foul water:A

B

CD

Natural experiment

A – BDifference-in-difference

1849 epidemic was more severe

(A – B) – (C – D)

Validity rests on assignment within the natural experiment being truly random

Controls for the potential non-randomness

“The DD idea was probably pioneered by physician John Snow (1855), who studied cholera epidemics in London in the mid-nineteenth century.”

Friday, September 8

—————

THE PUMP HANDLE

“DEATH’S DISPENSARY”

On Thursday night, the Board of Governors of St. James Parish had held an emergency meeting to discuss the ongoing outbreak and the neighborhood’s response. Halfway into the meeting, they received notice that a gentleman wished to address them. It was John Snow, armed with his survey of the past week’s devastation. He stood before them, and in his odd, husky voice told them that he knew the cause of the outbreak, and could prove convincingly that the great majority of cases in the neighborhood could be traced to its original source. It is unlikely that Snow went into the intricacies of his broader case against the miasma theory—better to go straight to the telling patterns of death and life, leave the philosophizing for another day. He explained the dismal ratios of survival among the people living near the pump, and the unusual exemptions granted to people who had not drunk the water.

He told the Board of Governors of deaths that had transpired far from Golden Square, connected to the area only by the consumption of Broad Street water. He may have told them of the brewery or the workhouse on Poland Street. Death after death after death had been linked to the water at the base of the Broad Street well. And yet the pump remained in active use.

The members of the Board were skeptical. They knew as well as any other locals how highly regarded the Broad Street water was—particularly as compared to the other nearby pumps. But they also knew firsthand the smells and noxious fumes that were rampant in the neighborhood; surely these were more responsible for the outbreak than the reliable Broad Street water. Yet Snow’s argument was persuasive—and,, besides, they had few other options. If Snow was wrong, the neighborhood might go thirsty for a few weeks. If he was right, who knew how many lives they might save? And so, after a quick internal consultation, the Board voted that the Broad Street well should be closed down.

2. Broad Street Pump

Evidence that Cholera was waterborne from the 1854 Cholera Epidemic

a) Spatial Pattern of Deaths

4¼ inches

a) Spatial Pattern of Deaths

a) Spatial Pattern of Deaths

Natural Experiment—random whether people choose to live on the corner of Husband St. & New Street versus at the end of William and Mary Court. One is randomly assigned to live further from the Broad Street Pump.

c) 2nd Examination of the Broad Street Pump.

2. Broad Street Pump

Evidence that Cholera was waterborne from the 1854 Cholera Epidemic

After discovering the “baby Lewis” case, Rev. Whitehead hired (engineer) York who uncovered leaks from the Lewis cesspool into the Broad Street pump’s well.

Rev. Whitehead