4, Lecture January
Todays Outline Cholera
Epidemiology 1854 outbreak John Snow
Henry Whitehead
Announcements Discussion DF p.67107 Exam 1 approaching Good Book
The Ghost Map by Steven Johnson
Cholera today
Clinical features
diarrhea vomiting (early) dehydration death
Diarrhea
early on, fecal and malodorous later rice water stool
painless non-straining sometimes a little cramping
Massive
can be more than 1/5 of your entire weight in a single day!
Dehydration
symptoms
sunken eyes and cheeks slow pinch response rapid and weak or missing pulse
can be diagnosed on sight! Death can occur in 12 hours or less (but can be treated with rehydration)
Origins of Cholera
Known since ancient times in India (500 B.C.) Doesnt appear in Europe until the 1800s
Why? The shipping routes were better established and disease could spread more efficiently
There have been 7 pandemics since the 1800s
Definitions
Endemic
When a disease maintains a steady, low-level frequency at a moderately regular interval. Malaria is a constant worry in parts of Africa.
Epidemic
An outbreak affecting many people at once and a sudden increase in the occurrence of the disease above the expected level.
Pandemic
An increase in disease occurrence with a large population over a very wide region.
Cholera in Britain
First appears on British soil in 1830s First epidemic (1831-1833)
> 20,000 deaths
Second epidemic (1848-1849)
> 50,000
Third epidemic (1852-1859)
Well focus on London
London in the 1800s
Explosive growth Crowded cities Row houses separated by narrow alleys One family per room Common outside water supplies and privies
The Sanitation Issue
So much waste and too little space The scavengers of London
Mudlarks, pure-finders, sewer hunters, bone collectors Night soil men--the elite
Too costly to pay the night-soil men
Waste accumulates in cesspools
Miasmatic Theory of Cholera
Von Pettenkofers experiment
Drank vial of pure V.Cholerae (no ill effects) No mention of student who did the same and got cholera (Rudolph Emmerich)
Disease caused by:
Porous soil with decaying matter in it reacting with an infectious element to produce a toxic substance in the air
Edwin Chadwicks Contribution
Head of the board of health Miasmist In the 1840s decided to do something about all the bad air Sewers could now be used for waste
Previously used for surface water
Thames became one giant cesspool
The Sewers
Emptied into the rivers
Used river water for drinking and bathing
Fast moving rivers carried away waste Slow moving or tidal rivers (like the Thames)--waste remains
John Snow
Received his MD in London Pioneer anesthetist Chloroform for Queen Victoria (1853) birth of prince Leopold Published research article on ether in 1847
How would you figure out the cause or source of an outbreak?
Snow Gathers Data From Three London Epidemics
Epidemics of 1832 and 1848 Epidemic from August 1853-January 1854 Epidemic in August 1854
The famous Broad Street Pump
1. 1832 and 1848
Patient data
Rice water stools suggested intestinal involvement Dr. did not get sick when treating patients
Found a greater incidence of cholera cases among those getting their water south of the Thames
Southwark and Vauxhall Water Co. dirty Lambeth Water Co. dirty Cholera about the same for both Chelsea Water Works, clean
much less cholera
Snows Proposal
On the Mode of Transmission of Cholera 1849 Cholera is spread through the water It is not something inhaled, but swallowed Went against Miasmists
2. August 1853-Jan 1854
Lambeth found new source of water
upstream of Londons sewage outlet
Some districts purely Southwark and Vauxhall, some purely Lambeth Some districts had BOTH sets of pipes on the same street!
1853/1854 Outbreak, cont.
Look at districts supplied by BOTH on house by house basis Complicated because of confusing pipe system Snow tried to distinguish the water supply based on salt
Remember--no way to see germs
Differences in the water
S&V water had 37.9 grains of salt per gallon Lambeth water had 0.95 grains of salt per gallon
easy to tell apart Vibrio cholerae requires some salt for survival
Lambeth, clean; dirty
Findings
S&V, Southwark and Vauxhall
315 deaths/10,000 houses
Lambeth
37 deaths/10,000houses
Further confirmation for John Snow
3. Outbreak at the Broad Street Pump
London 1854 Over 500 cases within 250 yards of the pump in span of 10 days Direct analysis of water showed inconsistent impurity Led him to ask for statistics on deaths and map them
The first 83 cases
All but 10 near to the Broad St. pump
5 families preferred water from Broad St. 3 were children who went to school near the pump 2 occurred before the real outbreak
Of the 73 living near the pump
61 known to drink from the pump 6 no info (whole family died) 6 did NOT drink from the pump
May have drunk indirectly Water in drinks (liquor) or sodas
Some other data
Workhouse near Broad St.
Had its own pump and had lower mortality
Brewery
Low mortality; workers drank beer, not water
Pump handle removed Sept. 8th
John Snow brings his data to the Board of Governors Ended the outbreak (as did the departure of 3/4 of residents) Water may have been cleared by then Probably did stop a second epidemic
Continued Studies
Snow joined forces with Henry Whitehead
Initially skeptical about Snows theory
Identified the index case
Discovered baby Lewis, decaying cesspool 2 feet from well
Vestry published a report supporting Snows theory
Water Theory not Accepted
Board of health: We see no reason to adopt this belief. Own investigation weighed down by irrelevant statistics (direction of wind, elevation, ~50 different items) Pump was eventually put back into service
How could so many intelligent people be so wrong for such an extended time
Didnt know about germ theory Many poor neighborhoods with unsanitary conditions also had poor air quality
Long-term Consequences of Snows findings
Birth of Epidemiology
Help invent a way of thinking about urban space A model for managing and sharing info
Modern day sewage construction?
Cities now a viable option
Why do you think the broad street outbreak was successful at bringing about change? (though it took another 15 years--last cholera outbreak in London was in 1866)
Modern Day Cholera
Infection
Causative agent the bacteria Vibrio cholerae
16 known strains (01 and 0139 most deadly)
Grows in humans, but also in environment
salt water best association with chitin (shellfish) and plankton
fecal-oral transmission contaminated water supply most common source Normally requires high dose (about a billion cells) for infection
Pathology
onset of symptoms usually 12-72 hours after ingestion
depends on dose
Vibrio cholerae dont invade cells, just attach to intestine Secrete a toxin
Cholera toxin has two parts
an enzyme that damages the salt/water balance a hormone-like part that fools the cell into taking it up
Cholera toxin causes one of our normal enzymes to work constantly
The end result is that there is a high concentration of salts in the small intestine water follows salt Too much water in the intestine causes diarrhea
Toxin injected Into cells
This part Attaches to cell
Therapy
In the 1800s, didnt know how to treat it. Intravenous solutions to rehydrate after dehydration sets in Oral Rehydration to maintain fluid (and electrolyte) balance Immunity follows and is both effective and long-lasting
Rehydration to replace
water (4 gallons a day is not a lot) salts (mostly sodium chloride [salt] and potassium bicarbonate) glucose (energy for transport and survival) rice water stool isotonic with plasma, so replace quart for quart
Cholera cot
plastic cot with a hole calibrated bucket replace with gatorade
orally if strong enough nasogastric tube if not
Antibiotic therapy/Vaccines
Antibiotics
reduces recovery time by half; 2-3 days of diarrhea rather than 4-6 days untreated, a very few will become carriers for a few months Some antibiotic resistance occuring
Vaccines have varying degrees of effectiveness
Is Cholera a problem today?
Developing countries have similar scavenger system of 1800s London Recent outbreak in Zimbabwe (2009) Current outbreak in Haiti
Death can occur within 2 hours
Mortality rate
With treatment < 1% Without treatment approximately 50-60%