Lecture 17 : The Epidemiological Transition 2 Overview

1
Lecture 17 The Epidemiological Transition
(2)Overview

• POSSIBLE EXPLANATIONS (Continued)
• 3. Reduced Exposure To Infection
• 19th century reforms
• The Cholera pandemics
• McKeowns assessment
• 4. Increased Resistance To Infection
• CRITICISMS OF McKEOWN

2
3. Reduced Exposure To Infections

• Early C19 industrial cities became very unhealthy
  places to live.
• High densities increased risk of airborne
  infections (e.g. tuberculosis).
• Unsanitary conditions increased risk of water-
  and food- borne infections (e.g. cholera,
  typhoid).
• Deaths rates increased 1831-1844 in Birmingham
  (14.6 to 27.2 per thousand) in Bristol (16.9 to
  31) and in Liverpool (21 to 34.8).

3
Reformers

• The atrocious living conditions of the urban poor
  were brought to the attention of the educated
  middle classes by a series of enlightened
  reformers such as Edwin Chadwick, Friedrich
  Engels, Charles Booth and Seebohm Rowntree.
• Publicised by novelists like Charles Dickens and
  Benjamin Disraeli.
• Statistical information was collected by William
  Farr (who initiated the statistics on mortality).

4
Reforms

• Public Health Act (1848) established a General
  Board of Health to furnish guidance and aid in
  sanitary matters to local authorities.
• Sanitary Act (1866) which made public health law
  compulsory.
• Public Health Act (1875) created a public health
  authority in every area.
• Artisans' and Labourers' Dwellings Improvement
  Act (Cross Act) in 1875 empowered municipal
  authorities to buy and demolish slums and to
  build housing for rent.
• Bye-laws passed at local level.

5
(No Transcript)
6
(No Transcript)
7
(No Transcript)
8
Sanitary Improvements

• Water closets (i.e. toilets) introduced in
  private houses at the beginning of the C19,
  connected to cesspools.
• By mid-C19 toilets were connected into storm
  sewers.
• Water treatment (e.g. filtration through sand,
  chlorination) was introduced towards the end of
  the C19 to kill the pathogens in drinking water.
• Sewage treated to reduce pollution in rivers.
• Separate sewage systems were introduced for storm
  water and domestic sewage in the early C20.
• Reforms prompted by miasmatic theory.

9
Cholera

• Caused by bacteria (Vibrio cholerae).
• Unknown in Europe before the 19th century.
• Six pandemics in 19th century originated from
  Ganges Delta / Sea of Bengal.
• Britain and Ireland affected by the 2nd to 5th
  pandemics in 1831-2, 1848-9, 1853-4 and 1865-6.

10
(No Transcript)
11
Medical Cartography

• Henry Wentworth Acland (1856). Dots were used to
  identify cases in Oxford. However, Acland also
  drew maps of other features, including altitude
  and undrained areas. The maps can be compared in
  much the same way as they would be in a modern
  GIS.
• John Snow (1855). Snows famous map showed the
  cluster of cases around the water pump in Broad
  Street in Soho which resulted in 500 deaths in 10
  days. Once the pump was disabled, the epidemic
  receded almost immediately demonstrating that
  cholera was somehow linked with the water supply.

12
(No Transcript)
13
(No Transcript)
14
(No Transcript)
15
(No Transcript)
16
(No Transcript)
17
The 6th Pandemic

• Britain and Ireland were largely unaffected by
  the 6th pandemic.
• Hamburg was ravaged by cholera in 1892, but the
  adjoining city of Altona (in Prussia) was
  unaffected.
• Hamburgs drinking water came from river Elbe,
  whereas Altona used treated water.
• Soil and air the same, so miasmatic theory could
  not explain the differences in disease rates.
• R.Koch was able to demonstrate the importance of
  clean water.

18
(No Transcript)
19
(No Transcript)
20
McKeowns Assessment

• Water- and food-borne infections were reduced by
  sanitary reforms and improved personal hygiene.
  Pasteurisation of milk reduced exposure to
  foodborne infections.
• Reforms had little direct effect on airborne
  infections.
• Decline in airborne infections (due to other
  factors) had an indirect effect by reducing
  exposure to infection.
• Given that decline in airborne infections was
  more significant than water- and food- borne,
  McKeown concludes that public health
  interventions were not the major factor.

21
4. Increased Resistance To Infection

• Having eliminated the other three possibilities,
  McKeown argues that the improvements must have
  been caused by increased resistance to infection.
• He attributed this to better diets.
• Poor nutrition would result in increased
  mortality due by
• Weakening resistance
• Impairing the immune response
• Reducing resistance to secondary infections
• Retarding convalescence

22
Criticisms

• McKeowns views are contested (e.g. Szreter,
  1988).
• Diet is assumed important by McKeown by a process
  of elimination no direct evidence provided.
• Other possible explanations not considered (e.g.
  labour movement / working conditions, public
  transport).
• Many airborne diseases improved for other known
  reasons apart from diet role of diet for
  airborne diseases may be overstated.
• Timing of TB improvements may be wrong TB may
  have improved because of decline of other
  diseases.

23
Summary

• Almost everyone appears to accept McKewons
  arguments that curative medicine played a minor
  role social and environmental factors much more
  important.
• However, his critics argue that he underestimated
  the impact of public health reforms (for which
  medical science can claim some credit).