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Lecture 18 : The Epidemiological Transition (2) Overview. POSSIBLE EXPLANATIONS (Continued) 3. Reduced Exposure To Infection 19 th century reforms The Cholera pandemics McKeown’s assessment 4. Increased Resistance To Infection CRITICISMS OF McKEOWN.
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Lecture 18 : The Epidemiological Transition (2)Overview POSSIBLE EXPLANATIONS (Continued) 3. Reduced Exposure To Infection • 19th century reforms • The Cholera pandemics • McKeown’s assessment 4. Increased Resistance To Infection CRITICISMS OF McKEOWN
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).
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).
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.
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.
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.
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). Snow’s 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.
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. • Hamburg’s 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.
McKeown’s 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.
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
Criticisms • McKeown’s 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.
Summary • Almost everyone appears to accept McKewon’s 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).
