Case Study Example: “Spanish Flu” Estimated to have infected up to 28% of the world’s population. (Frost 1920; Burnet & Clark, 1942) Caused the deaths of 50 – 100 million people (2.8–5.6% of the total world population) (Johnson & Mueller, 2002) Killed more people (At least 5 times as many) than combat during World War I. Among Americans, the epidemic killed 675,000 people, including 43,000 servicemen (Crosby, 1989)

Quantitative Shortcomings The 1918 epidemic was unique The infectious agent had never been so virulent. The disease killed many strong and healthy people Elderly people were less prone to the infection than would normally be expected

Qualitative Advantages Qualitative methodology allowed examination of: Unusual shifts in populations Comparison with 1889 flu outbreak Studies of nutrition and general health Effects of toxic gasses used in combat Resource allocation in wartime Suppression of data on flu outbreak for military strategic reasons.

“Spanish Flu” Seasonal influenza usually kills approximately 0.1% of the victims it infects. The mortality rate of the 1918 influenza was greater than 2.5%, making the epidemic 25 times more deadly (Marks & Beatty 1976; Rosenau & Last, 1980)

“Spanish Flu” There were so many deaths that the American life expectancy dropped by 10 years during the epidemic (Grove & Hetzel, 1968) Glasgow was the first British city infected in May 1918 In the next few months 228,000 people died in Britain

Quantitative Studies Taubenberger et al., 1997; Reid et al., 1999 sequenced the DNA from preserved lung tissue Looking for hemagglutin (HA) and neuraminidase protein (NA) known to increase virulence Sequencing of the 1918 influenza virus did not reveal any obvious reason why the virus might be virulent

“Spanish Flu” Case Studies The purpose of the case studies was to understand the reason the disease was so virulent “The medical situation in Europe was not the same in 1918 as it is today. The mortality from several infectious diseases was much higher” McKeon, 1976 McKeon’s case study examined the socio-economic health related issues

“Spanish Flu” Case Studies Population displacement is associated with increased infectivity in epidemics Moxnes & Christophersen, 2008 Poor nutrition is associated with increased infectivity (selenium and Vitamin D deficiency) Christophersen & Haug, 2007 Both factors had been caused by World War One

“Spanish Flu” Case Studies Quantitative analysis alone cannot explain the epidemiological phenomenon that occurred in “Spanish Flu” Actual fatalities may still be underestimated Many countries did not have a a proper system for measuring death toll World figure extrapolated from US, Canada and Western Europe