A Missed Summer Wave of the 1918-1919 Influenza Pandemic: Evidence From Household Surveys in the United States and Norway
Journal article, Peer reviewed
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OriginalversjonMamelund, S. E., Haneberg, B., & Mjaaland, S. (2016, January). A Missed Summer Wave of the 1918–1919 Influenza Pandemic: Evidence From Household Surveys in the United States and Norway. In Open Forum Infectious Diseases (Vol. 3, No. 1, p. ofw040). Oxford University Press. http://dx.doi.org/10.1093/ofid/ofw040
Background.Reanalysis of influenza survey data from 1918 to 1919 was done to obtain new insights into the geographic andhost factors responsible for the various waves.Methods.We analyzed the age- and sex-specificinfluenza morbidity, fatality, and mortality for the city of Baltimore and smallertowns and rural areas of Maryland and the city of Bergen (Norway), using survey data. The Maryland surveys captured the 1918 fallwave, whereas the Bergen survey captured 3 waves during 1918–1919.Results.Morbidity in rural areas of Maryland was higher than in the city of Baltimore during the fall of 1918, that was almostequal to that in Bergen during the summer of 1918. In Bergen, the morbidity in the fall was only half of that in the summer, withmore females than males just above the age of 20 falling ill, as seen in both regions of Maryland. In contrast, more males than femalesfell ill during the summer wave in Bergen. Individuals <40 years had the highest morbidity, whereas school-aged children had thelowest fatality and mortality.Conclusion.A previously unrecognized pandemic summer wave may have hit the 2 regions of Maryland in 1918.