Abstract
BackgroundPrediction of timing for the onset and peak of an influenza pandemic is of vital importance for preventive measures. In order to identify common spatiotemporal patterns and climate influences for pandemics in Sweden we have studied the propagation in space and time of A(H1N1)pdm09 (10,000 laboratory verified cases), the Asian Influenza 1957–1958 (275,000 cases of influenza-like illness (ILI), reported by local physicians) and the Russian Influenza 1889–1890 (32,600 ILI cases reported by physicians shortly after the end of the outbreak).MethodsAll cases were geocoded and analysed in space and time. Animated video sequences, showing weekly incidence per municipality and its geographically weighted mean (GWM), were created to depict and compare the spread of the pandemics. Daily data from 1957–1958 on temperature and precipitation from 39 weather stations were collected and analysed with the case data to examine possible climatological effects on the influenza dissemination.ResultsThe epidemic period lasted 11 weeks for the Russian Influenza, 10 weeks for the Asian Influenza and 9 weeks for the A(H1N1)pdm09. The Russian Influenza arrived in Sweden during the winter and was immediately disseminated, while both the Asian Influenza and the A(H1N1)pdm09 arrived during the spring. They were seeded over the country during the summer, but did not peak until October-November. The weekly GWM of the incidence moved along a line from southwest to northeast for the Russian and Asian Influenza but northeast to southwest for the A(H1N1)pdm09. The local epidemic periods of the Asian Influenza were preceded by falling temperature in all but one of the locations analysed.ConclusionsThe power of spatiotemporal analysis and modeling for pandemic spread was clearly demonstrated. The epidemic period lasted approximately 10 weeks for all pandemics. None of the pandemics had its epidemic period before late autumn. The epidemic period of the Asian Influenza was preceded by falling temperatures. Climate influences on pandemic spread seem important and should be further investigated.
Highlights
Prediction of timing for the onset and peak of an influenza pandemic is of vital importance for preventive measures
The study is based on reported case data from the Russian Influenza in 1889–90 [9,10,11,12], the Asian Influenza in 1957–58 [13] (An animated map of the global spread can be found in Additional file 1) and the A(H1N1) pdm2009-2010 [14,15,16,17]
The weekly geographic weighted mean (GWM) of the incidence moved along a line from southwest to northeast for the Russian and the Asian influenza, but northeast to southwest for the A(H1N1)pdm09
Summary
Prediction of timing for the onset and peak of an influenza pandemic is of vital importance for preventive measures. In order to identify common spatiotemporal patterns and climate influences for pandemics in Sweden we have studied the propagation in space and time of A(H1N1)pdm (10,000 laboratory verified cases), the Asian Influenza 1957–1958 (275,000 cases of influenza-like illness (ILI), reported by local physicians) and the Russian Influenza 1889–1890 (32,600 ILI cases reported by physicians shortly after the end of the outbreak). An early understanding of factors allowing for efficient spread of a new influenza virus is vital for the handling of a pandemic. To better understand factors governing the dissemination of pandemic viruses we have investigated the spread patterns for three past influenza pandemics in Sweden, using spatiotemporal analysis, spatial modeling and visualization. The paper discusses possible co-variation of influenza dissemination with temperature and precipitation for the years 1957–1958
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