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. 2014 Jul 9;14:378.
doi: 10.1186/1471-2334-14-378.

Spatiotemporal Characteristics of Pandemic Influenza

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Free PMC article

Spatiotemporal Characteristics of Pandemic Influenza

Lars Skog et al. BMC Infect Dis. .
Free PMC article

Abstract

Background: 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)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).

Methods: All 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.

Results: The 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.

Conclusions: The 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.

Figures

Figure 1
Figure 1
Locations mentioned in the article. The map indicates the centroids for municipalities mentioned in the article as well as the county limits for the counties Gävleborg, Kronoberg and Skåne.
Figure 2
Figure 2
Distribution in time for the three pandemics. These diagrams show the distribution in time of absolute numbers of ILI cases for the Russian and the Asian Influenza and laboratory verified cases for the A(H1N1)pdm09).
Figure 3
Figure 3
z-scores for the values presented in Figure2(distribution in time of absolute numbers of ILI cases for the Russian and the Asian influenza and laboratory verified cases for the A(H1N1)pdm09).
Figure 4
Figure 4
Time for onset of peaking period vs latitude. The two graphs depict the association between time for onset of peaking period vs latitude for the 21 county capitals of Sweden for the Asian Influenza and the A(H1N1)pdm09. Standard error and p-value for the predicted trend line are 1.09 and 0.017 respectively for the Asian and 1.22 and 0.087 for the A(H1N1)pdm09.
Figure 5
Figure 5
Peaking week for all municipalities with cases for the three pandemics. Municipalities represented with darker colours were peaking later than the ones with brighter colours.
Figure 6
Figure 6
Onset of pandemic period at county capitals and temperature prior to onset. The map shows time for onset of pandemic period at all Swedish county capitals. Diagrams depicting temperature fall many weeks prior to the onset are attached for 8 major cities representing 24.4% of the Swedish population in 1957. Weather stations are located at these cities. Norrköping and Sundsvall are not county capitals, but the major cities in their respective counties. Regression statistics are available in Table 2.
Figure 7
Figure 7
Temperature, precipitation and number of cases for locations with weather stations. The diagrams show weekly z-score values ((observation-mean value)/standard deviation) for mean temperature (red graph) and number of Asian Influenza cases (green graph) during 1957–1958. The time series starts with week 5726 (week 1 in the diagrams) and ends with week 5805 (week 31 in the diagrams).
Figure 8
Figure 8
GWM for incidence. The three maps depict the path of the GWM (geographic weighted mean) of the incidence per municipality for the 10 weeks epidemic of the Russian Influenza 1889–1890 (left), the Asian Influenza 1957–1958 (middle) and the A(H1N1)pdm2009-2010 (right).

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