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The 2009-2010 H1N1 influenza pandemic was caused by a novel strain, made up of genetic material from human, swine and avian influenza viruses. While the 2009 H1N1 strain originated in Mexico, Southeast Asia, and southern China in particular, remains the putative epicenter of new viral emergence. Using genetic and epidemiological information from 433 H1N1 viral isolates taken during the 2009-2010 pandemic in China, we examined the spatial and temporal characteristics of viruses in concert with their genetic characteristics, identifying the spatial and temporal diffusion patterns. Then we applied Moran's I test to see if the gene distances of the H1N1 virus are spatially autucorrelated. We then explored the suspected factors driving the evolution of H1N1 viruses during the pandemic. Regression methods were applied to test the association of H1N1 virus's spatial and temporal patterns with environmental, social and biological variables. Temperature& humidity, railway transportation, population density, morbidity of H1N1, population's accessibility to tap water, sampled patient's age are some of the variables considered in the regression.
We find that during the 2009- 2010 pandemic H1N1 influenza viruses evolved more through time, that further evolved strains have a trend of spreading from Northern China to Southern China, and continued evolving in the Southern China. Among the 8 genes of H1N1 virus, the HA gene and MP gene showed statistically significant positive spatial autocorrelation, showing that the genetic distances of the genes are related to the genetic distances of those genes in nearby isolates. Statistically significant positive spatial autocorrelation is also shown for the total 8 genes' genetic distance. Results of the spatial regression models indicate that the influence of environmental, social and biological variables varies not only across space but also by gene segment under consideration.
We find that population, environment and behavior are all playing a role in the evolution of H1N1 viruses in the 2009 pandemic in China. Thus understanding the dynamics of H1N1 incidence and the ecology of H1N1 virus evolution in China can be enlightening in establishing public health policy.