Spatiotemporal pattern and risk factors of the reported novel avian-origin influenza A(H7N9) cases in China

A total of 134 laboratory-confirmed human cases of the novel avian-origin influenza A(H7N9) were reported in China between February to July 2013. To illustrate the spatiotemporal patterns of H7N9 outbreaks in humans and investigate the risk factors associated with their distribution, we mapped the distribution of affected human cases and carried out directional distribution analysis and a direction test. We also collected data on anthropogenic, vegetation, climatic, and topographic factors, and used multiple logistic regression to examine the contribution of each factor. Two different spatiotemporal patterns were found: clustered and regular directional distributions in four distinct temporal phases in the Yangtze River Delta, and sporadic but spread in three direction across the provinces adjacent to the Yangtze River Delta. Mean monthly precipitation, mean monthly temperature, normalized difference vegetation index, and poultry consumption were significantly associated with the occurrence of human H7N9 infection. The model generated a map showing the high-risk areas for human H7N9 infection for mainland China. These findings provide an empirical basis for identifying priority areas for implementing preventive intervention to reduce the number of future human infections.