A generalized additive model (GAM) with a log link function and Poisson error was fitted to the weekly numbers of deaths. The Poisson model has been widely applied to the estimation of influenza associated disease burden and recently been validated by an empirical dataset of laboratory confirmed influenza cases [19] . First, long-term trends and seasonal patterns of causespecific mortality counts, as well as environmental factors including temperature and relative humidity, were adjusted for as confounders by building a core model: