Clinical and community-based studies with primary data collection in humans were identified through a literature search conducted in November 2008 ( Figure 1 ). Studies conducted exclusively in Hong Kong special administrative region (SAR), Macao SAR or Taiwan, China, were excluded. We also excluded studies focusing exclusively on SARS and avian influenza, outbreak reports, diagnostic studies of pneumonia etiologies, and studies that did not include population-based estimates of incidence or mortality.