Location-specific patterns of exposure to recent pre-pandemic strains of influenza A in southern China

Variation in influenza incidence between locations is commonly observed on large spatial scales. It is unclear whether such variation occurs on smaller spatial scales and whether it is the result of heterogeneities in population demographics or more subtle differences in population structure and connectivity. Here we show significant differences in immunity to influenza A viruses among communities in China not explained by differences in population demographics. We randomly selected households from 5 randomly selected locations near Guangzhou, China to answer a questionnaire and provide a blood sample for serological testing against 5 recently circulating influenza viruses. We find a significant reduction in the frequency of detectable neutralization titers with increasing age, leveling off in older age groups. There are significant differences between locations in age, employment status, vaccination history, household size and housing conditions. However, after adjustment, significant variations in the frequency of detectable neutralization titers persists between locations. These results suggest there are characteristics of communities that drive influenza transmission dynamics apart from individual and household level risk factors, and that such factors have effects independent of strain.