Measuring the effect of influenza A(H1N1)pdm09: the epidemiological experience in the West Midlands, England during the 'containment' phase.

The West Midlands was the first English region to report sustained community transmission during the ‘containment’ phase of the influenza A(H1N1)pdm09 pandemic in England. To describe the epidemiological experience in the region, West Midlands and national datasets containing laboratory-confirmed A(H1N1)pdm09 virus cases in the region during the ‘containment’ phase were analysed. The region accounts for about 10·5% of England's population, but reported about 42% of all laboratory-confirmed cases. Altogether 3063 cases were reported, with an incidence rate of 56/100 000 population. School-associated cases accounted for 25% of cases. Those aged <20 years, South Asian ethnic groups, and residents of urban and socioeconomically deprived areas were disproportionately affected. Imported cases accounted for 1% of known exposures. Regional R 0 central estimates between 1·41 and 1·43 were obtained. The West Midlands experience suggests that interpretation of transmission rates may be affected by complex interactions within and between sub-populations in the region.