Estimate of 2009 H1N1 influenza cases in Shenzhen - The biggest migratory city in China

Abstract

The 2009 novel H1N1 influenza pandemic had a significant impact on Shenzhen's population with 2063 laboratory-confirmed human H1N1 cases and five deaths being reported. We used parameters from two population-based surveys and the Shenzhen Influenza Surveillance System to estimate the total number of H1N1 influenza infections in Shenzhen in the 2009 pandemic. The attack rate of influenza-like illness (ILI) in family households was 112% (95% CI 94-130), with 802% (95% CI 778-825) seeking medical care. The ILI attack rate in workers was 381% (95% CI 343-417) with 725% (95% CI 669-780) seeking medical care. The average H1N1 positive rate in individuals reporting ILI and testing by polymerase chain reaction was 227%. A total of 611 000-768 000 people, or 47-59% of the Shenzhen population, are estimated to have experienced H1N1 influenza. The estimated total number of cases of H1N1 is likely to be 330 times greater than the number of laboratory-confirmed cases. © Copyright Cambridge University Press 2011.