16 December 2011
The Guangzhou Center for Disease Control and Prevention reported their findings from influenza surveillance between March 2008 and April 2011(Li et al 2011).
The first case of influenza A(H1N1)pdm09 in China was reported on 18 May 2009, and the report focuses on the evolution of the pandemic virus in Guangzhou over two influenza seasons. The surveillance report indicates that the second epidemic year (May 2010 – April 2011) found significantly reduced scale, duration of outbreaks, disease severity, and fatality rates than found in the first epidemic year (May 2009 – April 2010). The surveillance report further indicates that the severe disease and fatality rates, as well as length and scale of the A(H1N1)pdm09 outbreaks were similar to the rates found in surveillance of seasonal influenza. However, outbreak of the pandemic virus had very different timing than the usual seasonal influenza seen in Guangzhou. Other seasonal influenza viruses occurred primarily in the spring/summer seasons, whereas the influenza A(H1N1)pdm09 season was during autumn/winter in the first year (2009-10), and winter/spring in the second year (2010-11). The authors also note that circulation of the influenza B virus appears to peak some months prior to the peaks of influenza type A viruses.
Detailed surveillance of severe disease was carried out during this time period also, and the authors report on the relative risk for severe disease based on potential risk factors. Only chronic lung disease was found to be a statistically significant risk of death.
This report by the Guangzhou Center for Disease Control and Prevention shows the utility and importance of collecting detailed surveillance data. The ability to monitor influenza virus circulation timing and relative prevalence by type of virus is very valuable and a more detailed understanding of the seasonal patterns of different viruses and their relative impact will be available once data covering more years are available. Continuous surveillance of risk factors for severe influenza by influenza type, for seasonal as well as pandemic influenza, is an important element to consider given the value this may have for public health planning for influenza prevention, control, and treatment.