The Lancet
Oct 03, 2009  Volume 374  Number 9696   Pages 1119 – 1212
http://www.thelancet.com/journals/lancet/issue/current

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How to maintain surveillance for novel influenza A H1N1 when there are too many cases to count
Marc Lipsitch, Frederick G Hayden, Benjamin J Cowling, Gabriel M Leung

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Surveillance during the present pandemic of influenza A H1N1 (pandemic H1N1) is needed to provide estimates of quantities such as disease incidence and rates of change of incidence, severity of infection, and risks to specific population groups. Estimates of these quantities inform decisions about control measures, resource procurement and allocation, and responses to other public health needs.1 They also affect public perceptions of illness severity and risk, which change the willingness of people to comply with control measures.