Ratio of Excess ED ILI Visits to Seroprevalence, Influenza A/H1N1 Infection, FL, 2009

Introduction A seroprevalence survey carried out in four counties in the Tampa Bay area of Florida (Hillsborough, Pinellas, Manatee and Pasco) provided an estimate of cumulative incidence of infection due to the 2009 influenza A (H1N1) as of the end of that year’s pandemic (1). During the pandemic, high-level decison-makers wanted timely, credible forecasts as to the likely near-term course of the pandemic. The cumulative percentage of people who will be infected by the end of the epidemic can be estimated from the intrinsic reproductive number of the viral strain, its R0, which can be measured early in the epidemic (2). If the current cumulative number of infections can be estimated, then one can determine what fraction of the eventual total number of infected people have already been infected.