In June 2009, the CDC defined a confirmed case of H1N1 as a person with an ILI and laboratory confirmed novel influenza A H1N1 virus infection. ILI is defined by the CDC as fever and cough and/or sore throat, in the absence of a known cause other than influenza. ILI cases are usually reported without accounting for alternate diagnoses (that is, pneumonia). Therefore, evaluation is needed to determine the impact of alternate diagnoses on the accuracy of the ILI case definition.
Objective
This study investigates the impact of alternate diagnoses on the accuracy of the Centers for Disease Control and Prevention’s (CDC) case definition for influenza-like illness (ILI) when used as a screening tool for influenza A (H1N1) virus during the 2009 pandemic, and the implications for public health surveillance.