Figure 4

Receiver Operator Curve (ROC) comparing the capability of different case definitions (CD) for hospitalized respiratory infections (RI) to capture cases of influenza A/H1N1 2009 (pH1N1). Areas under the ROC curve for CD2, CD3 and CD4 using pH1N1 PCR results as the gold standard for the overall study period (left) and the period with significant pH1N1 in Berlin (right). Data based on cases of respiratory infections hospitalized in the participating hospitals and tested for influenza, Berlin, December 2009 to December 2010. pH1N1 negative cases included only if period between symptom onset and nasopharyngeal swab ≤ 7 days.