Fifty seasonal infl uenza A infections and 17 pandemic (H1N1) 2009 infections were detected by rRT-PCR. Fortynine of the 50 seasonal infl uenza A infections were subtyped as H1N1; one was subtype H3N1 (Figure 2 ; with dual virus infection were not signifi cantly more ill than those with infl uenza A infection alone (3/7 vs. 26/60; p = 1.0). Illnesses for 205 (67%) patients met the strict case definition for ILI or pneumonia; 100 (33%) met only the expanded case defi nitions. Age distribution and proportion of infl uenza A viruses did not differ signifi cantly between the strict and expanded case defi nition groups. However, a signifi cantly higher proportion of patients with ILI (18/25 vs. 6/46; p<0.001) or pneumonia (99/180 vs. 5/54; p<0.001) whose illnesses met the strict case defi nition were hospitalized, which suggests that the expanded case defi nitions captured patients with milder illnesses.