According to univariate analysis, case-patients infected with influenza A(H1N1)pdm09 virus were less likely than case-patients infected with influenza A(H3N2) virus to be co-infected with another virus (crude RRR [cRRR] 0.6, 95% CI 0.4-0.8), and case-patients infected with influenza B virus were more likely to be infected with HIV (cRRR
1.7, 95% CI 1.2-2.3), have stridor (cRRR
2.1, 95% CI 1.2-3.6), have symptoms [greater than or equal to]3 days before admission (cRRR
1.6, 955 CI 1.2-2.1), and to have been hospitalized for [greater than or equal to]2 days (cRRR
1.6, 95% CI 1.2-2.2), and were less likely to have a measured fever of [greater than or equal to]38[degrees]C (cRRR
0.5, 95% CI 0.4-0.7) (Table 1).