Adjusted hazard ratios of explanatory variables associated with death, as shown in multivariate Cox regression models (censored at 30 days)
| Adjusted hazard ratio (95% CI) | p-value | |
| Model 1# | ||
| Age per 20 years | 1.13 (0.95–1.36) | 0.170 |
| Male sex | 1.38 (1.00–1.92) | 0.053 |
| H1N1pdm09 | 1.35 (0.90–2.02) | 0.142 |
| Bacterial superinfection | 2.18 (1.52–3.11) | <0.001 |
| NAI treatment | 0.28 (0.19–0.43) | <0.001 |
| Statin use | 0.44 (0.23–0.84) | 0.013 |
| Systemic corticosteroids | 1.11 (0.79–1.56) | 0.554 |
| Model 2¶ | ||
| Age per 20 years | 1.21 (1.00–1.46) | 0.050 |
| Male sex | 1.48 (1.05–2.09) | 0.024 |
| H1N1pdm09 | 1.15 (0.74–1.79) | 0.538 |
| Bacterial superinfection | 2.14 (1.48–3.10) | <0.001 |
| NAI treatment | ||
| 0–2 days | 0.20 (0.12–0.32) | <0.001 |
| 3–5 days | 0.35 (0.21–0.58) | <0.001 |
| >5 days | 0.49 (0.27–0.88) | 0.017 |
| None | ||
| Statin use | 0.49 (0.26–0.94) | 0.032 |
| Systemic corticosteroids | 1.04 (0.73–1.48) | 0.839 |
| Model 3+ | ||
| Age per 20 years | 1.15 (0.95–1.38) | 0.148 |
| Male sex | 1.34 (0.96–1.86) | 0.083 |
| H1N1pdm09 | 1.11 (0.75–1.65) | 0.611 |
| Bacterial superinfection | 2.18 (1.53–3.11) | <0.001 |
| NAI treatment§ | 0.39 (0.27–0.57) | <0.001 |
| Statin use | 0.42 (0.22–0.81) | 0.009 |
| Systemic corticosteroids | 1.09 (0.77–1.53) | 0.629 |
| Model 4ƒ | ||
| Age per 20 years | 1.01 (0.82–1.24) | 0.935 |
| Male sex | 1.16 (0.82–1.65) | 0.392 |
| H1N1pdm09 | 0.65 (0.42–1.02) | 0.062 |
| Bacterial superinfection | 1.50 (1.03–2.19) | 0.034 |
| NAI treatment§ | 0.39 (0.26–0.59) | <0.001 |
| Statin use | 0.59 (0.30–1.13) | 0.112 |
| Systemic corticosteroids | 1.12 (0.78–1.61) | 0.553 |
In all models, neuraminidase inhibitors (NAI) treatment propensity score was included as a covariate (see methods), and had a p-value <0.05. An adjusted hazard ratio <1 indicated a lower probability of death. #: model 1 was adjusted for NAI treatment, bacterial superinfection, statin and corticosteroid use (yes versus no) and H1N1pdm09 (versus seasonal influenza A/B viruses). ¶: model 2 was adjusted for NAI treatment; “none” was the reference group. +: time-dependent Cox regression. §: models 3 and 4 were time-dependent Cox regressions; NAI treatment initiation with respect to day of illness onset was analysed as a time-dependent covariate (versus none). ƒ: pneumonia subgroup.