Table 2.
Results From Mixed-Effects Negative Binomial Regression Analyses
| Variable | Unadjusted, IRR (95% CI) | Adjusted,a IRR (95% CI) |
|---|---|---|
| Primary analysis: NAI treatment on day of hospital admission vs later/no NAI treatmentb | ||
| Overall | 0.83 (.79–.87)c | 0.81 (.78–.85)c |
| Laboratory-confirmed A(H1N1)pdm09 infection | 0.83 (.79–.86)c | 0.81 (.77–.85)c |
| Children (age <16 y) | 0.90 (.83–.97)c | 0.85 (.78–.92)c |
| Elderly (age ≥65 y) | 0.78 (.67–.91)c | 0.78 (.67–.91)c |
| Patients requiring standard ward-based care only | 0.81 (.77–.85)c | 0.81 (.78–.86)c |
| ICU-admitted patients onlyd | 0.80 (.73–.88)c | 0.79 (.72–.87)c |
| Confirmed absence of influenza-related pneumonia | 0.71 (.66–.77)c | 0.73 (.68–.79)c |
| Confirmed presence of influenza-related pneumonia | 0.91 (.84–.98)c | 0.85 (.79–.93)c |
| Sensitivity analysis: NAI treatment on day of hospital admission vs no NAI treatmentb | ||
| Overall | 1.14 (1.07–1.22)c | 1.06 (.99–1.13) |
| Laboratory-confirmed A(H1N1)pdm09 infection | 1.15 (1.07–1.22)c | 1.04 (.97–1.12) |
| Children (age <16 y) | 1.09 (.98–1.20) | 0.98 (.88–1.09) |
| Elderly (age ≥65 y) | 0.84 (.67–1.06) | 0.83 (.65–1.07) |
| Patients requiring standard ward-based care only | 0.93 (.87–.99)c | 0.92 (.85–.98)c |
| ICU-admitted patients onlyd | 1.14 (.96–1.36) | 1.08 (.90–1.31) |
| Confirmed absence of influenza-related pneumonia | 0.83 (.75–.92)c | 0.81 (.73–.90)c |
| Confirmed presence of influenza-related pneumonia | 1.28 (1.12–1.47)c | 1.28 (1.11–1.48)c |
| Secondary analyses | ||
| NAI anytime vs no NAI treatment | ||
| Overall | 1.21 (1.17–1.26)c | 1.11 (1.07–1.16)c |
| Laboratory-confirmed A(H1N1)pdm09 infection | 1.31 (1.25–1.37)c | 1.17 (1.12–1.23)c |
| Children (age <16 y) | 1.18 (1.11–1.25)c | 1.11 (1.04–1.18)c |
| Elderly patients (age ≥65 y) | 1.00 (.86–1.17) | 0.98 (.83–1.14) |
| Patients requiring standard ward-based care only | 1.06 (1.02–1.10)c | 1.02 (.98–1.05) |
| ICU-admitted patients onlyd | 1.33 (1.19–1.49)c | 1.26 (1.13–1.41)c |
| Confirmed absence of influenza-related pneumonia | 0.98 (.90–1.07) | 0.97 (.89–1.06) |
| Confirmed presence of influenza-related pneumonia | 1.36 (1.24–1.49)c | 1.28 (1.16–1.40)c |
| Early NAI treatment vs later NAI treatment | ||
| Overall | 0.70 (.68–.73)c | 0.77 (.74–.80)c |
| Laboratory-confirmed A(H1N1)pdm09 infection | 0.70 (.68–.73)c | 0.77 (.74–.80)c |
| Children (age <16 y) | 0.80 (.74–.86)c | 0.87 (.81–.93)c |
| Elderly patients (age ≥65 y) | 0.71 (.62–.81)c | 0.71 (.62–.82)c |
| Patients requiring standard ward-based care only | 0.78 (.75–.81)c | 0.83 (.79–.86)c |
| ICU-admitted patients onlyd | 0.69 (.64–.74)c | 0.74 (.69–.80)c |
| Confirmed absence of influenza-related pneumonia | 0.80 (.75–.86)c | 0.84 (.78–.90)c |
| Confirmed presence of influenza-related pneumonia | 0.84 (.78–.90)c | 0.82 (.77–.88)c |
| Early NAI treatment vs no NAI treatment | ||
| Overall | 1.04 (.98–1.11) | 0.93 (.87–.99)c |
| Laboratory-confirmed A(H1N1)pdm09 infection | 1.05 (.98–1.11) | 0.93 (.87–.99)c |
| Children (age <16 y) | 1.00 (.91–1.10) | 0.92 (.83–1.01) |
| Elderly patients (age ≥65 y) | 0.82 (.67–1.01) | 0.79 (.63–.997)c |
| Patients requiring standard ward-based care only | 0.93 (.87–.99)c | 0.88 (.82–.94)c |
| ICU-admitted patients onlyd | 1.01 (.86–1.20) | 0.93 (.79–1.10) |
| Confirmed absence of influenza-related pneumonia | 0.79 (.71–.89)c | 0.76 (.68–.85)c |
| Confirmed presence of influenza-related pneumonia | 1.09 (.95–1.24) | 1.01 (.88–1.16) |
Abbreviations: A(H1N1)pdm09, 2009 pandemic influenza A(H1N1) virus; CI, confidence interval; IRR, incidence rate ratio; NAI, neuraminidase inhibitor.
aAdjusted for propensity scores (quintiles) for receiving treatment, antibiotic treatment received in the hospital, and steroid treatment received in the hospital.
bThe IRR was further adjusted for time from onset to admission.
cStatistically significant (P < .05).
dData are for patients admitted to the ICU at any point. The IRR was calculated for the total length of hospital stay, not time in the ICU. Our sensitivity analyses and secondary analyses must be interpreted with caution because they may be affected by various time-dependent biases