Effect of Early Oseltamivir Treatment on Mortality in Critically Ill Patients With Different Types of Influenza: A Multiseason Cohort Study.

BACKGROUND: The available evidence on whether neuraminidase inhibitors reduce mortality in patients with influenza is inconclusive and focuses solely on influenza A/H1N1pdm09. We assessed whether early oseltamivir treatment (≤48 hours from symptom onset) decreases mortality compared to late treatment in a large cohort of critically ill patients with influenza of all types. METHODS: The study included all adults with laboratory-confirmed influenza hospitalized in intensive care units (ICUs) in Greece over 8 seasons (2010-2011 to 2017-2018) and treated with oseltamivir. The association of early oseltamivir with mortality was assessed with log-binomial models and a competing risks analysis estimating cause-specific and subdistribution hazards for death and discharge. Effect estimates were stratified by influenza type and adjusted for multiple covariates. RESULTS: A total of 1330 patients were studied, of whom 622 (46.8%) died in the ICU. Among patients with influenza A/H3N2, early treatment was associated with significantly lower mortality (relative risk, 0.69 [95% credible interval {CrI}, .49-.94]; subdistribution hazard ratio, 0.58 [95% CrI, .37-.88]). This effect was purely due to an increased cause-specific hazard for discharge, whereas the cause-specific hazard for death was not increased. Among survivors, the median length of ICU stay was shorter with early treatment by 1.8 days (95% CrI, .5-3.5 days). No effect on mortality was observed for A/H1N1 and influenza B patients. CONCLUSIONS: Severely ill patients with suspected influenza should be promptly treated with oseltamivir, particularly when A/H3N2 is circulating. The efficacy of oseltamivir should not be assumed to be equal against all types of influenza.