The effect of timing of oseltamivir chemoprophylaxis in controlling influenza A H3N2 and influenza B outbreaks in long term care facilities in Manitoba, Canada, 2014-2015: a retrospective cohort study
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This study examines the effect of the timing of administration of oseltamivir chemoprophylaxis for the control of influenza A H3N2 and influenza B outbreaks among residents in long term care (LTC) facilities in Manitoba, Canada during the 2014-2015 influenza season. A retrospective cohort study was conducted of all LTC facility influenza A H3N2 outbreaks (n=94) and influenza B outbreaks (n=11) using a hierarchical logistic regression analysis. Delay of oseltamivir chemoprophylaxis was associated with increased odds of infection in both univariate (t = 5.41, df = 51, p < 0.0001), and multivariate analyses (t = 6.04, df = 49, p < 0.0001) with an adjusted odds ratio of 1.3 (95% CI: 1.2-1.5) per day for influenza A H3N2. No meaningful statistical analyses regarding influenza B could be conducted. From this study, we can conclude that the sooner chemoprophylaxis is initiated, the lower the odds of secondary infection with influenza in LTC facilities during outbreaks caused by influenza A H3N2 in Manitoba.