Estimated impact of aggressive empirical antiviral treatment in containing an outbreak of pandemic influenza H 1 N 1 in an isolated F irst N ations community

Background The 2009 influenza A ( H 1 N 1) pandemic was mild by historical standards, but was more severe in isolated C anadian I ndigenous communities. O seltamivir was used aggressively for outbreak control in an isolated northern O ntario F irst N ations community. We used mathematical modeling to quantify the impact of antiviral therapy on the course of this outbreak. Methods We used both a R ichards growth model and a compartmental model to evaluate the characteristics of the outbreak based on both respiratory visits and influenza‐like illness counts. Estimates of best‐fit model parameters, including basic reproductive number ( R 0 ) and antiviral efficacy, and simulations, were used to estimate the impact of antiviral drugs compared to social distancing interventions alone. Results Using both approaches, we found that a rapidly growing outbreak slowed markedly with aggressive antiviral therapy. R ichards model turning points occurred within 24 hours of antiviral implementation. Compartmental models estimated antiviral efficacy at 70–95%. Plausible estimates of R from both modeling approaches ranged from 4·0 to 15·8, higher than published estimates for southern C anada; utilization of aggressive antiviral therapy in this community prevented 962–1757 cases of symptomatic influenza and as many as 114 medical evacuations in this community. Conclusion Although not advocated in other settings in C anada, aggressive antiviral therapy markedly reduced the impact of a pandemic‐related influenza A ( H 1 N 1) outbreak in an isolated C anadian F irst N ations community in northern O ntario, C anada. The differential risk experienced by such communities makes tailored interventions that consider risk and lack of access to medical services, appropriate.