Effectiveness of oseltamivir in preventing influenza in household contacts- A randomized controlled trial

Context Influenza virus is easily spread among the household contacts of an infected person, and prevention of influenza in household contacts can con trol spread of influenza in the community. Objective To investigate the efficacy of oseltamivir in preventing spread o f influenza to household contacts of influenza-infected index cases (ICs). Design and Setting Randomized, double-blind, placebo-controlled study condu cted at 76 centers in North America and Europe during the winter of 1998-19 99. Participants Three hundred seventy-seven ICs, 163 (43 %) of whom had labora tory-confirmed influenza infection, and 955 household contacts (aged greate r than or equal to 12 years) of all ICs (415 contacts of influenza-positive ICs). Interventions Household contacts were randomly assigned by household cluste r to take 75 mg of oseltamivir (n=493) or placebo (n=462) once daily for 7 days within 48 hours of symptom onset in the IC. The ICs did not receive an tiviral treatment. Main Outcome Measure Clinical influenza in contacts of influenza-positive I Cs, confirmed in a laboratory by detection of virus shedding in nose and th roat swabs or a 4-fold or greater increase in influenza-specific serum anti body titer between baseline and convalescent serum samples. Results In contacts of an influenza-positive IC, the overall protective eff icacy of oseltamivir against clinical influenza was 89% for individuals (95 % confidence interval [CI], 67%-97%; P<.001) and 84% for households (95% CI , 49%-95%; P<.001). In contacts of all ICs, oseltamivir also significantly reduced incidence of clinical influenza, with 89% protective efficacy (95% CI, 71%-96%; P<.001). Viral shedding was inhibited in contacts taking oselt amivir, with 84% protective efficacy (95% CI, 57%-95%; P<.001). All virus i solates from oseltamivir recipients retained sensitivity to the active meta bolite. Oseltamivir was well tolerated; gastrointestinal tract effects were reported with similar frequency in oseltamivir (9.3 %) and placebo (7.2%) recipients. Conclusion In our sample, postexposure prophylaxis with oseltamivir, 75 mg once daily for 7 days, protected close contacts of influenza-infected perso ns against influenza illness, prevented outbreaks within households, and wa s well tolerated.