Background: Large clinical trials have demonstrated the therapeutic efficacy of oseltamivir against influenza. We assessed the indirect effectiveness of oseltamivir in reducing secondary household transmission in an incident cohort of influenza index patients and their household members.
Methods: We recruited index outpatients whose rapid test results were positive for influenza from February through September 2007 and January through September 2008. Household contacts were followed up for 7-10 days during 3-4 home visits to monitor symptoms. Nose and throat swabs were collected and tested for influenza by reverse-transcription polymerase chain reaction or viral culture.
Results: We followed up 384 index patients and their household contacts. Index patients who took oseltamivir within 24 h of symptom onset halved the time to symptom alleviation (adjusted acceleration factor, 0.56; 95% confidence interval [CI], 0.42-0.76). Oseltamivir treatment was not associated with statistically significant reduction in the duration of viral shedding. Household contacts of index patients who had taken oseltamivir within 24 h of onset had a nonstatistically significant lower risk of developing laboratory-confirmed infection (adjusted odds ratio, 0.54; 95% CI, 0.11-2.57) and a marginally statistically significant lower risk of clinical illness (adjusted odds ratio, 0.52; 95% CI, 0.25-1.08) compared with contacts of index patients who did not take oseltamivir.
Conclusions: Oseltamivir treatment is effective in reducing the duration of symptoms, but evidence of household reduction in transmission of influenza virus was inconclusive.