Oseltamivir Ring Prophylaxis of 2009 H1N1 Influenza

The 2009 H1N1 influenza pandemic prompted novel containment interventions. Although these (and other) measures failed to prevent worldwide spread of the virus, they may be effective in closed environments, where attack rates can be extremely high. Investigators recently described their experience with using oseltamivir “ring chemoprophylaxis” during outbreaks of 2009 H1N1 influenza in four semiclosed military camps in Singapore.

All personnel with suspected infection were tested, and those with positive test results were isolated. Ring prophylaxis with oseltamivir (75 mg daily for 10 days) was given to “co-workers” of patients with confirmed infection. “Co-worker” was defined as a member of the same military unit, which allowed administration of postexposure prophylaxis to a wide group of individuals.

Eighty-two confirmed cases of 2009 H1N1 influenza occurred during the outbreaks. The overall infection rate across all four military units before containment interventions was 6.4%. Following intervention, the infection rate was reduced to 5.9% of the original rate. Interventions were successful in three of the four outbreaks. Molecular analysis of the isolated viruses indicated that each outbreak consisted of transmitted cases rather than unrelated infections. Among 816 oseltamivir recipients who were surveyed, 63 (7.7%) reported mild adverse effects (predominantly gastrointestinal), none of them serious.