Emergence of oseltamivir-resistant pandemic H1N1 virus during prophylaxis.

To the Editor: Neuraminidase inhibitors (oseltamivir and zanamivir) are recommended for treatment of severe illness caused by the 2009 pandemic influenza A (H1N1) virus, and their use has also been advocated for postexposure prophylaxis in high-risk persons.1 We report the emergence of an oseltamivir-resistant virus in a familial cluster of infections with the 2009 H1N1 virus. In a 13-year-old boy with asthma, infection with the 2009 H1N1 virus developed and was confirmed by reverse-transcriptase polymerase-chain-reaction (RT-PCR) testing of a nasopharyngeal aspirate. Administration of oseltamivir (60 mg twice a day for 5 days for this boy who weighed 32 kg) was . . .