Presence of Oseltamivir-Resistant Pandemic A/H1N1 Minor Variants Before Drug Therapy. Influenza A virus strain:H1N1

We used ultra-deep sequencing of viral populations from serial nasopharyngeal specimens from an immunocompromised child and from 2 individuals in a household outbreak. We observed that the Y275 mutation was present as a minor variant in infected hosts before the onset of therapy. We also found evidence for the transmission of this drug-resistant variant with drug-susceptible viruses. These observations provide important information on the relative fitness of the Y275 mutation in the absence of oseltamivir treatment.