Detection of oseltamivir resistance during treatment of 2009 H1N1 influenza virus infection in immunocompromised patients: utility of cycle threshold values of qualitative real-time reverse transcriptase PCR.

Two immunocompromised patients with 2009 H1N1 influenza pneumonia had viral shedding for over 5 weeks despite therapy with oseltamivir. Declining or persistently low cycle threshold values noted on serial qualitative real-time reverse transcriptase PCR (rRT-PCR) of respiratory specimens implied increasing viral load and probable drug resistance. Oseltamivir resistance was later confirmed by pyrosequencing.