Effects of Early Oseltamivir Therapy on Viral Shedding in 2009 Pandemic Influenza A (H1N1) Virus Infection

Background. Pandemic influenza (H1N1) 2009 is susceptible to oseltamivir. There are few reports on its clinical and virologic response to oseltamivir. Methods. During the pandemic containment response in Singapore, all patients with positive polymerase chain reaction (PCR) results for pandemic influenza (H1N1) 2009 were hospitalized, given oseltamivir for 5 days, and discharged when daily PCR results for combined nasal and throat swab samples became negative. Six patients had concurrent positive viral culture and PCR results. Results. The median age of the first 70 consecutive patients was 26 years (interquartile range, 21-38 years); 60% were men, and 29% had comorbidity. The mean time (+/- SD) from illness onset to hospital admission was 3 +/- 2 days. Influenza-like illness was noted in 63% of patients. Fever occurred in 91%, cough in 88%, sore throat in 66%, and rhinorrhea in 53% of patients. The mean duration (+/- SD) of viral shedding from illness onset was 6 +/- 2 days. Viral shedding persisted beyond 7 days in 37% of patients. Clinical features and viral shedding were similar between those with and without comorbidity, except the former had more cough and lower oxygen saturation. Patients receiving oseltamivir on days 1 to 3 of illness had significantly shorter viral shedding duration, compared with those treated from day 4 onwards (P < .05). The mean durations (+/- SD) of positive PCR and viral P < .05 culture results were 5 +/- 0.8 and 4 +/- 1.8 days, respectively, for 6 patients with concurrent positive viral culture and PCR results. Conclusions. Prolonged viral shedding was noted in young immunocompetent adults with mild pandemic influenza (H1N1) 2009 despite receipt of oseltamivir. When prescribed during the first 3 days of illness, oseltamivir shortened the duration of viral shedding.