Comparisons of oseltamivir-resistant (H275Y) and concurrent oseltamivir-susceptible seasonal influenza A(H1N1) virus infections in hospitalized adults, 2008-2009.

In an observational cohort study, we found that adults hospitalized for oseltamivir-resistant (H275Y) seasonal H1N1 influenza (n = 46) were older than those infected with oseltamivir-susceptible strains (n = 31) [74(IQR 59-83) versus 64(IQR 48-76) years; P = 0·045], and most had major comorbidities (78% versus 65%). Disease severity and clinical outcomes were comparable between the two groups: radiographic pneumonia 40-42%, supplemental oxygen use 47-48%, critical illness 11-13%, median duration of hospitalization 5-6 days, death rate 6-9%. Failure to receive effective antiviral therapy was associated with progression to critical illness (23% versus 0%, P = 0·016) and death (20% versus 0%, P = 0·033) in hospitalized patients with seasonal H1N1 influenza.