A severely immunocompromised child with uncomplicated oseltamivir-resistant 2009 H1N1 pandemic influenza infection

Of those patients hospitalized in the United States during the 2009 H1N1 influenza pandemic, approximately one-third were under the age of 18 yr (1). The attributed mortality was relatively higher among young children, pregnant women, and individuals with immunosuppression, severe obesity, and other comorbidities when compared to seasonal influenza (2, 3). The virologic and immunologic mechanisms accounting for differences in clinical manifestations and disease outcomes between 2009 H1N1 and seasonal influenza A infections have not yet been fully elucidated. In addition, emerging resistance of the 2009 H1N1 virus to oseltamivir, a NA inhibitor and the mainstay of treatment, has led to pulmonary complications, severe disease, and poor outcomes especially among immunocompromised individuals (4, 5). We report a case of an immunosuppressed pediatric renal transplant patient with mild pneumonia caused by oseltamivir-resistant 2009 H1N1 influenza and successfully treated with zanamivir. This case highlights the complex interplay between pathogen and host, underscores the possible importance of the innate immune system in influenza, and raises questions regarding viral fitness and resistance.