Pathogenesis of pandemic influenza A (H1N1)

With typical seasonal influenza, infection occurs primarily in the upper or major airways of the body. However, during the 2009 H1N1 pandemic, evaluation of tissue samples from fatal cases showed that the H1N1 virus also infected the cells within the lungs.

These studies also showed early evidence that bacterial pneumonia was contributing to deaths related to H1N1. Pathologists determined that microscopic examination of tissue could be used to identify bacterial coinfections after death.

The findings played an important role in treatment recommendations for H1N1 infections and for the treatment and prevention of bacterial coinfections.