Clinical factors predictive of pneumonia caused by pandemic 2009 H1N1 influenza virus.

Pneumonia was the most common cause of death during the 2009 pandemic H1N1 influenza virus infection. Clinical risk factors for pneumonia caused by this virus are limited. We enrolled consecutive patients treated at the H1N1 Clinic in Thungsong Hospital in Nakhon Si Thammarat, Thailand, during June-December 2009 who had positive polymerase chain reaction results for H1N1 virus.