"Overall fatality was 11 percent (118/1,088) and was highest (18 percent - 20 percent) in persons aged 50 years or older," the researchers write. "Of the deaths, 8 (7 percent) were children younger than 18 years. Among fatal cases, the median time from onset of symptoms to death was 12 days." The most common causes of death were viral pneumonia and acute respiratory distress syndrome.

"In the first 16 weeks of the current pandemic, 2009 influenza A(H1N1) appears to be notably different from seasonal influenza, with fewer hospitalizations and fatalities occurring in elderly persons. In contrast with the common perception that pandemic 2009 influenza A(H1N1) infection causes only mild disease, hospitalization and death occurred at all ages, and up to 30 percent of hospitalized cases were severely ill. Most hospitalized cases had identifiable established risk factors; obesity may be a newly identified risk factor for fatal pandemic 2009 influenza A(H1N1) infection and merits further study."

"Clinicians should maintain a high level of suspicion for pandemic 2009 influenza A(H1N1) infection in patients presenting currently with influenza-like illness who are older than 50 years or have known risk factors for influenza complications, regardless of rapid test results. Hospitalized infected cases should be carefully monitored and treated promptly with antiviral agents," the authors conclude.

Source: California Department of Public Health