JAMA Study Reveals H1N1 Kills 1 in 10 of Those Hospitalized

Data from a California study published today in the November 4 issue of the Journal of the American Medical Association have revealed that Swine Flu kills more than 1 in 10 of those it affects severely enough to put in a hospital.  The study, conducted by the California Department of Public Health investigated H1N1 flu cases in California between April 23 and August 11, 2009, including fatality and other clinical features.  The authors found that the overall fatality associated with H1N1 flu in California was 11 percent and was highest (18 percent – 20 percent) in persons aged 50 years or older.

For those affected severely by the H1N1 virus, it appears that the most common cause of death has been Pneumonia and Acute Respiratory Distress Syndrome, occurring within twelve days of onset of flu symptoms.  These findings are supported by the World Health Organization’s report on The Clinical Features of Severe Cases of Pandemic Influenza.  According to WHO, Primary viral pneumonia is the most common finding in severe cases and a frequent cause of death.  Secondary bacterial infections have been found in approximately 30% of fatal cases, and Respiratory failure and refractory shock have also been the most common causes of death.

The message to take home from this latest study is that overall, severe symptoms of the H1N1 infection appear to be occurring across all age groups with the highest fatality rates being among those over age 50, contrary to the common perception that H1N1 flu affects mostly young people.  Additionally, both the JAMA study and WHO findings suggest that obesity, and especially morbid obesity,  have been present in a large portion of severe and fatal cases of the virus, although the exact role of obesity is not well understood at present.

For more information on distinguishing the clinical features of a severe H1N1 infection, please refer to the following report: WHO – Clinical features of severe cases of pandemic influenza