California H1N1 study shows high rates of death over age 50

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An examination of H1N1 fatalities in California shows that after hospitalization, most deaths from swine flu occurred in those over age 50. The findings differ from reports that H1N1 flu primarily affects younger people and causes mild illness.

The study, appearing in the November 4 issue of JAMA, revealed that thirty percent of H1N1 flu cases have required admission to intensive care units.

Janice K. Louie, M.D., M.P.H., of the California Department of Public Health, Richmond, Calif., and colleagues looked at H1N1 flu cases in California between April 23 and August 11, 2009, including fatality and other clinical features. The California Department of Public Health and 61 local health departments initiated enhanced surveillance of H1N1 April 23.

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The authors found, "Overall fatality associated with H1N1 flu in California was 11 percent (118/1,088) and was highest (18 percent - 20 percent) in persons aged 50 years or older." Sixty five percent of cases required mechanical ventilation from respiratory complications.

Among 884 available cases of H1N1 flu, thirty one percent of patients were admitted to intensive care. Seventy one percent of patients had other risk factors for development of severe influenza symptoms. Thirty four percent of patients had false negative rapid antigen H1N1 test results.

The authors write, "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."

The most common cause of death from H1N1 flu was the result of pneumonia and acute respiratory distress syndrome, occurring within twelve days of onset of flu symptoms. Seven percent of H1N1 deaths were among those under age 18.

Clinicians are cautioned to remain alert to symptoms of H1N1 influenza, regardless of results of testing. Patients over age 50, presenting with flu like symptoms and with underlying risk factors, should be closely monitored. H1N1 flu should be suspected when symptoms are present, even if rapid testing is negative. Patients hospitalized with H1N1 flu should receive antiviral agents promptly say the study authors. According to the California study, H1N1 flu symptoms have been severe, and are occurring in all age groups, with the highest fatality rates among those over age 50, contrary to common perception that H1N1 flu affects mostly young people.

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