Who’s dying from the H1N1 flu pandemic?

Originally published in MedPage Today

by Michael Smith, MedPage Today North American Correspondent

Although the pandemic H1N1 flu tends to strike younger people, it can be life-threatening when older people are infected, California researchers said.

In the first four months of the pandemic, 1,088 people in the state needed inpatient care or died of the pandemic flu strain, according to Janice Louie, MD, of the California Department of Public Health and colleagues.

The median age of the victims was 27 — younger than is usually seen with the seasonal flu — but the highest case fatality rate was seen among those 50 and older, Louie and colleagues reported in the Nov. 4 issue of the Journal of the American Medical Association.

Those findings are based on statewide enhanced public health surveillance between April 23 and Aug. 11, the researchers said. The first cases of the pandemic flu in the U.S. were reported in Southern California on April 17.

For this analysis, the researchers defined a case as anyone who needed inpatient care or died with a laboratory finding of confirmed or probable H1N1 influenza.

Of the 1,088 patients who met the outlined criteria, Louie and her colleagues found that:

* The median age of the patients was 27, with 32% under 18, although the oldest victim was 92.
* Overall, 11% died but the case-fatality rate was highest in people 50 or older, at between 18% and 20%.
* 31% required intensive care and 25% needed mechanical ventilation.
* The overall rate of hospitalization and/or fatality per 100,000 population for all age groups was 2.8, but it ranged from 11.9 in infants younger than a year to 1.5 in those 70 or older.
* 68% of the patients had risk factors for seasonal influenza complications.
* Of the 833 patients who had chest x-rays on admission, 66% had infiltrates suggesting pneumonia or acute respiratory distress syndrome.
* Only 4% had a secondary bacterial infection.
* 21% were not treated with antiviral medication.

About 57% of the patients were tested for flu using a rapid antigen test, but physicians got a false negative 34% of the time, Louie and colleagues said.

“We found many physicians delayed treatment of their patients because they were falsely reassured by the rapid test,” she said.

The findings about older victims are consistent with what’s already known about the pandemic flu, according to Thomas Frieden, MD, director of the CDC.

In a telephone news briefing, he said the H1N1 strain tends to strike younger people, rather than the old. For that reason, the CDC recommends the young get priority for vaccine, and there are no plans to change that recommendation, he said.

But, Frieden said, if older people get the H1N1 strain, “it can be every bit as serious as the seasonal flu.”

Louie and colleagues acknowledged that the study had design limitations: Data were extracted from nonstandardized medical records and case ascertainment was based on passive reporting, which may have led to under-reporting.

They added that laboratory testing to confirm cases had limited availability, which may have also led to under-reporting.

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