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1 Million Swine Flu Cases in U.S.

CDC Says Vast Majority of Cases Were Mild

By Daniel J. DeNoon
WebMD Health News

Reviewed By Louise Chang, MD

June 25, 2009 -- Over 1 million Americans have had swine flu, the CDC estimates. Half those cases have been in New York City.

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H1N1 Swine Flu

The estimate, from a still-being-analyzed CDC study, was reported by CDC flu researcher Lyn Finelli, DrPH, at a meeting of the U.S. Advisory Committee on Immunization Practices.

"Right now, we are estimating over 1 million cases in the U.S.," Finelli said.

About 6% of U.S. households in major cities have had at least one case, according to data from New York City, Chicago, and the University of Delaware.

The vast majority of cases have been mild. While over one in 10 reported cases have sent patients to the hospital, Finelli says that the large number of unreported cases means that a much lower percentage of people with swine flu actually get severe disease.

But a significant minority of cases has been severe. As with seasonal flu, the highest rates of severe cases occur in the very young -- children under age 4 years -- and adults over age 65.

Most swine flu hospitalizations are among people with underlying medical conditions:

An analysis of 99 of the 127 U.S. residents who have died of swine flu shows that 87 of them suffered underlying conditions:

  • 11% had asthma
  • 24% had other lung diseases
  • 13% had diabetes
  • 11% were morbidly obese
  • 34% were obese

The CDC is currently investigating the emergence of obesity as a risk factor for severe swine flu.

Finelli said there have been five swine flu deaths among pregnant women; most were in their 20s. They died at various trimesters of pregnancy: one in the first, one in the second, and three in the third. Underlying conditions are not known for all the women, but several had none.

SOURCES: Lyn Finelli, DrPH, influenza division, CDC; report to the Advisory Committee on Immunization Practices, June 24-26, 2009; Atlanta.

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