Extremely obese individuals, those with a BMI (body mass index) of over 40, have a significantly higher chance of dying from 2009 A(H1N1) swine flu infection compared to other people, researchers revealed in the journal Clinical Infectious Diseases. The scientists gathered data from a public health surveillance database in California and found extreme obesity to be a “powerful risk factor for death”.

The authors wrote that half of all patients in California aged at least 20 who were hospitalized with 2009 H1N1 were obese.

The researchers analyzed data on 534 adults who were hospitalized with swine flu during four months of 2009. Their aim was to determine whether obesity had an impact on swine flu mortality.

They focused specifically during the period April 20th to August 11th, 2009, on data collected by the California Department of Public Health (CDPH). The database included all reported cases of swine flu sent to CDPH by health providers during that period. The researchers excluded details on pregnant women and patients aged under 20 years.

There were 534 adult cases of 2009 H1N1 infection where BMI data were available. The authors revealed the following highlighted information:

  • 43% (228) of them were aged at least 50 years
  • 72% (378) had flu-related high-risk conditions as risk factors for severe influenza (recognized by the Advisory Committee on Immunization Practices)
  • 51% (274) had a BMI of over 30 (twice the Californian average for adults)
  • 61% of those who died had a BMI of over 30 (obese patients)
  • 30% of those who died had a BMI of over 40 (extremely obese patients)

Janice K. Louie, MD, MPH, of the California Department of Public Health, wrote:

“Extremely obese persons with a body mass index equal to or over 40 should get vaccinated annually for influenza. They should also see their health provider early if symptoms of influenza develop, so that they can get diagnosed and treated as quickly as possible. This is especially important if the influenza virus is known to be circulating in the community and causing illness.”

Dr. Louie emphasized that further studies are required to explain why exactly extreme obesity significantly raises the risk of death from 2009 H1N1 influenza infection.

The authors concluded in the journal’s abstract:

“Half of Californians >20 years of age hospitalized with 2009 H1N1 infection were obese. Extreme obesity was associated with increased odds of death. Obese adults with 2009 H1N1 infection should be treated promptly and considered in prioritization of vaccine and antiviral medications during shortages.”

“A Novel Risk Factor for a Novel Virus: Obesity and 2009 Pandemic Influenza A (H1N1)”
Janice K. Louie, Meileen Acosta, Michael C. Samuel, Robert Schechter, Duc J. Vugia, Kathleen Harriman, Bela T. Matyas, and the California Pandemic (H1N1) Working Group
Clin Infect Dis. (2011) doi: 10.1093/cid/ciq152

Written by Christian Nordqvist