Obesity puts swine flu sufferers at greater risk, study suggests A study in
California shows that about a quarter of the people hospitalized for H1N1
complications were morbidly obese, even though less than 5% of the
population falls into that category.

By Thomas H. Maugh II and Karen Kaplan

November 4, 2009
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Obesity appears to be a risk factor on a par with pregnancy for developing
complications from an infection with pandemic H1N1 influenza, according to
the most comprehensive look yet at swine flu hospitalizations.

About a quarter of those hospitalizations have been for people who were
morbidly obese, even though such people make up less than 5% of the
population. That fivefold increase in risk is close to the sixfold increase
observed in pregnant women, according to the report published today in the
Journal of the American Medical Assn.

When the merely obese are included with the morbidly obese, they make up 34%
of the American population. Yet they accounted for 58% of the
hospitalizations in the study.

"It makes intuitive sense," said Dr. Thomas R. Frieden, director of the
Centers for Disease Control and Prevention, who noted that obese people have
a higher risk of many diseases and thus a lower life expectancy. "It should
be added as one of the underlying conditions."

The CDC considers adults to be obese if their body mass index is 30 or above
and morbidly obese if their BMI tops 40. A person who is 5 feet 8 would be
obese if he or she weighs at least 197 pounds and morbidly obese if he or
she weighs at least 262 pounds.

Researchers have seen anecdotal reports throughout the course of the
pandemic that the obese might be at greater risk of complications from
infection, but it has never been clear whether this was a result of obesity
or of risk factors associated with obesity.

In the JAMA study, which analyzed data from all 1,088 swine-flu-related
hospitalizations that occurred in California from the beginning of the
outbreak this spring through Aug. 11, researchers from the state Department
of Public Health identified 268 adults whose BMIs were known. Of those, 156
were obese, including 67 who were morbidly obese. Forty-six of those obese
adults died, according to the study.

In addition, 19% of hospitalized swine flu patients between the ages of 2
and 17 were considered obese, with a BMI above the 95th percentile for their
age. None of those patients died.

The researchers found that two-thirds of the obese patients had a health
problem that was previously recognized as an underlying risk factor for
swine flu. The most common were chronic lung disease, heart disease and

But that still left one-third of obese patients without other risk factors,
said Dr. Janice K. Louie, lead author of the study and chief of the state
health department's influenza and respiratory syndromes section.

There are many possible explanations.

Some of them are physiological. The lungs of obese patients are compressed
because the abdomen presses up on the diaphragm. In addition, the chest wall
is heavier, so it's more difficult for the lungs to stay inflated.

Both of those factors make it difficult for blood and oxygen to travel
throughout the lungs and fight off infection, said Dr. Lena Napolitano,
chief of acute-care surgery at the University of Michigan Health System. She
recently published a report in the CDC's Morbidity and Mortality Weekly
Report on 10 swine flu patients admitted to the intensive care unit there;
of the 10, nine were obese, including seven who were morbidly obese.

The compromised immune system of obese people probably also plays a role,
said Dr. David Heber, director of the Risk Factor Obesity Program at UCLA's
David Geffen School of Medicine. Scientists believe that people who are
obese have a baseline level of inflammation that diminishes the body's
ability to fight diseases.

Studies of obese mice help explain why.

Researchers at the University of North Carolina in Chapel Hill found that
42% of obese mice died when infected with a human strain of flu, while the
same virus killed only 5% of lean mice. The lungs of the obese mice failed
to produce two crucial kinds of immune cells called cytokines that fight off
viruses. There was also a decrease in natural killer cells and T-cells, two
other components of the immune system, said Patricia Sheridan, a nutritional
immunologist at UNC who worked on the study.

Those results raise questions about whether flu vaccines prompt enough of an
immune response to offer any protection to obese people. UNC researchers are
studying that, Sheridan said.

In addition to the findings on obesity, the JAMA study found that:

* More than a third of the patients reported nausea or vomiting, and a fifth
reported diarrhea. Such gastrointestinal symptoms are observed in fewer than
5% of those hospitalized with seasonal flu.

* Rapid tests for influenza commonly used for initial screening gave false
negatives 34% of the time, an unexpectedly high rate.

Since Aug. 11, nearly 3,000 more Californians have been hospitalized with
swine flu and 131 have died, Louie said.

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 Copyright  2009, The Los Angeles Times <>

Michael Balter
Contributing Correspondent, Science

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