Report links obesity to H1N1 complications

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 complications have been in people who were morbidly obese, even though such people make up less than 5 percent of the population. That fivefold increase in risk is nearly the same as the sixfold increase observed in pregnant women, according to the report published in the Journal of the American Medical Association.

Even the merely obese were at increased risk of severe cases of swine flu, the analysis found. Although 34 percent of Americans are obese, they accounted for 58 percent 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 inches tall 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 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 associated risk factors.

In the study, which analyzed data from the 1,088 swine-flu-related hospitalizations 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 percent 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 diabetes.

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

There are many possible explanations.

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 things make it difficult for blood and oxygen to travel throughout the lungs and fight 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 ICU 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 the University of California, Los Angeles’ David Geffen School of Medicine. Scientists believe that obese people have a baseline level of inflammation that diminishes the body’s ability to fight diseases.

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

Ÿ 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 percent of those hospitalized with seasonal flu.

Ÿ Rapid tests for influenza commonly used for initial screening gave false negatives 34 percent of the time, an unexpectedly high rate. Such negative tests were much less common in the young, who shed flu viruses longer than adults do.