KALAMAZOO, MI -

- Kalamazoo College students and staff are getting a warning right up front that is buried, or missing entirely, from other literature that warns of complications from H1N1 influenza.

Kathleen Winkworth administers a flu vaccine at Borgess Health and Fitness Center flu clinic last January.

That is: If you are overweight, you may want to take extra care this flu season.

"This virus primarily affects young and middle-age adults. Those with underlying medical conditions or obesity have an increased risk for severe complications, hospitalization and death," warns a message sent to faculty, staff and students from the college health center.

Obesity?

Yes, doctors know a little more this time around about the risk factors associated with H1N1, the nasty strain of flu that killed many young, healthy people in 2009, the last time there was an outbreak.

Obesity is one of them.

"It's really very specific, said Dr. Richard VanEnk, Director of Infection Control at Bronson Methodist Hospital.

A study at the University of Michigan after the 2009 pandemic found that "the more obese you are, the more at risk you are" for hospitalization and the need for critical care if you contract H1N1, Van Enk said.

That's a departure from the risk factors generally associated with seasonal flu, such as lung disease or an immune system weakened by other underlying medical conditions.

The other findings of that 2009 study of H1N1 patients were perhaps more well publicized-- that H1N1 targets younger people, 18-65, not seniors, and that pregnant women, too, are at higher risk for complications.

Of people who get the H1N1 strain of influenza, pregnancy and body mass were the two most significant risk factors for serious complications, Van Enk said.

Researchers aren't quite sure yet why that might be, he said. In the case of pregnancy, "we don't know if it is the pregnancy itself, hormonal changes, or the additional stress on heart and lungs, but if you get H1N1 and are pregnant, you are at much higher risk," he said.

"Obesity is equal in significance," he said, again for as yet unknown reasons.

"Is it stress on the heart and lungs? I don't know that that has been teased out, " he said, but in both men and women, a higher body mass index --ratio of weight to height--spells greater risk.

An excerpt from an article on the University of Michigan's website about the study says:

"Obesity alone is not considered a risk factor for regular seasonal flu. The high prevalence of obesity among the H1N1 patients is striking..."

"Most of the patients had no other illness that would make them prone to advanced viral infection," the lead author of the study said.

Do obese people know they are at risk?

A follow-up study in California supports those findings-- yet obesity is not generally listed among the risk factors that would suggest an increased need for precautions.

Walgreen's questions-and-answer page about flu vaccinations mentions that this year's vaccine includes protection for the H1N1 strain and lists pregnancy as a risk for complications-- but does not list obesity.

The CDC website currently lists a BMI of 40 or higher, termed morbidly obese, as an "additional risk factor," but it is not included on the main list of risks.

Van Enk said the lack of attention to that risk may be because it is still not clear if obesity alone increases the risk of complication, or if it is a co-factor because obese people often have diabetes and problems with their lungs and heart.

"I tend to think that it is related to other things, that you get sicker with influenza if you are obese because your heart and lungs have less reserve capacity," Van Enk said.

Van Enk said that although these risk factors have been "pretty widely known in the medical community since 2009, it is probably true that the information has not been communicated to the community and specifically to people with large BMI by their primary care providers.

" I guess because of the negative stigma our society attaches to people of size, we don’t tend to single them out and market health interventions to them very much," he said. "We tell them to lose weight but we don’t do a good job helping them manage their health at the weight they are."

The H1N1 strain is moving into Southwest Michigan; it is already causing hospitalizations in Southeast Michigan. Washtenaw County hospitals have admitted 30 patients in the last three weeks and doctors have already seen more than 50 flu cases requiring hospitalization this season.

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in the CDC’s Morbidity and Mortality Weekly Report from 2009 while the outbreak was occurring, a paper that focused on the obesity factor.