An unexpected characteristic has emerged among many swine flu victims who become severely ill: They are fat.

Doctors tracking the pandemic say they see a pattern in hospital reports from Glasgow to Melbourne and from Santiago to New York. People infected with the bug who have a body mass index greater than 40, deemed morbidly obese, suffer respiratory complications that are harder to treat and can be fatal.

With the new virus on a collision course with the obesity epidemic, the World Health Organization says it's gathering statistics to confirm and understand this development. Drugmaker Roche Holding AG is combing through studies to determine whether heavier people should get bigger doses of its Tamiflu antiviral.

"Morbid obesity is one of the most common findings turning up in severely ill patients," said Nikki Shindo, who is leading the investigation of swine flu patients at the WHO in Geneva. "It's a huge problem."

In Canada's Manitoba province, three out of five people treated for the new flu strain in intensive care units are obese, said Ethan Rubenstein, head of infectious diseases at the University of Manitoba in Winnipeg. Patients with flu symptoms should be considered at risk of complications if they carry excess weight, according to Rubenstein.

So far, the evidence is anecdotal. No global or national data have been reported. Scotland, where deep-fried foods such as Mars bars and pizzas contribute to the highest obesity rate in Europe, reported the continent's first two deaths from H1N1 and has experienced a fifth of the region's fatalities.

Growing Trend

"We do seem to have more than our fair share of people in intensive care," said Hugh Pennington, 71, emeritus professor of bacteriology at the University of Aberdeen. "When the dust has settled, people will look at that."

No deaths or severely ill patients have been recorded from among the 2,146 laboratory-confirmed cases in Japan, said Yasuyuki Abe, a health ministry spokesman in Tokyo. Only 1.6 percent of adults in Japan are obese, according to the WHO.

"You don't have to go to Scotland or Japan to figure this out," said Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases in Bethesda, Maryland. "About 75 percent of patients have underlying conditions, and clearly obesity stands out as a statistically significant factor involved in the seriousness of the disease."

'Shake Out'

It's the first time that the prominence of obesity has been noticed among severely ill flu sufferers, Fauci said in an interview yesterday. "It's very likely that if we went back retrospectively and looked at people who did poorly during seasonal flu, what would shake out is that obesity would be one of the risks," he said.

Researchers at the Centers for Disease Control and Prevention in Atlanta noted the association among Californian H1N1 patients in a May 22 report. The agency is investigating whether overweight people need different antiviral treatment or flu vaccinations. Last year, 26.1 percent of adults in the U.S. were obese, up from 25.6 percent in 2007, the CDC said in a July 8 statement.

"We were surprised by the frequency of obesity among the severe cases that we've been tracking," Anne Schuchat, director of the CDC's National Center for Immunization and Respiratory Diseases, told reporters on May 19. "If there truly is an increased risk of severe complications on obese patients, it would be important to take steps to attend to that."


The bug is reported to have killed 429 people worldwide since its discovery in the U.S. and Mexico in April. The infection, which has now spread as far as New Zealand and Norway, causes little more than a fever and cough in most cases. The majority of those who died were pregnant, had asthma, diabetes or other chronic diseases, according to the WHO.

Drugmakers including Sanofi-Aventis SA, GlaxoSmithKline Plc and Novartis AG are preparing vaccines to have them ready by the time the weather turns colder in the Northern Hemisphere later this year.

Some patients are showing up at hospitals with viral pneumonia so severe they are suffocating.

The first two people to die from the bug in Peru -- a 38- year-old woman and a 4-year-old girl from impoverished areas on the outskirts of Lima -- were both obese, El Peruano newspaper reported on July 6.

Shallow Breaths

Scientists don't yet know whether extremely overweight people get sicker because of associated conditions like heart disease and asthma, or whether the excess fat itself makes them more vulnerable. Both may be to blame.

Fat cells secrete chemicals that cause chronic, low-level inflammation that can hamper the body's immune response and narrow the airways, says Tim Armstrong, a doctor working in the WHO's chronic diseases department in Geneva.

What's more, excess fatty tissue compresses the chest, and the fatty infiltration of the chest wall causes a decrease in lung function and an increase in the pulmonary blood volume, Armstrong said. "If you are obese, you tend to be less physically active and have an associated shallower breathing pattern. All these compound, leading to breathing difficulties."

The morbidly obese are also more likely to experience insulin resistance, a condition that makes it harder for doctors to lower the level of sugar in the blood of critically ill patients, said Greet Van den Berghe, head of acute medical sciences at Belgium's Catholic University of Leuven.

Studies in Mice

"The question has always been, is it the obesity or the other problems?" said Melinda Beck, professor of nutrition at the University of North Carolina, Chapel Hill. "There haven't been studies that looked just at weight. In my research, it appears to be the obesity itself."

In mouse studies, flu killed about half of the rodents made obese by a high-fat diet, compared with a mortality rate of about 4 percent in lean animals, according to Beck's research. She is studying whether obese humans might need stronger doses of vaccine or a different method of delivery.

Of the first 32 people who died from swine flu in New York City, three-quarters had one or more underlying medical conditions, most often diabetes and heart disease, said Isaac B. Weisfuse, deputy commissioner of disease control at the city's Department of Health and Mental Hygiene. Of seven with no known medical condition, at least four were reported to be obese, Weisfuse said.

The city plans to look at how many of the 32 patients were obese, Weisfuse said in a July 6 presentation to the European Centre for Disease Prevention and Control in Stockholm.

No Smoking

People may reduce their risk of developing complications from swine flu -- as well as many other diseases -- by maintaining a healthy weight, quitting smoking, exercising regularly and moderating alcohol intake, said Frederick Hayden, a clinical virologist at the University of Virginia.

Obesity rates have tripled in the U.S., U.K. and Australia during the past three decades, according to the Organization for Economic Cooperation and Development. The ranks of the overweight are also swelling in the developing world. In China, obesity doubled among women and tripled in men between 1989 and 2000 and it may double again in 20 years, according to research released last year in the journal Health Affairs.

Studies are needed to better understand the immune response of obese people and determine whether excess body weight impairs their ability to fight the infection, said Pamela Fraker, a professor of biochemistry at Michigan State University.

"It's sort of strange that it's been neglected with this major population," Fraker said. "We need to know about this for the further care and protection of the growing number of obese we have and for society in general."

To contact the reporters on this story: Jason Gale in Singapore at