A new risk factor?

People who are obese but otherwise healthy may be at special risk of severe complications and death from the new influenza pandemic (H1N1) 2009 virus, U.S. researchers reported on Friday [10 Jul 2009]. They described the cases of 10 patients at a Michigan hospital who were so ill they had to be put on ventilators. 3 died. 9 of the 10 were obese, 7 were severely obese, including 2 of the 3 who died.

The study, published in advance in the Centers for Disease Control and Prevention’s (CDC) weekly report on death and disease, also suggests doctors can safely double the usual dose of oseltamivir, Roche AG’s <ROG.VX> antiviral drug sold under the Tamiflu brand name.

“What this suggests is that there can be severe complications associated with this virus infection, especially in severely obese patients,” said CDC virus expert Dr. Tim Uyeki. “And 5 of these patients had … evidence of blood clots in the lungs. This has not been previously known to occur in patients with severe influenza virus infections,” Uyeki said in a telephone interview.

How obese is obese?

Dr. Lena Napolitano of the University of Michigan Medical Center and colleagues studied the cases of 10 patients admitted to the university’s intensive care unit with severe acute respiratory distress syndrome caused by infection with H1N1. “Of the 10 patients, 9 were obese (body mass index [BMI] more than 30), including 7 who were extremely obese (BMI more than 40),” they wrote in their report.

Their study was not designed to see if obesity or anything else poses a special risk factor for flu. But the researchers were surprised to see that 7 of the 10 patients were extremely obese. 9 had multiple organ failure, which can be seen in influenza, but 5 had blood clots in the lungs, and 6 had kidney failure. None has fully recovered, the researchers said.

“The high prevalence of obesity in this case series is striking,” the CDC’s commentary accompany the report reads. “Whether obesity is an independent risk factor for severe complications of novel influenza A (H1N1) virus infection is unknown. Obesity has not been identified previously as a risk factor for severe complications of seasonal influenza.”