Doctors say most patients, nearly 90 percent, will have a mild H-1-N-1 flu, but the virus is packing a powerful pneumonia punch

A serious complication of pneumonia is acute respiratory distress syndrome (ARDS). This condition affects the tiny air sacs (the alveoli) in the lungs, where oxygen is normally absorbed into the bloodstream. The sacs collapse or become filled with fluid, interfering with the ability of the lungs to take in oxygen. As a result, the body’s tissues don’t get enough oxygen. Organs may not function well or, in some cases, may fail. Patients may require a ventilator or ECMO (like a heart-lung bypass machine to oxygenate the blood) and intensive care treatment for many weeks.

The National Heart, Lung and Blood Institute estimates, annually, there are about 190,000 cases of ARDS in the U.S. About 30 percent of patients die. Some of those who survive are left with permanent lung damage. In a small observational study,

Lena Napolitano, M.D., Critical Care Surgeon with the University of Michigan Health System, looked at 10 patients admitted to a surgical intensive care unit for severe ARDS associated with H1N1 infection. None of the 10 patients had any evidence of secondary bacterial infection, typically an important cause of severe illness in flu patients. The researchers also noted some other unusual characteristics of these patients. Normally, flu-related pneumonia affects older people, the very young and those with weak immune systems. But the patients with ARDS were all middle aged, ranging from 21 to 53 years old. Nine of the ten patients were obese; seven were extremely obese. Half the patients had developed lung clots.

Napolitano says the cases highlight the need for doctors to be aware that patients coming into the hospital for treatment of ARDS may also have H1N1 influenza and should receive antiviral medication. Doctors should also be aware of the potential for severe complications among those who are extremely obese, though the reasons for this link are unclear. A new report from the CDC found secondary bacterial lung infections are now becoming more prevalent in H1N1.

Roughly 29 percent of patients who died of H1N1 complications between May and August had secondary bacterial infections. Thus, researchers now say doctors should now also consider the need for antibiotics in patients with H1N1-associated pneumonia.