Clinical Picture of Hospitalized H1N1 Patients Is Slowly Emerging

Kate Traynor

BETHESDA, MD 19 May 2009—A study of patients who were hospitalized in California hospitals with a diagnosis of infection by the novel H1N1 influenza virus is offering clues about what might predispose patients to severe disease.

Of the 30 H1N1-infected inpatients in California hospitals during April and May, 37% had chronic lung disease, and 20% took immunosuppressive medications or had a condition other than lung disease that suppresses the immune system, according to a report from the Centers for Disease Control and Prevention (CDC).

Four of the patients had diabetes mellitus and four were classified as obese, an underlying condition that CDC has not considered to be an independent risk factor for complications of influenza virus infection.

"We were surprised by the frequency of obesity among the severe cases that we have been tracking and do think that this is an important result," said Anne Schuchat, acting director of CDC's National Center for Immunization and Respiratory Diseases, during a briefing this afternoon.

"The question of whether people with obesity need to be treated differently in terms of antiviral treatment or our seasonal flu vaccine recommendations, for instance, is one that we're looking into right now," she said.

CDC's most recent recommendations for antiviral use in patients with known or suspected H1N1 infection call for the use of neuraminidase inhibitors in patients hospitalized with H1N1 illness. Also recommended for treatment are people in the community who are infected with the virus and also are at high risk of complications from seasonal influenza. This group includes pregnant women, seniors, and people with chronic lung, liver, or cardiovascular disease as well as those with diabetes or other metabolic disorders.

Obesity may be clinically associated with diabetes or other chronic conditions but is not called out as a separate risk factor in CDC's guidelines.

About half of the California patients described in the report had multiple chronic conditions. Those described as obese also had at least one other chronic condition, but only one patient also had diabetes.

Schuchat said CDC is investigating several theories about whether obesity is a risk factor for H1N1 influenza complications.

"Some people with morbid obesity have something called a Pickwickian syndrome, where they have fairly severe respiratory compromise just based on the extra weight that they're carrying over their chest," Schuchat said.

She said there is not enough data yet to know whether the condition, also known as obesity hypoventilation syndrome, contributes to poor outcomes in patients with H1N1 infection. Also complicating the clinical picture, she said, is the "epidemic of obesity" that is occurring in the United States.

"We have much higher rates of obesity in the U.S. than we had 10 or 20 years ago, both in children and in adults. So I think it's hard for us at this point to say whether the numbers of patients with reported obesity is significantly higher than we would expect," she said.

Five of the hospitalized patients in California were pregnant women, a population CDC has long recognized as being at risk for complications of influenza.

According to the report, all but one patient had fever at the time of admission to the hospital, and 77% had cough. Vomiting, which has been noted previously in H1N1-infected patients, was a symptom in nearly half of those hospitalized in California.

Other common symptoms described in the report include shortness of breath, chills, sore throat, and body aches.

Schuchat said that as of today, none of the California patients had died, but some remain hospitalized with severe illness.

"We don't know if they'll make it or not," she said.