In United States, most H1N1-related hospitalizations also involve underlying medical conditions

More than 70% of patients who were hospitalized with influenza A (H1N1) had at least one underlying medical condition, according to results of a recent study.

Analysis was conducted on 272 patients who were hospitalized for a minimum of 24 hours with influenza-like illness and who had a positive test for influenza A (H1N1) using a real-time reverse-transcriptase-polymerase-chain-reaction assay.

ICU admission occurred for 25% of the cohort. The mortality rate in the study population was 7%.

Children aged younger than 18 years accounted for 45% of the patients in the study and adults older than 65 comprised 5% of the study population.

Few severe illnesses were reported among patients aged 65 years and older.

At least one underlying medical condition was observed in 73% of patients. These conditions included asthma, diabetes, pregnancy and heart, lung and neurologic diseases.

There were 249 patients who underwent chest radiography on admission, 40% of whom had findings consistent with pneumonia.

Antiviral drug use was reported in 75% of the 268 patients for whom antiviral therapy data were available. These patients had been using those medications for a median of three days after the onset of illness.

Antiviral drug use was beneficial for hospitalized patients, according to the researchers. Early initiation of antiviral therapy was more beneficial than later initiation.

Jain S et al. N Engl J Med. 2009;361:1935-1944.