Virus hospitalizes kids at same rate as flu

A respiratory virus that was unknown to doctors until 2001, and has no treatment, causes the same severity of illness in young children as the flu, according to the largest study to estimate the infection's U.S. prevalence.

The research, published in the New England Journal of Medicine, found that one of every 1,000 children younger than 5 is hospitalized each year because of human metapneumovirus, the same rate as for flu. MPV also occurs in winter and shares the same symptoms as the flu, the study said.

The virus, which can lead to bronchitis and pneumonia, is often misdiagnosed because there is no quick test to distinguish it from flu and other respiratory viruses, said senior study author John Williams. There's no vaccine or drug against the virus, and children often are given antibiotics or flu medicines to no avail, he said.

"Here's a virus that was unknown 10 years ago and turns out to be one of the most common causes of severe respiratory infection," said Williams, an associate professor of pediatrics at Vanderbilt University in Nashville, Tenn.

MPV may be the reason that the flu vaccine appears to fail in some people who may in fact have the virus, not the flu, Williams said.

Researchers in the study used the New Vaccine Surveillance Network of the U.S. Centers for Disease Control and Prevention to identify kids younger than 5 with MPV in three U.S. counties from 2003 through 2009.

They found that 200 of 3,490 hospitalized children, or 6 percent; 222 of 3,257 children in outpatient clinics; and 224 of 3,001 children in the emergency rooms, or 7 percent, had MPV. About 40 percent of the children hospitalized with the virus had an underlying condition such as premature birth or asthma, the study found.

The researchers estimated that about 20,000 kids younger than 5 are hospitalized each year in the United States because of this virus, which also causes 1 million outpatient clinic visits and 263,000 emergency room visits, the authors wrote. Those estimates are similar to the flu rates for U.S. children younger than 5, he said.

Knowing the frequency and severity of the disease adds urgency to developing a vaccine as well as a test for the virus, Williams said. He said a vaccine against MPV is a minimum 5 to 10 years away.

Smaller studies of adults have suggested that MPV is as common as flu in adults older than 65, Williams said.