WASHINGTON — A respiratory virus that was unknown to doctors until 2001 and that 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 US prevalence.
The research, published in the New England Journal of Medicine, found that one of every 1,000 children under age 5 is hospitalized each year because of human metapneumovirus, the same rate as that for flu. MPV also occurs during the 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 such as Tamiflu by mistake, he said.
‘‘We’re still learning so much about disease,’’ said Williams, an associate professor of pediatrics at Vanderbilt University in Nashville, said in a Monday interview. ‘‘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.’’
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 US Centers for Disease Control and Prevention’s New Vaccine Surveillance Network to identify children younger than 5 with MPV in three US 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 under 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 children under 5 in the United States, he said.
Knowing the frequency and severity of the disease adds urgency to developing a vaccine against the virus as well as a test that allows doctors and hospitals to check for the virus, Williams said. A vaccine against MPV is a minimum 5 to 10 years away, he said. Williams’s lab is among a handful of research centers working on a potential vaccine, he said.