To track down these answers, Williams and his Vanderbilt colleague Dr. Kathryn Edwards, along with other researchers, collected data on the virus from hospitals in three U.S. counties from 2003 through 2009.
They found the virus in 200 of 3,490 children (6 percent) hospitalized during that time period. Of 3,257 outpatient clinic visits, they found 7 percent of children had HPMV. And, of 3,001 children seen in emergency rooms, 7 percent had the virus. The researchers also tested 770 children who weren't having any symptoms, and found the virus in 1 percent.
Annually, one out of every 1,000 hospitalizations in children less than 5 years old was due to human metapneumovirus. In those less than 6 months of age, the rate of hospitalization due to HPMV was three per 1,000. In children aged 6 months to 1 year, that number was two per 1,000, according to the study.
Children hospitalized with an HPMV infection were more likely to also have pneumonia or asthma, to need oxygen therapy and to have a longer stay in the intensive care unit. Children with asthma or who had been born prematurely were more likely to be hospitalized with HPMV. However, most children who contracted the virus were otherwise healthy, according to the study.
The researchers estimate that the annual number of outpatient visits is about 55 per 1,000 children, and the number of ER visits is likely 13 per 1,000 children. That means about 1 million outpatient visits and 263,000 emergency room visits in children under 5 years old each year are due to this virus.
"The study suggests that 20,000 hospitalizations annually in kids under 5 are due to this virus. That would be a good argument for developing a vaccine," said Dr. Kenneth Bromberg, director of the
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