Bob Roehr

Sept. 16, 2003 (Chicago) — Human metapneumovirus (hMPV), isolated and identified in 2001, appears to be one of the most common respiratory infections among children. It rarely appears in adults, but when it does so, the outcome can be fatal.

James E. Crowe, Jr., MD, a pediatrician and virologist at the Vanderbilt University Medical Center, shared his research on hMPV here yesterday at the 43rd Annual Interscience Conference on Antimicrobial Agents and Chemotherapy.

Dr. Crowe and his colleague John V. Williams, MD, also from Vanderbilt, examined frozen nasal wash specimens and clinical files from more than 2,000 children, gathered over the last 25 years at Vanderbilt. The specimans and files were assayed for the presence of the polymerase gene for hMPV.

The researchers found that hMPV caused about 12% of lower respiratory illnesses that were characterized by wheezing, croup, or pneumonia. It also seemed to be responsible for about 15% of common colds and about one third of complicated inner ear infections.

"It may be the second most common cause of respiratory illness in children," he said. The first is respiratory syncytial virus (RSV), responsible for about half of all such infections.

"[hMPV] is probably not an emerging virus, because as far back as we can look, we can see it." Dr. Crowe said. Incidence appears to be stable over time, adding further support to that interpretation.

The virus clusters into four genetic families, but there does not appear to be any difference between them in terms of clinical manifestations of disease. Dr. Crowe said, "For all practical purposes, there is one type of virus."

He told Medscape that "approximately 5%" of hMPV patients were coinfected with another virus, a rate that is consistent with previous studies looking at other respiratory viral infections. He suggested that hospitalized patients might have a higher rate of coinfection.

There is a seasonality to the infections, with RSV appearing from November to March, and hMPV from December to April, "so hMPV occurs during the tail end of the RSV season," said Dr. Crowe.

Reinfection with hMPV does occur, he added, but of the 3 of 49 cases of recurrence that they identified, the second occurrence was as a cold, not as a severe respiratory problem.

The severity of hMPV and rhinovirus infections "are about the same," said Peter Heymann, MD, from the University of Virginia Health System in Charlottesville. "Infants seem to build up immune protection and by age three "it is hard to find coinfection."

Ann Falsey, MD, a professor at the University of Rochester School of Medicine in New York, pointed to a recent study showing hMPV infection rates ranging from 0.9% to 2.9% in healthy and frail elderly adults during one year. But the virus accounted for 10% of hospitalizations.

"The incidence [of hMPV] goes down but the significance goes up" in the elderly, she said.

Michael Boeckh, MD, from the Fred Hutchinson Cancer Research Center at the University of Washington in Seattle, saw a similar pattern in immunosuppressed transplant patients. Infection with hMPV "is characterized by high morbidity and mortality."

43rd ICAAC: Abstract 1142. Presented Sept. 15, 2003.

Reviewed by Gary D. Vogin, MD

Bob Roehr is a freelance writer for Medscape.

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