Researchers at Children's Hospital of Pittsburgh are participating in a study to determine how often a common virus causes serious respiratory problems in vulnerable groups of children.

The study focuses on human metapneumovirus infection of the lower respiratory tract in hospitalized children at high risk for severe disease.

While the virus, also known as hMPV, was discovered by Dutch researchers only four years ago, experts believe it has been a source of infection for many years.

Lower respiratory problems in patients infected by hMPV are similar to those caused by other viruses and can include asthma attacks, croup, pneumonia and inflammation of air passages in the lungs, known as bronchiolitis.

Very young children, particularly premature infants and children with certain chronic health conditions, are especially at risk, said Dr. Ellen Wald, chief of infectious diseases at Children's and leader of the study at the hospital.

Wald said the study began in fall 2003 and will continue through this spring. It has involved about 30 children 2 and younger with congenital heart disease and children younger than 6 months who were born prematurely, who came to Children's with respiratory infections.

She said specimens taken from the nasal passages of those patients and details of their conditions and treatments are being sent for analysis to MedImmune Inc., a company based in Gaithersburg, Md., that is funding the study in Pittsburgh and other communities.

Clarencia Stephen, a spokeswoman for MedImmune, said preliminary findings may be released this spring at a meeting of the Society for Pediatric Research.

A finding that hMPV causes a substantial number of serious illnesses among hospitalized infants would "provide a strong incentive for investigators to develop preventive and therapeutic strategies," Wald said.

According to MedImmune's Web site, the company has worked to develop antibody therapies for infants at risk of hMPV infection and a combination vaccine targeting hMPV and other viruses.

MedImmune already produces palivizumab, marketed under the name Synagis, to prevent serious lower respiratory tract disease that can result from another common virus. Synagis is used in children at high risk of disease caused by respiratory syncytial virus, also known as RSV.

MedImmune says Synagis is the first monoclonal antibody successfully developed to combat an infectious disease. Monoclonal antibodies are produced in the laboratory and act like human antibodies to target specific invading viruses.

Synagis and flu vaccine are the only drugs available to prevent lower respiratory tract disease due to viruses in children, Wald said. Antiviral medications also are available to treat influenza.

Patients are given fluids intravenously if they are unable to drink or oxygen if they have trouble breathing.

In a study published last year in the New England Journal of Medicine, a research team at Vanderbilt Children's Hospital concluded that hMPV is a leading cause of respiratory infection in the first years of life.

The study suggested that hMPV ranks just after RSV as a cause of lower respiratory illnesses in otherwise healthy children, and that it is a more common source of those illnesses than the influenza virus.

Parents should take common-sense steps to protect their children from infection, particularly in the first year of life when most of them are especially vulnerable, Wald said.

Those measures include frequent hand-washing and keeping infants away from older children and others who may be infected.