A team of Swedish researchers say they have identified a previously unknown virus that may cause many cases of serious respiratory infections in children.
The researchers have named the virus 'human bocavirus' and the discovery has prompted the researchers to call for a systematic search for all the viruses that cause respiratory infections.
The report serves to emphasise how little doctors know about the sources of most respiratory infections.
In other research, a separate team of California researchers has found they could only identify about 40 percent of viruses infecting patients, and both teams said rapid testing for viruses would be useful in diagnosing and treating respiratory illnesses.
According to health experts this step is particularly important because there are fears that influenza, in particular avian influenza, could cause a global pandemic.
The ability to test quickly to find out what is making someone sick can mean the difference between life and death, because antiviral medications must be given early on to prevent serious illness in the case of influenza.
The Swedish researchers found in their sample of 540 children in a pediatric hospital ward, that the new bocavirus was responsible for 17 of the cases.
Tobias Allander of the Karolinska Institute in Stockholm and colleagues, say that lower respiratory tract infection is a leading cause for hospitalization of infants and young children, and the most important viral agent in this group of patients is respiratory syncytial virus (RSV).
Other important agents are apparently the influenza viruses, parainfluenza viruses, adenoviruses, rhinoviruses, coronaviruses, and human metapneumovirus.
However according to the researchers, the causes of between 12 percent and 39 percent of these serious infections are never identified.
Janice Louie of the California Department of Health Services, Lawrence Drew of the University of California, San Francisco and colleagues, in the second study checked patients reporting to the hospital with flulike illness including "unspecified upper respiratory infection," acute bronchitis, sinus infections and pneumonia.
They found that they could only identify a virus in 103, or 39 percent, of the patients. These included influenza A or B in 54 patients, picornavirus in 28, RSV in 12, human metapneumovirus in four and human coronavirus OC43 in two patients.
The Swedish study is published in the current issue of the Proceedings of the National Academy of Sciences.