Six of 72 phlegm samples taken from children in Chenzhou, a city in the central province of Hunan, since October have tested positive, Xinhua said, citing Duan Zhaojun, a researcher from China's Centers for Disease Control and Prevention.

It did not give any details on the cases, except that the samples were taken from infants a year old or younger.

Human bocavirus has been found in respiratory secretions of children with lower respiratory tract infections, according to findings presented at the International Conference on Emerging Infectious Diseases in March.

It was first reported in Sweden in September 2005 and very little is known about the infection and its root.

Human bocavirus has been found in nearly 5 percent of pneumonia patients in rural Thailand, mostly young children, the researchers said. Cases have also been identified in children with respiratory tract infections in Australia and Japan.

The conference included researchers from the Centers for Disease Control and Prevention in the United States and the World Health Organization.