Three out of the seven specimens taken from patients of the Hong Kong Caritas Medical Center outbreak have tested positive for parainfluenza, the Center for Health Protection said Thursday, hinting the two-week long "mysterious disease" may be determined soon.

All seven were negative for other common respiratory pathogens. Laboratory tests on other specimens are proceeding, said the Center for Health Protection.

The total number of cases increased to 32 by Thursday after one more patient showed signs of fever and respiratory tract infection.

The disease started to break out early this month and medical staff has had until now no conception about the cause of it.

Two kids are still down with fever, said a Hospital Authority spokesman.

As at 10 a.m. Thursday, 19 boys and 13 girls aged four to 17 from the hospital's Development Disability Unit had come down with the illness, said a Hospital Authority spokesman, adding that two still have fever.

Enhanced infection control measures implemented in affected wards are effectively hindering the virus' spread, said the spokesman.

Parainfluenza virus is spread by respiratory secretions through contact with infected people or contaminated surfaces. Infections caused by the virus are common, especially in infants and small children. Severe illnesses, however, can occur among young children and patients with immunodeficiencies. The incubation period is generally one to seven days.

Hospital Authority said more tests will be carried out on the specimens to find out the real cause of the disease.