Thirty-two children who fell ill with a mysterious respiratory disease in a hospital in Hong Kong were infected by a parainfluenza virus, the government said.

Parainfluenza viruses commonly attack infants and small children and are spread by respiratory secretions through close contact with infected people or contaminated objects.

The children were all patients in paediatric wards for the mentally handicapped at the Caritas Medical Centre when they began falling ill with high fever and respiratory infection in early November.

Tests on three of seven specimens taken from the children showed they were infected by parainfluenza virus, the Centre for Health Protection said in a statement late on Thursday.

Two children still have fever and the rest have recovered. Doctors said earlier that their illnesses had been mild.

The mysterious cases revived memories of the SARS epidemic in early 2003, in which nearly 300 people died in Hong Kong, and raised questions about whether the city’s healthcare system was prepared for another outbreak.

Scientists earlier ruled out SARS as well as influenza A and B.

With the advent of cooler weather and the start of the flu season, the government has ordered schools to step up precautions against influenza.

An outbreak of deadly bird flu in parts of Asia this year, which killed 32 people in Thailand and Vietnam, has added to the concern.