School officials in Hong Kong are telling some students to stay at home for a week because they have been exposed to a form of pneumonia that appears resistant to common treatments.

Sunday’s order affects only 180 of the 1.2 million students in the area, but officials say the number will grow if cases of the disease continue to mount. So far, five Hong Kong students, a teacher and a school assistant have contracted the illness, a school system statement said.

First recognized in Asia in the middle of last month, the pneumonia strain, called severe acute respiratory syndrome (SARS), has hit nearly 400 people in three continents and by Saturday had claimed 11 lives.

Hong Kong, where authorities have reported 222 cases, remains the most seriously affected area in the world.

Symptoms include a fever above 38C (100.4 F), muscle aches, chills and sore throat, followed by shortness of breath, coughing, and evidence of pneumonia in a chest X-ray.

Hong Kong’s secretary for education, Arthur Li, said Sunday that students and school staff who have had contact with SARS sufferers will be told to stay at home for a week, until the disease’s incubation period passes.

Meanwhile a team of scientists at the University of Hong Kong has isolated a virus that causes SARS, the World Health Organization says.