China Confirms Its Sixth Case of SARS

International health experts have widened their inquiry into China’s latest SARS outbreak as the government confirmed one more case of the deadly respiratory disease.

So far, China’s cases of the highly contagious ailment are limited to people who worked at Beijing’s Institute of Virology -- where samples of the virus are kept -- and others who had close contact with them or people infected by them.

The Health Ministry said Saturday that one of the institute’s lab workers was confirmed to have SARS after being hospitalized for more than a week as a suspected case.

The announcement raised China’s confirmed cases to six. One patient has died. Three other patients are hospitalized as suspected SARS cases.

Meanwhile, millions of Chinese boarding planes and trains for the weeklong May Day holiday were being screened for symptoms of severe acute respiratory syndrome in an attempt to contain the disease.

The World Health Organization says the cases aren’t a public health threat because they are limited to a small group with a clear chain of transmission.

The agency blames lab security for the outbreak, but has yet to determine exactly what happened.

“It still remains very uncertain, the source of this infection,” said Dr. Julie Hall, SARS team leader for the U.N. organization in Beijing. “This is going to take some time.”

The lab and its equipment are new, she said, and there were no obvious spills reported.

Experts will need to interview more researchers at the lab to learn their day-to-day practices and figure out what went wrong, she added.

China had confirmed Friday that a 53-year-old woman who died last week was the world’s first SARS death this year. Her daughter worked at the lab and is also a confirmed case.

The other confirmed cases are a nurse who treated the daughter, and the nurse’s mother and aunt.

SARS sparked a global health crisis last year when it killed nearly 800 people worldwide and infected thousands.