Over 900 people are now being monitored for symptoms of SARS. Credit: © Science Photo Library

Health officials are investigating another four suspected cases of SARS in China. The cases bring the total number affected to eight, with more expected.

All of the cases can be traced to a laboratory at the Beijing Center for Disease Control and Prevention, China, where the coronavirus that causes SARS (severe acute respiratory syndrome) was being studied. The first person to fall ill, on 25 March, was a 26-year-old female researcher who had worked in the lab.

The lab worker is thought to be at the root of all but one of the suspected cases. The victims include her mother, who died on 19 April, and a 20-year-old nurse who cared for her in Beijing. The four new cases make up a third generation of contacts: the mother, father and aunt of the nurse, and one of her hospital contacts.

Over 900 other contacts of these patients are now being monitored for symptoms of SARS, says World Health Organisation (WHO) spokesman Dick Thompson in Geneva, Switzerland. He expects several more cases to be reported, although measures are being taken to curb further spread of the disease. "We do not know how the outbreak will evolve," he says.

One cause for concern is that the lab worker travelled twice on the train between Beijing and her home in Anhui Province after catching the virus, so there is a risk that she might have passed it on to other passengers.

Some SARS experts have criticized the level of safety precautions at the Beijing laboratory where the outbreak appears to have started. The eighth person involved in the outbreak is a 31-year-old researcher from the same laboratory who fell sick on 17 April, several weeks after his colleague.

The Chinese Ministry of Health and the WHO have already launched a formal investigation into safety at the laboratory. It is not clear whether there was one safety breach that continued over time and infected both workers, or two separate events.

The WHO recommends that laboratories growing the SARS virus follow biosafety level 3 measures to contain the virus. The measures require special training and facilities, which include containment measures such as air-tight safety cabinets and protective clothing.

The WHO is sending a team of researchers, biosafety experts, epidemiologists and others to help with the outbreak and investigation, after a formal request from the Chinese authorities over the weekend.