China is stepping up its cooperation with the World Health Organization, as a team of experts meets in the south to study Severe Acute Respiratory Syndrome. Hong Kong and the adjacent Chinese province, Guangdong, together account for roughly 75 percent of the nearly 2,300 SARS cases worldwide.

According to the World Health Organization, China's Guangdong province is the site of the world's worst outbreak of Severe Acute Respiratory Syndrome.

On Friday, WHO officials met with medical experts in Guangdong where the disease may have originated. The WHO experts are tracking the patterns of SARS transmission, clinical profiles of patients, and certain viruses suspected of causing SARS.

The disease, which has been reported in more than a dozen countries, is spreading in ways health authorities do not fully understand. Once contracted, SARS is a serious and potentially fatal form of pneumonia.

The rapid infection of more than 200 people in a Hong Kong high-rise last week led to a theory that some SARS patients with underlying illnesses carry high doses of the virus and are capable of infecting large numbers of people.

This hypothesis, dubbed the "super-spreader theory," may be validated by epidemiological research in China. Some doctors believe SARS patients with chlamydia, a bacterial infection, could be the "super-spreaders."

Chris Powell is a WHO spokesman in Guangdong. "There's now investigations going on into other co-factors," he explained. "It's one virus acting with something else, and in China, that happens to have been chlamydia."

Right now, doctors believe SARS is spread mainly by droplets of mucus and saliva, and through close and prolonged contact with very sick people. More study of the disease's origins may yield clues about how to stop it.

Hong Kong, which like Guangdong has seen hundreds of SARS cases, reported 26 new cases on Friday, bringing the total to 761 cases. The death toll remained unchanged at 17.

Singapore reported an additional death from SARS on Friday, but WHO says the outbreak there might be over. Japan reported a number of new suspected SARS cases on Friday.

Concerns about SARS prompted the U.S. Navy's 7th Fleet on Friday to cancel all port calls to southern China and Hong Kong.