HONG KONG (AP) -- The virus that causes SARS is mutating rapidly, which could complicate efforts to develop a solid diagnosis and a vaccine, researchers said Friday, as eight more people died in Hong Kong from the respiratory disease, pushing the death toll here to 170.

"This rapid evolution is like that of a murderer who is trying to change his fingerprints or even his appearance to try to escape detection," said Dr. Dennis Lo, a chemical pathologist at the Chinese University of Hong Kong.

University doctors said they have completed genetic sequencing on virus samples taken from 11 SARS patients, and that by late March there were two forms of the illness present in Hong Kong.

"We have shown that the SARS coronavirus is undergoing rapid evolution in our population," Lo told a news conference. The coronavirus that's believed to cause severe acute respiratory syndrome comes from a family of viruses that can also cause some common colds.

Hong Kong Health Director Dr. Margaret Chan told reporters she was aware of the work at Chinese University, but it was too soon to say for certain whether the SARS virus was mutating.

A University of Hong Kong microbiologist predicted earlier Friday that there could be fewer SARS cases in the summer, but that more people could get sick in the winter, if the SARS virus behaves like other coronaviruses.

Chan called that viewpoint speculative.

Hong Kong health officials reported only 11 new cases of the disease on Friday, the same as on Thursday -- both were the lowest daily since officials here began releasing daily statistics in March. Some see the lower numbers as a sign the disease is coming under control, although Hong Kong officials have avoided making such predictions.

There now have been 1,611 people sickened by SARS in Hong Kong.

Outlining the latest Hong Kong research on SARS, Lo said one strain was detected in a woman whose illness was linked to an outbreak caused by a mainland Chinese medical professor who spread SARS to other people at a hotel here. The other strain came from a Hong Kong man believed to have caught it in the mainland border city of Shenzhen, Lo said.

Lo said researchers need to find out whether people who get SARS can develop immunity to any form of it. If that is not the case, then finding ways to better diagnose it and to develop a vaccine could be more difficult, Lo said.

More work needs to be done before researchers can say whether the virus has become more infectious and lethal, Lo said.

The microbiologist who predicted SARS might go into a lull in the summer and then bounce back was Yuen Kwok-yung, who said he based his view on the documented behavior of two other coronaviruses that have infected humans.

Experts have expressed doubts that the SARS virus can be eradicated.

"It'll come back unless the virus is eradicated completely in every part of the world this summer and no one is infected," Yuen said.

In Hong Kong, summer is generally regarded as lasting from May to August. The winter months are from November to January.

To minimize any impact from SARS, Hong Kong needs to become "super clean" through stepped-up hygiene practices and to stop infected people from entering the territory, Yuen said. Hong Kong has already begun screening people by taking their temperatures at all immigration control points, though the checks are still random at some crossings.

Five World Health Organization officials, making an independent assessment of the outbreak in Hong Kong, spent Friday in laboratories, where they were examining environmental samples taken from pipes and off walls earlier this week at an apartment complex where more than 300 people were sickened by SARS.

The Hong Kong education secretary, Arthur Li, said Friday that some primary students who have been out of school since late March will go back to class on May 12 and others are expected to be back by May 19.

Hong Kong officials also announced that two privately funded welfare programs have been set up to provide money to families affected by SARS through deaths and infections. The government is offering financial assistance to those quarantined as a precaution.

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