Cases of atypical pneumonia are still on the rise in Hong Kong, China and Vietnam, and a fourth outbreak may have struck Singapore. Health authorities have not identified the agent causing the flu-like illness, but say it is unusual because hospital workers appear to be particularly vulnerable.
Five more people in Hong Kong were diagnosed with atypical pneumonia on Friday, bringing the number up to 29.
A total of 43 people in Hong Kong have symptoms of a mysterious flu-like illness that experts say is spreading mostly in hospitals.
Adding to the mystery of the fast-spreading illness are similar hospital outbreaks in Vietnam and mainland China.
On Friday, after six people including two hospital staff became ill with pneumonia, the Singapore government warned its residents against any unnecessary travel to Hong Kong, Hanoi and Southern China
Earlier in the week a Chinese-American man died in a Hong Kong hospital after returning from a trip to Vietnam. The man was first hospitalized in Hanoi with flu-like symptoms. According to reports, more than 20 health workers in the Hanoi hospital subsequently became ill.
World Health Organization officials sent out a worldwide alert this week warning hospitals of the pneumonia outbreaks. WHO did not say if the Hanoi and Hong Kong outbreaks were related or if the man traveling between Vietnam and Hong Kong spread the illness.
Last month more than 300 people in China's Guangdong province were diagnosed with flu-like symptoms and atypical pneumonia. Five patients died.
A top scientist at Hong Kong University says the illness is unusual in that it does not strike those with compromised immune systems but healthy adults.
"If you have a particularly bad virus or bacteria that is causing an outbreak, usually the very young, very old and the very sick suffer first," explained Dr. K.Y. Yeun, head of the Hong Kong University Microbiology Department. "But this time there is something unusual happening, which is affecting mainly the young imuno-competent individual in the healthcare setting."
He added that the rates of flu and pneumonia in the general public are normal. Dr. Yeun says the mystery pneumonia is called "atypical" because of its fast onset and severe symptoms.
Hong Kong's hospital authority says the agent is most likely an airborne virus, but government laboratories are still trying to identify it. WHO scientists also have taken samples from Hong Kong, Mainland China and Vietnam for examination.
On Thursday, Hong Kong's Department of Health ruled out the possibility that the illness is caused by an avian flu virus commonly found in poultry in Southern China. In the late 1990s a strain of avian flu killed at least six people in Hong Kong. Earlier this year, two members of a Hong Kong family died from an avian flu virus after visiting China.