Investigators are probing whether Amoy-style factors are linked to Sars cases in five Sha Tin households in the same apartment complex Hong Kong's efforts to eliminate Sars took a worrying turn yesterday when a fifth household in a Sha Tin public housing estate block was infected - raising the possibility of an Amoy Gardens-type outbreak linked to environmental factors at the building. Eleven residents, including a four-month-old baby, of Wing Shui House in Lek Yuen Estate have now come down with severe acute respiratory syndrome (Sars), prompting the government to launch an investigation into the source of contamination. In another indication that infection-control measures have not been entirely effective, 41 staff and patients at a public hospital were put in quarantine after two nurses developed Sars symptoms. One of the medics did not work in a Sars ward. Hong Kong has gone 19 days with single-digit daily infections and is on the alert for signs of mini-outbreaks that could dash hopes for the early lifting of a World Health Organisation advisory against unnecessary travel to Hong Kong. Although only three new cases were announced yesterday, Director of Health Margaret Chan Fung Fu-chun said it was worrying that one of them was a tenant of Wing Shui House. 'We are all the more concerned because, earlier on, in the same building, several families were infected, and today we have another case involving this building.' Government investigators had moved in to investigate the source of the infections, Dr Chan said. A meeting was held yesterday between residents' representatives, government officials, legislators and district councillors to discuss the situation, she said. Samples will be taken and checks conducted on the building's plumbing and sewage systems. Earlier tests at the building found no problems, Dr Chan said. A massive outbreak of Sars at Kwun Tong's Amoy Gardens estate in March, which infected 321 residents, was traced to a faulty sewage system. So far, 1,722 people have come down with the virus. Three women, aged 70 to 85, died yesterday, bringing the Sars death toll to 258. The isolation of staff and patients at Caritas Medical Centre was sparked after a nurse who works in the hospice ward came down with suspected Sars on Sunday, the hospital said. The nurse lives on the same floor in the staff quarters as another nurse who was confirmed with Sars on May 13, the spokeswoman said. The 21 other staff members who live on the same floor began 10 days of isolation on Monday, as did 20 cancer patients at the hospice. Sixteen of the staff were sent on Wednesday to the Lady MacLehose Holiday Village, used as an isolation camp. The remaining five staff members are in home confinement. Daniel Chua Tsin-tien, clinical oncology professor at the University of Hong Kong, said terminal cancer patients were more vulnerable to infections such as Sars. Dr Chua also warned that the anti-Sars treatment, a combination of Ribavirin and steroids, would be too strong for cancer patients. 'Ribavirin would bring more harm than good to terminal patients' organs, which have already been severely damaged.' A spokeswoman for Caritas Medical Centre said the hospital had tightened its surveillance and precautionary measures since the nurses had developed Sars symptoms. She said the hospital believed the chance of infection among the group of cancer patients was not high. The hospital did not see a need to isolate all medical workers and patients at this stage, she said.