HOUSTON, Aug. 14 (Xinhua) -- The Seattle health department said on Friday that two immuno suppressed patients being treated for A/H1N1 flu had been identified as resistant to Tamiflu.

    One case involved a male teenager with leukemia who received a stem cell transplant in early May, according to local health experts. While recovering in hospital in a single room he contracted A/H1N1 flu, they said, adding the boy has recovered.

    The second case involved a woman in her 40s, who also has leukemia and had a stem cell transplant late last year, the health experts said. That woman remains in hospital and is being treated with an intravenous form of the only other flu drug available, Relenza, and another antiviral drug, ribavirin, they disclosed, saying the two patients have no links to each other.

    Local health officials also said that there is no evidence indicating that people who came in contact with the two patients became infected with a Tamiflu-resistant virus.

    Since the pandemic began, 11 cases of Tamiflu resistance have been reported. Three of those were reported Friday -- the two in Seattle and a new case in Hong Kong.

    Japan and China have each reported three. In the case of China, one case occurred in Hunan province on the mainland and two in Hong Kong. Canada, Denmark and Singapore have each found one. Most of these cases have occurred in people who took the drug as treatment for the flu or to prevent infection with the flu.

    The sole exception so far is the case of the California teenager who traveled to Hong Kong. She had not previously taken Tamiflu, suggesting she was infected from the start with a resistant virus. The source of her infection was not found and no other cases of resistance have been reported from the San Francisco area, where she lives.

    "Viruses can develop drug resistance over time. It's important that antiviral treatments only be used as recommended by a health care provider, to minimize drug resistance and preserve an important tool against the illness for those who need it," said Dr. David Fleming, Director and Health Officer for Public Health of Seattle & King County.

    "The vast majority of people with H1N1 virus continue to be treatable with Tamiflu, and in cases where it becomes ineffective, other options are available," Dr. Fleming said.

Special Report:  World Tackles A/H1N1 Flu