Two patients have been given blood infected with dengue fever after the disease worked its way into Hong Kong's blood transfusion supply. One patient later died of cancer, while a 72-year-old woman was infected with dengue fever after receiving blood during an operation at Queen Mary Hospital, health officials said last night. Some of the contaminated blood was sent to Australia but was recalled before it was used, the Hospital Authority said. The blood came from a 17-year-old Ma Wan resident, who developed symptoms on July 18. A day earlier he gave blood through one of Hong Kong's Blood Transfusion Service centres. He was confirmed as a dengue case on October 7 and the Hospital Authority was alerted about his blood donation. The elderly woman received the donor's red blood cells on August 24. She developed a fever on August 27 and was transferred to Tsuen Wan Hospital. She was discharged on October 1, a spokesman for the Department of Health said. Tests were done on her earlier this week and yesterday the diagnosis of dengue fever was confirmed. 'While it is uncommon to be infected with dengue fever through blood transfusion, there is a probability that the patient receiving the red blood cells was infected through blood transfusion,' the Hospital Authority said. The authority appealed to donors to inform the Blood Transfusion Service as soon as possible if they had symptoms of dengue fever after donating blood. The dengue virus might be present in the blood of infected individuals from one to two days before the onset of symptoms to five days after the onset. The virus can stay in stored blood for weeks, as happened in this case. The authority insisted no country with incidents of dengue fever was testing donated blood for dengue fever, but promised staff at the Blood Transfusion Service would remain vigilant. The service screens for HIV, hepatitis B and C, syphilis and Human T-lymphotropic virus. As well as the elderly woman, a 36-year-old man who worked in Ma Wan was confirmed as having contracted dengue locally, bringing to 20 the number of such cases in the current outbreak. The dengue virus is usually spread by the Aedes mosquito biting an infected person and passing it on, but it is not transmitted by one person to another. News of the blood transfusion cases came on the eve of the first meeting today of a high-powered government steering committee formed to set long-term strategies to control dengue fever. Legislator for the medical sector Lo Wing-lok said there were tests available for dengue fever in blood but these might not be cost-effective for places with a low incidence of the disease. Dr Lo advised donors not to give blood if they were not feeling 100 per cent well. A new imported case was also detected yesterday, taking the number of such cases to 16 this year.