Antibodies carried by recovered swine flu patients will be used to develop a 'last resort' weapon against the virus that is causing life-threatening infections in Hong Kong. The Food and Health Bureau is working with the University of Hong Kong to use antibodies collected from patients to make a drug for those who fail to respond to Tamiflu and Relenza. This emerged as it was announced that a 39-year-old woman in critical condition at the Caritas Medical Centre had become the seventh severe case. The woman, who had been treated for flu symptoms and discharged before being readmitted five days ago, was confirmed to have swine flu yesterday. A 37-year-old Filipino domestic helper at United Christian Hospital and a 48-year-old woman at Queen Elizabeth Hospital remain in critical condition while three others are serious. A man with a formerly severe infection is in a stable condition. A man with a superbug who died last week was found to have swine flu but it has not been confirmed as the cause of death. The number of swine flu cases in Hong Kong reached 1,640 yesterday, with 88 newly reported cases. The Caritas patient developed flu symptoms last Thursday and went to the accident and emergency department on Sunday. She was diagnosed with an upper respiratory tract infection, treated and discharged. When she failed to recover, she sought consultation at the same department again on Monday. The hospital admitted her and diagnosed her with a chest infection. She tested negative for swine flu on Tuesday. Her condition deteriorated yesterday and she needed breathing assistance. Medical sources, meanwhile, said recovered patients would be asked to donate blood to the Red Cross transfusion service so the antibodies could be extracted. The US Centres for Disease Control and Prevention is working on the same project. University microbiologist Ho Pak-leung said antibodies in blood serum could be collected through a special process and made into a drug. 'The serum therapy will not be the first choice for treating swine flu, because there are no clinical trials to prove its effectiveness. It can only be used when patients do not respond to antivirals such as Tamiflu and Relenza,' he said. Professor Ho advised doctors to prescribe Tamiflu to patients with flu symptoms without waiting for laboratory confirmation. He said Tamiflu should be prescribed if patients had high risk factors, such as old age and chronic illness and pregnancy, and if they suffered from pneumonia requiring hospital care. Among the seven patients who developed complications, the average time between symptom onset and admission was three to 10 days. Tamiflu works best if the drug is given to patients within 48 hours of the development of flu symptoms. In some cases, patients are not given Tamiflu immediately after being admitted to hospital, meaning they miss the so-called 'golden period' for Tamiflu therapy. New cases reported yesterday included a nurse at Queen Mary Hospital and six people from SAHK Erik Kvan Workshop in Shau Kei Wan, a residential centre for the physically and mentally disabled.