The first case of human swine flu in a medical worker was confirmed yesterday and another secondary school was closed as a record 54 patients were found with the rapidly spreading virus in a single day. A nurse who had previously cared for a confirmed patient - a 10-month old baby at United Christian Hospital, and who had gone to work despite having earlier suffered from a sore throat - tested positive for the flu, raising fears the virus could be passed to patients by infected frontline medical staff. Meanwhile, 26 students and the father of a student at the Australian International School also tested positive, taking the number there to 29, the largest cluster of infections so far. And the ECF Saint Too Canaan College in Shun Lee Estate became the fifth secondary school to suspend classes due to swine flu after a Form Three student was infected. The new cases brought the number of confirmed patients to 172. Centre for Health Protection controller Thomas Tsang Ho-fai said the nurse, who worked in the emergency room and the isolation ward at United Christian Hospital, reported for duty on Sunday and Monday despite having a slightly sore throat on Saturday, which later eased. She suffered from a low fever on Tuesday and was immediately quarantined. The Hospital Authority's director for quality and safety, Leung Pak-yin, said it was unlikely that she caught the virus in the hospital, as she was wearing full protective clothing. But University of Hong Kong microbiologist Ho Pak-leung said the chance could not be ruled out, especially in United Christian Hospital where resources were comparatively limited. 'If the workload is too heavy and there is a shortage of labour, it is more than natural to miss things. The nurse should not be blamed,' he said. He said the authority should prepare a contingency plan in the event that 30 per cent of the medical staff could not work due to swine flu. Health services sector legislator Joseph Lee Kok-long, who is chairman of the Association of Hong Kong Nursing Staff, said there would be 'big trouble' if the nurse had carried the virus back to the wards. He urged all frontline medical workers not to go to work if they had flu symptoms, and to see a doctor as soon as possible. Dr Tsang said the government would scale down its efforts to trace patients' contacts, as the fight against swine flu entered what he termed the 'late mitigation phase'. People in quarantine camps would be allowed to leave and known close contacts of confirmed cases would be medically observed, instead of having to report daily to a clinic to take Tamiflu. Only confirmed swine flu patients will be admitted to hospital from today, while suspected cases will be given Tamiflu and asked to stay at home. Tourists arriving at the airport with flu symptoms will be taken to a designated emergency room for testing but then allowed to continue their visits. However, they will be admitted to hospital within 24 hours if they test positive for swine flu. But this policy will not apply to children aged under two, pregnant women, those showing serious symptoms or those with a low blood-oxygen level. Dr Leung said if the pandemic continued to spread, patients with serious complications would have priority for drugs such as Tamiflu. He believed the 1,400 isolation beds in public hospitals would be sufficient to serve the increasing number of swine flu patients. The government will announce details on the implementation of the free vaccination programme against swine flu, seasonal flu and pneumococcal infection by October, according to a paper submitted to the Legislative Council.