Hong Kong is to scale back its swine flu surveillance programme after a Centre for Health Protection review showed the virus was milder than first thought. It is estimated that as many as half a million city residents have been infected with the disease - 20 times the number of confirmed cases - but cases have been so mild that a majority have gone undetected. The scaled-back programme followed advice from World Health Organisation head Dr Margaret Chan Fung Fu-chun, who said on Monday in Hong Kong that the city should focus its efforts on reducing serious cases. Under changes to be adopted from Monday, swine flu tests will be carried out only for pregnant women, babies younger than 12 months, health care workers, patients in residential homes, and patients with persistent fever. An additional 250 to 300 specimens will be tested each week for surveillance purposes. This compares with the current practice of testing all patients with flu symptoms. From next week, the government will not release daily figures of confirmed swine flu cases. Instead, it will announce each week the percentage testing positive for the disease, the number of people going to government-designated clinics with flu-like illnesses, and consultation rates for such illnesses at private clinics. The move came as the disease claimed another life in Hong Kong yesterday. The 20th victim of the virus in the city was a 44-year-old woman with asthma and hyperlipidemia - the presence of raised or abnormal levels of lipids (fatty molecules) and/or lipoproteins in the blood. She had been in intensive care at Yan Chai Hospital where she was admitted on Tuesday with respiratory problems. She tested positive for swine flu the next day and died yesterday. Hong Kong reported 624 more swine flu cases yesterday, taking the city's total to 25,305. Of these, a total of 203 patients were still in public hospitals, with eight in serious condition and 10 critical. Dr Thomas Tsang Ho-fai, Centre for Health Protection controller, said the government was not relaxing its swine flu measures, but was improving the strategy. He said a review of cases so far showed the number of severe ones accounted for less than 0.5 per cent of all confirmed cases. And the death rate was less than 0.08 per cent. The centre's review found that swine flu had become the main flu virus circulating in Hong Kong, and more than 60 per cent of patients with flu symptoms were likely to have been infected. Tang said: 'We believe that laboratory-confirmed cases are no longer a satisfactory indictor to monitor human swine flu. The WHO has also advised against testing on a large scale. After all, we need to conserve laboratory and personnel resources.' But he said there were no plans to drop screening measures at border checkpoints. Hong Kong reported its first confirmed swine flu case - a tourist from Mexico - on May 1. This was also the first confirmed case in Asia. The case triggered panic among the public, and the government closed a Wan Chai hotel, where the Mexican had stayed, for a week. A critic of the government's swine flu measures, Dr Lo Wing-lok, a microbiologist and former legislator representing the medical sector, hailed the scaled-back programme. 'What the government has done for the past few months has only wasted manpower and resources,' he said. Health secretary Dr York Chow Yat-ngok said: 'People should not take flu as a very mild disease, although for many of us it will be a mild one. Occasionally they could have complications.' He also warned of a possible 'second wave', saying: 'We have to prepare for the worst. According to microbiologists, the virus should be more virulent during winter.' But he said Hong Kong would be able to obtain the swine flu vaccine before the end of the year.