More than 100 schools might be hit by a swine flu outbreak when the academic year starts next Tuesday as the virus continues to spread, health officials have warned. The government estimates that up to 200,000 people have been infected, even though just 10,000 cases have been confirmed. A further 381 new cases were reported yesterday, bringing the total to 10,849. Thomas Tsang Hoi-fai, controller of the Centre for Health Protection, said Hong Kong was still in the grip of a flu peak. Sixty per cent of all flu cases are caused by the H1N1 virus, with most of the rest caused by the seasonal H3 virus. The number of new daily swine flu cases has jumped from 100 in the early stage of the outbreak to more than 400. Four in every 10 patients seeking help at government flu clinics have swine flu. Undersecretary for Food and Health Gabriel Leung said on average each swine flu patient infected 1.2 to 1.3 people. 'According to experts' mathematical model, we estimate there are 10 to 20 unreported cases for every confirmed case. The confirmed cases are just the tip of the iceberg. Some people with flu may not go to government clinics for consultation and a laboratory confirmation.' Dr Tsang said 100 schools had reported outbreaks during last year's winter flu peak. There are more than 2,000 kindergarten, primary and secondary schools in Hong Kong. 'I would not be surprised if we have a similar number in this peak,' he said. Since mid-August, some international schools, kindergartens and nurseries have restarted classes and 20 have reported swine flu infections. 'Once a large number of children gather together, the risk of having a flu outbreak is much higher,' Dr Tsang said. 'We expect that the number of cases will increase in the first two weeks after the resumption of classes. We are also prepared to see some students having severe complications.' The government would consider a one-week suspension of classes at individual schools if more than 10 per cent students were infected. Dr Tsang said it was difficult to come up with a guideline for deciding on city-wide school closures. Whether all schools should be closed would depend on the nature of the outbreaks, including their speed and severity, and also if the virus showed any sign of mutation. The age of the 10,000 people confirmed so far to have the virus ranged from 10 days to 93 years. Fifty-five per cent were under 22, and 42 patients suffered from severe complications. Of these, 80 per cent were in the high-risk category because they were obese, smoked or had diseases. There have been four deaths. University of Hong Kong microbiologist Ho Pak-leung expects the first wave of swine flu to end in about a month, based on overseas' experience. 'When the school year starts, we will be seeing more cases among young people and there will be fewer and fewer cases among the working population,' he said. The chairwoman of the Kindergarten Association, Mary Tong Siu-fun, said children were required to have their temperature taken at home and when they got to school. A total of 105 swine flu patients are receiving hospital care. Among them, 88 are in stable condition, seven in serious and 10 in critical condition. The latest confirmed critical case is a 47-year-old man at Pamela Youde Nethersole Eastern Hospital.