More cases of the hand, foot and mouth disease that has killed 28 children in China are expected in June and July as the Government has ordered better public education and mandated punishments for officials who fall short.

However, the World Health Organisation (WHO) said that there was no special cause for alarm. The current outbreak of the disease, a common childhood intestinal illness, is no more virulent than usual but cases have been more concentrated in a single place resulting in an unusually high fatality rate.

Hans Troedsson, the WHO representative in China, said: “This is not a new virus, it is a virus we know, and there is no indication that it has changed so there is no need to worry."

The number of cases across China has climbed to 15,799, up from 12,000 reported on Tuesday. Officials said that the rise was due to tighter rules on reporting and not because of the spread of the infection.

Hand, foot and mouth is a common childhood illness and is endemic in much of Asia, but the outbreak has been linked with enterovirus 71 (EV71), which can cause a severe form of the disease characterised by high fever, paralysis and meningitis. Mr Troedsson said: "There is no indication of a change or a more virulent virus.”

However, there were still questions about why there were so many cases in Fuyang, in the eastern province of Anhui where 22 children have died, and why they presented unusual symptoms that made it difficult to identify the virus. That delay may have cost lives. Mr Troedsson added: “We usually don't see a cluster like this . . . so we have to investigate that further together with the Government."

The outbreak has not been confined to China. Around Asia, cases of the disease, which mostly affects children under five, were at higher than usual levels. Singapore reported a 75 per cent surge to 10,490 so far this year compared with last year. Vietnam's health ministry said it had about 3,000 cases in the first four months of the year, more than the total number for 2007. Ten children had died in Vietnam.

China reported 80,000 cases last year, and 17 fatalities. In the hardest hit province of Anhui, problems with improper treatment and unscrupulous doctors have occurred, state media said. A total of ten doctors there have been punished for malpractice relating to the outbreak.

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