Enteroviral infections usually subside in a week without treatment, but officials are alarmed because of the deaths of at least 20 mainland children in Anhui province. Virologists have suggested there are different strains of enterovirus 71 circulating in Hong Kong. As of press time, there were no details about the strain circulating in the Anhui outbreak. In Hong Kong, before the three new confirmed cases emerged yesterday, there were seven EV71 cases, involving four boys and three girls, aged from one to 13 years. Two brothers and another child who had visited them were linked. The rest were sporadic cases. Five children had been to the mainland before they were infected and one to Taiwan. All have recovered. The strain of EV71 circulating in Hong Kong, called C4, is different from the B5 strain in Taiwan. 'The strain of the disease in Hong Kong is usually C4 and the strain in Taiwan is B5,' said Chuang Shuk-kwan, consultant in communicable diseases with the Centre for Health Protection. But she added the centre could not say whether one strain was more serious than the other. If EV71 causes hand, foot and mouth disease, complications may develop including inflammation of the heart, encephalitis or polio-like paralysis. But complications from hand foot and mouth disease were 'uncommon', the centre said. Common symptoms are fever, sore throat and skin rashes. 'The rash usually appears over the fingers and palms, feet [including the soles] and other parts of the body such as the buttocks and thighs. Vesicles [blisters] can also be found in the [mouth],' it said. 'In most cases, the fever, rash and ulcers subside spontaneously in one week and full recovery is usual.' Hand, foot and mouth disease is mainly transmitted by discharges from the nose and throat, and the faecal-oral route. 'Direct contact with open and weeping skin vesicles or contaminated objects may also transmit the virus,' it said. The last big outbreak in the city was in 2004, with 35 cases. There were eight in 2005, 16 in 2006 and 12 last year, the centre said.