Classes at a Kwai Fong nursery will remain suspended for another week as a precaution against the further spread of enterovirus-71. Health authorities said the lowering of personal hygiene since the Sars crisis had led to a drastic rise in cases. Eleven cases of EV-71 have been recorded this year, compared to one for all of last year and five in 2002. There were 30 confirmed cases in 2001 and six in 2000. The Centre for Health Protection yesterday reiterated that the public and child-care institutions should maintain strict hygiene. The centre's controller, Leung Pak-yin, said the spike in cases of EV-71, one of the viruses causing hand-foot-mouth-disease, was expected at this time of the year. 'There are more cases in the summer as the disease is seasonal,' he said. The centre said the closure order on Po Leung Kuk Kwai Fong Nursery would be extended until June 14 as 'a precautionary measure' while further laboratory tests were carried out. The nursery was to have opened tomorrow.