Health officials in Hong Kong have declared an outbreak of scarlet fever, closing a kindergarten after a five-year-old boy died Tuesday in the city after a week-long illness.

Authorities say the boy is the second child in the past three weeks to die from the disease, which mainly affects children between ages 2 and 8. The kindergarten, attended by some 400 preschoolers, is to remain closed for at least a week.

The city's chief health protection officer, Thomas Tsang, says investigators believe a genetic mutation in the scarlet fever bacteria may be spreading a drug resistant form of the disease more rapidly this year than previously seen. He calls the situation “rather serious,” and says cases have also been detected in Macau and on the Chinese mainland.

The agency says more than 400 cases have been reported since the first of the year, already the highest annual total ever recorded in the city.

Scarlet fever symptoms include fever, sore throat, rashes and a strawberry-colored tongue. Symptoms, when countered effectively with antibiotics, normally subside within 48 hours.