A mutated strain of scarlet fever more resistant to antibiotics has killed a second child in Hong Kong, the first deaths from the illness in the southern Chinese city in at least a decade, authorities say.

The scarlet fever rash first appears as tiny red bumps on the chest and abdomen that may spread all over the body. (Courtesy CDC) Certain characteristics of the new strain likely make it more contagious, and it may be responsible for an outbreak sweeping Hong Kong, Professor Kwok-yung Yuen, head of Hong Kong University's microbiology department said Wednesday.

The new strain has about 60 per cent resistance to antibiotics used to treat it, compared with 10 to 30 per cent in previous strains, he said.

A 5-year-old boy who died at a hospital Tuesday was confirmed to have scarlet fever Wednesday. A 7-year-old girl who died in May was the first patient in Hong Kong to die of the illness in at least 10 years.

Hong Kong has had 466 reported cases of scarlet fever so far this year, about double the annual total. The outbreak may have spread to neighbouring Macau and mainland China.

About 9,000 cases have been reported on the mainland, about double the average from recent years, although no information is available on deaths, the Hong Kong Standard newspaper reported, citing health officials. Macau has 49 cases, a jump from 29 cases in 2009 and 16 in 2010, but no deaths have been reported, the Macau Daily Times said.

Scarlet fever Looking like a sunburn, scarlet fever feels like a rough piece of sandpaper, and lasts about two to five days. Source: CDC

"We are facing an epidemic because the bacteria causing scarlet fever is widely circulating in the region — not only in Hong Kong but neighbouring places such as the mainland and Macau," said Thomas Tsang, controller of Hong Kong's Centre for Health Protection, the Standard reported.

Scarlet fever is a streptococcal disease characterized by a bright red skin rash, fever and sore throat. It's most common in children under 10.

Infectious diseases are a particular concern in Hong Kong, where the 2003 SARS outbreak killed 299 people. Nearly 500 more deaths were reported in other countries.