The microbiologist whose crucial work helped Hong Kong deflect a series of infectious disease threats says the city's over-reliance on antibiotics is behind the deadly scarlet fever outbreak that has killed two children and made hundreds ill.

As a five-year-old boy's death was confirmed as the second from scarlet fever, Professor Yuen Kwok-yung, head of microbiology at the University of Hong Kong, said the abuse of antibiotics might have led to the emergency of a highly contagious, deadly mutant strain of the disease.

Yuen said antibiotic abuse could have caused the bacteria to become resistant to the macrolide group of antibiotics used to treat scarlet fever. These drugs are now proving to be ineffective.