A senior medical expert said that more research is needed to identify the origin of the recent super bug cases, which some have suggested might have been imported to Hong Kong from the Chinese mainland.

Xiao Yonghong, an expert at the Institute of Clinical Pharmacology at Peking University, said the NDM-1 gene, which makes bacteria resistant to antibiotics, had only been identified in Acinetobacter baumannii bacteria on the mainland.

In Hong Kong, however, it was found in Enterobacteriaceae, according to the Special Administrative Region's Centre for Health Protection.

"These are two different kinds of bacteria and both can harbor the NDM gene," Xiao noted.

NDM was first discovered in a Swedish national who fell ill in India at the end of 2009.

On July 23, a 30-year-old man died of the super bug in Hong Kong, the center said.

The man underwent surgery in a hospital on the mainland at the end of June, it said.

On July 17, he was hospitalized in Hong Kong with abdominal problems, and he died six days later.

The center found NDM producing Enterobacteria in the man's blood samples.

According to Hong Kong's Ta Kung Pao newspaper, it was the 10th case of NDM Enterobacteria detected in Hong Kong.

Eight of the other nine cases were confirmed to have been contracted on the Chinese mainland, the paper reported.

Xiao thought otherwise.

"NDM Enterobacteria have not been detected on the mainland before, so the mainland could hardly be the source for the Hong Kong cases," he noted.

China discovered NDM bacteria in lab samples from three people on the mainland in October 2010.

Two of them were newborns who were successfully treated for diarrhea and respiratory infections, previous reports said.

The other was a lung cancer patient who died.

In efforts to improve surveillance, to date "health authorities have set up 1,400 State-level centers across the mainland to monitor antibiotic resistance," Xiao said.

Also, the Ministry of Health issued tough regulations to control the clinical use of antibiotics, which took effect on Aug 1.

The ministry estimates that an average of 138 grams of antibiotics were used per person on the mainland each year, nearly 10 times the amount in the United States.