A microbiologist on Monday called on the government to instruct doctors to notify the authorities of all cases of melioidosis to help officials better understand the spread of the potentially deadly bacterial infection.

So far this year, Hong Kong has recorded 31 cases of melioidosis, with most of the patients being from Sham Shui Po. But Ho Pak-leung from the University of Hong Kong told a Commercial Radio programme that there might be cases in other districts that the government was not aware of.

"Did the transmission happen 100 percent in Sham Shui Po or also in other districts? It's uncertain, because the government may not know about some mild cases. If [melioidosis] is listed as a statutory notifiable infectious disease, at least you can then step up testing," he said.

Doctors must report all suspected or confirmed cases of statutory notifiable infectious diseases to the Centre for Health Protection.

Ho noted that analysis has shown that there is a chain of melioidosis transmission around the Pak Tin Estate in Sham Shui Po, but the source of infection remains uncertain.

He said the fact that four soil samples from a construction site in the Pak Tin Estate had positive for the bacteria did not prove that the site was the source of infections, as he said melioidosis was endemic in Hong Kong and the bacteria might be found in different places.

Meanwhile, infectious disease specialist Leung Chi-chiu said it was appropriate for authorities to advise chronically-ill workers at the site to get tested, but residents in the area would not need to be included.

"It would be like finding a needle in a haystack. Because when you don't even know the level of exposure at the construction site, where the bacteria was found, testing the whole district would not be practical," he told an RTHK programme.

He added that infections should wane as the weather becomes dry and cool, which makes transmission of the bacteria less likely.

Melioidosis is transmitted through muddy water and soil, though human-to-human and person-to-person transmission is rare. The Centre for Health Protection says the mortality rate can be between 40 and 75 percent, although it is treatable with antibiotics.

Seven people, all of them with other underlying illnesses or immunodeficiency, have so far died after contracting melioidosis in Hong Kong this year.