Melioidosis outbreak in Hong Kong may have originated at reservoir in West Kowloon but water is safe, expert says
- Expert team still cannot say how it spread but highlighted several possibilities including bacterium entering reservoir through air vents
- We have to accept the disease has become endemic but there is no need to be too concerned, says expert
An abnormal spate of melioidosis, a fatal infectious disease, in Hong Kong might have originated from the bacterium found in the soil on top of a reservoir in West Kowloon after a government investigation found the DNA profiles highly identical.
Revealing the findings on Thursday, a top microbiologist leading the investigation said it was unknown how the bacterium had been passed on to the patients, stressing the city’s fresh water supply was still safe.
“The tests conducted on water samples collected from the reservoir in Shek Kip Mei so far all tested negative,” Professor Yuen Kwok-yung from the University of Hong Kong said. “All we know is that the DNA [of patients and soil samples] are almost the same, and the soil samples were collected on top of the reservoir.”
Caused by the bacterium Burkholderia pseudomallei, which is abundant in soil, especially moist clay, and muddy water, melioidosis is an infectious disease with symptoms including fever, headache, cough, chest pain, ulceration and localised pain or swelling.
A total of 34 melioidosis cases have been found in Hong Kong this year, considered as unusual compared with previous years, with 23 detected in the Sham Shui Po district. Seven patients have died of the disease.
Health authorities found that the cases in Sham Shui Po district were in the proximity of the Shek Kip Mei and Butterfly Valley reservoirs, and a construction site at Pak Tin Estate.
Among the 471 environmental samples obtained from the area, 38 of them contained the bacterium, with 32 being collected from the soil on top of the reservoirs. Four of the soil samples from the reservoir were genetically similar to the samples collected from the patients in the district.
Hong Kong melioidosis outbreak: what is causing it and how can you stay safe?
Yuen said the team could not tell how it spread despite conducting multiple inspections, but he highlighted several possibilities: bacterium entering the reservoir through the air vents; increase in water temperature lowering the chlorine levels in fresh water; more elderly people living in the Sham Shui Po district; and global warming increasing the volume of Burkholderia pseudomallei in soil.
Apart from an earlier suggestion to increase the chlorine levels in water, the expert team also recommended the government install air filters at the air vents and some ultraviolet lamps at the reservoir.
The chlorine levels at the Sha Tin Water Treatment Plant facility, the largest in the city, which services Sha Tin, Kowloon Central and part of Hong Kong Island, were raised last week in a bid to kill the bacteria that might have caused the outbreak.
Hong Kong logs spate of melioidosis cases, but experts urge public not to panic
The public, especially the elderly, was also advised to let the taps run for at least a minute before use and to boil water before drinking it.
“The investigation has come to an end at this stage,” Yuen said, “We have to accept that the disease has become endemic … the public need not be overly concerned if the cases do not share a common origin.”
Dr Albert Au Ka-wing, of the Centre for Health Protection, said authorities were revising the laws to include melioidosis as a statutory notifiable disease, which meant doctors would have to report suspected or confirmed cases.
Two cases of melioidosis were also reported at Eastern Hospital last month. Au said results of whole genome sequencing were different from the Sham Shui Po cluster.
“We believe that the two cases are not related to the Sham Shui Po cluster and are sporadic cases that are found locally from time to time,” he noted.
Melioidosis should be made notifiable to Hong Kong authorities, experts say
Yuen added that different genome sequencing results meant the cases did not have a common source of infection, therefore there was no cause for concern.
Last week, 26 workers from a construction site in Pak Tin Estate who had chronic illnesses were selected to undergo a test by the authorities. Eight males and two females aged 39 to 66, all asymptomatic, were found to have antibodies against melioidosis bacteria.
Infectious diseases expert Dr Wilson Lam said there might be multiple sources of infection including inhaling of contaminated soil or drinking of compromised water.
10 Hong Kong construction workers test positive for bacterium that causes melioidosis
“It is difficult to determine the actual transmission route. You can only raise suspicions as the samples collected around the reservoir [were positive],” he said.
Lam warned that the residents living next to the reservoir who suffered from chronic illness, especially diabetes, should only use boiled water for drinking or brushing teeth.
Respiratory medicine expert Dr Leung Chi-chiu suggested the authorities testing the elderly or those with chronic illnesses in Pak Tin Estate check whether they had been exposed as well.
