MTR commuters exposed to daily cocktail of bacteria that flourish in different areas of Hong Kong, HKU study says
But researchers say there’s no need to fear – no severe pathogens were detected on train handrails and the antibacterial coating applied on them has helped curb the spread of germs
Commuters on Hong Kong’s MTR trains bring in bacteria that are unique to the areas they live in, creating a cocktail of germs that passengers are exposed to throughout the network by the end of every day, according to a University of Hong Kong-led study.
About 5 million passengers – and the bacteria they bring on board – use the railway system’s 11 lines daily, with lines serving the New Territories close to the Shenzhen border having bacteria with more antibiotic resistance genes during the earlier part of the day, researchers said in a paper in scientific journal Cell Reports.
“It appears that these antibiotic resistance genes disperse into different lines in the MTR system with the carriage of human traffic and finally become relatively abundant in every line in the later hours of the day,” the researchers wrote.
Samuel Kang Kang, first author of the study, told the Post that the study was to “raise awareness of the possibility of pathogens’ and antibiotic resistance genes’ transmission via mass transit”, which was a key message to policymakers.
But Kang also assured MTR passengers there was no cause to shun the city’s most popular mode of public transport as no severe pathogens had been detected. He also cited the use of antibacterial nano-silver-titanium dioxide coating on handrails by the MTR Corporation as a mitigating factor.
The research team, comprising members from Hong Kong and Denmark, and supervised by HKU associate professor Gianni Panagiotou, said their findings could help officials adopt public health plans to stop the spread of disease within and between cities.
Hong Kong was devastated by a rapidly spreading Sars outbreak in 2003, which left 299 people dead and more than 1,700 infected.
To collect data for the study, volunteers with washed hands were sent to eight MTR lines and made to touch the different handrails in trains for 30 minutes. Samples from their palms were collected in the morning and evening three times within three consecutive weeks.
Analysis of the samples found distinct patterns of microbiomes – or microorganisms in a particular environment – especially during the morning commute.
Other types of bacteria were also found, with Propionibacterium acnes, which has been linked to the skin condition of acne, being a dominant germ.
Besides unique findings on the Ma On Shan line, which had a larger amounts of aquatic and sewage bacteria as it runs along the brackish Shing Mun River channel, the West Rail line, which passes through a mountainous region in the New Territories, showed the highest abundance of bacteria species that prefer a habitat 1,000 metres above sea level.
During the evening commute, some lines began to have fewer unique species of bacteria.
“Under heavy traffic, microbiota from different lines will exchange bacterial compositions through hand contact. Microbiota of train cars from different lines will be highly mixed after hours,” Kang said.
The research paper pointed out that microorganisms found on the East Rail line in the morning contributed “a notable proportion” to those found on other lines in the evening, including the Ma On Shan, Tung Chung, West Rail and Tsuen Wan lines.
The study also suggested possible cross-border antibiotic resistance transmission, as the East Rail line, the only one connecting to Shenzhen, was found to have more bacteria with antibiotic resistance genes.
Eventually, the bacteria could morph into multidrug-resistant organisms, known as superbugs.
Researchers said genes in some bacteria found on the East Rail line showed resistance to antibiotics such as tetracycline, a commonly used drug at swine feedlots on the mainland and also detected in the soil in the Pearl River Delta area, where Hong Kong and Shenzhen are located.
Top microbiologist Yuen Kwok-yung, who is from HKU but was not involved in the study, described the paper as “interesting”.
He said it supported scientists’ understanding that “cumulative exposure” to certain environments and possibly “cross-border transit” would increase people’s exposure to microorganisms including those with antimicrobial resistance genes.
The research team suggested policymakers continue to review antimicrobial strategies for public transit systems and checkpoints, “especially between regions with different norms and regulations in industrial and clinical antibiotic usage”.
They also suggested providing hand sanitiser dispensers at the exits of stations, trains, bike-sharing stations, airports and hospitals to reduce transmission of pathogens.
Fu Yihui, a resident of Sha Tin and a regular commuter on the Ma On Shan line, said she usually avoided touching handrails as well as sitting in train carriages, as she felt they were not very clean.
“Especially during summer, handrails will become sticky and wet after people hold them,” said the 25-year-old postgraduate student. “So I would rather stand and try my best to keep my balance.”
Still, Fu said, she would do more to stay clean, such as washing her hands right after leaving the MTR station.
Sam Luk To-sum, a recent university graduate, said he used to take the East Rail line twice a day to commute from home to school.
He said he was not concerned as it was “natural” for there to be microbes in the air.
“I only wash my hands when I get home, as it is hard to find a place to do so in most of the MTR stations,” Luk said, adding he would wear a mask when taking the train only if he was sick enough to require a visit to the doctor.
Dr Dominic Tsang Ngai-chong, a consultant microbiologist at Queen Elizabeth Hospital who was not involved in the study, advised people not to touch their mouth, nose or eyes after putting their hands on public surfaces that other people frequently came into contact with.
“Also, wash your hands before you use them to pick up food,” Tsang said.
In the long run, he said, health authorities could consider monitoring the types and levels of bacteria on public surfaces to assess effectiveness of sanitary measures.
The MTR Corp said it cleaned stations and train compartments regularly and would increase the frequency when it was necessary. The railway operator said it reviewed its sanitary measures from time to time and would look into the HKU study.
Additional reporting by Mandy Zheng