Compactness of wet markets may help virus spread: Experts

Wet markets can fit a large number of people in a compact space, and people have continued to flock to them even during the recent period of heightened alert.

It is not surprising, therefore, that Covid-19 cases have surfaced there, said experts.

The increased number of cases recently might also be due to a variant of Covid-19 that spreads more easily, they said.

A cluster at 115 Bukit Merah View Market and Food Centre has 56 cases, said the Ministry of Health (MOH) yesterday, making it the third-largest open cluster.

Other wet markets have also had to take precautions after positive cases were found linked to them.

Stallholders at the nearby Redhill Market and Food Centre took mandatory Covid-19 tests earlier this week. Testing was also conducted for people working at the Telok Blangah Drive Food Centre and Market, which has been closed for disinfection.

Associate Professor Alex Cook, vice-dean of research at the National University of Singapore's (NUS) Saw Swee Hock School of Public Health, said some wet markets may be quite compact relative to the number of visitors, which would heighten the risk of spread, even with natural ventilation.

He said the recent market clusters have a mix of three types of cases: market workers, visitors and household contacts of cases.

Household contacts, while epidemiologically linked, were not infected at the market per se, he said. "So the risk of infection within a wet market isn't quite as high as it may appear from the size of these clusters."

Professor Paul Tambyah, president of the Asia-Pacific Society of Clinical Microbiology and Infection, said the spread in well-ventilated open-air wet markets suggests that the virus is transmitted through droplets or surfaces.

As to whether markets should be avoided, he said: "The key has to be vaccination. That is how every single viral disease from smallpox to measles to polio has been controlled."

The authorities have established a possible link between the Bukit Merah and Telok Blangah market cases. MOH said on Monday that a Singaporean man, 42, who works as a hawker at the Telok Blangah food centre is a family member of a 47-year-old cooking assistant at the Bukit Merah market.

Professor Teo Yik Ying, dean of NUS' Saw Swee Hock School of Public Health, said it is highly likely that the cases at the Bukit Merah and Redhill markets are linked, given the markets' proximity to each other.

He said malls and supermarkets have been where outbreaks were detected recently.

"I do not see them as a new weak link, but rather as a consequence of Singapore having to deal with a much more infectious Delta variant that is driving these outbreaks."

MOH told The Straits Times earlier this month that as at the end of last month, 550 Covid-19 cases in Singapore were of the Delta variant of the coronavirus first detected in India.

Prof Teo said that the increased transmissibility of the variant means there is a possibility of a large outbreak happening whenever infected cases move about in the community.

"If these cases were going to work or going about their social activities, then I expect the venues associated with the large outbreaks would be linked to workplaces or public spaces for social activities.

"But precisely because the default continues to be working from home and social activities are kept to a minimum now, people are frequenting malls, supermarkets and wet markets for necessities and food. This is why we are seeing outbreaks in such venues," he said.

Prof Tambyah, however, disagreed that the spread in wet markets was related to the Delta variant, noting that the first Covid-19 super-spreading event in the world was at the Huanan seafood market in Wuhan, China.

Residents of Telok Blangah and Bukit Merah expressed concern about the growing number of cases in the neighbourhood as well as non-compliance with the rules.

Compliance officer Gideon Goh, 37, who lives in Bukit Merah, told The Straits Times he had seen people smoking or talking in groups without wearing masks properly.