Coronavirus Foreign workers

Much lower Covid-19 prevalence rate in community than among migrant workers, according to study

This lower rate reflects people's adherence to Covid-19 safety measures, said Associate Professor Kenneth Mak. ST PHOTO: LIM YAOHUI

Unlike the migrant worker population - where almost 50 per cent of those staying in dormitories have tested positive for Covid-19 - the prevalence rate of the virus in the larger community is much smaller, the Health Ministry's director of medical services Kenneth Mak said yesterday.

This lower rate, based on a serology sampling study conducted in the community between September and October, reflects people's adherence to Covid-19 safety measures, he said.

Associate Professor Mak said the study found that only four out of 1,600 subjects had a positive serology test, which translates to a possible community prevalence rate of 0.25 per cent.

In comparison, about 47 per cent of the 323,000 migrant workers staying in dorms have tested positive for Covid-19 as at Sunday, based on polymerase chain reaction (PCR) and serology tests.

Prof Mak gave the figures at a virtual press conference when asked whether there is a group of Singaporeans who do not need the vaccine jab because they may have antibodies from a past infection to shield against reinfection.

Those with a positive serology test would have been infected in the past, at least 10 to 14 days back, while those with a positive PCR test are highly likely to be currently infected with Covid-19.

But, at the same time, the serology results in the community do indicate a higher prevalence rate of Covid-19 infection compared with the prevalence rate derived from positive PCR results, Prof Mak said.

The prevalence of Covid-19 in the community, based on positive PCR results, was around 0.04 per cent, much lower than the 0.25 per cent rate found in the community sampling study.

Similarly, fewer dorm residents tested positive for Covid-19 with the PCR testing than the serology testing. There were 54,505 who tested positive with PCR tests, compared with 98,289 who were positive with serology tests, although they did not have a positive PCR test.

Prof Mak said: "This is in keeping with our understanding that Covid-19 infection can occur in an asymptomatic fashion among people. This is also the reason why we need to continue our vigilance and not assume there is no cryptic spread of Covid-19 infection in the community."

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A version of this article appeared in the print edition of The Straits Times on December 15, 2020, with the headline Much lower Covid-19 prevalence rate in community than among migrant workers, according to study. Subscribe