SINGAPORE: Community transmission of COVID-19 remained low up to the last two weeks of March, a Singapore study that tested blood samples from the general population has found.
To measure how widespread COVID-19 infection was in the community, the National Centre for Infectious Diseases (NCID) and the Duke-NUS Medical School examined leftover blood samples from people who had their blood taken as part of routine care.
While the samples were collected anonymously from various hospitals and clinics, they were grouped by age to test if adults are more likely to carry antibodies than children, given how some infections are mild or without symptoms - especially for children.
Of the 774 samples tested, none were infected with COVID-19. It confirms that "the burden of COVID-19 in children remains low", said NCID in a press release on Wednesday (Apr 29).
The centre added: "This demonstrates that COVID-19 exposure in the community is extremely uncommon, indicating no widespread community transmission as of the last two weeks of March."
This was before the recent spike in cases in the migrant worker community, particularly among those living in dormitories. The total number of cases here have jumped from 1,000 on Apr 1 to 15,641 as of Wednesday.
But the number of new daily cases has fallen in recent days and of the 690 new cases reported on Wednesday, most were from foreign worker dormitories, the Health Ministry said.
READ: Migrant workers with COVID-19 symptoms isolated before getting tested to prevent potential transmission
This is the first time such a study is being done for COVID-19, but the method has been used for other infectious diseases such as measles, dengue and H1N1. The seroepidemiological test uses antibodies that remain in a person's blood to identify which population segments have been exposed to an infectious disease.
The study was one of three commissioned by the COVID-19 Research Workgroup, and were planned in January, soon after COVID-19 started spreading outside China.
“Rigorous research is critical to ensuring a coordinated, effective national-level outbreak response. In the case of COVID-19, of which much remains unknown, a swift response in clinical aspects as well as research is especially crucial to outpace the virus’ rapid spread,” said Professor Leo Yee Sin, NCID executive director and chair of the workgroup.
HALF OF THOSE INFECTED SHOW FEW SYMPTOMS
Another study aimed at estimating the number of asymptomatic COVID-19 infections found that each COVID-19 case spreads the disease to 5 per cent of their household members, and of these, half would be asymptomatic or minimally symptomatic.
About 2,000 household and close contacts of COVID-19 cases are being contacted for this study, which is expected to be completed in two months.
But results from about 300 participants showed that 2.5 per cent had antibodies which "clearly indicate" that they were infected with COVID-19, despite not having a positive test during the time they were quarantined, said NCID.
Another 2.7 per cent had tested positive for the virus during their quarantine, meaning that about 5 per cent of household members were eventually infected.
ADEQUATE PROTECTION FOR FRONTLINE WORKERS
Initial results from a third study focusing on the extent of COVID-19 exposure and infections among healthcare workers in Singapore have found no infections among the workers in the study. They include frontline staff in direct contact with COVID-19 patients, hospital staff working in non-COVID-19 patient care, as well as support staff.
"Despite some staff having worked with COVID-19 patients for at least two months prior to the time of blood taking, our analysis suggests that none of these workers had antibody results indicative of COVID-19 infection at the time that they joined the study," said NCID.
"This provides strong evidence that infection control and prevention procedures in Singapore’s public hospitals have been adequate to protect frontline healthcare workers."
This is one of the first COVID-19 seroepidemiological studies on healthcare workers in the world. Close to 1,100 healthcare workers have been enrolled so far and the study is expected to continue until the third quarter of 2021.
The COVID-19 cases reported by the Health Ministry have included several healthcare workers. A nurse at Changi General Hospital (CGH) was among the new cases on Monday, and on Apr 24, a nurse at Bukit Merah Polyclinic tested positive.