SINGAPORE - A major exercise is under way to discover the actual rates of Covid-19 infection in the community.
Thousands of people are being tested after having been in close contact with patients, since they could have been infected without realising it.
The National Centre for Infectious Diseases (NCID) is approaching people who were placed under quarantine from the start of contact tracing in January until April 4.
The aim is to determine the rates of infection and to assess exposure risks among close contacts of Covid-19 patients, whether they are in the home, at work or in social settings. These rates will also allow NCID to better estimate the number of undiagnosed cases among close contacts.
Serology tests check blood samples for antibodies that would have developed if the person had already been infected.
Some of these people might have been asymptomatic, had mild symptoms or were never diagnosed to be Covid-19 positive.
Associate Professor Ng Oon Tek, an NCID senior consultant, said all participants in the study would have already completed their quarantine orders.
Participants will have to answer a questionnaire via phone or government e-form, which includes questions about exposure risks related to the Covid-19-positive patient. Thus, they need to be able to identify the infected person they could have been in contact with, either by name or face.
Participants will also be required to provide a blood sample for antibody testing using a test developed by Duke-NUS Medical School.
The study includes household, work and social close contacts of Covid-19-positive patients.
NCID has approached about 2,500 household contacts and 1,800 social contacts so far. It aims to approach about 3,000 social contacts and 2,300 work contacts in total.
Overall, NCID has identified 1,100 contacts who are appropriate and agreeable to participate in the study. It hopes to enrol 2,000 contacts for the study, the results of which should be available in two months.
The study is one of three spearheaded by NCID.
The second study involves healthcare workers and the third is concerned with the rest of the population.
NCID said improved understanding of asymptomatic Covid-19 infections can lead to more effective transmission risk assessments and estimations of fatality rates.
"In addition, exposure risk factors for Covid-19 can offer insight into the nature of transmission, informing guidance and policies to stop its spread," it added.