Contact tracing begins with mapping out virus patient's movements
MOH teams tasked with finding those who might have had close contact with an infected person
Phone lines in a lecture room at the Ministry of Health (MOH) have been busy every day since the first confirmed coronavirus case here last month.
A key part in containing the outbreak, seven teams of 10 people each from the MOH and its statutory boards have been working out of the room in two shifts to contact the more than 900 people who might have come into close contact with patients so far.
While most who pick up the team's calls have been cooperative, some have been unhappy or even grown angry at the situation, said Mr Pream Raj, assistant director at MOH's Communicable Diseases Division.
Another challenge is locating people who do not answer, especially foreigners who may not have a working phone number and may not stay at one location.
Speaking to the media on Saturday, Mr Raj, 35, said they are often asked to verify that they are indeed from MOH's contact tracing centre, with some asking for verification e-mails.
And this is not even the hardest part, said Dr Olivia Oh, 36, also an assistant director in the same division at MOH.
Before the calls are made, a core team would have already asked airlines for flight manifests, interviewed patients' families or even called hotels to help review surveillance footage.
All this to ensure a patient's movements are verified and accounted for and all possible close contacts identified.
Said Dr Oh: "That is the most difficult part... Only after we corroborate the information can we dish them out to the contact tracers to make the calls."
Contact tracing starts at the hospital where a patient is warded, with doctors and nurses drawing an activity map - a detailed breakdown of a patient's movements from 14 days before symptoms appear and until he is isolated.
When there are gaps, the contact tracers might interview patients again or, if they are too sick, talk to the next-of-kin.
They also get help from third parties such as hotels - to review surveillance footage or identify taxis if patients cannot recall the licence plate number and do not have a receipt or booking.
To help identify links between cases, a separate data management team also uses the activity maps, cross-referencing them with other cases to see if there are overlaps in locations.
If such overlaps are found, the contact tracing team conducts a follow-up investigation.
Mr Raj said the team usually gets the activity map of a patient two hours after being notified of the case and tries to reach out to all possible close contacts within 24 hours.
Once the contact's identity is verified, the team will need to determine if he is a close contact and needs quarantine.
There is no hard and fast rule, said Mr Raj.
"It depends on the length of exposure, the type of exposure and what they do during the exposure," he added.
Those not deemed as close contacts may still be placed on phone surveillance and have their state of health tracked.