Epidemiological investigation
We interviewed people with confirmed COVID-19 to obtain data for demographic characteristics, clinical symptoms, and activity patterns, from 14 days preceding symptom onset until isolation in hospital. We initiated contact tracing to identify close contacts (ie, people who spend a prolonged time within 2 m of a confirmed case) and other contacts who had some interactions with the case. We asked people with confirmed COVID-19 about possible contact with confirmed cases reported overseas in the 14 days before symptom onset. We used open source information from other countries (including government websites), news aggregators (eg, ProMed), and media reports to identify secondary transmissions in the respective clusters. For each cluster, we investigated the implicated setting to ascertain potential interactions. We reviewed activity maps of other confirmed cases in Singapore to identify potential epidemiological links to each cluster.
We placed close contacts under quarantine for 14 days from last exposure to the individual with confirmed COVID-19, either at home or at designated government quarantine facilities. We monitored their health status daily; people who developed symptoms were conveyed in dedicated ambulances to hospital for isolation and testing as part of active case-finding. We video-called individuals who were quarantined at home three times a day to verify their location; quarantine violators were tagged with a continuous tracking device. We placed other contacts (depending on risk stratification) on phone surveillance or advised them to self-monitor and visit a primary-care clinic if they became unwell.