Close household contacts of a laboratory-confirmed COVID-19-infected case in Singapore, a city-state in South-East Asia with a population of 5.7 million, were contact traced and interviewed for demographic characteristics. We limit our analysis to contacts of the first 400 COVID-19-infected cases in Singapore, that is those identified before 21 March 2020 as the number of cases in the population with unidentified source of infection was less than 40 at that point and the likelihood of household cases being exposed to the population was low. This is also prior to the tightening of precautionary measures introduced by the government to minimise the spread of COVID-191, 2 that may have modified the risk of acquiring infection in the home.

We tested household contacts for SARS-CoV-2 when (a) they exhibit recent or active symptoms compatible with COVID-19 or (b) they are aged 12 and below (with effect from March 2020), regardless of their symptoms, as this age group may not report symptoms. Those testing negative and other well household contacts were quarantined at home or in government quarantine facilities and monitored daily for development of symptoms for 14 days from their last exposure to a case.

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