Research in context
Evidence before this study
We searched PubMed up to Feb 15, 2020 for reports published in English with no date limitations using the keywords “COVID-19” and “cluster”. A family cluster of coronavirus disease 2019 (COVID-19) was reported in Shenzhen, Guangdong. Transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has also been reported among co-workers in Germany.
Added value of this study
We analysed three clusters of COVID-19 in Singapore to assess interactions and possible modes of transmission. Our findings show that SARS-CoV-2 is transmissible in community settings beyond household clusters. Importation and limited local transmission of SARS-CoV-2 could have occurred before the lockdown of Wuhan and China's institution of travel restrictions.
Implications of all the available evidence
Countries should focus on enhancing detection and containment of local clusters of COVID-19, through surveillance of individuals with general pneumonia or influenza-like illnesses, and of people who have been in contact with unwell travellers from China. It is also important for countries to do active case-finding among close contacts of affected individuals, including contacts with mild symptoms, to contain clusters and stop them from spreading.