Cluster A
The Ministry of Health in Singapore was alerted to two individuals with locally acquired COVID-19 on Feb 3, 2020 (AC1 and AC2; figure 1 upper panels). They did not fit the case-definition for suspected COVID-19 but were tested because they reported frequent occupational contact with Chinese tourists. These two people were later identified to be linked epidemiologically to two other affected individuals (AGX1 and AGX2), a father and daughter reported by official and media websites in Guangxi, China,8, 9, 10 to be Chinese tourists who travelled to Singapore on Jan 22, 2020, and who visited several tourist sites on Jan 22–23, 2020, as part of a tour group. AGX1 and AGX2 subsequently departed for Malaysia before re-entry into Singapore for their flight to Guangxi on Jan 27, 2020, and they developed symptoms on Jan 28, 2020, after arrival in Guangxi. Details of the tour participants and the itinerary, obtained through the Singapore-based tour guide for the Singapore tour segment (AT1, who also tested positive for SARS-CoV-2) corroborated with details for AGX1 and AGX2 reported by Guangxi websites.
Of 20 tourists in the tour group from Guangxi, five or six were reported by AT1 to be coughing during the tour. To the best of our knowledge, only AGX1 and AGX2 had laboratory-confirmed COVID-19 (positive PCR for SARS-CoV-2).8 However, in view of the reported respiratory symptoms among tour group participants, it is possible that other tour group members were the primary cases.
Among the places visited by the tour group in Singapore were a complementary health products shop and a jewellery shop; both shops are patronised frequently by Chinese tour groups. The visits to the complementary health products shop lasted approximately 30 min, and the visit to the jewellery shop lasted roughly 1 h. Four assistants in the complementary health products shop (AC1, AC2, AC3, and AC4) and one assistant in the jewellery shop (AJ1) were identified to have COVID-19. All five shop assistants were at work on the day the tour group from Guangxi visited. AC1, AC2, AC3, and AC4 reported that they would assist customers to apply samples of medicinal oil on their bodies, and handwashing was not usually done between customers. Three secondary transmission cases were identified in the household of AC1 (AH1, AH2, and AH3), none of whom were contacts of other cases.
For the cases who were confirmed on or before Feb 5, 2020, 179 close contacts who were in Singapore and contactable were placed under quarantine, of whom two close contacts (AC3 and AC4) subsequently reported to be unwell and tested positive for SARS-CoV-2. An additional six close contacts were quarantined. For active surveillance, 16 shop assistants at the complementary health products shop and the sole remaining uninfected household member of AC1, who were all asymptomatic, were tested and none were positive for SARS-CoV-2.
Viral genomic sequences were available for four cases (AH1, AH2, AH3, and AT1) and phylogenetic analysis confirmed their linkage, as suggested by the epidemiological data (appendix pp 2–3).