Table 3.
Epidemiological analysis of a cluster of 11 patients with SARS-CoV-2 VOC B.1.351 in Hong Kong
| Case | Sex/Age | Clinical symptomsa (date) | Epidemiological background | Source of acquisition | Date of diagnosisb | Reason for testing | Diagnosis after first exposurec (day) | Total number of contact to be quarantined for 21 days among household members or household gathering, (workplace), and [residential building]; remark |
|---|---|---|---|---|---|---|---|---|
| Case 1 [11643] |
M/29 | Nil | Travelling from Dubai | Quarantine hoteld | 17th Apr 2021 | Attend CTC for COVID-19 test for departure from HK | 24 | 163: 1, (42) [120]e |
| Case 2 [11672] |
F/31 | Nil | Friend of case 1; working as clinic nurse in HK | Household | 18th Apr 2021 | Close contact to case 1 | 11 | 106: 6, (100); Contact of residential building: same as case 1 |
| Case 3 [11773] |
F/39 | Cough (23 Apr 2021) |
FDH working in Lantau island, HK | Social gatheringf | 30th Apr 2021 | Respiratory symptoms | 8 | 1057: 3, [1054]; CTN to all 0.37 million FDHs working in HKg |
| Case 4 [11774] |
F/10 months | Diarrhea (29 Apr 2021) | Cared by case 3 | Household | 30th Apr 2021 | Close contact to case 3 | 9 | Contact of residential building: same as case 3 |
| Case 5 [11792] |
F/36 | Nil | Mother of case 4 and household member of case 3 | Household | 5th May 2021 | Close contact to case 3 | 15 | Contact of residential building: same as case 3 |
| Case 6 [11793] |
F/46 | Nil | FDH working in Eastern district, HK | Social gatheringf | 5th May 2021 | CTN to all FDHs in HK | 18 | 516: 7, [509] |
| Case 7 [11797] |
F/38 | Nil | FDH working in Southern district, HK | Social gatheringf | 5th May 2021 | CTN to all FDHs in HK | 18 | 123: 4, [119] |
| Case 8 [11800] |
F/67 | Nil | Mother of case 2 | Social gatheringh | 7th May 2021 | Retrospective contact tracingi | 25 | 1: 1 |
| Case 9 [11815] |
M/42 | Nil | Brother of case 2 | Social gatheringf,h | 12th May 2021 | Retrospective contact tracingi | 30 | 110: 3, [107] |
| Case 10 [11816] |
F/40 | Nil | Girlfriend of case 9 | Social gatheringf,h | 13th May 2021 | Retrospective contact tracingi | 31 | Nil |
| Case 11 [11825] |
M/4 months | Nil | Son of case 10 | Social gatheringf,h | 16th May 2021 | Retrospective contact tracingi | 35 | Nil |
Note. CTC, community testing center; CTN, compulsory testing notice; FDH, foreign domestic helper; HK, Hong Kong.
Clinical symptoms suggestive of COVID-19 were reported and non-specific clinical manifestation was not included.
The date of official report by Centre for Health Protection, Hong Kong (https://www.chp.gov.hk/files/xls/previous_cases_covid19_en.xlsx).
Either attending an event of social gathering with exposure to COVID-19 case or being household member with exposure to COVID-19 case.
An imported case (M/28) from Philippine stayed in the adjacent room with case 1 in the quarantine hotel for 13 days (from 25th March 2021 to 6th April 2021). Whole genome sequencing showed that this imported case was the ancestor of the community outbreak of SARS-CoV-2 VOC B.1.351 in Hong Kong.
Since all 120 persons staying in the residential building of the first 2 cases of SARS-CoV-2 VOC B.1.351 (case 1 and 2) were not infected during quarantine period, the non-household resident would be subjected to compulsory testing on the 3rd, 7th, 12th, and 19th day after isolation of the confirmed case of SARS-CoV-2 VOC B.1.351 without an epidemiological source. Quarantine of the all residents in the residential building for 21 days would be enforced if there were more than one case of SARS-CoV-2 VOC B.1.351 without epidemiological link.
Social gathering of cases 3, 6, 7, 9, 10 and 11 in the apartment of case 9 (No. 37 Fuk Wing Street) with alcohol consumption on 18th April 2021.
Compulsory testing for COVID-19 could be exempted for FDHs who had received two doses of COVID-19 vaccine for 14 days.
Social gathering of cases 1, 2, 8, 9, 10 and 11 in the apartment of case 8 (Fung Hing House, Hing Wah II Estate) without alcohol consumption on 13th April 2021 but case 1 & 2 did not disclose this information until 5th May 2021. Therefore, contact tracing could not be performed timely for identification of case 8, 9, 10, and 11.
The case was retrospectively identified when case 1 and 2 disclosed the events of social gathering.