Table.
Characteristics of confirmed COVID-19 cases, SARS-CoV-2 sequences, and genomic clusters over the four discrete periods of SARS-CoV-2 emergence and transmission in Victoria, Australia
| Period 1: Jan 25 to April 30, 2020 (n=1365)* | Period 2: May 1 to May 30, 2020 (n=285)* | Period 3: May 31 to Dec 6, 2020 (n=18 694)* | Period 4: Dec 7, 2020, to Jan 31, 2021 (n=107)* | Periods 1–4: Jan 25, 2020, to Jan 31, 2021 (n=20 451) | |
|---|---|---|---|---|---|
| Demographics | |||||
| Age, years | 47 (29–61) | 36 (24–51) | 34 (23–54) | 34 (23–47) | 35 (24–54) |
| Lives in residential care | 7 (0·5%) | 4 (1·4%) | 1946 (10·4%) | 0 | 1957 (9·6%) |
| Health-care worker† | 175 (12·8%) | 20 (7·0%) | 3706 (19·8%) | 3 (2·8%) | 3904 (19·1%) |
| Source of COVID-19 acquisition | |||||
| Case contact | 455 (33·3%) | 155 (54·4%) | 14 988 (80·2%) | 28 (26·2%) | 15 626 (76·4%) |
| Unknown source | 107 (7·8%) | 60 (21·1%) | 3594 (19·2%) | 2 (1·9%) | 3763 (18·4%) |
| Overseas travel | 803 (58·8%) | 70 (24·6%) | 112 (0·6%) | 77 (72·0%) | 1062 (5·2%) |
| Sequence availability | |||||
| Sequence data available | 870 (63·7%) | 120 (42·1%) | 10 646 (56·9%) | 75 (70·1%) | 11 711 (57·3%) |
| Did not pass quality control | 283 (20·7%) | 81 (28·4%) | 3324 (17·8%) | 32 (29·9%) | 3720 (18·2%) |
| Not sequenced | 212 (15·5%) | 84 (29·5%) | 4724 (25·3%) | 0 | 5020 (24·5%) |
| Genomic clustering | |||||
| Genomic clusters or transmission networks circulating‡ | 107/128 (83·6%) | 11/128 (8·6%) | 13/128 (10·2%) | 6/128 (4·7%) | 128/128 (100%) |
| Number of cases per genomic cluster or transmission network§ | 3 (2–6; 1–76) | 3 (2–5; 1–66) | 2 (2–3; 1–10 416) | 4 (2–5; 2–25) | 3 (2–6; 2–10 426) |
| Duration of genomic cluster or transmission network circulation, days§¶ | 7 (2–14) | 3 (1–8) | 5 (2–30) | 5 (1–10) | 7 (3–14) |
| Number of unclustered cases¶‖ | 115/870 (13·2%) | 21/120 (17·5%) | 39/10 646 (0·4%) | 33/75 (44·0%) | 208/11 711 (1·8%) |
| Number of cases in travel-only clusters‖** | 167/870 (19·2%) | 20/120 (16·7%) | 15/10 646 (0·1%) | 12/75 (16·0%) | 214/11 711 (1·8%) |
Data are median (IQR), n (%), median (IQR; range); or n/N (%).
Confirmed cases by time of initial diagnosis.
Includes individuals engaged in both clinical and non-clinical work in a health-care setting.
Includes all clusters with positive cases diagnosed in a particular period; clusters might be counted in more than one period.
Includes clusters only within the relevant time period.
Includes cases that were not clustered at the highest resolution of clustering and that were not part of a larger genomic transmission network.
Presented as a proportion of the number of sequenced positive cases per period.
Genomic clusters in which 100% of cases were suspected to have acquired SARS-CoV-2 from overseas.