Table 1. Comparisons of the first example transmission chain in the COVID-19 outbreak in Harbin City, Heilongjiang Province, China, January 2021.
| Groups per links in the transmission chain | Number of persons | Total* | |
| Infected | Not infected | ||
| *: Numbers of exposed persons were obtained by asking for Zhengda Company and checking name lists in duty rosters. Odds ratios (ORs) with 95% confidence intervals (CIs) were based on a chi-square test. | |||
| Mr. A to Zhengda Company | |||
| Shifts in Mr. A’s workshop | |||
| Night shift (Mr. A’s shift) | 28 | 30 | 58 |
| Day shift (non-Mr. A’s shift) | 62 | 698 | 760 |
| OR (95% CI) | − | − | 10.51 (5.90–18.71) |
| Night shift in the clean work area | |||
| Mr. A’s team (material preparation) | 6 | 4 | 10 |
| Non-Mr. A’s team (packing and cleaning) | 22 | 26 | 48 |
| OR (95% CI) | − | − | 1.77 (0.44–7.09) |
|
Zhengda Company to Mr. B (Mr. A and Mr. B said that they had to change clothes before entering the workshop every time and they did not know each other due to working in different shift) | |||
| Work areas in Mr. A’s workshop | |||
| Clean area (Mr. A’s) | 90 | 728 | 818 |
| Dirty area (not Mr. A’s) | 4 | 119 | 123 |
| OR (95% CI) | − | − | 3.68 (1.33–10.20) |
| Dressing room in the clean area | |||
| Men’s room (multiple indoor environmental samples positive) | 49 | 237 | 286 |
| Women’s room (one outdoor environmental sample positive) | 57 | 489 | 546 |
| OR (95% CI) | − | − | 1.77 (1.17–2.68) |
| Mr. B to his community | |||
| Possible exposure sites | |||
| Commuter car (non-Mr. A’s) | 8 | 76 | 84 |
| Clean work area at the day shift | 62 | 698 | 760 |
| OR (95% CI) | − | − | 1.19 (0.55–2.57) |
| Residents sharing the common corridor and stairwell with Mr. B | |||
| Go out often | 10 | 5 | 15 |
| Stay at home occasionally; go out occasionally or never go out | 5 | 19 | 24 |
| OR (95% CI) | − | − | 7.60 (1.77–32.63) |