Table 2

Characteristics of well family members: univariable analysis

 Family members Total (n (%))(n=121) Families without transmission (n (%)) (n=81) Families with transmission (n (%)) (n=40) P value Unadjusted OR(95% CI) Family size (median (IQR)) 4 (3–5) 3 (3–5) 4 (3–6) – – ≤3 56 (46.3) 41 (50.6) 15 (37.5) – Ref >3 65 (53.7) 40 (49.4) 25 (62.5) 0.18 1.71 (0.79 to 3.71) Close contact with primary cases at home (within 1 m or 3 feet) (No of times)* – – – – – 0 41 (33.9) 36 (44.4) 5 (12.5) – Ref 1–3 61 (50.4) 38 (46.9) 23 (57.5) 0.005 4.55 (1.57 to 13.20) ≥4 19 (15.7) 7 (8.7) 12 (30.0) <0.001 12.34 (3.30 to 46.23) No of family members wearing mask at home before primary case’s illness onset date (median (IQR))† 0 (0–1) 0 (0–2) 0 (0–0) – – None 90 (74.4) 54 (66.7) 36 (90.0) – Ref One or more 31 (25.6) 27 (33.3) 4 (10.0) 0.009 0.22 (0.07 to 0.69) No of family members wearing mask at home after primary case’s illness onset date (median (IQR))‡ 1 (0–3) 2 (0–3) 0 (0–3) – – None 47 (38.8) 26 (32.1) 21 (52.5) – Ref Some 38 (31.4) 24 (29.6) 14 (35.0) 0.47 0.72 (0.30 to 1.73) All 36 (29.8) 31 (38.3) 5 (12.5) 0.004 0.20 (0.07 to 0.60)
• *Family members stay with the primary case at a short distance (within 1 m or 3 feet) for more than 10 min at a time. For example, they have dinner with the primary case around a table or watch TV sitting near.

• †Before the primary case developed the illness, the primary case or his/her family contacts wear masks all the time at home.

• ‡When the primary case developed the illness, the primary case’s family contacts wear masks all the time living with the primary case at home.