Table 2. Unadjusted symptomatic secondary attack rates and odds ratios for secondary SARS-CoV-2 infection (probable and confirmed secondary cases), United Kingdom, January to March 2020 (n =440).

	Variable levels	SAR	95% CI	OR	95% CI
Household
Household size	2	0.49	0.37–0.60	1.00	Reference value
	3	0.41	0.30–0.51	0.62	0.26–1.53
	4	0.32	0.22–0.42	0.36	0.15–0.90
	≥ 5	0.25	0.13–0.37	0.23	0.07–0.71
Interactions
Sex	Male → Male	0.37	0.26–0.48	1.00	Reference value
	Male → Female	0.42	0.33–0.50	1.36	0.69–2.69
	Female → Male	0.34	0.26–0.43	0.85	0.34–2.13
	Female → Female	0.29	0.16–0.42	0.59	0.19–1.84
Comorbidities	None → none	0.37	0.29–0.45	1.00
	None → comorbidities	0.46	0.30–0.62	1.70	0.58–4.95
	Comorbidities → none	0.36	0.25–0.47	0.95	0.39–2.29
	Comorbidities → comorbidities	0.46	0.28–0.64	1.71	0.53–5.56
Characteristics of contact
Sex	Male	0.36	0.29–0.43	1.00	Reference value
	Female	0.38	0.31–0.45	1.15	0.68–1.94
Age group (years)	< 18	0.30	0.21–0.39	0.62	0.28–1.38
	18–34	0.37	0.28–0.47	1.00	Reference value
	35–64	0.43	0.35–0.51	1.38	0.67–2.85
	≥ 65	0.35	0.13–0.57	0.86	0.19–3.87
Characteristics of primary case
Sex	Male	0.41	0.33–0.49	1.00	Reference value
	Female	0.33	0.25–0.41	0.61	0.30–1.26
Age group (years)	< 18	0.89	0.7–1.05	41.89	4.46–393.02
	18–64	0.35	0.29–0.41	1.00
	≥ 65	0.42	0.25–0.59	1.51	0.53–4.26
Hospital admission	Without hospital admission	0.43	0.36–0.51	1.00	Reference value
	With hospital admission	0.28	0.20–0.36	0.37	0.18–0.77
Cough sneezing	Without cough/sneeze	0.32	0.19–0.46	1.00
	With cough/sneeze	0.38	0.32–0.44	1.42	0.54–3.70
Overall		0.37	0.31–0.43	NA

CI: confidence interval; NA: not applicable; OR: odds ratio; SAR: secondary attack rate; SARS-CoV-2: severe acute respiratory syndrome coronavirus 2.