Table 4. Univariate and multivariate analysis of pandemic (H1N1) 2009 virus infection SAR for virologically confirmed cases of pandemic (H1N1) 2009 virus infection, by gender, age group, and prophylaxis, United Kingdom, 2009*.

Variable	No. contacts†	No. secondary case-patients	Univariate analysis			Multivariate analysis
			SAR, % (95% CI)	p value‡		OR (95% CI)	p value
Sex, n = 745
M	364	37	10.2 (7.5–13.7)			1.0, baseline
F	381	25	6.6 (4.0–10.7)	0.08		1.0 (0.5–2.0)	0.96
Age, y
<16	212	40	18.9 (14.2–24.7)			18.2 (3.9–85.5)
16–49	378	20	5.3 (3.1–9.0)			3.5 (0.7–16.2)
>50	171	2	1.2 (0.3–4.7)	<0.001		1.0, baseline	<0.001
Prophylaxis, n = 587
No	143	45	31.5 (24.4–39.5)			1.0, baseline
Yes	444	8	1.8 (0.8–3.9)	<0.001		0.05 (0.02–0.09)	<0.001
Primary case-patient treatment
>48 h	453	48	10.6 (8.1–13.8)			1.0, baseline
<48 h	308	14	4.5 (2.5–8.1)	0.003		0.30 (0.13–0.68)	0.004
Total	761	62	8.1 (6.4–10.3)

*n = 761 except as indicated. Hosmer-Lemeshow goodness-of-fit test for multivariate model, p = 0.751. SAR, secondary attack rate; CI, confidence interval; OR, odds ratio.
†Excludes co-primary cases.
‡Indicates overall p value for differences by group.