Table 3.

Univariate Exact Poisson regression of secondary transmission by household characteristics of index cases.

Variable	Case	No Case	Total	IRR	95% CI	p
n. Household members
2	6	13	19	1
3	9	27	36	1.583	0.563–4.448	0.383
4	21	51	72	2.770	1.118–6.865	0.028
5	20	40	60	1.965	1.696–10.513	0.002
>5	29	110	139	7.064	2.932–17.014	<0.001
n. Bedrooms
2	8	13	21	1
3	32	53	85	2.133	0.983–4.629	0.055
4	22	57	79	1.760	0.783–3.953	0.171
>4	15	113	128	2.000	0.847–4.717	0.113
n. Bathrooms				0.973	0.902–1.050	0.486
n. Persons/Bedroom
<1	8	13	21	1
1	32	53	85	2.213	0.908–5.396	0.080
1–1.499	22	57	79	2.125	0.825–5.477	0.119
≥1.5	15	113	128	5.167	2.156–12.383	<0.001
n. persons/bathroom
>1	9	62		1
1–2	44	133		2.095	1.022–4.292	0.043
>2	24	41		1.368	1.627–7.529	0.001