Table 4. Secondary attack rates for susceptible household contacts of index case-patients with pandemic (H1N1) 2009, Victoria, Australia, May 18–June 3, 2009*.

Variable	Total no. household contacts	No. with influenza-like illness	Secondary attack rate, % (95% CI)
Individual-level associations
Sex
M	58	5	8.62 (1.08–14.4)
F	64	13	20.3 (11.3–32.2)
Age, y
0–4	11	1	9.09 (0.230–41.3)
5–19	35	6	17.1 (6.50–33.6)
20–49	66	10	15.2 (7.51–26.1)
>50	10	1	10.0 (0.25–44.5)
Relationship to index case-patient
Parent/child/partner	65	10	15.4 (7.63–26.5)
Sibling	44	8	18.2 (8.19–32.7)
Other family member	13	0	0 (0–24.7)
Prevention and control measures reported
Antiviral prophylaxis	57	1	1.8 (0.04–9.39)
Quarantined >1 d with index case-patient	73	15	20.5 (12.0–31.6)
Household-level associations
No. persons
2–3	7	2	28.6 (3.67–71.0)
4–5	75	10	13.3 (6.58–23.2)
>6	40	6	15.0 (5.71–29.8)
No. children
1	31	6	19.4 (7.45–37.5)
2	47	7	14.9 (6.20–28.3)
>3	44	5	11.4 (3.79–24.6)
Cultural and linguistic diversity
Only English spoken at home	53	5	9.4 (3.13–20.7)
English and/or other language(s) spoken at home	69	13	18.8 (10.4–30.1)

*CI, confidence interval.