Assessing secondary attack rates among household contacts at the beginning of the influenza A (H1N1) pandemic in Ontario, Canada, April-June 2009: A prospective, observational study

Table 2 Household secondary attack rates by secondary case definition and age group.

Secondary Case Definition	Age Group	Contacts (N)	Secondary Cases	SAR (%)	95% CI	P-value*
ARI	Overall	253	51	20.2	15.4 - 25.6
	Children <16 years	59	25	42.4	29.6 - 55.9	<0.001
	Adults ≥16 years	145	25	17.2	11.5 - 24.3
ILI	Overall	253	26	10.3	6.8 - 14.7
	Children <16 years	59	15	25.4	15.0 - 38.4	0.001
	Adults ≥16 years	145	11	7.6	3.8 - 13.2

Note: Age was missing for 49 contacts.
ARI, acute respiratory illness. ILI, influenza-like illness. CI, confidence interval.
*Pearson chi-squared test for the difference in SAR between children and adults.

ISSN: 1471-2458