Table 1.

Characteristics of infants <6 months of age hospitalized with and without laboratory-confirmed influenza.

Characteristic		Total	Influenza +	Influenza −	p-value
			(row %)
		N=1510	N=151	N=1359
Maternal Influenza Vaccine	No	1216	133 (11%)	1083 (89%)	0.01
	Yes	294	18 (6%)	276 (94%)
Influenza Season	Early	572	51 (9%)	521 (91%)	0.51
	Middle	485	50 (10%)	435 (89%)
	Late	453	50 (11%)	403 (89%)
Age Group	0 months	399	49 (12%)	350 (87%)	<0.001
	1 month	507	66 (13%)	441 (87%)
	2–3 months	411	24 (6%)	387 (94%)
	4–5 months	193	12 (6%)	181 (94%)
Gender	Female	664	68 (10%)	596 (90%)	0.78
	Male	846	83 (10%)	763 (90%)
Study Site	Nashville	554	60 (11%)	494 (89%)	0.53
	Rochester	425	44 (10%)	381 (90%)
	Cincinnati	531	47 (9%)	484 (91%)
Study Year	2002–2003	99	9 (9%)	90 (91%)	<0.001
	2003–2004	251	38 (15%)	213 (84%)
	2004–2005	322	40 (12%)	282 (88%)
	2005–2006	176	16 (9%)	160 (91%)
	2006–2007	230	8 (3%)	222 (97%)
	2007–2008	232	29 (13%)	203 (88%)
	2008–2009	200	11 (6%)	189 (95%)
Race-ethnicity	White	706	59 (8%)	647 (92%)	0.11
	Black	439	53 (12%)	386 (88%)
	Hispanic	365	39 (11%)	326 (89%)
Medical covariates
Premature	Yes	178	13 (7%)	165 (93%)	0.20
	No	1325	138 (10%)	1187 (90%)
High Risk Condition	Yes	119	7 (6%)	112 (94%)	0.12
	No	1391	144 (10%)	1247 (90%)
Social covariates
Exposed to Smoke	Yes	613	62 (10%)	551 (90%)	0.85
	No	896	88 (10%)	808 (90%)
# of Siblings	0	341	33 (10%)	308 (90%)	0.10
	1	539	42 (8%)	497 (92%)
	2	341	43 (13%)	298 (87%)
	3+	289	33 (11%)	256 (89%)
Daycare	Yes	152	7 (5%)	145 (95%)	0.02
	No	1356	144 (11%)	1212 (89%)
Insurance	Public	891	94 (11%)	797 (89%)	0.67
	Private	507	46 (9%)	461 (91%)
	None	105	10 (10%)	95 (90%)
Ever Breastfed	Yes	916	97 (11%)	819 (89%)	0.34
	No	594	54 (9%)	540 (91%)

Percentages may not sum to 100% due to rounding.