Table 1. Descriptive Characteristics of Enrolled Patients with Medically Attended Acute Respiratory Illness by Case Control Status.

Characteristics	Influenza Positive Cases		Influenza Negative Controls
	N = 1,011	%	N = 5,746	%	P Value
Study community					<0.0011
Marshfield, WI	533	53%	2,388	42%
Rochester, NY	178	18%	259	5%
Southeast, MI	198	20%	1,086	19%
Nashville, TN	102	10%	2,013	35%
Age group					<0.0011
6 months–9 years	377	37%	1,791	31%
10–49 years	536	53%	2,193	38%
50+ years	98	10%	1,762	31%
Median (IQR)	6 13 28		6 29 54		<0.0012
Sex					0.0861
Female	536	53%	3,216	56%
Male	475	47%	2,532	44%
Race 3					<0.0011
White	702	74%	4133	73%
Black	133	14%	1099	20%
Other	119	12%	394	7%
Insurance status					<0.0011
None	83	8%	290	5%
Private	720	71%	3,427	60%
Public only	208	21%	2,029	35%
Enrollment site					<0.0011
Outpatient Clinic	802	79%	3,326	58%
Emergency Room	117	12%	739	13%
Inpatient	92	9%	1,681	29%
High-risk condition					<0.0011
No	692	68%	3,126	54%
Yes	319	32%	2,620	46%
Onset to test					<0.0011
<3 days	632	63%	2,516	44%
3–6 days	338	33%	2,442	42%
7+ days	41	4%	788	14%
Vaccine (interval)
Pandemic (14 days)	15	1%	1042	18%	<0.0011
Pandemic (7 days)	22	2%	1107	19%	<0.0011
Seasonal (14 days)	203	20%	2182	38%	<0.0011

¹Pearson test;

²Wilcoxon test;

³missing data for race (n = 177).