Table 2.

Characteristics of cases and controls included in the study

	Cases (n = 140)			Controls (n = 308)
	No	%	Mean (SD)	No	%	Mean (SD)	P value
Mean age			60.6 (17.8)			62.1 (17.1)	0.40
≥65 years	70	50.0		169	54.9		0.36
Male	80	57.1		179	58.1		0.92
Vaccinations in 6 weeks before index date
Seasonal influenza vaccination 2010–2011	20	14.3		27	8.8		0.10
Other vaccinations	1	0.7		1	0.3		0.53
Infections in 6 weeks before index date (%)
Influenza-like illness (ILI)	40	28.6		12	3.9		<0.001
Upper respiratory tract infection (URI)	37	26.4		25	8.1		<0.001
Gastrointestinal infection (GI)	30	21.4		8	2.6		<0.001
Chronic comorbidity
Malignancy	15	10.7		34	11.0		0.99
Immunocompromised	9	6.4		4	1.3		0.005
Autoimmune disorders	11	7.9		11	3.6		0.06
Epstein-Barr virus	7	5.0		7	2.3		0.15
Other conditions in 6 months before index date
Pregnancy	0	0.0		2	0.6		0.99
Surgery	8	5.7		14	4.5		0.64
Influenza-like illness (ILI)	45	32.1		31	10.1		<0.001
Upper respiratory tract infection (URI)	42	30.0		45	14.6		<0.001
Gastrointestinal infection (GI)	33	23.6		17	5.5		<0.001
Drug use: n (Mean)	403	2.9		777	2.5		0.18
Patients with >5 drugs	19	13.6		42	13.6		0.99
Vaccination
Seasonal influenza vaccination 2010–2011	45	32.1		85	27.6		0.37
Seasonal influenza vaccination >6 weeks	25	17.9		58	18.8		0.90
Other vaccinations	2	1.4		5	1.6		0.99