Table 1. Characteristics of laboratory-confirmed influenza cases and test-negative controls in northern Spain, 2010/11 to 2015/16.

	All laboratory-confirmed influenza cases		All test-negative controls			Outpatient cases		Outpatient controls			Inpatient cases		Inpatient controls
	n	%	n	(%)	p valuea	n	%	n	%	p valuea	n	%	n	%	p valuea
Age groups (years)
50–59	412	33	354	22	<0.001	291	52	182	49	0.148	121	18	172	14	0.023
60–69	318	26	353	22		173	31	106	28		145	21	247	20
70–79	268	22	419	26		81	15	72	19		187	27	347	27
≥ 80	244	20	515	32		12	2	13	4		232	34	502	40
Sex
Male	622	50	866	53	0.152	258	46	175	47	0.838	364	53	691	54	0.589
Female	620	50	775	47		299	54	198	53		321	47	577	46
Major chronic conditions
No	459	37	414	25	<0.001	336	60	203	54	0.079	123	18	211	17	0.453
Yes	783	63	1,227	75		221	40	170	46		562	82	1,057	83
Hospitalisation in the previous 12 months
No	1,008	81	1,131	69	<0.001	513	92	348	93	0.440	495	72	783	62	<0.001
Yes	234	19	510	31		44	8	25	7		190	28	485	38
Functional dependence
No	1,210	97	1,589	97	0.349	557	100	373	100	NA	653	95	1,216	96	0.549
Yes	32	3	52	3		0	0	0	0		32	5	52	4
Influenza vaccine status
Unvaccinated	764	61	766	47	<0.001	412	74	252	68	0.033	352	51	514	40	<0.001
Vaccinated	478	39	875	53		145	26	121	32		333	49	754	60
Influenza season
2010/11	100	8	237	14	<0.001	50	9	55	15	0.061	50	7	182	14	<0.001
2011/12	129	10	116	7		112	20	62	17		17	3	54	4
2012/13	90	7	131	8		66	12	52	14		24	4	79	6
2013/14	279	23	314	19		93	17	53	14		186	27	261	21
2014/15	279	23	313	19		114	21	67	18		165	24	246	19
2015/16	365	29	530	32		122	22	84	23		243	36	446	35
Total	1,242	100	1,641	100		557	100	373	100		685	100	1,268	100

NA: not applicable.

^a Chi-squared test.