Table 1. Demographic data and clinical characteristics among patients.

	Control		Case
	(n = 222,012)		(n = 37,002)	P-value
Age, years	42.6 ± 17.1		42.6 ± 17.1	>0.999
Age group				>0.999
≤45 years	130,680 (58.9)		21,780 (58.9)
> 45 years	91,332 (41.1)		15,222 (41.1)
Gender				>0.999
Female	81,522 (36.7)		13,587 (36.7)
Male	140,490 (63.3)		23,415 (63.3)
CCI	0.23 ± 0.74		0.37 ± 0.91	<0.001
CCI group				<0.001
0	192,289 (86.6)		28,573 (77.2)
≥1	29,723 (13.4)		8,429 (22.8)
Appendicitis	1,187 (0.5)		269 (0.7)	<0.001
Interval between appendicitis and AS	NA		3.4 ± 2.3
Periodontitis	50,614 (22.8)		10,716 (29.0)	<0.001
Interval between periodontitis and AS	NA		3.2 ± 2.2
Tonsillitis	80,316 (36.2)		16,852 (45.5)	<0.001
Interval between tonsillitis and AS	NA		3.8 ± 2.4
Number of visits for tonsillitis				<0.001
No tonsillitis	141,696 (63.8)		20,150 (54.5)
1 visit	31,799 (14.3)		5,772 (15.6)
2 visits	15,569 (7.0)		3,165 (8.6)
3–4 visits	15,252 (6.9)		3,288 (8.9)
>4 visits	17,696 (8.0)		4,627 (12.5)
Cumulative cost of tonsillitis-related visits (New Taiwan dollars)				<0.001
No tonsillitis	141,696 (63.8)		20,150 (54.5)
Q1 (0< dollars ≤396)	21,312 (9.6)		3,829 (10.3)
Q2 (396< dollars ≤770)	19,754 (8.9)		3,760 (10.2)
Q3 (770< dollars ≤1,611)	19,929 (9.0)		4,293 (11.6)
Q4 (>1,611 dollars)	19,321 (8.7)		4,970 (13.4)
Interval between the tonsillitis and AS				<0.001
No tonsillitis	141,696 (63.8)		20,150 (54.5)
Q1 (0≤ years <1.8)	21,341 (9.6)		3,981 (10.8)
Q2 (1.8≤ years <3.3)	19,722 (8.9)		3,987 (10.8)
Q3 (3.3≤ years <5.4)	20,154 (9.1)		4,300 (11.6)
Q4 (≥5.4 years)	19,099 (8.6)		4,584 (12.4)

Abbreviation: CCI, Charlson comorbidity index; AS, ankylosing spondylitis; NA, not available.