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Table 2 Sensitivity analyses of the associations between childhood infections and a later diagnosis of ankylosing spondylitis

From: Childhood hospitalisation with infections and later development of ankylosing spondylitis: a national case-control study

Including only cases matched at an age of 27 years or older Cases (n = 1757) Controls (n = 7305) OR 95 % CI
 All infectionsa 258 (14.7) 964 (13.2) 1.13 0.97–1.32
 Entericb 74 (4.2) 333 (4.6) 0.91 0.70–1.19
 Appendicitis 30 (1.7) 169 (2.3) 0.72 0.49–1.07
 Appendectomy 46 (2.6) 234 (3.2) 0.82 0.59–1.13
 Respiratory tractc 159 (9.0) 529 (7.2) 1.27 1.05–1.54
 Tonsillitis 49 (2.8) 169 (2.3) 1.16 0.83–1.61
 Tonsillectomyd 43 (2.4) 151 (2.1) 1.12 0.79–1.59
 Skin 15 (0.9) 66 (0.9) 0.93 0.53–1.64
 Urogenital tract 6 (0.3) 24 (0.3) 1.02 0.41–2.50
 Other 35 (2.0) 113 (1.5) 1.34 0.91–1.97
Including only cases treated with methotrexate, sulphasalazine, and/or TNFi Cases (n = 794) Controls (n = 3288) OR 95 % CI
 All infectionsa 141 (17.8) 553 (16.8) 1.06 0.86–1.31
 Entericb 40 (5.0) 185 (5.6) 0.87 0.61–1.25
 Appendicitis 12 (1.5) 85 (2.6) 0.58 0.31–1.06
 Appendectomy 20 (2.5) 116 (3.5) 0.71 0.44–1.16
 Respiratory tractc 93 (11.7) 329 (10.0) 1.20 0.93–1.54
 Tonsillitis 34 (4.3) 96 (2.9) 1.48 0.98–2.24
 Tonsillectomyd 27 (3.4) 78 (2.4) 1.42 0.90–2.24
 Skin 12 (1.5) 38 (1.2) 1.37 0.71–2.66
 Urogenital tract 1 (0.1) 16 (0.5) 0.28 0.037–2.10
 Other 14 (1.8) 59 (1.8) 0.991 0.54–1.81
Including only cases matched 2007–2011 and excluding all with immunosuppressive or cytostatic treatment, as well as specific treatment for inflammatory bowel disease, 1 year prior to match Cases (n = 471) Controls (n = 1836) OR 95 % CI
 All infectionsa 96 (20.4) 329 (17.9) 1.16 0.89–1.52
 Entericb 26 (5.5) 102 (5.6) 0.92 0.59–1.45
 Appendicitis 6 (1.3) 38 (2.1) 0.57 0.24–1.36
 Appendectomy 11 (2.3) 48 (2.6) 0.84 0.43–1.63
 Respiratory tractc 63 (13.4) 191 (10.4) 1.33 0.97–1.81
 Tonsillitis 27 (5.7) 67 (3.6) 1.58 0.99–2.53
 Tonsillectomyd 20 (4.2) 54 (2.9) 1.40 0.82–2.38
 Skin 3 (0.6) 21 (1.1) 0.56 0.16–1.90
 Urogenital tract 4 (0.8) 8 (0.4) 2.03 0.61–6.78
 Other 14 (3.0) 45 (2.5) 1.29 0.70–2.40
Prescription of antibiotics 1 year prior to match 131 (27.8) 478 (26.0) p = 0.446
Excluding inflammatory bowel diseasee Cases (n = 2307) Controls (n = 9584) OR 95 % CI
 All infectionsa 405 (17.6) 1555 (16.2) 1.10 0.97–1.25
 Entericb 108 (4.7) 528 (5.5) 0.84 0.67–1.04
 Appendicitis 35 (1.5) 244 (2.5) 0.59 0.41–0.84
 Appendectomy 56 (2.4) 312 (3.3) 0.74 0.55–0.98
 Respiratory tractc 258 (11.2) 873 (9.1) 1.25 1.08–1.46
 Tonsillitis 87 (3.8) 257 (2.7) 1.37 1.07–1.77
 Tonsillectomyd 78 (3.4) 219 (2.3) 1.42 1.09–1.85
 Skin 23 (1.0) 102 (1.1) 0.94 0.59–1.49
 Urogenital tract 9 (0.4) 40 (0.4) 0.90 0.44–1.86
 Other 53 (2.3) 192 (2.0) 1.18 0.87–1.62
  1. All values are shown as n (%)
  2. Exposure data are based on registered events of an infection in inpatient care before the age of 17 years
  3. aIncluding all infectious foci, but not the procedures appendectomy or tonsillectomy; bincluding appendicitis; cincluding tonsillitis; dalso including adenoidectomy; eexcluding all cases/controls with a diagnosis of ulcerative colitis, Crohns’ disease, or any other non-infectious bowel inflammation (see Additional file 1) up until 2 years after the first AS diagnosis of the index case
  4. CI confidence interval, OR odds ratio, TNFi tumour necrosis factor alfa inhibitors