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Table 3 Association and additive interaction between smoking and anti-viral antibodies in ACPA-positive RA

From: Low levels of antibodies against common viruses associate with anti-citrullinated protein antibody-positive rheumatoid arthritis; implications for disease aetiology

Factors

Cases (%)

Controls (%)

OR (95% CI)a

Smoking

EBV

   

-

highb

20 (3.82)

55 (9.06)

1.0 ref

-

lowc

126 (24.09)

197 (32.45)

1.6 (0.9–2.8)

+

high

73 (13.96)

96 (15.82)

2.1 (1.1–3.9)

+

low

304 (58.13)

259 (42.67)

3.2 (1.9 − 5.6)

AP (95% CI)

 

0.2 (-0.2–0.5)

  

Smoking

B19

   

-

high

18 (3.44)

61 (10.05)

1.0 ref

-

low

128 (24.47)

191 (31.47)

2.3 (1.3–4.1)

+

high

69 (13.19)

89 (14.66)

2.8 (1.5–5.2)

+

low

308 (58.89)

266 (43.82)

4.4 (2.5–7.7)

AP (95% CI)

 

0.1 (-0.3–0.4)

  

Smoking

CMV

   

-

high

24 (4.59)

51 (8.40)

1.0 ref.

-

low

122 (23.33)

201 (33.11)

1.4 (0.8–2.3)

+

high

109 (20.84)

100 (16.47)

2.6 (1.5–4.6)

+

low

268 (51.24)

255 (42.01)

2.5 (1.5–4.3)

AP (95% CI)

 

-0.2 (-0.6–0.3)

  
  1. ACPA anti-citrullinated protein antibody, RA rheumatoid arthritis, AP attributable proportion due to additive interaction, CI confidence interval, EBV Epstein-Barr virus, CMV cytomegalovirus, ref reference
  2. aOdds ratios (OR) were adjusted for age, gender and residential area. Significant ORs are shown in italics
  3. bHigh indicates the highest quartile of antibody titres (25% highest)
  4. cLow indicates the lower three quartiles of antibody titres (75% lowest)