Table 4

Adjusted risk of infection in patients with rheumatoid arthritis (RA)

Adjusted IRR (95% CI)p Value
Current RA treatments
    TNF antagonists1.52 (1.30 to 1.78)<0.001
    MTX1.30 (1.12 to 1.50)<0.001
    Prednisone1.05 (0.97 to 1.15)0.251
    Other DMARDsReference
Clinical variables
    Smoking (ever)1.52 (1.38 to 1.67)<0.001
    Chronic lung disease1.31 (1.15 to 1.50)<0.001
    Diabetes mellitus1.33 (1.15 to 1.52)0.001
    Tender joint count1.01 (1.00 to 1.02)0.009
    ACR functional class1.23 (1.12 to 1.34)<0.001
    Body mass index1.01 (1.00 to 1.02)0.002
  • The interaction term for MTX and TNF antagonist combination therapy was significant (p = 0.001), indicating that patients on combination therapy had a reduced risk (IRR 0.75, 95% CI 0.62 to 0.89) compared with the expected multiplicative risk based on individual risk contributions.

  • The multivariable model included demographic variables (age, gender, race and education level) as well as the treatment and clinical variables listed in the table. Female gender (IRR 1.43, 95% CI 1.28 to 1.60) and age (IRR 0.995, 95% CI 0.99 to 1.00) were both significantly associated with the risk of infection in this model; race and education were not.

  • DMARD, disease-modifying antirheumatic drug; IRR, incident rate ratio; MTX, methotrexate; TNF, tumour necrosis factor.