Table 1

Influenza studies characteristics, influenza incidence rates and incidence rate ratios

Author, YearCountryStudy designAIIRD, Controls,
Sample size
Influenza definition/ascertainmentIR AIIRDIR ControlsIRR,
95% CI
Level of evidence
Dirven 201211 The NetherlandsCross-sectional879 RAInfluenza symptoms (patient-report)5.9% of the cohortNANA4
Blumentals 201210 USACohort (Marketscan)46 030 RA;
46 030 controls
ICD-9409.3/100 000 PY306.1/100 000 PY1.2
(1.1 to 1.4)
Mohammad 201713 SwedenCohort186 AAV;
744 age and gender-matched controls
ICD-10*5010/100 000 PY*1530/100 000 PY*3.3
(2.2 to 4.8)
Bello 201212 ItalyCross-sectional159 RA, PsA, AS, SpA on bDMARDInfluenza-like illness (patient-report)17% of the cohortNANA4
  • *Combined incidence of influenza and pneumonia.

  • AAV, ANCA-associated vasculitis; AIIRD, autoimmune inflammatory rheumatic disease(s); AS, ankylosing spondylitis; bDMARD, biologic disease-modifying antirheumatic drug(s); IR, incidence ratio; IRR, incidence rate ratio; NA, non-available/non-applicable; PsA, psoriatic arthritis; PY, patient years; RA, rheumatoid arthritis; SpA, spondyloarthropathy.