Abstract
BackgroundPatients with rheumatoid arthritis (RA) are known to be at increased risk of infection, particularly if they are taking drugs with immunomodulatory effects. There is a need for more information on the risk of influenza in patients with RA.MethodsA retrospective cohort study was carried out using data gathered from a large US commercial health insurance database (Thomson Reuters Medstat MarketScan) from 1 January 2000 to 31 December 2007. Patients were ≥18 years of age, with at least two RA claims diagnoses. The database was scanned for incidence of seasonal influenza and its complications on or up to 30 days after an influenza diagnosis in RA patients and matched controls. Other factors accounted for included medical conditions, use of disease-modifying anti-rheumatic drugs (DMARDs), use of biological agents, influenza vaccination and high- or low-dose corticosteroids. Incidence rate ratios (IRRs) were calculated for influenza and its complications in patients with RA.Results46,030 patients with RA and a matching number of controls had a median age of 57 years. The incidence of influenza was higher in RA patients than in controls (409.33 vs 306.12 cases per 100,000 patient-years), and there was a 2.75-fold increase in incidence of complications in RA. Presence or absence of DMARDs or biologics had no significant effect. The adjusted IRR of influenza was statistically significant in patients aged 60–69 years, and especially among men. A significantly increased rate of influenza complications was observed in women and in both genders combined (but not in men only) when all age groups were combined. In general, the risk of influenza complications was similar in RA patients not receiving DMARDs or biologics to that in all RA patients. Pneumonia rates were significantly higher in women with RA. Rates of stroke/myocardial infarction (MI) were higher in men, although statistical significance was borderline.ConclusionsRA is associated with increased incidence of seasonal influenza and its complications. Gender- and age-specific subgroup data indicate that women generally have a greater rate of complications than men, but that men primarily have an increased rate of stroke and MI complications. Concomitant DMARD or biological use appears not to significantly affect the rate of influenza or its complications.
Highlights
Patients with rheumatoid arthritis (RA) are known to be at increased risk of infection, if they are taking drugs with immunomodulatory effects
A large case-control study based on data from 443 UK general practices, clarified a number of conditions known to increase the risk of community-acquired pneumonia (CAP), and identified seven new independent risk factors [9]
We found similar increases in risk whether disease-modifying anti-rheumatic drugs (DMARDs)/biologics were used or not after controlling for baseline factors including vaccination
Summary
Patients with rheumatoid arthritis (RA) are known to be at increased risk of infection, if they are taking drugs with immunomodulatory effects. The literature suggests that, even before the use of corticosteroids became widespread, patients with rheumatoid arthritis (RA) had an increased susceptibility to infection [3]. This is supported by the Notable diseases in patients with RA include pulmonary infections, pneumonia [5]. The increased risk of infection in patients with chronic rheumatic or autoimmune disease is reported to be linked to compromised immunological functioning and to the immunosuppressive therapies used to control these disorders and their organ-specific complications [2]. After adjustment for known risk factors and confounders, the OR for risk of pneumonia in 387 patients with RA was 1.84 (95% CI: 1.62, 2.10)
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