Objectives The association of anti-tumor necrosis factor therapy with opportunistic infections in rheumatoid arthritis (RA) patients has been reported. The goal of this study was to clarify the clinical characteristics and the risk factors of RA patients who developed Pneumocystis jirovecii pneumonia (PCP) during etanercept therapy. Methods We conducted a multicenter, case-control study in which 15 RA patients who developed PCP were compared with 74 RA patients who did not develop PCP during etanercept therapy. Results PCP developed within 26 weeks following the first injection of etanercept in 86.7% of the patients. All PCP patients presented with a rapid and severe clinical course and the overall mortality was 6.7%. Independent risk factors were identified using multivariate analysis and included age ≥65 years [hazard ratio (HR) 3.35, p = 0.037], coexisting lung disease (HR 4.48, p = 0.009), and concomitant methotrexate treatment (HR 4.68, p = 0.005). In patients having a larger number of risk factors, the cumulative probability of developing PCP was significantly higher (p<0.001 for patients with two or more risk factors vs. those with no risk factor, and p = 0.001 for patients with one risk factor vs. those with no risk factor). Conclusion Physicians must consider the possibility of PCP developing during etanercept therapy in RA patients, particularly if one or more risk factors are present.
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