Pneumonia in patients with rheumatoid arthritis: effect of microbial airway colonization

Rheumatoid arthritis frequently complicates airway diseases and is associated with high rates of pneumonia and mortality. The relationship between microorganisms colonizing the lower respiratory tract and the subsequent incidence of pneumonia in patients with rheumatoid arthritis is unclear. In this study, we aimed to identify microorganisms colonizing the lower respiratory tract in patients with rheumatoid arthritis related to the risk of developing subsequent pneumonia in these patients. A retrospective cohort study was designed to include a total of 121 patients with rheumatoid arthritis (median age, 67 years; women, 78.5%) who underwent bronchoscopy at three hospitals from January 2008 to December 2017. The following information was extracted from their electronic medical records: patient characteristics, microorganisms detected by bronchoscopy, and subsequent incidences of pneumonia. The patients were divided into groups based on the microorganisms isolated from the lower respiratory tract and compared with control subjects. The cumulative incidence of pneumonia was assessed using the Kaplan-Meier method and log-rank test. Risk factors for pneumonia were analyzed using the Cox proportional-hazards analysis. The most frequently isolated microbes from the lower respiratory tract in descending order were Pseudomonas aeruginosa, Staphylococcus aureus, and Haemophilus influenzae. The annual incidence rates of pneumonia per 1000 patients were 100, 62, 132, and 38, in the P. aeruginosa, S. aureus, H. influenzae, and control group, respectively. Patients colonized with P. aeruginosa had a higher frequency of macrolide use and a higher degree of bronchiectasis than patients in the control group. The rate of the subsequent incidence of pneumonia was higher in the P. aeruginosa group (P = 0.038), and P. aeruginosa was an independent risk factor for pneumonia (hazard ratio, 3.504; 95% confidence interval, 1.153-10.330). The colonization of the lower respiratory tract by P. aeruginosa in patients with rheumatoid arthritis was associated with the subsequent incidence of pneumonia.