Clinical characteristics and prognostic factors of pneumonia in patients with and without rheumatoid arthritis

BACKGROUND: To elucidate the characteristics of pneumonia in rheumatoid arthritis (RA) patients and to assess whether pneumonia in RA patients differs from that in non-RA patients. METHODS: We retrospectively divided pneumonia patients into two groups, those with RA and those without RA, and compared the two groups. We evaluated the risk factors for mortality with univariate and multivariate logistic regression analysis. RESULTS: Among 1549 patients, 71 had RA. The RA patients with pneumonia were 71.0±8.9 years old, 54.9% were female, 40.9% had a smoking history, and 71.8% had underlying respiratory disease. Female sex, non-smoker, and respiratory comorbidities were statistically more frequent in the RA patients than non-RA patients. The most frequent causative microbial agents of pneumonia in the RA patients were Streptococcus pneumoniae, Pseudomonas aeruginosa, Haemophilus influenzae, Mycoplasma pneumoniae, and influenza virus, whereas those of pneumonia in non-RA patients were S. pneumoniae, influenza virus, M. pneumoniae, Legionella spp., P. aeruginosa, H. influenzae, and Moraxella catarrhalis. Polymicrobial infection were identified as etiologies more frequently in the RA patients than non-RA patients. Although the severity of pneumonia did not differ between the two groups, mortality was statistically higher in the RA patients than non-RA patients. Multivariate analysis showed RA to be an independent risk factor for mortality. CONCLUSIONS: P. aeruginosa, H. influenzae, M. catarrhalis, and polymicrobial infection were statistically more frequent etiologies of pneumonia in the RA patients than non-RA patients. RA itself was found to be an independent risk factor for mortality from pneumonia.