from a single U.S. medical system.
“Patients with seropositive RA, particularly RF [rheumatoid factor]-positive RA, had increased risk for pneumonia throughout the RA disease course that was not explained by measured confounders, including smoking status, multimorbidity, medications, and [erythrocyte sedimentation rate] level,”, said at the annual European Congress of Rheumatology, held online this year due to COVID-19.
“There has been much interest about the relationship between lung inflammation and the generation of RF and CCP [cyclic citrullinated protein] prior to the onset of RA. We hypothesized that patients with seropositive RA might have subclinical lung injury that could predispose them to pneumonia after clinical RA onset,” Dr. Sparks said in an interview. “Pneumonia is one of the most common serious infections in both patients with RA and the general population, and it causes serious morbidity and mortality.”
The doubled relative risk for pneumonia seen in the findings “translates into a clinically meaningful finding when considering the high rate and the many patients at risk since RA is relatively common,” said Dr. Sparks, a rheumatologist at Brigham and Women’s Hospital in Boston.
“Patients with RF-positive RA who present with symptoms concerning for pneumonia should be evaluated carefully for this and for other possible pulmonary manifestations of RA. Vaccination for pneumonia should be strongly considered for patients with RA who are on disease-modifying antirheumatic drugs, and we hope that our report encourages clinicians and patients” to undertake vaccination, he said.
His study used a database of more than 60,000 patients diagnosed with RA as of November 2013 in the records of a large Boston-area medical system that includes physicians affiliated with Brigham and Women’s Hospital and Massachusetts General Hospital. The researchers applied a validated algorithm for calculating a patient’s probability of having RA, and at the level of 97% probability they narrowed the cohort down to just under 10,000 patients. Additional winnowing because of missing data or a history of pneumonia yielded a study group of 4,110, which included 3,279 (80%) who were seropositive for either or both CCP and RF, and 831 (20%) who were seronegative. During a median follow-up of 7.8 years and total follow-up of more than 32,000 patient-years, the overall pneumonia incidence was 5.8%, with a 2.8% rate among the seronegatives and a 6.6% rate among seropositives. After adjustment for age, sex, glucocorticoid use, disease-modifying antirheumatic drug use, and several other possible confounders, the researchers calculated a 99% relative increased rate of pneumonia among all seropositive patients, compared with the seronegatives.
Further analysis looked at pneumonia incidence rates among patients positive only for CCP antibody, positive only for RF antibody, or both, compared with seronegative patients. This showed that CCP seropositivity had no statistically significant link with incident pneumonia, while RF seropositivity linked with a statistically significant, roughly twofold higher rate. Only 6% of all seropositive patients were positive only for CCP antibody, 59% were positive specifically for RF antibody, and 35% for both.
The data Dr. Sparks presented did not include information on pneumonia type, the timing of the pneumonia, compared with the onset of RA, disease activity, or smoking intensity.
“We anticipated that both RF positive and CCP positive would each be associated with pneumonia, so it was somewhat surprising that we only detected this for RF,” Dr. Sparks said. But he added that, because the number of patients with only CCP positivity was relatively so small, “it is still possible that CCP [antibody] could also increase pneumonia risk.”
The study had no commercial funding. Dr. Sparks had no disclosures.