Risk of pneumonia in individuals with rheumatoid arthritis: a nationwide cohort study.

Background: Limited information is available on the influence of serologic status and different types of disease-modifying antirheumatic drugs (DMARDs) on risk of pneumonia. This study aimed to evaluate the risk of pneumonia according to rheumatoid arthritis (RA) seropositivity and type of DMARD.

Methods: This population-based cohort study enrolled individuals with RA (RA cohort, n=41 187) and 1:5 age-matched and sex-matched controls (n=205 935) between 2010 and 2017. Participants were followed from 1 year after RA diagnosis or matched control date until the first occurrence of pneumonia, pneumonia-related hospitalisation, death or 31 December 2019. The risks of pneumonia and related hospitalisation were evaluated according to serological status and type of DMARD.

Results: During a median follow-up duration of 4.2 years, increased risks of pneumonia (adjusted HR (aHR) (95% CI)=1.73 (1.69 to 1.78)) and related hospitalisation (2.26 (95% CI 2.15 to 2.37)) were observed in individuals of the RA cohort compared with controls. Compared with the controls, individuals with seropositive RA showed the highest risk of pneumonia (1.86 (95% CI 1.80 to 1.92)) and related hospitalisation (2.52 (95% CI 2.39 to 2.65)), followed by those with seronegative RA (1.43 (95% CI 1.36 to 1.50) for pneumonia; 1.60 (95% CI 1.46 to 1.76) for related hospitalisation). Individuals in the RA cohort showed a higher risk of pneumonia/related hospitalisation compared with controls, with an aHR (95% CI) of 1.77 (95% CI 1.62 to 1.94)/3.23 (95% CI 2.82 to 3.69), respectively, for biological DMARD-exposed RA, and 1.74 (95% CI 1.69 to 1.79)/2.22 (95% CI 2.11 to 2.33), respectively, for conventional synthetic DMARD-exposed RA. In contrast, targeted synthetic type did not show a significantly increased risk of pneumonia/related hospitalisation (0.93 (95% CI 0.66 to 1.31)/1.21 (95% CI 0.67 to 2.18), respectively).

Conclusions: Individuals with RA showed increased risk of pneumonia and related hospitalisation, and this was especially higher in those with seropositive RA. Except for targeted synthetic DMARDs, all other types were associated with increased risk of pneumonia. These findings emphasise the need for heightened awareness of pneumonia risk in the management of RA.