Background
Inhaled corticosteroids (ICS) increase the risk of pneumonia in COPD and are commonly used in patients with COPD-bronchiectasis overlap.

Research Question
Is the risk of pneumonia associated with ICS further heightened in COPD-bronchiectasis?

Study Design and Methods
Electronic healthcare records (2004-2019) were used to obtain a cohort of COPD patients and a nested case-control (age-gender matched 1:4). Analyses were conducted to determine the risk of hospitalised pneumonia in COPD associated with ICS use in those with bronchiectasis. Findings were confirmed by several sensitivity analyses. Additionally, a smaller nested case-control, containing only patients with COPD-bronchiectasis overlap and those with recent blood eosinophil counts (BEC), was used to determine any association with BEC.

Results
316,663 were eligible for the COPD cohort; bronchiectasis significantly increased the risk of pneumonia (AHR=1.24, 95% CI 1.15-1.33). In the first nested case-control of 84,316 COPD patients, ICS was found to increase the odds of pneumonia (AOR=1.26, 95% CI 1.19-1.32), only if used in the previous 180 days. However, bronchiectasis was a significant modifier such that ICS use did not further augment the already elevated bronchiectasis-associated pneumonia risk (AOR, 95% CI: COPD-bronchiectasis=1.01, 0.8-1.28; no bronchiectasis=1.27, 1.20-1.34). Several sensitivity analyses and a second smaller nested case-control, confirmed these findings. Lastly, we found BEC modified the ICS-associated pneumonia risk in COPD-bronchiectasis overlap, where lower BEC was significantly associated with pneumonia (AOR, 95% CI: BEC≤3x109/L=1.56, 1.05-2.31, BEC>3x109/L=0.89, 0.53-1.24).

Interpretation
ICS use does not further augment the already increased risk of hospitalised pneumonia associated with concomitant bronchiectasis in COPD.