Risk of community-acquired pneumonia in patients with a diagnosis of pernicious anemia: a population-based retrospective cohort study.

OBJECTIVE

Pernicious anemia (PA) is an autoimmune disease that causes achlorhydria or profound hypochlorhydria. We conducted a population-based study to determine whether individuals with PA are at an increased risk for community-acquired pneumonia (CAP).

METHODS

We performed a retrospective cohort study using The Health Improvement Network (THIN) from the UK (1993-2009). The eligible study cohort included individuals 18 years of age or older, with at least 1 year of THIN follow-up. The exposed group consisted of individuals with a diagnosis code for PA. The unexposed group consisted of individuals without a diagnosis of PA and was frequency matched with the exposed group with respect to age, sex, and practice site. Cox regression analysis was used to determine the hazard ratio with the 95% confidence interval for CAP associated with PA, accounting for a comprehensive list of potential confounders.

RESULTS

The study included 13,605 individuals with PA and 50,586 non-PA individuals. The crude incidence rate of CAP was 9.4/1000 person-years for those with PA, versus 6.4/1000 person-years for those without PA. The multivariable adjusted hazard ratio for CAP associated with PA was 1.18 (95% confidence interval 1.08-1.29).

CONCLUSION

In this large population-based cohort study, individuals with PA and presumed chronic achlorhydria were at an increased risk for CAP.