title: Risk of community-acquired pneumonia in patients with a diagnosis of pernicious anemia: a population-based retrospective cohort study.
abstract: 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).
  
  
  CONCLUSIONS
  In this large population-based cohort study, individuals with PA and presumed chronic achlorhydria were at an increased risk for CAP.
authors.affiliation: aCedars-Sinai Center for Outcomes Research and Education (CS-CORE) bDepartment of Medicine, Division of Gastroenterology, Cedars-Sinai Medical Center cDepartment of Medicine, Division of Digestive Diseases, University of California Los Angeles, Los Angeles, California dDepartment of Medicine, Division of Gastroenterology, Hospital of the University of Pennsylvania eDepartment of Biostatistics and Epidemiology, Center for Clinical Epidemiology and Biostatistics, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania, USA.
authors.forename: Christopher V
authors.initials: CV
authors.lastname: Almario
authors.forename: David C
authors.initials: DC
authors.lastname: Metz
authors.forename: Kevin
authors.initials: K
authors.lastname: Haynes
authors.forename: Yu-Xiao
authors.initials: YX
authors.lastname: Yang
mesh_terms: D000126:Achlorhydria / Q000453:epidemiology; D000368:Aged; D000369:Aged, 80 and over; D000752:Anemia, Pernicious / Q000175:diagnosis / Q000453:epidemiology*; D002908:Chronic Disease; D017714:Community-Acquired Infections / Q000453:epidemiology; D005260:Female; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D011014:Pneumonia / Q000453:epidemiology*; D012189:Retrospective Studies; D012307:Risk Factors; D006113:United Kingdom / Q000453:epidemiology