title: Bidirectional relationship between cognitive function and pneumonia.
abstract: BACKGROUND
  Relationships between chronic health conditions and acute infections remain poorly understood. Preclinical studies suggest crosstalk between nervous and immune systems.
  
  
  OBJECTIVE
  To determine bidirectional relationships between cognition and pneumonia.
  
  
  METHODS
  We conducted longitudinal analyses of a population-based cohort over 10 years. We determined whether changes in cognition increase risk of pneumonia hospitalization by trajectory analyses and joint modeling. We then determined whether pneumonia hospitalization increased risk of subsequent dementia using a Cox model with pneumonia as a time-varying covariate.
  
  
  RESULTS
  Of the 5,888 participants, 639 (10.9%) were hospitalized with pneumonia at least once. Most participants had normal cognition before pneumonia. Three cognition trajectories were identified: no, minimal, and severe rapid decline. A greater proportion of participants hospitalized with pneumonia were on trajectories of minimal or severe decline before occurrence of pneumonia compared with those never hospitalized with pneumonia (proportion with no, minimal, and severe decline were 67.1%, 22.8%, and 10.0% vs. 76.0%, 19.3%, and 4.6% for participants with and without pneumonia, respectively; P < 0.001). Small subclinical changes in cognition increased risk of pneumonia, even in those with normal cognition and physical function before pneumonia (β = -0.02; P < 0.001). Participants with pneumonia were subsequently at an increased risk of dementia (hazard ratio, 2.24 [95% confidence interval, 1.62-3.11]; P = 0.01). Associations were independent of demographics, health behaviors, other chronic conditions, and physical function. Bidirectional relationship did not vary based on severity of disease, and similar associations were noted for those with severe sepsis and other infections.
  
  
  CONCLUSIONS
  A bidirectional relationship exists between pneumonia and cognition and may explain how a single episode of infection in well-appearing older individuals accelerates decline in chronic health conditions and loss of functional independence.
authors.affiliation: Division of Pulmonary, Allergy, and Critical Care Medicine, University of Pittsburgh Medical Center, PA, USA.
authors.forename: Faraaz Ali
authors.initials: FA
authors.lastname: Shah
authors.forename: Francis
authors.initials: F
authors.lastname: Pike
authors.forename: Karina
authors.initials: K
authors.lastname: Alvarez
authors.forename: Derek
authors.initials: D
authors.lastname: Angus
authors.forename: Anne B
authors.initials: AB
authors.lastname: Newman
authors.forename: Oscar
authors.initials: O
authors.lastname: Lopez
authors.forename: Judith
authors.initials: J
authors.lastname: Tate
authors.forename: Vishesh
authors.initials: V
authors.lastname: Kapur
authors.forename: Anthony
authors.initials: A
authors.lastname: Wilsdon
authors.forename: Jerry A
authors.initials: JA
authors.lastname: Krishnan
authors.forename: Nadia
authors.initials: N
authors.lastname: Hansel
authors.forename: David
authors.initials: D
authors.lastname: Au
authors.forename: Mark
authors.initials: M
authors.lastname: Avdalovic
authors.forename: Vincent S
authors.initials: VS
authors.lastname: Fan
authors.forename: R Graham
authors.initials: RG
authors.lastname: Barr
authors.forename: Sachin
authors.initials: S
authors.lastname: Yende
mesh_terms: D000368:Aged; D003072:Cognition Disorders / Q000150:complications* / Q000209:etiology; D003704:Dementia / Q000150:complications; D005260:Female; D006760:Hospitalization / Q000706:statistics & numerical data; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D009483:Neuropsychological Tests; D011014:Pneumonia / Q000150:complications* / Q000209:etiology; D016016:Proportional Hazards Models; D012307:Risk Factors