Bidirectional relationship between cognitive function and pneumonia

Abstract

Rationale: Relationships between chronic health conditions and acute infections remain poorly understood. Preclinical studies suggest crosstalk between nervous and immune systems.

Objectives: 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.

Measurements and main 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.

Figure 1.

Representative trajectories of cognitive function over 10 years in all participants (top panel). Trajectories were constructed using Teng Modified Mini-Mental State (3MS) examination status scores for all participants, and before the index event and using all available data for those never hospitalized with pneumonia. Three trajectories were identified in the study population: no, minimal, and severe decline based on baseline scores and change in scores over time (4,420 [75.1%], 1,161 [19.7%], and 307 [5.2%], participants respectively). Distribution of the trajectories among those with and without pneumonia and severe sepsis is stratified by illness severity in the bottom panels. Participants hospitalized with pneumonia were more likely to be on trajectory of severe and minimal decline compared with no decline. Similar patterns were seen in those with sepsis and when stratified by illness severity.