An Infection-Cognition Connection

Pneumonia infections and cognition tied in new study of the elderly and dementia

/ Author:  / Reviewed by: Robert Carlson, M.D Beth Bolt, RPh

(RxWiki News) Many older adults deal with chronic health conditions as they age. And according to a new study, these chronic conditions often seem to be preceded by a single infection in elderly patients. 

To explore the possible connection between infection and chronic disease, the researchers looked at pneumonia, an infection of the lungs, and dementia, a range of issues involving mental function, in a long-term study of older adults.

These researchers found a two-way association between hospitalization for pneumonia and problems with cognition. The study showed that elderly patients who became ill with pneumonia were also more likely to be coping with mental decline, and that patients with dementia were more likely to later develop pneumonia.

"Wash your hands carefully to help prevent the spread of illness."

Led by Faraaz Ali Shah, MD, of the Division of Pulmonary, Allergy, and Critical Care Medicine at the University of Pittsburgh Medical Center, the researchers analyzed data from the Cardiovascular Health Study (CHS) to find potential connections between chronic health conditions and infections.

Dr. Shah and colleagues looked at 5,888 adults over the age of 65 who were followed over 10 years. Participants were "well-functioning" and "community-dwelling" when the CHS took place in the 1990s. The average age at the study's start was 72.8 years old.

The researchers looked at participants' cognitive function — a broad term used to describe mental processes like memory, understanding, problem solving and language.

These participants were identified as having one of three cognition trajectories, or paths: no decline, minimal decline or severe rapid decline. Several different tests were used to determine these distinctions. The researchers determined that 21 percent of patients had minimal decline and 5.8 percent had severe rapid decline over time.

During the course of the study, 639 participants (10.9 percent) were hospitalized with pneumonia at least once.

The researchers found that a larger proportion of those hospitalized with pneumonia had trajectories of minimal decline (22.8 percent) or severe decline (10 percent) before they developed pneumonia than those who were never hospitalized with the infection. By comparison, 19.3 percent of those who never developed pneumonia had trajectories of minimal decline and 4.6 percent had trajectories of severe decline.

The researchers also noted that only 9.7 percent of those with a trajectory of no cognitive decline were hospitalized with pneumonia, compared to 12.6 percent of those with minimal decline and 20.8 percent of those with severe decline.

Dementia was assessed in 3,602 of the participants (61.1 percent). Of this group, 707 developed dementia over the course of the study.

Of the 3,602 assessed for dementia, 320 (8.8 percent) were hospitalized for pneumonia. Among those hospitalized, 39 (12.2 percent) later developed dementia.

Dr. Shah and colleagues reported that hospitalization with pneumonia was associated with an increased risk for later dementia, even after adjusting for factors like other chronic health conditions, demographics and health behaviors.

The researchers noted that the association between pneumonia and dementia seemed to be bidirectional — meaning not only did earlier pneumonia seem to affect later cognition, but earlier cognition issues seemed to affect later pneumonia chances.

"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,"' wrote Dr. Shah and colleagues.

It is important to note that this study only hints at an association and not a causal relationship between pneumonia and dementia.

The researchers also noted, "Compared with participants never hospitalized with pneumonia, those who were hospitalized were older, more likely to be male, and had a higher prevalence of chronic conditions." These factors could have played a role in the outcomes.

This study was published in the American Journal of Respiratory and Critical Care Medicine on September 1. Some funding for the study was provided by the National Institutes of Health.

Review Date: 
September 3, 2013
Last Updated:
September 4, 2013