The Increase in Dementia Risk After Bacterial Pneumonia Differs by Causative Pathogen

Köln,Nordrhein-Westfalen,Deutschland, Seniorin hält die Hände vor das Gesicht,Trauer,Depression
Researchers assessed whether the increased risk for dementia observed among older adults diagnosed with bacterial pneumonia differs by causative pathogen.

The risk for Alzheimer disease (AD), vascular dementia (VaD), and unspecified dementia was increased among older adults diagnosed with bacterial pneumonia and differed by causative pathogen, according to study findings published in Brain Behavior and Immunity.

Although bacterial pneumonia is known to increase the risk for dementia, researchers sought to identify the associative risk in regard to specific causative pathogens. They conducted a longitudinal study between January 1997 and December 2012 among patients aged 45 years and older with a discharge diagnosis of bacterial pneumonia and no history of dementia. Enrolled patients were matched in a 1:10 fashion against patients with no prior bacterial pneumonia diagnosis (controls) on the basis of age, sex, time of enrollment, dementia-related comorbidities, income, and residence. The researchers compared the incidence of developing dementia between the 2 groups. Further analysis also was performed after matching the 2 patient groups in a 1:4 fashion to increase statistical power.

Among the total population of patients in the bacterial pneumonia (n=11,712) and control groups (n=117,120), the mean age at enrollment was 68.07 and 68.0 years. Additionally, the incidence of any dementia was 3.9% and 1.2% (P <.001), the mean age at dementia diagnosis was 76.03 and 80.23 years, and the mean duration between enrolled and dementia diagnosis was 5.91 and 6.96 years, respectively.

Compared with the control group, patients in the bacterial pneumonia group had an increased risk for developing any dementia (hazard ratio [HR], 2.83; 95% CI, 2.53-3.18), AD (HR, 2.44; 95% CI 1.65-3.61), VaD (HR, 4.15; 95% CI, 3.20-5.38), and unspecified dementia (HR, 2.62; 95% CI, 2.29-3.00).

After stratification by bacterial origin, 7 pathogens were associated with a significantly increased risk for any dementia, including Streptococcus, Staphylococcus, Pseudomonas, Klebsiella, Hemophilus, Mycoplasma, and other gram-negative bacteria (all P <.05). Patients with bacterial pneumonia due to Hemophilus bacteria had an increased risk for AD (HR, 3.85; 95% CI, 1.66-8.96) compared with those in the control group, but no similar associations were observed for the other 6 pathogens. With the exception of Mycoplasma and gram-negative bacteria, a prior diagnosis of bacterial pneumonia was associated with an increased risk for VaD and unspecified dementia, respectively.

This study may have limited generalizability as the majority of patients with bacterial pneumonia had severe disease. Other limitations included the lack of adjustment for potential confounders such as smoking status, exercise, and lifestyle, and the inclusion of only patients with bacterial pneumonia who were diagnosed by at least 2 physicians.

According to the researchers, “the underdiagnosis dementia needs to be considered in the association between bacterial pneumonia and dementia risk.” They also noted that the “prevention or timely intervention for bacterial pneumonia might [decrease] the risk [for] subsequent dementia among older adults.”


Chu C-S, Liang C-S, Tsai S-J, et al. Bacterial pneumonia and subsequent dementia risk: a nationwide cohort study. Brain Behav Immun. Published online April 4, 2022. doi.10.1016/j.bbi.2022.04.002