The finding:
In a large cohort of 11,712 Taiwanese patients, the risk of being diagnosed with dementia was almost 3 times higher among patients who had bacterial pneumonia than among controls without an infection. Most pathogens increased risk for Vascular (VaD), unspecified, and Alzheimer’s (AD) presentations in that order. (Here, the unspecified category meant AD as a clinical presentation in the presence of CNS lesions.) Hemophilus infections were specifically associated with increased risk of AD. This risk was amplified in proportion to the number of hospitalizations for pneumonia, with three or more hospitalizations being associated with a 3.7-fold increased likelihood of neurocognitive disorders.

Strength and weaknesses:
The study uses a large nationwide dataset through Taiwan’s National Health Insurance and has a large sample size. The authors performed sensitivity analysis that could account for temporal association of these infections with prodromal dementia, and their subsequent figures do not vary substantially from their observation of increased risk. They also categorized risk by types of infection and underlying etiology while adjusting for comorbidities such as MDD and substance use.

Limitations include the inability to adjust for important lifestyle factors such as smoking, and for patients who may not have sought similar treatment for either pneumonia or cognitive deficits. Importantly, there was no explanation about the possibility of delirium in this sample, its characteristics, or its links with a subsequent dementia diagnosis.

Relevance:
Bacterial infections, especially pneumonia, have established correlations with delirium and have been associated with an elevated risk for developing neurocognitive disorders (NCD) in elderly patients. While the paper does not address this potential confounder, there is mounting evidence for persistence of features of delirium in the elderly and the increased cumulative incidence of NCDs following episodes of delirium. C-L psychiatrists, especially those in collaborative care, should be mindful of these risks by screening for cognitive impairment and monitoring for prodromal features of NCDs among elderly patients who develop bacterial pneumonia. The need to carefully monitor and ease the cognitive burden of medications including sedative and anticholinergic agents may be a modifiable iatrogenic risk factor.