TOPLINE:

Hospital-treated cystitis and bacterial infection of an unspecified site were each independently associated with a nearly 20% higher risk of developing dementia, even after adjusting for prior noninfectious dementia-related comorbidities. 

METHODOLOGY:

• Researchers used Finland’s nationwide health register data to evaluate whether severe infections increased the risk of developing dementia, at least partly independent of prior noninfectious comorbidities.
• A total of 62,555 individuals newly diagnosed with late-onset dementia aged ≥ 65 years (60.1% women) were matched to 312,772 control individuals without dementia based on age, sex, and follow-up period.
• Researchers identified hospital-treated infectious and noninfectious diseases that had a prevalence of at least 1%, occurred 1-21 years before the diagnosis of dementia, and were linked to a nearly 20% higher risk for incident dementia.
• The association between the hospital-treated diseases and the risk for incident dementia was assessed, and the independent effect of infections was evaluated after further adjustment for all other noninfectious dementia-related comorbidities.
• Analyses were also adjusted for education, marital status, employment status, and the region of residence.

TAKEAWAY:

• Overall, 29 diseases were robustly associated with incident dementia; among these, two were infectious diseases — cystitis and bacterial infection of an unspecified site — and 27 were noninfectious comorbidities, including mental and behavioral disorders, cardiovascular diseases, neurologic diseases, endocrine disorders, and injuries.
• Cystitis was associated with a 22% higher risk for dementia (rate ratio [RR], 1.22), which showed a subtle change to 19% after further adjusting for all prior noninfectious dementia-related comorbidities (RR, 1.19; P < .001 for both).
• Likewise, bacterial infections of an unspecified site were initially associated with a 21% higher risk for dementia and a 19% higher risk after adjusting for prior noninfectious dementia-related comorbidities (P < .001 for both).
• Only 10.8%-13.8% of the excess risk for dementia following these infections was attributable to comorbidities. The association between infections and dementia was even stronger for early-onset dementia (< 65 years), where infections — including bacterial infection of an unspecified site, pneumonia, and dental caries — were associated with an elevated risk.

IN PRACTICE:

“Overall, our findings support the possibility that severe infections increase dementia risk; however, intervention studies are required to establish whether preventing or effectively treating infections yields benefits for dementia prevention,” the authors wrote.

SOURCE:

The study was led by Pyry N. Sipilä, University of Helsinki, Helsinki, Finland. It was published online on March 24, 2026, in PLOS Medicine.

LIMITATIONS: 

The registries lacked data on psychosocial, behavioral, and biological confounders, as well as baseline cognitive assessments and detailed clinical examination results for dementia and other diagnoses. All individuals were assumed to have remained covered by the Finnish healthcare system throughout follow-up, potentially introducing bias from unrecorded emigration. Delays in the diagnosis of dementia may have caused some true cases to be misclassified as control individuals.

DISCLOSURES:

The study was funded by multiple sources, including the Emil Aaltonen Foundation, the Finnish Medical Foundation, the Päivikki and Sakari Sohlberg Foundation, the Research Council of Finland, the Wellcome Trust, the Medical Research Council (UK), and the National Institute on Aging (US). The authors declared having no competing interests.

This article was created using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.