Heightened Prevalence of Common Hospital-Treated Infections Preceding Dementia Diagnosis with Accelerated Dementia Onset after Influenza.

Background: Since the beginning of Alzheimer's disease research, the hypothesis that infections are to some extent associated with neurodegenerative processes has been tested repeatedly. Epidemiological studies on the associations between infections and dementia have reported conflicting results.

Objectives: This study analyses common hospital-treated infections (herpes, influenza, intestinal infections, pneumonia, sepsis, urinary tract infections) and their association with subsequent dementia and time until dementia onset.

Design, Setting, And Participants: For this nationwide population-based case-control study, the dataset of the Austrian National Health Insurance Association was used, including dementia patients (dementia cohort) and age- and gender-matched non-demented individuals (control cohort). Only subjects with data availability of at least 10 years prior to the index date (date of dementia diagnosis or date of censoring) were included.

Measurements: The incidence of six common infections in older adults (herpes, influenza, intestinal infections, pneumonia, sepsis, and urinary tract infections) was analyzed over a period of 10 years before the censoring date.

Results: The study population consists of 58208 subjects (29104 per study cohort), mean age: 81 years, 54% females. Patients of the dementia cohort had suffered from infections significantly more often than patients of the control cohort (6002, 20.6% vs. 4826, 16.6%; p < 0.001). Influenza, urinary tract infections, intestinal infections, and sepsis showed independent positive associations with subsequent dementia diagnosis, irrespective of other comorbidities (odds ratios: 1.26 (95% CI: 1.06-1.49), 1.23 (95% CI: 1.16-1.30), 1.16 (95% CI: 1.07-1.27), 1.17 (95% CI: 1.01-1.37), respectively). Time from infection to dementia diagnosis was shorter after influenza compared to all other infections (median: 3.4 years (95% CI: 3.1-3.7) vs. 6.6 years (95% CI: 6.4-6.8); p < 0.001).

Conclusion: This is the first study to assess the association between infections and dementia over such a long minimum reporting period. These results, supported by consistent data from other epidemiological studies, emphasize the critical importance of infection prevention measures, especially for older adults. Further research is crucial to better understand the nature of the relationship between infections and dementia.