Severe infections, domain-specific cognitive vulnerability, and future infection risk in older adults

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Abstract Objective Severe infections have been implicated in dementia risk, but their associations with detailed patterns of cognitive performance, and whether poorer cognition in turn increases risk for certain infections, remain unclear. We examined bidirectional associations between hospital-treated infections and domain-specific cognitive function in a cohort of older adults. Methods We analysed data from the English Longitudinal Study of Ageing Harmonised Cognitive Assessment Protocol (ELSA-HCAP), conducted in 2018 and linked to national inpatient records. Pre-HCAP hospital-treated infections were identified from 1997 to 2018; post-HCAP incident infections were ascertained from 2018 to 2024. Cognitive performance was assessed at HCAP using 21 standardised neuropsychological tests summarised into general and four domain-specific scores (executive function, memory, language, and visuospatial ability). Linear regression assessed associations between pre-HCAP hospital-treated infections and standardised cognitive scores; Cox models estimated associations between cognition and risk of incident hospital-treated infections after HCAP. All models were adjusted for sociodemographic, lifestyle, and health covariates. Results Of 1,159 participants aged ≥65 at HCAP (631 [54.1%] female; mean [SD] age, 75.6 [7.2] years), 351 (30.3%) had a hospital-treated infection before HCAP. Prior hospitalisation for any infection was associated with lower general cognition (β = –0.11 SD, 95% CI –0.21 to –0.02) and poorer executive function (β = –0.19, –0.28 to –0.09), with similar patterns across infection types. Lower respiratory tract infections were additionally associated with poorer memory (β = –0.20, –0.36 to –0.04). Cognitive scores were progressively lower among individuals with more frequent or prolonged infection-related hospitalisations, sepsis, or cardiovascular disease. Prospectively, over a mean (SD) 4.8 (1.9) years of follow-up, 271 incident hospital-treated infections occurred. Each 1-SD higher general cognition was associated with a 36% lower risk of any subsequent hospital-treated infection (HR 0.64, 0.53 to 0.78), and with consistent associations across cognitive domains for all-cause and bacterial infections. Executive function alone showed a strong association with viral infections, especially COVID-19 (HR 0.59, 0.44 to 0.80). Conclusion Severe infections were primarily associated with poorer executive function. Conversely, cognitive vulnerability across multiple domains was associated with increased susceptibility to infections requiring hospital care, while poorer executive function was specifically associated with viral infection risk. These findings support a reinforcing infection–cognition cycle in later life and cognitively tailored infection-prevention strategies.

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