HealthDay News — Hospital-treated infections, especially repeated infections in early life and midlife, are associated with increased risks for Alzheimer disease and Parkinson disease before age 60, according to study findings published in PLOS Medicine.

Previous studies have suggested that infection plays a role in neurodegenerative disease development, noted Jiangwei Sun, PhD, and colleagues from the Karolinska Institutet in Stockholm. Because of the long incubation stage of neurodegenerative diseases, “it is still unclear whether infection constitutes a risk factor or merely a comorbidity or secondary event,” the authors wrote.

Dr Jiangwei and colleagues examined the association between the risk for the 3 most common neurodegenerative diseases (Alzheimer disease, Parkinson disease, or amyotrophic lateral sclerosis [ALS]) and prior inpatient or outpatient episodes of hospital-treated infections (1970 to 2016). For each case (291,941 Alzheimer disease cases; 103,919 Parkinson disease cases; and 10,161 ALS cases), 5 controls randomly selected from the general population were matched based on sex and year of birth.

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The researchers found that a hospital-treated infection 5 or more years prior was associated with an increased risk for Alzheimer disease and Parkinson disease. Results were similar across bacterial, viral, and other infections, as well as among different sites of infection, including gastrointestinal and genitourinary infections. The greatest risk for Alzheimer disease and Parkinson disease was seen for multiple infections before age 40 years. The associations were driven by Alzheimer disease and Parkinson disease diagnosed before age 60 years. There was no association observed between hospital-treated infection and the risk for Alzheimer disease or Parkinson disease diagnosis at or after 60 years of age. No association was observed between infection and ALS, regardless of age at diagnosis.

“These findings suggest that infectious events may be a trigger or amplifier of a preexisting disease process, leading to clinical onset of neurodegenerative disease at a relatively early age,” the authors wrote. “However, due to the observational nature of the study, these results do not formally prove a causal link.”

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