WEDNESDAY, Sept. 28, 2022 (HealthDay News) — Hospital-treated infections, especially repeated infections in early life and midlife, are associated with increased risks for Alzheimer disease (AD) and Parkinson disease (PD), according to a study published online Sept. 15 in PLOS Medicine.

Jiangwei Sun, Ph.D., from the Karolinska Institutet in Stockholm, and colleagues examined the association between the risk for the three most common neurodegenerative diseases (AD, PD, or amyotrophic lateral sclerosis [ALS]) and prior inpatient or outpatient episodes of hospital-treated infections (1970 to 2016). For each case (291,941 AD cases; 103,919 PD cases; and 10,161 ALS cases), five controls randomly selected from the general population were matched based on sex and year of birth.

The researchers found that a hospital-treated infection five or more years prior was associated with an increased risk for AD and PD. 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 AD and PD was seen for multiple infections before age 40 years. The associations were driven by AD and PD diagnosed before age 60 years. There was no association observed between hospital-treated infection and the risk for AD or PD diagnosis at or after 60 years of age. There was also no association 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 write. “However, due to the observational nature of the study, these results do not formally prove a causal link.”

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