Repeat infections linked to increased risk of neurodegenerative diseases

People with hospitalized infections in early and midlife had the greatest risk of Alzheimer’s and Parkinson’s disease later in life.

Infections treated with specialist hospital care in early and midlife are associated with an increased later risk of Alzheimer’s disease (AD) and Parkinson’s disease (PD), but not amyotrophic lateral sclerosis (ALS). This is according to a new study published recently in the open access journal OLP Medicine by Jiangwei Sun of the Karolinska Institute, Sweden, and colleagues.

According to the CDC, approximately 6.5 million Americans are living with Alzheimer’s disease. Nearly one million people in the United States live with Parkinson’s disease, according to the Parkinson’s Foundation.

Experimental studies in animals have indicated that infection plays a role in the development of certain neurodegenerative diseases. However, supporting evidence in humans is limited. In the new study, the scientists used data on people diagnosed with AD, PD or ALS from 1970 to 2016 in Sweden, along with five case-matched controls, all identified from the Swedish National Patient Registry. The analysis included 291,941 AD cases, 103,919 PD cases and 10,161 ALS cases.

Infection treated in hospital 5 or more years before diagnosis was associated with a 16% increased risk of AD (95% CI: 1.15-1.18, P

Recurrent infections Increased risk of neurodegenerative diseases

Researchers assess the infection treated in the hospital and the risk of neurodegenerative diseases. Credit: Jiangwei Sun (CC-BY 4.0)

“These findings suggest that infectious events may be a trigger or amplifier of a pre-existing disease process, leading to the clinical onset of neurodegenerative disease at a relatively early age,” the authors state, while emphasizing that ” due to the observational nature of the study, these results do not formally prove a causal relationship.

Sun adds, “Infections treated in hospital, particularly in early and midlife, were associated with an increased risk of Alzheimer’s disease (AD) and Parkinson’s disease (PD), primarily among cases AD and PD diagnosed before age 60.

Reference: “Hospital-treated infections in early and mid-life and the risk of Alzheimer’s disease, Parkinson’s disease, and amyotrophic lateral sclerosis: a nationwide nested case-control study in Sweden” by Jiangwei Sun, Jonas F. Ludvigsson, Caroline Ingre, Fredrik Piehl, Karin Wirdefeldt, Ulrika Zagai, Weimin Ye and Fang Fang, September 15, 2022, PLoS medicine.
DOI: 10.1371/journal.pmed.1004092

Funding: This study was supported by the Swedish Research Council (Grant Nos. 2019-01088 (FF), 340-2013-5867 (FF) and 2017-02175 (KW)), Joint Program on Neurodegenerative Diseases ( JPND, grant number: 2021-00696 (FF)), and the Chinese Scholarship Council (JS). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Norma A. Roth