Link between increased risk of some neurodegenerative diseases and repeated infections

Infections treated with specialty hospital care in early- and mid-life are associated with an increased subsequent risk of Alzheimer's (AD) and Parkinson's diseases (PD), but not amyotrophic lateral sclerosis (ALS), according to a new study published in the open-access journal PLOS Medicine.

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

A hospital-treated infection 5 or more years before diagnosis was associated with a 16% higher risk of AD and a 4% higher risk of PD with similar risks seen for bacterial, viral, and other infections and for different sites of infection. The highest risk of disease was seen in people with multiple hospital-treated infections before the age of 40, with more than double the risk of AD and a more than 40% increase in the risk of PD. No association was observed for ALS, regardless of age at diagnosis.

Reference:

Sun J, Ludvigsson JF, Ingre C, Piehl F, Wirdefeldt K, Zagai U, et al. (2022) Hospital-treated infections in early- and mid-life and risk of Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis: A nationwide nested case-control study in Sweden. PLoS Med 19(9): e1004092.  https://doi.org/10.1371/journal.pmed.1004092