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The study is based on data on individuals diagnosed with Alzheimer’s disease, Parkinson’s disease or ALS, from 1970-2016 in Sweden, as well as five matched controls per case randomly selected from the general population. The analysis included more than 290,000 Alzheimer’s disease cases, 100,000 Parkinson’s disease cases and 10,000 ALS cases.
The results show that a hospital-treated infection five or more years before diagnosis was associated with a 16 percent higher risk of Alzheimer’s disease and a 4 percent higher risk of Parkinson’s disease. The associations only applied to individuals diagnosed before the age of 60, whereas no association was found for those diagnosed later in life.
Highest risk with infections before 40
The highest risk of disease was seen in people with multiple hospital-treated infections before the age of 40, with more than doubled risk of Alzheimer’s disease and more than 40 percent increase in the risk of Parkinson’s disease.
No association was observed for ALS, regardless of age at diagnosis.
”These findings suggest that infectious events may be a trigger or amplifier of a pre-existing disease process, leading to clinical onset of neurodegenerative disease at a relatively early age,” says Jiangwei Sun, the study’s first author and postdoctoral researcher at the Department of Medical Epidemiology and Biostatistics, Karolinska Institutet.
However, he also points out that due to the observational nature of the study, these results do not formally prove a causal link.
The research was supported by the Swedish Research Council, the Joint Program on Neurodegenerative Diseases, and the Chinese Scholarship Council.