Influenza infection is associated with increased risk for Parkinson disease (PD) more than 10 years after infection, according to study results published in JAMA Neurology.
Results of previous studies on the association between infection and risk for PD were mixed. The objective of the current study was to determine the link between influenza and other infections with PD more than 10 years after infection.
Using data from the Danish National Patient Registry from 1977 to 2016, a total of 10,271 patients (38.7% women; mean age, 71.4 years) diagnosed with PD between January 1, 2000, and December 31, 2016, were identified. Patients with PD were matched for age and sex to 51,355 controls without PD.
Data on influenza diagnoses were collected from inpatient and outpatient hospital clinics in the Danish National Registry from 1977 through 2016. The median number of diagnoses per month was calculated and months with more than 3-fold the median were identified as peaks.
Conditional logistic regression was used to calculate the association between infection and PD overall and according to the time between the infection and PD: more than 10 years, 10-15 years, and more than 15 years.
Influenza diagnosed at any time during a calendar year was associated with PD more than 10 years later (odds ratio [OR], 1.73; 95% CI, 1.11-2.71) after adjusting for cardiovascular disease, diabetes, chronic obstructive pulmonary disease, emphysema, lung cancer, Crohn’s disease, and ulcerative colitis. The risk was higher with a greater time from infection and for more than 15 years the adjusted OR was 1.91 (95% CI, 1.14-3.19; P =.01).
When influenza exposure was restricted to months of highest influenza activity, the risk was still elevated at more than 10 years, but with a wider confidence interval (OR, 1.52; 95% CI, 0.80-2.89; P =.21).
There was no evidence of an association with any type of infection more than 10 years prior to PD (OR, 1.04; 95% CI, 0.98-1.10).
For any type of infection, the overall result suggested increased odds of PD within 5 years of infection (OR, 1.27; 95% CI, 1.18-1.38), but results were null when exposure occurred more than 10 years prior (OR, 1.04; 95% CI, 0.98-1.10).
Several specific infections showed an increased OR for PD within 5 years, but most associations appeared to be null after more than 10 years, including pneumonia, gastrointestinal infection, miscellaneous bacterial infections, septicemia, and male genital infections.
The study had several limitations, including lack of laboratory confirmation of infections, inclusion limited to infections diagnosed in a hospital or hospital-associated outpatient clinic, and potential residual confounders.
“These observational data suggest a link between influenza and Parkinson disease but do not demonstrate causality. While other infections were associated with Parkinson disease diagnoses soon after infection, null associations after more than 10 years suggest these shorter-term associations are not causal,” concluded the researchers.
Cocoros NM, Svensson E, Szépligeti SK, et al. Long-term risk of Parkinson disease following influenza and other infections. JAMA Neurol. Published online October 25, 2021. doi: 10.1001/jamaneurol.2021.3895.