Risk for PD increases years after influenza infection

Patients infected with influenza are more likely to be diagnosed with Parkinson’s disease 10 years after infection when compared with controls, according to data published in JAMA Neurology.

“Whether influenza is associated with later development of Parkinson’s disease has been an open question for decades and originated from observations following the 1918 influenza pandemic,” Noelle M. Cocoros, DSc, MPH, research scientist at Harvard Pilgrim Health Care Institute and the Department of Population Medicine at Harvard Medical, told Healio. “More broadly, whether infections in general contribute to risk of Parkinson’s has been studied for some time. We examined whether prior infections, including influenza, are associated with Parkinson’s disease more than 10 years after infection.”

In a population-based case control study using data from the Danish National Patient Registry, Cocoros and colleagues identified 10,271 patients with incident inpatient or outpatient hospital-based diagnosis of PD from January 2000 through December 2016. A total of 51,355 control participants were matched according to age and sex with patients with PD in a 5-to-1 ratio. Patients with drug-induced secondary parkinsonism were excluded. Mean age of patients with PD was 71.4 years, with 86.3% aged older than 60 years at diagnosis.

Fewer patients with PD had chronic obstructive pulmonary disease or emphysema (6.5%) compared with controls (7.7%). However, both groups had a similar distribution of cardiovascular disease, diabetes, Crohn’s disease, ulcerative colitis and lung cancer, according to the study.

An increased odds ratio of 1.73 (95% CI, 1.11-2.71) was identified in the fully adjusted analysis when identifying influenza-specific codes in patients 10 years before PD diagnosis. The odds of PD manifesting after more than 15 years following an influenza infection was approximately 90%. Similar associations were not seen for pneumonia, other respiratory tract infections or most other infections, according to the study.

“Our population-based study included all Danish citizens diagnosed with Parkinson’s disease from 2000 through 2016,” Cocoros said. “We observed an association between influenza and Parkinson’s disease diagnosed more than 10 years after evidence of infection. Understanding the potential long-term consequences of influenza is important on both the patient and population level.”