Table 5.

Observational studies of comparative frequency of associated Helicobacter and idiopathic parkinsonism and its age relationship.

Study	Ascertainment of Helicobacter Positivity	Country	Number Participants or Samples	Participant/Sample Source	Findings
Dobbs et al. (2000) [62]	Anti-urease-IgG serology (ELISA)	UK	105 with IP, 210 controls	Call for volunteers with and without IP followed by screening for inclusion/exclusion criteria.	Controls showed birth cohort effect. Having IP obliterated this. Higher frequency of Helicobacter-positive, up to 72.5 years, in IP than in controls.
Weller et al. (2005) [52]	Immunoblot serology Anti-urease-IgG serology (ELISA)	UK	124 with IP, 196 without	Consecutive IP patients attending clinic and consecutive responders to call for healthy volunteers from same locality. Similar inclusion/exclusion criteria applied to both, except diagnosed IP an exclusion in controls.	Controls showed a birth cohort effect for odds of having VacA antibody. Having IP obliterated this. Predicted probability of IP greatest with CagA-positivity, VacA-negativity and urease-B negativity. Discrimination not complemented by ELISA.
Nielsen et al. (2012) [63]	Helicobacter eradication course	Denmark	4484 with IP, 22416 controls	Danish National Patient Register for diagnosis IP, dated to first prescription IP drug. National Prescription Registry. Index date for IP diagnosis between 2001 and 2008, eradication date from 1995. Danish Civil Registration System source of 5 matched controls per IP patient.	Frequency of historical Helicobacter eradication increased in IP, even when only eradications ≥5 years prior to IP assessed.
Blaecher et al. (2013) [64]	For H. pylori: culture and PCR in culture negative For H. suis: PCR.	UK	60 DNA extracts from people with IP, 256 DNA extracts from people attending endoscopy departments	Serial archived DNA extracts from Helicobacter Reference Laboratory, Public Health England, with selection for adequate documentation and whether from IP clinic or not.	Relative risk of H. suis compared with H. pylori 10 times greater in IP than in controls.
Fasano et al. (2013) [60]	UBT	Italy	33 with IP, 30 spouses of IP probands	Consecutive IP patients attending a hospital and their spouses.	Similar frequency of Helicobacter positivity in IP and spouses.
Bu et al. (2005) [54]	Anti-urease-IgG serology (ELISA)	China	131 IP, 141 controls	Consecutive IP patients attending a hospital. Controls randomly recruited from hospital’s clinics over same period.	Higher frequency of Helicobacter positivity in IP.
Esmael et al. (2016) [56]	Anti-urease-IgG serology (ELISA)	Egypt	50 with IP, 20 controls	IP patients from neurology outpatients. Age and gender matched controls with no diagnosed neurological disease.	Higher frequency of Helicobacter positivity in IP.
Huang et al. (2018) [65]	Endoscopic-biopsy, with UBT where endoscopy not tolerated	Taiwan	9186 Helicobacter-positive (reduced to 9105 after matching), 9105 Helicobacter-negative	“2000 Longitudinal Health Insurance Database”. Propensity score matching based on age, sex, income, urbanization, comorbidities, medication). Index date 2000 to 2011 inclusive. Follow-up until IP diagnosis, death or latest 2012.	Increased estimated incidence IP in Helicobacter-positive ≥60 years, irrespective of eradication therapy.
Roshan et al. (2018) [57]	Anti-urease-IgG serology (ELISA)	Iran	99 with IP, 297 controls Exclusion if history of Helicobacter eradication	Consecutive IP patients in neurology clinic. “Amirkola Health and Ageing Project”: three controls, with no history of IP drugs, matched to each IP proband for age and gender.	Lower frequency of Helicobacter positivity in IP.