{
  "schema_version": "2.0.0",
  "id": "walkerton-health-study",
  "name": "Walkerton Health Study (post-infectious IBS)",
  "aliases": [
    "WHS"
  ],
  "outbreak_event": "Walkerton waterborne gastroenteritis outbreak, May 2000 (Ontario, Canada)",
  "pathogen_id": "campylobacter-ecoli-walkerton",
  "pathogen_class": "mixed",
  "exposure_ascertainment": "clinical_diagnosis",
  "design": "retrospective_cohort",
  "denominator_defined": "yes",
  "denominator_method": "Adult Walkerton residents with no prior chronic GI disorder, classified by whether they had acute gastroenteritis during the May 2000 municipal water contamination; residents without acute GE form the unexposed comparison.",
  "recruitment_source": "community",
  "time_zero_definition": "May 2000 waterborne gastroenteritis outbreak (Campylobacter jejuni / E. coli O157:H7)",
  "time_zero_precision": "month",
  "control_group": "unexposed_unmatched",
  "control_matching_variables": [],
  "n_source_population": null,
  "n_enrolled": 2069,
  "n_analysed": 2069,
  "followups": [
    {
      "months": 24,
      "n_assessed": 2069,
      "n_lost": null
    },
    {
      "months": 96,
      "n_assessed": null,
      "n_lost": null
    }
  ],
  "max_followup_months": 96,
  "instruments": [
    "rome-criteria-ibs"
  ],
  "case_definition": "not_applicable",
  "pem_assessed": "no",
  "objective_measures": [
    "none"
  ],
  "specimens_collected": false,
  "specimen_types": [],
  "acute_phase_specimens": "no",
  "storage": null,
  "biobank_status": "not_applicable",
  "consent_future_use": "unknown",
  "external_access": "unknown",
  "contact": null,
  "registration_id": null,
  "funders": [
    "Ontario Ministry of Health and Long-Term Care",
    "Canadian Institutes of Health Research"
  ],
  "conflicts": null,
  "data_availability": null,
  "notes": "One of the strongest post-infectious cohorts in the database: a whole-community denominator with a within-town unexposed comparator, quantifying post-infectious IBS after bacterial gastroenteritis (36.2% after clinically suspected GE vs 10.1% without). Non-fatigue outcome (IBS), broadening the syndrome coverage. Exposure was ascertained by self-reported acute illness rather than culture, the main limitation.",
  "publications": [
    {
      "id": "marshall-2006",
      "title": "Incidence and epidemiology of irritable bowel syndrome after a large waterborne outbreak of bacterial dysentery",
      "authors": "Marshall JK, Thabane M, Garg AX, et al. (Walkerton Health Study Investigators)",
      "year": 2006,
      "journal": "Gastroenterology",
      "doi": "10.1053/j.gastro.2006.05.053",
      "pmid": "16890598",
      "url": "https://pubmed.ncbi.nlm.nih.gov/16890598/",
      "open_access": true,
      "is_primary_cohort_paper": true
    }
  ],
  "symptom_inventory_scope": "single_domain",
  "n_symptoms_queried": null,
  "symptom_instrument_note": null,
  "related_cohorts": [],
  "last_verified": "2026-07-20",
  "verified_by": "OSMF research-tracker (web-verified against source)",
  "harmonisation_ruleset": "pais-harmony-v1",
  "observations": [
    {
      "id": "walkerton-piibs-2yr",
      "cohort_id": "walkerton-health-study",
      "publication_id": "marshall-2006",
      "schema_version": "2.0.0",
      "measure_id": "sym:irritable-bowel-syndrome",
      "measure_verbatim": "post-infectious irritable bowel syndrome 2 years after outbreak in those with clinically suspected gastroenteritis vs those without acute gastroenteritis",
      "population": {
        "scope": "whole_cohort",
        "stratum": null,
        "denominator_basis": "unclear",
        "n_assessed": {
          "status": "measured_not_reported"
        }
      },
      "timing": {
        "timepoint_months": 24,
        "timepoint_band": "12-24mo",
        "reference_period": "not_reported",
        "is_cumulative": false
      },
      "method": {
        "ascertainment": "unclear",
        "instrument_id": "rome-criteria-ibs",
        "severity_threshold": null,
        "blinded_assessment": "not_reported"
      },
      "value": {
        "type": "proportion",
        "numerator": {
          "status": "measured_not_reported"
        },
        "denominator": {
          "status": "measured_not_reported"
        },
        "percent": 36.2,
        "ci": null,
        "precision": "approximate"
      },
      "comparator": {
        "group": "unexposed_unmatched",
        "value": {
          "type": "proportion",
          "percent": 10.1,
          "precision": "exact"
        },
        "effect": null
      },
      "harmonised": null,
      "provenance": {
        "source_locator": "Results/Abstract (36.2% with suspected GE vs 10.1% without)",
        "extracted_by": null,
        "extracted_on": null,
        "verified_by": "OSMF research-tracker (web-verified against source)",
        "verified_on": "2026-07-20",
        "extraction_method": "manual"
      }
    }
  ]
}