{
  "schema_version": "2.0.0",
  "id": "davis-2021-longcovid",
  "name": "Patient-Led Long COVID international cohort (Davis 2021)",
  "aliases": [
    "Patient-Led Research Collaborative Long COVID survey"
  ],
  "outbreak_event": "COVID-19 pandemic (onset before June 2020)",
  "pathogen_id": "sars-cov-2",
  "pathogen_class": "virus",
  "exposure_ascertainment": "mixed",
  "design": "survey",
  "denominator_defined": "no",
  "denominator_method": null,
  "recruitment_source": "patient_organisation",
  "time_zero_definition": "Self-reported onset of suspected or confirmed COVID-19 (illness lasting >28 days, onset prior to June 2020)",
  "time_zero_precision": "week",
  "control_group": "none",
  "control_matching_variables": [],
  "n_source_population": null,
  "n_enrolled": 3762,
  "n_analysed": 3762,
  "followups": [
    {
      "months": 6,
      "n_assessed": null,
      "n_lost": null
    },
    {
      "months": 7,
      "n_assessed": null,
      "n_lost": null
    }
  ],
  "max_followup_months": 7,
  "instruments": [
    "somatic-symptom-self-report"
  ],
  "case_definition": "none",
  "pem_assessed": "yes_single_item",
  "objective_measures": [
    "none"
  ],
  "specimens_collected": false,
  "specimen_types": [],
  "acute_phase_specimens": "no",
  "storage": null,
  "biobank_status": "not_applicable",
  "consent_future_use": "none",
  "external_access": "unknown",
  "contact": null,
  "registration_id": null,
  "funders": [
    "Patient-Led Research Collaborative (self-funded)"
  ],
  "conflicts": "Authors were members of the patient-led group and many were themselves Long COVID patients.",
  "data_availability": "Aggregate data reported in supplement.",
  "notes": "Deliberately included as a methodologically weak but historically pivotal cohort: a large (n=3762, 56 countries) self-selected online convenience sample recruited through patient support communities, with no control group, no laboratory confirmation for most respondents, and self-reported outcomes. Its breadth of symptom characterisation (203 symptoms across 10 organ systems) is unmatched, but the design cannot estimate population prevalence. Useful in the gap matrix to contrast against denominator-defined cohorts.",
  "publications": [
    {
      "id": "davis-2021",
      "title": "Characterizing long COVID in an international cohort: 7 months of symptoms and their impact",
      "authors": "Davis HE, Assaf GS, McCorkell L, et al.",
      "year": 2021,
      "journal": "EClinicalMedicine",
      "doi": "10.1016/j.eclinm.2021.101019",
      "pmid": "34308300",
      "url": "https://pubmed.ncbi.nlm.nih.gov/34308300/",
      "open_access": true,
      "is_primary_cohort_paper": true
    }
  ],
  "symptom_inventory_scope": "comprehensive_inventory",
  "n_symptoms_queried": 203,
  "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": "davis-fatigue-6mo",
      "cohort_id": "davis-2021-longcovid",
      "publication_id": "davis-2021",
      "schema_version": "2.0.0",
      "measure_id": "sym:fatigue",
      "measure_verbatim": "fatigue reported among respondents symptomatic after month 6",
      "population": {
        "scope": "whole_cohort",
        "stratum": null,
        "denominator_basis": "unclear",
        "n_assessed": {
          "status": "measured_not_reported"
        }
      },
      "timing": {
        "timepoint_months": 6,
        "timepoint_band": "3-6mo",
        "reference_period": "not_reported",
        "is_cumulative": false
      },
      "method": {
        "ascertainment": "unclear",
        "instrument_id": "somatic-symptom-self-report",
        "severity_threshold": null,
        "blinded_assessment": "not_reported"
      },
      "value": {
        "type": "proportion",
        "numerator": {
          "status": "measured_not_reported"
        },
        "denominator": {
          "status": "measured_not_reported"
        },
        "percent": 80.0,
        "ci": [
          78.5,
          81.6
        ],
        "precision": "approximate"
      },
      "comparator": {
        "group": "none",
        "value": {
          "status": "not_applicable"
        },
        "effect": null
      },
      "harmonised": null,
      "provenance": {
        "source_locator": "Results (most likely symptoms after month 6)",
        "extracted_by": null,
        "extracted_on": null,
        "verified_by": "OSMF research-tracker (web-verified against source)",
        "verified_on": "2026-07-20",
        "extraction_method": "manual"
      }
    },
    {
      "id": "davis-pem-6mo",
      "cohort_id": "davis-2021-longcovid",
      "publication_id": "davis-2021",
      "schema_version": "2.0.0",
      "measure_id": "sym:post-exertional-malaise",
      "measure_verbatim": "post-exertional malaise reported among respondents symptomatic after month 6",
      "population": {
        "scope": "whole_cohort",
        "stratum": null,
        "denominator_basis": "unclear",
        "n_assessed": {
          "status": "measured_not_reported"
        }
      },
      "timing": {
        "timepoint_months": 6,
        "timepoint_band": "3-6mo",
        "reference_period": "not_reported",
        "is_cumulative": false
      },
      "method": {
        "ascertainment": "unclear",
        "instrument_id": "somatic-symptom-self-report",
        "severity_threshold": null,
        "blinded_assessment": "not_reported"
      },
      "value": {
        "type": "proportion",
        "numerator": {
          "status": "measured_not_reported"
        },
        "denominator": {
          "status": "measured_not_reported"
        },
        "percent": 73.3,
        "ci": [
          71.5,
          75.1
        ],
        "precision": "approximate"
      },
      "comparator": {
        "group": "none",
        "value": {
          "status": "not_applicable"
        },
        "effect": null
      },
      "harmonised": null,
      "provenance": {
        "source_locator": "Results (most likely symptoms after month 6)",
        "extracted_by": null,
        "extracted_on": null,
        "verified_by": "OSMF research-tracker (web-verified against source)",
        "verified_on": "2026-07-20",
        "extraction_method": "manual"
      }
    },
    {
      "id": "davis-cognitive-6mo",
      "cohort_id": "davis-2021-longcovid",
      "publication_id": "davis-2021",
      "schema_version": "2.0.0",
      "measure_id": "sym:cognitive-dysfunction",
      "measure_verbatim": "cognitive dysfunction reported among respondents symptomatic after month 6",
      "population": {
        "scope": "whole_cohort",
        "stratum": null,
        "denominator_basis": "unclear",
        "n_assessed": {
          "status": "measured_not_reported"
        }
      },
      "timing": {
        "timepoint_months": 6,
        "timepoint_band": "3-6mo",
        "reference_period": "not_reported",
        "is_cumulative": false
      },
      "method": {
        "ascertainment": "unclear",
        "instrument_id": "somatic-symptom-self-report",
        "severity_threshold": null,
        "blinded_assessment": "not_reported"
      },
      "value": {
        "type": "proportion",
        "numerator": {
          "status": "measured_not_reported"
        },
        "denominator": {
          "status": "measured_not_reported"
        },
        "percent": 58.4,
        "ci": [
          56.5,
          60.2
        ],
        "precision": "approximate"
      },
      "comparator": {
        "group": "none",
        "value": {
          "status": "not_applicable"
        },
        "effect": null
      },
      "harmonised": null,
      "provenance": {
        "source_locator": "Results (most likely symptoms after month 6)",
        "extracted_by": null,
        "extracted_on": null,
        "verified_by": "OSMF research-tracker (web-verified against source)",
        "verified_on": "2026-07-20",
        "extraction_method": "manual"
      }
    },
    {
      "id": "davis-work-7mo",
      "cohort_id": "davis-2021-longcovid",
      "publication_id": "davis-2021",
      "schema_version": "2.0.0",
      "measure_id": "func:unable-to-work",
      "measure_verbatim": "not working at time of survey due to illness (a further 45.2% required a reduced work schedule)",
      "population": {
        "scope": "whole_cohort",
        "stratum": null,
        "denominator_basis": "unclear",
        "n_assessed": {
          "status": "measured_not_reported"
        }
      },
      "timing": {
        "timepoint_months": 7,
        "timepoint_band": "6-12mo",
        "reference_period": "not_reported",
        "is_cumulative": false
      },
      "method": {
        "ascertainment": "unclear",
        "instrument_id": "somatic-symptom-self-report",
        "severity_threshold": null,
        "blinded_assessment": "not_reported"
      },
      "value": {
        "type": "proportion",
        "numerator": {
          "status": "measured_not_reported"
        },
        "denominator": {
          "status": "measured_not_reported"
        },
        "percent": 22.3,
        "ci": null,
        "precision": "approximate"
      },
      "comparator": {
        "group": "none",
        "value": {
          "status": "not_applicable"
        },
        "effect": null
      },
      "harmonised": null,
      "provenance": {
        "source_locator": "Results (employment impact)",
        "extracted_by": null,
        "extracted_on": null,
        "verified_by": "OSMF research-tracker (web-verified against source)",
        "verified_on": "2026-07-20",
        "extraction_method": "manual"
      }
    },
    {
      "id": "davis-fatigue-6mo-sf",
      "cohort_id": "davis-2021-longcovid",
      "publication_id": "davis-2021",
      "schema_version": "2.0.0",
      "measure_id": "sym:fatigue",
      "measure_verbatim": "fatigue",
      "population": {
        "scope": "subgroup",
        "stratum": null,
        "denominator_basis": "symptomatic_subset",
        "n_assessed": 3762
      },
      "timing": {
        "timepoint_months": 6,
        "timepoint_band": "3-6mo",
        "reference_period": "current",
        "is_cumulative": false
      },
      "method": {
        "ascertainment": "structured_checklist",
        "instrument_id": "somatic-symptom-self-report",
        "severity_threshold": null,
        "blinded_assessment": "not_reported"
      },
      "value": {
        "type": "proportion",
        "numerator": {
          "status": "measured_not_reported"
        },
        "denominator": 3762,
        "percent": 80.0,
        "ci": [
          78.5,
          81.6
        ],
        "precision": "approximate"
      },
      "comparator": {
        "group": "none",
        "value": {
          "status": "not_applicable"
        },
        "effect": null
      },
      "harmonised": null,
      "provenance": {
        "source_locator": "Results, symptoms after month 6 (fatigue 80.0%, 95% CI 78.5-81.6)",
        "extracted_by": null,
        "extracted_on": null,
        "verified_by": "OSMF research-tracker (web-verified against source)",
        "verified_on": "2026-07-20",
        "extraction_method": "manual"
      }
    },
    {
      "id": "davis-pem-6mo-sf",
      "cohort_id": "davis-2021-longcovid",
      "publication_id": "davis-2021",
      "schema_version": "2.0.0",
      "measure_id": "sym:post-exertional-malaise",
      "measure_verbatim": "post-exertional malaise",
      "population": {
        "scope": "subgroup",
        "stratum": null,
        "denominator_basis": "symptomatic_subset",
        "n_assessed": 3762
      },
      "timing": {
        "timepoint_months": 6,
        "timepoint_band": "3-6mo",
        "reference_period": "current",
        "is_cumulative": false
      },
      "method": {
        "ascertainment": "structured_checklist",
        "instrument_id": "somatic-symptom-self-report",
        "severity_threshold": null,
        "blinded_assessment": "not_reported"
      },
      "value": {
        "type": "proportion",
        "numerator": {
          "status": "measured_not_reported"
        },
        "denominator": 3762,
        "percent": 73.3,
        "ci": [
          71.5,
          75.1
        ],
        "precision": "approximate"
      },
      "comparator": {
        "group": "none",
        "value": {
          "status": "not_applicable"
        },
        "effect": null
      },
      "harmonised": null,
      "provenance": {
        "source_locator": "Results, symptoms after month 6 (post-exertional malaise 73.3%, 95% CI 71.5-75.1)",
        "extracted_by": null,
        "extracted_on": null,
        "verified_by": "OSMF research-tracker (web-verified against source)",
        "verified_on": "2026-07-20",
        "extraction_method": "manual"
      }
    },
    {
      "id": "davis-cognitive-6mo-sf",
      "cohort_id": "davis-2021-longcovid",
      "publication_id": "davis-2021",
      "schema_version": "2.0.0",
      "measure_id": "sym:cognitive-dysfunction",
      "measure_verbatim": "cognitive dysfunction",
      "population": {
        "scope": "subgroup",
        "stratum": null,
        "denominator_basis": "symptomatic_subset",
        "n_assessed": 3762
      },
      "timing": {
        "timepoint_months": 6,
        "timepoint_band": "3-6mo",
        "reference_period": "current",
        "is_cumulative": false
      },
      "method": {
        "ascertainment": "structured_checklist",
        "instrument_id": "somatic-symptom-self-report",
        "severity_threshold": null,
        "blinded_assessment": "not_reported"
      },
      "value": {
        "type": "proportion",
        "numerator": {
          "status": "measured_not_reported"
        },
        "denominator": 3762,
        "percent": 58.4,
        "ci": [
          56.5,
          60.2
        ],
        "precision": "approximate"
      },
      "comparator": {
        "group": "none",
        "value": {
          "status": "not_applicable"
        },
        "effect": null
      },
      "harmonised": null,
      "provenance": {
        "source_locator": "Results, symptoms after month 6 (cognitive dysfunction 58.4%, 95% CI 56.5-60.2)",
        "extracted_by": null,
        "extracted_on": null,
        "verified_by": "OSMF research-tracker (web-verified against source)",
        "verified_on": "2026-07-20",
        "extraction_method": "manual"
      }
    }
  ]
}