Visit Occurrence

Epic equivalent: Encounter table / ADT (Admit-Discharge-Transfer)

The visit_occurrence table captures each encounter a patient has with the healthcare system — outpatient visits, inpatient admissions, ER encounters, telehealth, and more. This is the closest thing to Epic's encounter table in OMOP.

Each row is a distinct episode of care. Other clinical tables (condition_occurrence, drug_exposure, measurement, etc.) can link to visit_occurrence_id to anchor events to a specific encounter.

Epic-to-OMOP Field Mapping

Field reference (click to expand)

OMOP Field	Epic Equivalent	What It Captures
visit_occurrence_id	Encounter ID (CSN)	Unique identifier for the visit
person_id	Patient ID / MRN	Links the visit to the patient
visit_concept_id	Encounter type	Standardized type: Inpatient, Outpatient, ER, etc.
visit_start_date, visit_end_date	Admit/Discharge or Check-in/Check-out	Visit boundaries; *_datetime variants have time precision
visit_type_concept_id	Data provenance	Whether from EHR, claims, etc.
provider_id	Attending / Ordering provider	Provider associated with the encounter
care_site_id	Hospital or clinic	Facility or department where the visit occurred
visit_source_value	Raw encounter type	Original EHR value (e.g., "Office Visit", "Inpatient")
admitting_source_concept_id	Admit source	Where the patient came from (home, SNF, ER)
discharge_to_concept_id	Discharge disposition	Where the patient went after (home, rehab, expired)

What to Watch For

Common pitfalls

Many rows per patient

Unlike person (one row), expect hundreds of rows per patient here — one for every encounter.

Same-day end dates

Outpatient visits often have visit_end_date = visit_start_date. Don't interpret this as zero-length visits — it's a data artifact.

Inconsistent provider/care_site

Not all source systems populate provider_id or care_site_id on every encounter. Cross-validate before running attribution analyses.

Research Patterns

Question	Tables Involved
Average outpatient visits per patient per year	visit_occurrence filtered by visit_concept_id (outpatient)
30-day hospital readmission rate	visit_occurrence with inpatient filter, self-join on person_id + date math
Discharge to skilled nursing facility rates	discharge_to_concept_id
Length of stay for cancer patients	visit_occurrence + condition_occurrence (cancer concepts)
ER visits preceding stroke hospitalizations	visit_occurrence (ER + inpatient) + condition_occurrence (stroke) + temporal ordering
Time between outpatient visits and hospitalizations	visit_occurrence self-join by person_id + visit_concept_id