Implementing a FHIR Facade for a Clinical System Using Azure Health Data Services (AHDS)

Prerequisites

1. Azure Subscription: Ensure you have an active Azure subscription.
2. Set Up Azure Health Data Services: Deploy an instance of Azure API for FHIR or FHIR service in Azure Health Data Services.
3. Understand HL7 v2 and FHIR Standards: Familiarize yourself with HL7 v2 message structure and FHIR R4 resources.
4. Install Necessary Tools: Install the Azure CLI, FHIR Converter, and related dependencies.

Architecture Overview

Data Flow

1. HL7 v2 Messages → FHIR Service: HL7 v2 messages are ingested and converted to FHIR R4 bundles.
2. FHIR Server → Legacy System: Updates made in the FHIR server are converted back to HL7 v2 format and sent to the legacy system.

Key Components

• FHIR Service (Azure Health Data Services).
• FHIR Converter: Transforms HL7 v2 messages to FHIR R4 resources and vice versa.
• Event Hubs/Logic Apps: For message ingestion and routing.
• Custom APIs/Adapters: For bidirectional communication between the FHIR server and the legacy system.

Step 1: Ingest HL7 v2 Messages

1. Set Up an HL7 v2 Listener: Use Azure Logic Apps or Event Hubs to listen for incoming HL7 v2 messages from the legacy system. Example using Event Hubs: Configure an Event Hub namespace. Create a dedicated Event Hub for HL7 v2 messages.
2. Secure Message Transmission: Use TLS for secure communication. Configure authentication mechanisms such as Azure Managed Identity.
3. Validate HL7 v2 Messages: Use HL7 validators to ensure message integrity and compliance with HL7 standards.
4. Store Messages Temporarily: Use Azure Blob Storage or a queue for temporary storage, enabling reprocessing if needed.

Step 2: Convert HL7 v2 Messages to FHIR R4

1. Deploy the FHIR Converter: Use Azure’s FHIR Converter tool to transform HL7 v2 messages into FHIR R4 resources. Clone the FHIR Converter repository and deploy it in an Azure Function or App Service.
2. git clone https://github.com/microsoft/FHIR-Converter.git
3. Create Custom Mappings: Map HL7 v2 message segments (e.g., PID, OBX) to corresponding FHIR resources (e.g., Patient, Observation). Customize mappings using the FHIR Converter templates.
4. Test Conversions: Test sample HL7 v2 messages using the FHIR Converter API. Verify the generated FHIR bundles for accuracy.
5. Integrate with Logic Apps: Use Azure Logic Apps to invoke the FHIR Converter for each incoming HL7 v2 message. Pass the converted FHIR bundle to the Azure FHIR service.

Step 3: Store and Process FHIR Data

1. Configure the FHIR Service: Deploy the FHIR server using Azure Health Data Services. Set up SMART on FHIR applications if required.
2. Store FHIR Resources: Use the FHIR server’s API to store and manage resources such as Patient, Encounter, Observation, etc.
3. Implement Business Rules: Develop custom logic for resource validation, deduplication, and notifications using Azure Functions or other middleware.

Step 4: Update Clinical System from FHIR Service

1. Monitor Changes in FHIR Service: Use Azure Event Grid to subscribe to resource change events in the FHIR service. Capture create, update, or delete events for relevant resources.
2. Convert FHIR to HL7 v2: Configure the FHIR Converter to map FHIR resources back to HL7 v2 messages. Customize templates for HL7 v2 output.
3. Send HL7 v2 Messages: Use Logic Apps or Event Hubs to route the converted HL7 v2 messages back to the legacy system. Ensure the legacy system can receive and process these messages correctly.

Step 5: Implement Security and Compliance

1. Secure Data Transmission: Use HTTPS and OAuth 2.0 for FHIR API communication. Enable role-based access control (RBAC) for the FHIR service.
2. Ensure HIPAA/GDPR Compliance: Implement auditing for all FHIR transactions. Use Azure Monitor and Log Analytics for tracking data flows and identifying anomalies.
3. Encrypt Data: Use Azure Key Vault to manage encryption keys. Encrypt data at rest and in transit.

Step 6: Testing and Validation

1. Unit Tests: Validate individual components such as the FHIR Converter mappings and Logic Apps workflows.
2. Integration Tests: Simulate end-to-end data flow from the legacy system to the FHIR service and back.
3. Performance Tests: Test the system under load using Azure Load Testing tools.

Step 7: Monitoring and Maintenance

1. Set Up Monitoring: Use Azure Monitor and Application Insights to track performance and identify issues.
2. Automate Alerts: Configure alerts for failures in HL7 ingestion, FHIR conversions, or updates to the legacy system.
3. Routine Updates: Periodically update mappings, templates, and FHIR Converter components to comply with evolving standards.

Step 8: Deployment

Rollback Plan: Implement a rollback strategy for safe deployment.

Dev/Test/Prod Environments: Maintain separate environments for development, testing, and production. Use Azure DevOps or GitHub Actions for CI/CD pipelines.