Latent Tuberculosis Infection - Calgary Clinical Management Guide

Overview

Latent tuberculosis infection (LTBI) is common in refugees from high-prevalence countries. Detecting and treating LTBI prevents progression to active TB, which is infectious and potentially life-threatening. This guide covers the Calgary Refugee Health Program approach to LTBI screening, diagnosis, and treatment.

Who to Screen

*     All refugees aged 6 months to 50 years from countries with a TB incidence above 30 per 100,000 population

*     Screening up to age 65 is reasonable in patients with conditions that increase reactivation risk, such as diabetes, end-stage renal disease, or planned immunosuppression

*     Do NOT screen patients with a documented history of previously treated tuberculosis

*     Do NOT screen children under 2 years old with IGRA. Use TST for children aged 6 months to 2 years.

Screening Tests

Tuberculin Skin Test (TST)

Placed intradermally on the forearm. Read at 48-72 hours. A positive result in refugee patients is generally defined as induration of 10 mm or more.

Limitations: requires return visit for reading, false positives in BCG-vaccinated individuals, higher risk of patient not returning for read.

Interferon-Gamma Release Assay (IGRA)

A blood test that does not require a return visit. Preferred in BCG-vaccinated individuals as it is not affected by prior BCG vaccination.

In Calgary, IGRAs can only be ordered by TB Services, the Southern Alberta HIV Program, or the Calgary Refugee Health Program. If you do not have access to IGRA ordering, use TST and refer positive patients to TB Services for IGRA confirmation.

Ruling Out Active TB Before Treatment

Always rule out active TB before initiating LTBI treatment. Treating active TB with LTBI regimens leads to drug resistance.

Order a chest X-ray and assess for symptoms:

*     Cough lasting more than 3 weeks

*     Fever and night sweats

*     Unexplained weight loss

*     Hemoptysis

If the chest X-ray is abnormal OR the patient has any of the above symptoms, contact Calgary TB Services immediately before proceeding.

Calgary TB Services: Phone 403-955-6355

Confirming the Diagnosis

In Calgary, for refugee patients with a positive TST who have not had a prior IGRA, TB Services typically orders a follow-up IGRA to confirm the diagnosis. This helps reduce false-positive results, which are more common in BCG-vaccinated refugee populations.

Refer to TB Services using the Alberta TB Services Referral Form.

Treatment

TB Services manages LTBI treatment in Alberta and dispenses medications directly at their clinic, typically one month at a time. The two main regimens are:

Monitoring During Treatment

*     Monthly liver function tests are generally recommended

*     Ask patients on isoniazid about symptoms of hepatitis at each visit: nausea, vomiting, abdominal pain, jaundice, fatigue

*     Patients on rifampin: counsel that it causes orange discoloration of urine, sweat, tears, and contact lenses

*     Rifampin interacts with many medications. Review the full drug list including oral contraceptives, anticoagulants, and antiretrovirals.

Adherence

Adherence is often a challenge. Family physicians play an important role in monitoring:

*     Pill counts at each visit are a reliable way to assess adherence

*     Missed doses should be reported to TB Services promptly

*     Patients who miss more than 2 weeks of treatment may need to restart

Calgary Resources

*     TB Services referral form: albertahealthservices.ca/frm-07980.pdf

*     TB Services phone: 403-955-6355

*     Canadian Tuberculosis Standards (7th edition): canada.ca