Latent Tuberculosis
Both tuberculin skin tests (TSTs) and interferon-gamma release assays (IGRAs) are acceptable screening methods for latent tuberculosis in refugee patients. The main disadvantage of TSTs is the poor rate of return for TST reading in some patients. This is not an issue with IGRA testing, since it only requires a one-time screening blood test. However, IGRAs require fresh blood samples and special laboratory installations, and are thus not readily available everywhere in Canada.
POSITIVE SCREENING TEST
If a patient has a positive TST or IGRA, order a chest X-ray to look for signs of tuberculosis:
| - Apicoposterior consolidation with or without cavitation - Mediastinal or hilar lymphadenopathy - Nodular changes - Pleural effusion |
The patient should also be assessed for any potential symptoms of active TB:
| - Cough for > 3 weeks - Fever - Night sweats - Weight loss - Hemoptysis |
→ If the patient has an abnormal chest X-ray or any of the above symptoms, a local TB specialist should be immediately contacted, as well as the relevant Public Health authority.
LATENT TB DIAGNOSIS
Patients who were initially screened with an IGRA and who tested positive can be diagnosed right away with latent TB if they have no symptom/sign of active TB.
However, for refugee patients who were initially screened with a TST and who tested positive, a follow-up IGRA is then usually performed in order to confirm the diagnosis of latent TB. This is because of the risk of false-positive TST results in the refugee population.
LATENT TB TREATMENT
Patients diagnosed with latent TB should be referred to a TB specialist for treatment. Shorter regimens are now usually the mainstay of treatment in many places. Examples include a 3 month course of daily self-administered isoniazid and rifampin, or a 4 month course of daily rifampin (usually for patients at higher risk of hepatotoxicity).
The TB specialist might send instructions to the family doctor regarding follow-up during treatment. Depending on the patient’s age and risk factors, monthly liver function tests can be recommended by the specialist. Compliance to latent TB treatment is often an issue in refugee patients and the family physician should play a role in monitoring adherence to treatment. Pill counts are probably the most reliable way to monitor compliance in this population.
During latent TB treatment, patients taking isoniazid should also be asked periodically about symptoms of hepatitis. Patients on rifampin should know that the drug typically causes an orange discoloration of bodily fluids. Also keep in mind that rifampin can interact with multiple other drugs.
>> Refer to the Canadian Tuberculosis Standards for more information on the interpretation of TSTs and IGRAs, the advantages/disadvantages of both methods, and the management of latent and active TB.