Tuberculosis

Reflects an emerging shift toward GP-led management of latent TB infection (LTBI) in Australia — TBI is a common condition in the Australian community that can be managed effectively in general practice for many people.

Epidemiology

Low prevalence in Australia; high prevalence of latent TB in many Asian countries. Latent TB infection (TBI) is more common in the Australian community than commonly appreciated — see the guideline-update box below.

High-risk patients (for active TB): newborns/infants, age >60, HIV/AIDS, crowded living conditions, immigrants/refugees from endemic countries (India, PNG, South-East Asia, sub-Saharan Africa, South Africa). If considering TB, also consider and test for HIV.

Classical presentation

Malaise + cough + weight loss + night sweats + fever ± haemoptysis suggests pulmonary TB — but presentation may be limited to extrapulmonary manifestations alone.

Disease stages

Primary TB: usually symptomless or accompanied by a vague feeling of being unwell with cough. Erythema nodosum may develop during primary infection.

Progressive primary TB: if the immune response is inadequate, symptoms progressively worsen. May spread haematogenously (miliary TB) to sites such as the meninges, bone, or pleura (causing effusion).

Latent TB infection (LTBI): presence of TB bacilli without evidence of active disease (no symptoms, normal CXR). The infection is walled off by macrophages and is not infectious in this state, but around 10% of people with LTBI go on to reactivate.

Post-primary (adult-type) pulmonary TB: most adult TB cases are reactivation of latent infection, driven by poor living conditions or immunosuppression (diabetes, immunosuppressive drugs, steroids, lymphoma, HIV).

TB in children: children in close contact with active TB cases are highly vulnerable to infection. 5–15% of children with latent TB develop active disease in their lifetime.

Diagnosis

• Tuberculin skin test (Mantoux) — screening test only; false negatives are an issue; takes 2–3 days to read; read the diameter of induration, not redness.
• Interferon-gamma release assay (IGRA) — blood test, lower false-negative rate than Mantoux.
• Chest X-ray — normal in LTBI, abnormal in active disease.
• Sputum for culture and acid-fast bacilli — at least 3 samples, ≥8 hours apart, one an early-morning sample; bronchoscopy may be needed to obtain a sample; culture takes up to 8 weeks. NAAT (PCR) for rifampicin resistance should be done before starting treatment.

BCG vaccination

Aim is to reduce rates of TB meningitis in children. Not routinely given in Australia. Consider in children at high risk of exposure (check the current Immunisation Handbook):

• Aboriginal and Torres Strait Islander infants in the NT, Qld and northern SA
• Children travelling to high-risk countries, risk-assessed by age (<5), length of stay, and destination incidence
• Infants born to parents with leprosy

Tuberculin skin testing is required before vaccination in anyone ≥6 months old — if positive, do not vaccinate. Vaccinate at least 3 months before possible exposure where practicable.

Treatment

Handled by specialists, based on culture susceptibilities — multidrug therapy is required to limit resistance.

Standard regimen for uncomplicated active TB:

• Intensive phase (2 months): rifampicin + isoniazid + pyrazinamide + ethambutol
• Continuation phase (4 months): rifampicin + isoniazid
• Pyridoxine 25 mg daily throughout isoniazid therapy, to prevent peripheral neuropathy

Latent TB infection — currently most commonly treated in Australia with rifampicin or isoniazid (as monotherapy regimens); rifapentine-based shorter/intermittent regimens (e.g. weekly isoniazid+rifapentine for 3 months) are used internationally but are not routinely accessible in Australia at present.