Lucan · Conditions

Tuberculosis

Australian guidance: AU National TB Advisory Committee Guidelines + eTG Antibiotic

1. Definition and epidemiology

Tuberculosis (TB) is an infectious disease caused by Mycobacterium tuberculosis, a slow-growing aerobic bacillus transmitted via airborne droplet nuclei. In Australia, TB is relatively uncommon, with annual incidence remaining below 7 per 100,000 population since the 1980s; however, more than 85% of notified cases occur in overseas-born individuals, with a rate of 18.4/100,000 in overseas-born Australians compared with 0.7/100,000 in non-Indigenous Australian-born people. Latent TB infection (LTBI) is common in refugee and humanitarian entrant cohorts, with Australian studies reporting LTBI prevalence of 7 to 71% in resettled refugee populations.

2. Pathophysiology

Following inhalation of aerosolised droplets, M. tuberculosis reaches the alveoli where it is engulfed by alveolar macrophages. Rather than being destroyed, the organism resists phagolysosomal fusion through production of cord factor and other virulence determinants. An initial Ghon focus forms in the lung parenchyma; draining lymph node involvement produces the Ghon complex. In immunocompetent hosts, a T helper 1 (Th1) cell-mediated granulomatous response containing caseous necrosis walls off the organism, producing LTBI. The person remains asymptomatic and non-infectious. If cellular immunity is overwhelmed or impaired (per Robbins Ch 8), viable bacilli persist within granulomata and may reactivate years or decades later, producing progressive cavitating pulmonary disease or haematogenous dissemination to extrapulmonary sites including lymph nodes, meninges, kidneys, bone, and the adrenal glands. The lifetime risk of reactivation from LTBI is approximately 5 to 10% in immunocompetent individuals; this rises to an estimated 100% in untreated HIV coinfection.

3. Clinical presentation and diagnostic criteria

LTBI is by definition asymptomatic and non-infectious. Active pulmonary TB classically presents with a productive chronic cough lasting more than three weeks, haemoptysis, fever, drenching night sweats, anorexia, and weight loss. Fatigue and failure to thrive or poor growth are prominent features in paediatric cases. Lymphadenopathy, particularly cervical or axillary, is common and raises concern for both pulmonary and extrapulmonary disease. In the early stages of pulmonary disease, respiratory symptoms may be subtle or absent. Extrapulmonary TB accounts for a higher proportion of total TB cases in overseas-born individuals than in Australian-born people, and can affect virtually any organ. Miliary TB and tuberculous meningitis are the most serious manifestations and are disproportionately common in children under five years. TB is a notifiable disease in all Australian states and territories.

4. Investigations and AU-specific cutoffs

Active TB must be excluded before any LTBI workup or treatment. If active TB is suspected, refer urgently to specialist TB services and implement airborne infection control precautions; neither the Tuberculin Skin Test (TST) nor the Interferon Gamma Release Assay (IGRA) should be used to exclude active TB.

For suspected active pulmonary TB: chest x-ray (CXR) showing upper lobe cavitation, consolidation, or hilar lymphadenopathy; sputum microscopy for acid-fast bacilli (three samples on separate days); mycobacterial culture (gold standard, may take up to 8 weeks); nucleic acid amplification testing (NAAT/Xpert MTB/RIF) for rapid detection and rifampicin resistance screening.

For LTBI screening: all people from refugee-like backgrounds aged 35 years or younger should be offered LTBI testing, ideally within one month of arrival. The TST or blood IGRA may be used; TST is preferred for children under five years. IGRA may be preferable in individuals with prior BCG vaccination given after infancy, as BCG does not cause a false positive IGRA result.

AU-specific TST cutoffs: a positive TST is induration of 10 mm or greater in adults and children from high TB prevalence backgrounds. The threshold falls to 5 mm or greater in the setting of severe malnutrition, HIV infection, immunosuppression, or in children who are recent contacts of an active TB case. IGRA is not currently Medicare rebatable unless the person is immunosuppressed. CXR is required in anyone aged 11 years or older with a positive TST or IGRA; a post-arrival CXR is not needed if a recent migration CXR (within 3 months) is available and the person is asymptomatic.

Baseline liver function tests (LFTs) must be performed before commencing LTBI treatment.

5. Management

Active TB requires immediate notification to the relevant state or territory TB service and initiation of directly observed therapy (DOT). The standard regimen for drug-susceptible active pulmonary TB per eTG Antibiotic is: isoniazid plus rifampicin plus pyrazinamide plus ethambutol for two months (intensive phase), followed by isoniazid plus rifampicin for four months (continuation phase), giving a total of six months. Drug susceptibility testing must guide therapy; multidrug-resistant TB (MDR-TB), defined as resistance to at least isoniazid and rifampicin, requires specialist management with second-line agents and prolonged treatment. The rate of MDR-TB in Australia remains low at approximately 2% of bacteriologically confirmed cases.

For LTBI, treatment should only begin after active disease is excluded and is administered by experienced clinicians in coordination with a state TB service. The first-line preventive regimen per the National TB Advisory Committee (NTAC) is isoniazid 10 mg/kg/day (maximum 300 mg daily) for 6 to 9 months, pregnancy category A. Shorter rifamycin-containing regimens are effective alternatives (pregnancy category C). LTBI treatment significantly reduces the individual risk of subsequent active TB and is recommended unless contraindicated. Relative contraindications include significant liver disease, older age, and anticipated poor adherence. Pyridoxine 6.25 to 25 mg/day by age (not per kg) should be co-prescribed to prevent isoniazid-induced peripheral neuropathy in malnourished individuals. LTBI treatment is not compulsory and does not affect visa or asylum claim outcomes in Australia.

6. Pharmacology and AU PBS notes

First-line active TB drugs: isoniazid (INH), rifampicin, pyrazinamide, and ethambutol are all PBS-listed for TB treatment. Rifampicin is a potent CYP450 inducer with extensive drug interactions including oral contraceptives, antiretrovirals, and warfarin. Ethambutol causes dose-dependent optic neuritis; baseline and monthly visual acuity and colour vision testing are required.

LTBI first-line: isoniazid 10 mg/kg/day (maximum 300 mg) is PBS-listed. An alternative shorter course is 3 months of rifampicin plus isoniazid (3RH) or 4 months of rifampicin alone (4R), which have improved completion rates and are effective for preventive therapy.

Second-line agents for MDR-TB (used only under specialist guidance): fluoroquinolones (levofloxacin, moxifloxacin), bedaquiline (PBS listed under Section 100 Authority), linezolid, clofazimine, and cycloserine. BCG vaccine (Sanofi-Aventis Australia is registered but currently unavailable; BCG Vaccine SSI from Statens Serum Institut Denmark is available via state and territory TB services) is recommended for selected high-risk groups including Aboriginal and Torres Strait Islander children in high-incidence regions, and healthcare workers at high risk of exposure to drug-resistant TB.

7. Complications and monitoring

Active TB complications include: cavitation with haemoptysis, pneumothorax, tuberculous pleuritis and empyema, miliary dissemination with multiorgan failure, tuberculous meningitis (associated with high mortality and severe neurological sequelae), Pott disease (vertebral TB), Addison disease from adrenal involvement, and immune reconstitution inflammatory syndrome (IRIS) in HIV coinfected patients commenced on antiretroviral therapy.

During LTBI treatment with isoniazid, monitoring includes: LFTs at baseline and at 4 to 6 weekly intervals in those with pre-existing liver disease or age over 35 years; clinical review for hepatotoxicity symptoms (anorexia, nausea, jaundice, dark urine, pale stools, right upper quadrant pain); peripheral neuropathy symptoms. An asymptomatic rise in LFTs of up to 3 times the upper limit of normal does not mandate treatment cessation, but symptomatic hepatitis requires immediate drug withdrawal.

For active TB: monthly clinical review during treatment; repeat sputum cultures at 2 months to confirm culture conversion; CXR at completion of treatment. Contacts of active cases require screening with TST or IGRA and CXR. Children who are close contacts of any active pulmonary TB case should be assessed by a paediatric specialist given the higher risk of rapid progression to severe disease.

Written for Australian practice and grounded in the guidance named above. Study material only — not medical advice. Always check against current guidelines.