Tuberculosis (TB)
Understanding TB infection, treatment and contact tracing
Tuberculosis (TB) is a serious infectious disease caused by the bacterium Mycobacterium tuberculosis. Although rates have fallen significantly in the UK over recent decades, TB remains one of the leading infectious disease killers worldwide, with around 4,500 new cases notified in England each year. TB is treatable and curable with appropriate antibiotics.
What is Tuberculosis?
TB is caused by Mycobacterium tuberculosis, a slow-growing, aerobic bacterium. It is spread person-to-person via airborne droplet nuclei — tiny particles released when someone with active pulmonary TB coughs, sneezes, or speaks. The bacterium can remain suspended in the air for hours. Not everyone exposed to TB becomes infected, and not everyone infected develops active disease. TB most commonly affects the lungs (pulmonary TB) but can affect almost any organ in the body — including the lymph nodes, spine (Pott's disease), kidneys, brain (TB meningitis) and abdomen. TB is a statutory notifiable disease in the UK — all confirmed and suspected cases must be notified to Public Health England (UKHSA).
Latent vs Active TB
After initial infection, most people's immune systems contain the bacteria without eliminating them — this is known as latent TB infection (LTBI). People with LTBI have no symptoms, are not infectious, and have a normal chest X-ray. However, the bacteria remain dormant and can reactivate years or decades later if immunity is weakened. Approximately 5–10% of people with LTBI will develop active TB during their lifetime, with the greatest risk in the first two years after infection. Active TB occurs when the immune system cannot contain the bacteria, which multiply and cause disease. Immunosuppression (HIV, steroids, anti-TNF therapy, transplantation), malnutrition, diabetes, and alcohol misuse significantly increase the risk of reactivation.
Symptoms
The hallmark symptoms of active pulmonary TB include a persistent cough lasting three or more weeks (which may produce blood-stained sputum — haemoptysis), night sweats, unexplained weight loss, and low-grade fever. Fatigue and loss of appetite are also common. These constitutional symptoms may develop insidiously over weeks to months. Extrapulmonary TB presents with organ-specific symptoms: swollen lymph nodes (most common extrapulmonary site), back pain and neurological symptoms in spinal TB, haematuria and loin pain in renal TB, and headache, photophobia and neck stiffness in TB meningitis. A high index of suspicion is needed in high-risk groups — including people born in high-incidence countries, immunosuppressed individuals, and homeless or prison populations.
Diagnosis
Diagnosis of active TB typically requires microbiological confirmation. Three sputum samples for acid-fast bacilli (AFB) smear and Mycobacterium tuberculosis culture should be obtained on consecutive days. Culture (on Lowenstein–Jensen media or MGIT liquid culture) remains the gold standard but takes 4–8 weeks for a result; rapid molecular tests (GeneXpert MTB/RIF) can detect M. tuberculosis and rifampicin resistance within 2 hours. Chest X-ray typically shows upper lobe infiltrates, cavitation or hilar lymphadenopathy. CT chest provides more detail. For latent TB, NICE NG33 recommends the tuberculin skin test (Mantoux test — 2TU PPD) and/or interferon-gamma release assay (IGRA, such as QuantiFERON-TB Gold or T-SPOT.TB). IGRAs are preferred in BCG-vaccinated individuals as they are not affected by prior BCG. Bronchoscopy with BAL, biopsy of lymph nodes, or lumbar puncture may be needed for extrapulmonary or smear-negative cases.
Treatment — RIPE Regimen
Active TB is treated with a standard four-drug regimen known by the mnemonic RIPE: Rifampicin, Isoniazid, Pyrazinamide, and Ethambutol — all taken daily for the first 2 months (intensive phase). This is followed by a continuation phase of Rifampicin and Isoniazid daily for a further 4 months (total 6 months for pulmonary TB). CNS TB (including TB meningitis) requires 12 months of treatment. Treatment is directly observed therapy (DOT) for high-risk patients. All patients on isoniazid should receive pyridoxine 10–25 mg daily to prevent peripheral neuropathy. Rifampicin is a potent enzyme inducer — it significantly reduces the efficacy of many medications including oral contraceptives, warfarin, antiretrovirals and corticosteroids; drug interactions must be carefully reviewed. Liver function tests should be checked at baseline and monitored during treatment as all RIPE drugs can cause hepatotoxicity. Ethambutol requires baseline visual acuity and colour vision testing, with ongoing monitoring, as it can cause optic neuritis.
BCG Vaccine
The Bacille Calmette–Guérin (BCG) vaccine provides significant protection against severe and disseminated forms of TB, including TB meningitis in children (up to 80% efficacy). In the UK, the neonatal BCG programme targets babies at higher risk of TB — those born in areas with high TB incidence (>40 per 100,000) or with a parent or grandparent born in a high-incidence country. BCG is a live vaccine and is contraindicated in immunosuppressed individuals. It is given as a single intradermal injection in the left upper arm. It does not reliably prevent pulmonary TB in adults and does not prevent LTBI reactivation — hence it does not alter the requirement for IGRA screening in contacts.
Contact Tracing
Contact tracing is a mandatory component of TB control in the UK, coordinated by the local TB Health Protection Team (HPT). Close contacts of smear-positive pulmonary TB cases (those sharing household or prolonged indoor exposure) undergo screening with chest X-ray and IGRA/Mantoux testing. NICE NG33 defines close contacts as those sharing the same household, or having face-to-face contact for more than 8 hours (or total 40 hours) in an enclosed space. Contacts found to have LTBI are offered preventive treatment — isoniazid for 6 months, or rifampicin plus isoniazid for 3 months (3HR). Contacts with active TB are started on full treatment. Employers, schools and health settings may require workplace contact tracing in the event of a case. All cases must be notified to the local authority designated officer (LADO) via the HPT.