Infectious Disease

Tuberculosis

A chronic Mycobacterium tuberculosis complex infection that may remain latent or reactivate as active pulmonary or extrapulmonary disease, requiring microbiological diagnosis, multi-drug treatment and public-health contact tracing.

In a nutshell

TB may be latent and non-infectious or active and transmissible, usually presenting with chronic cough, fever, night sweats and weight loss but sometimes with extrapulmonary disease. Diagnose with site-appropriate imaging and microbiology, start specialist multi-drug treatment, notify active disease, trace contacts and treat latent infection only after active disease is excluded.

Classic presentation

A cough lasting more than 3 weeks with sputum or haemoptysis, fever, night sweats, fatigue, anorexia and weight loss, especially after exposure or in someone from a higher-incidence setting. Consider extrapulmonary TB in lymphadenopathy, meningitis, spinal disease, sterile pyuria or unexplained systemic illness.

Key points

Latent TB causes no symptoms and is not infectious; active pulmonary or laryngeal TB can transmit through the air.
A normal chest X-ray or negative smear does not exclude TB, particularly in early, extrapulmonary or immunosuppressed disease.
Send site-appropriate samples for culture and susceptibility with rapid molecular testing where indicated; culture remains essential for resistance information.
Drug-susceptible active pulmonary TB is usually treated with an initial four-drug phase followed by a continuation phase; use the TB service, BNF and local protocol for the exact regimen.
Exclude active disease before treating latent TB with IGRA or tuberculin testing; a positive test alone does not diagnose active disease.
Notify active TB, arrange infection-control precautions and trace close contacts through the TB service.
Offer HIV testing in TB; ART timing is usually early but differs for very low CD4 counts and CNS TB because of IRIS and interactions.
Rifampicin interactions, hepatotoxicity, ethambutol visual toxicity, adherence problems and drug resistance require active monitoring.

First-line investigation

Chest X-ray plus multiple appropriate respiratory or site-specific specimens for microscopy, culture, rapid molecular testing and susceptibility; use IGRA or tuberculin testing only within a latent-TB pathway after active disease assessment.

Management

Recognise, isolate and notify active disease

Use airborne precautions for suspected infectious pulmonary or laryngeal TB, notify active TB through UKHSA pathways and involve the specialist TB service urgently.^1,7,4

Obtain specimens and stage the disease

Use chest or site-directed imaging, send appropriate specimens for culture, molecular testing and susceptibility, and assess HIV, pregnancy, organ function, interactions and extrapulmonary complications.^1,4,5

Treat active TB with a specialist combination regimen

Start the current multi-drug regimen for drug-susceptible disease after appropriate samples where safe; adapt treatment to site, susceptibility, pregnancy, age, interactions and response using the TB service and BNF.^1,6,4

Support adherence and monitor toxicity

Provide named TB-team follow-up, adherence support and toxicity monitoring, including liver, renal and visual safety checks and careful review of rifampicin interactions.^1,6

Manage latent, resistant, extrapulmonary and HIV-associated TB

Exclude active disease before latent-TB treatment, refer resistant or complex-site disease to specialists, and coordinate ART timing in HIV/TB co-infection, especially with CNS TB.^1,8,5

Trace contacts and complete treatment

Arrange contact tracing, document susceptibility and treatment completion, continue therapy until the TB team confirms the course is complete, and safety-net for relapse, toxicity, treatment interruption or new neurological or respiratory symptoms.^1,2,7,3

Exam traps

Latent TB is not the same as active TB: it is asymptomatic and non-infectious, but active disease must be excluded before preventive treatment.
A negative smear does not exclude TB; culture and molecular tests may still confirm it.
Do not treat active TB with a single antibiotic; combination therapy prevents selection of resistance.
Do not label a positive IGRA as active TB without symptom, examination, imaging and microbiological assessment.
Ethambutol toxicity is visual; rifampicin causes major drug interactions and can alter the effectiveness of other medicines.
In HIV/TB co-infection, ART is usually early but CNS TB requires specialist timing because of potentially harmful IRIS.

Illustrations

Granuloma formationDiagram of macrophages and lymphocytes containing Mycobacterium tuberculosis within a granuloma, contrasting latent containment with later reactivation.PassFinals · original

Apical cavitation on chest X-rayChest radiograph showing upper-lobe cavitating consolidation in post-primary pulmonary tuberculosis; imaging is supportive and requires microbiological correlation.Unknown author, Wikimedia Commons · Public domain

Acid-fast bacilli on Ziehl-Neelsen stainMicroscopy image showing red-staining acid-fast bacilli against a blue counterstain; smear sensitivity is limited and culture or molecular testing is still needed.CDC/Dr George P. Kubica, Wikimedia Commons · Public domain

Key sources

This page is exam revision material, not medical advice, and must not be used for patient care. Always check drug doses against the BNF and current guidance. Full disclaimer.