Active TuberculosisEdit
Active tuberculosis is a form of tuberculosis disease caused by the Mycobacterium tuberculosis complex that presents with clinical illness and typically bronchopulmonary involvement, though it can affect virtually any organ. It contrasts with latent tuberculosis infection, in which the bacteria are present without symptoms or contagiousness. Active disease is infectious and capable of spreading through airborne droplets, making diagnosis, treatment, and public health measures essential to prevent transmission. The syndrome encompasses pulmonary tuberculosis as well as extrapulmonary manifestations, and its management relies on a combination of pharmacology, patient adherence, and infection-control strategies.
Historically a leading cause of morbidity and mortality, active tuberculosis remains a major global health concern, particularly in areas with limited resources and high rates of HIV infection or malnutrition. Advances in rapid diagnostic tests, first-line drug regimens, and public health approaches have significantly improved outcomes for drug-susceptible disease, while drug-resistant forms pose ongoing challenges. Public health authorities emphasize screening of high-risk populations, contact tracing, vaccination policies, and measures to improve living conditions that contribute to transmission. The disease is widely studied in tuberculosis research and intersects with topics ranging from Mycobacterium tuberculosis biology to public health policy.
Epidemiology
Active tuberculosis affects people around the world, with a disproportionately high burden in low- and middle-income regions. Global data indicate tens of millions living with active disease or prior TB, and millions of new cases occur each year. Risk factors for developing active disease after infection include HIV infection, malnutrition, chronic illnesses, immunosuppression, and crowded living conditions. Transmission is enhanced in settings with poor ventilation and prolonged close contact, and health care facilities must implement robust infection-control practices to minimize nosocomial spread. See also tuberculosis and HIV.
Transmission and Pathogenesis
M. tuberculosis is primarily transmitted through airborne particles expelled when an infectious person coughs, sneezes, or speaks. Inhaled bacilli reach the alveoli and can establish infection within macrophages, triggering an immune response that forms granulomas. These lesions can contain bacteria for years, a state known as latent tuberculosis infection. Reactivation or new infection can lead to active disease, particularly when immunity wanes. Pulmonary tuberculosis is the most common form and is typically responsible for most transmission, but extrapulmonary tuberculosis can occur when infection disseminates via the bloodstream to other organs. For more on the organism and disease mechanisms, see Mycobacterium tuberculosis and granuloma.
Clinical Presentation
Active tuberculosis most often presents with a gradual onset of cough that lasts several weeks, sometimes with sputum production or hemoptysis. Other frequent symptoms include fever, night sweats, weight loss, and fatigue. Chest pain or shortness of breath may occur in pulmonary forms, while extrapulmonary disease can affect lymph nodes, pleura, bones, the central nervous system, and other sites. The clinical picture depends on the site of infection and the host’s immune status. Diagnostic evaluation combines symptom assessment with laboratory testing, imaging, and microbiologic confirmation. See pulmonary tuberculosis and extrapulmonary tuberculosis for site-specific details, as well as sputum smear and NAAT diagnostics.
Diagnosis
Diagnosis of active tuberculosis relies on multiple lines of evidence. Microbiologic confirmation is essential and typically includes:
- Sputum smear microscopy for acid-fast bacilli (AFB), a rapid, inexpensive test that lacks sensitivity in many patients.
- Nucleic acid amplification tests (NAAT), such as the Xpert MTB/RIF assay, which detect Mycobacterium tuberculosis DNA and can identify rifampin resistance.
- Mycobacterial culture, the gold standard for definitive diagnosis and drug susceptibility testing, though culture can take several days to weeks.
Radiographic evaluation, especially chest radiography, provides supportive information and may show upper-lobe infiltrates, cavitary lesions, or adenopathy. Distinguishing active disease from latent infection involves symptom review, imaging, and microbiologic testing. Tests to identify latent infection, such as the tuberculin skin test or IGRA tests, help guide prevention strategies but are not sufficient alone to diagnose active disease. See also latent tuberculosis and Xpert MTB/RIF.
Treatment
Management of drug-susceptible active tuberculosis typically follows a two-phase approach totaling about six months:
- Initial intensive phase (commonly 2 months) with four first-line drugs: isoniazid, rifampin, pyrazinamide, and ethambutol.
- Continuation phase (commonly 4 months) with two drugs, typically isoniazid and rifampin.
Adherence is critical, and programs often use directly observed therapy (DOT) to ensure completion. For drug-resistant tuberculosis, regimens are longer and more complex, often incorporating second-line agents and newer drugs such as bedaquiline or linezolid, guided by drug-susceptibility testing. Vaccination with BCG vaccine can reduce severe disease in young children in high-burden settings, though its effectiveness against adult pulmonary TB varies. See also drug-resistant TB and latente tuberculosis for related topics.
Prevention and Public Health
Efforts to prevent transmission and disease progression include vaccination policies, early detection, prompt isolation of infectious cases, and treatment of latent infection to prevent reactivation. Infection-control measures in health-care and community settings, improved ventilation, and UV light can reduce environmental transmission. Contact tracing and population-based strategies are used to identify and treat those at risk. Public health programs often coordinate TB care with broader infectious disease prevention efforts through public health systems and directly observed therapy initiatives.
Controversies and debates
Because active tuberculosis intersects with clinical care and public policy, debates exist over resource allocation, vaccination strategies, and screening practices. Questions commonly raised include the cost-effectiveness of universal vaccination in different epidemiological contexts, the balance between individual rights and public health duties in screening and isolation, and the best approaches to screen and treat latent infection in diverse populations. Proponents of targeted, evidence-based interventions emphasize efficient use of limited resources and outcomes, while critics may advocate broader measures in high-burden settings. In all cases, policy choices aim to reduce transmission, prevent severe disease, and minimize unintended consequences, with ongoing evaluation of outcomes.