Tuberculosis

肺结核

Tuberculosis (TB) remains the world's leading cause of death from a single infectious agent, with 1.23 million fatalities recorded in 2024. This bacterial disease primarily affects the lungs but can involve multiple organ systems. Despite being preventable and curable, TB continues to impose a substantial global health burden, particularly in low- and middle-income countries where approximately half of all cases concentrate in just eight nations.

Definition

Tuberculosis is an infectious disease caused by the bacterium Mycobacterium tuberculosis. The organism most commonly targets the pulmonary system, though it can affect virtually any organ. Classification codes include ICD-10 A15-A19 and ICD-11 1B10. The disease exists in two states: latent infection, where individuals harbor the bacteria without symptoms or transmissibility, and active disease, characterized by clinical manifestations and potential for transmission.

Clinical features

Active tuberculosis typically presents with a chronic cough producing blood-tingled sputum, fever, night sweats, and weight loss. However, symptoms may remain mild for extended periods, facilitating undetected transmission. While pulmonary involvement predominates, extrapulmonary manifestations can affect the kidneys, brain, and spine. Approximately 5-10% of infected individuals will progress to active disease during their lifetime, with infants and children demonstrating elevated susceptibility once infected. Without appropriate antibiotic treatment, active TB carries significant mortality risk.

Epidemiology

An estimated one-quarter of the global population has been infected with TB bacteria, though most harbor latent infection without progressing to disease. Ten million people develop active TB annually, with 1.23 million deaths recorded in 2024, including 150,000 among HIV-positive individuals. The disease burden concentrates disproportionately in low- and middle-income countries, with eight nations—Bangladesh, China, India, Indonesia, Nigeria, Pakistan, Philippines, and South Africa—accounting for approximately half of all cases. TB serves as the leading cause of mortality among people living with HIV and represents a major driver of antimicrobial resistance.

Transmission

Mycobacterium tuberculosis spreads through airborne particles when individuals with active pulmonary TB cough, sneeze, or expectorate. Inhalation of relatively few organisms can establish infection. Critically, persons with latent TB infection neither experience symptoms nor transmit the disease; only those with active pulmonary disease pose transmission risk. The prolonged symptomatic phase of active disease, which may persist for months before diagnosis, facilitates ongoing community transmission.

Risk groups

Individuals with compromised immune systems face substantially elevated risk of progressing from latent infection to active disease. This includes people living with HIV, those with malnutrition, diabetes mellitus, or tobacco use disorder. Household contacts of active TB cases, healthcare workers, and residents of high-burden regions demonstrate increased exposure risk. Infants and young children who become infected carry higher probability of developing active disease compared to immunocompetent adults.

Prevention

Prevention strategies encompass vaccination with the Bacille Calmette-Guérin (BCG) vaccine, administered to infants in endemic areas, which prevents mortality and protects children from severe TB manifestations. Public health measures emphasize early case detection through rapid diagnostic testing, contact investigation, and treatment of latent infection in high-risk individuals. Infection control in healthcare settings and community education about respiratory hygiene contribute to reducing transmission. Source-backed detail on chemoprophylaxis regimens is not yet available from the provided sources.

Surveillance note

Interpretation of TB surveillance data requires consideration of diagnostic capacity variations across settings, as underdiagnosis remains common in resource-limited areas. The WHO recommends rapid molecular assays as initial diagnostic tools, providing results within 48 hours. Surveillance systems must account for the distinction between latent infection prevalence and active disease incidence. Monitoring drug-resistant TB patterns, including multidrug-resistant and extensively drug-resistant forms, constitutes an essential component of epidemiological tracking given the disease's contribution to antimicrobial resistance.

References