What is Latent Tuberculosis Infection (LTBI)?
Latent tuberculosis infection (LTBI) is characterized by the presence of immune responses to previously acquired Mycobacterium tuberculosis infection without any clinical evidence of active tuberculosis disease. 1
Key Defining Features
No symptoms or signs of active TB disease – Patients with LTBI are completely asymptomatic and have no clinical manifestations of tuberculosis 1
Not infectious – Individuals with LTBI cannot transmit the infection to others, as the bacteria are dormant and not actively replicating 1
Positive immunologic testing – LTBI is detected through positive tuberculin skin test (TST) or interferon-gamma release assay (IGRA), indicating immune response to M. tuberculosis 1
Normal chest radiograph – There is no radiographic evidence of active pulmonary tuberculosis, though old calcifications or pleural thickening may suggest prior exposure 1
Epidemiology and Risk of Progression
Approximately one-third of the world's population is estimated to be infected with Mycobacterium tuberculosis 1
Lifetime reactivation risk is 5-15% for persons with documented LTBI, with the majority developing active TB disease within the first 5 years after initial infection 1
Risk varies significantly by host factors – HIV infection, immunosuppressive therapy (especially anti-TNF agents), diabetes, silicosis, chronic renal failure, and malnutrition substantially increase the risk of progression from LTBI to active disease 1
Clinical Significance
The reactivation of LTBI to active TB can be prevented by treatment, with currently available regimens demonstrating 60-90% efficacy, with protection lasting up to 19 years 1. This makes identification and treatment of high-risk individuals a critical component of TB elimination strategies, particularly in low TB incidence countries 1.
The distinction between LTBI and active TB disease is crucial because treatment regimens, duration, public health implications, and monitoring requirements differ substantially between the two conditions 1, 2, 3.