Latent Tuberculosis

Latent Tuberculosis

Latent Tuberculosis Infection (LTBI) represents a condition characterized by a persistent immune response to stimulation by Mycobacterium tuberculosis antigens, without any evidence of active Tuberculosis (TB). Individuals with LTBI typically exhibit no signs or symptoms of TB, but they are at risk of developing active TB, potentially becoming infectious. Approximately 5 to 10% of those with TB infection may progress to active TB during their lifetimes, with the highest risk occurring within the first five years post-infection. The occurrence of active TB is contingent upon various factors, with immunological status being a pivotal determinant, particularly among children under the age of 5.

TB Disease: Understanding Active Infection

TB bacteria become active when the immune system fails to impede their growth. This active multiplication of TB bacteria in the body is referred to as TB disease, rendering affected individuals visibly sick and capable of transmitting the bacteria to those they interact with daily. While many with latent TB infection never develop TB disease, some individuals may become ill shortly after infection, often within weeks, before their immune system mounts an effective defence. Alternatively, TB disease may manifest years later, especially when the immune system weakens due to unrelated factors. Those with weakened immune systems, particularly individuals with HIV infection, face a substantially elevated risk of progressing from latent TB infection to active TB disease.

Diagnosing Latent TB Infection

Accurate diagnosis of latent TB infection is crucial for implementing effective preventive measures. Two primary diagnostic methods include the Tuberculin Skin Test (TST) and the Interferon Gamma Release Assay (IGRA). A positive result from either test prompts a medical evaluation to rule out TB disease.

1. Medical History Assessment: Clinicians conduct a comprehensive evaluation of the patient's medical history, exploring TB exposure, infection, or prior disease. Demographic factors such as age, ethnicity, race, and occupation are considered, along with medical conditions like HIV infection or diabetes that heighten the risk of latent TB infection progressing to active TB.
2. Physical Examination: A thorough physical examination provides valuable insights into the patient's overall health. It aids in identifying factors that may impact TB treatment, such as concurrent HIV infection or other illnesses.
3. Testing for TB Infection: The Mantoux tuberculin skin test (TST) or IGRA is employed to detect M. tuberculosis infection. Additional tests are necessary to confirm or exclude TB disease.
4. Chest Radiograph: A posterior-anterior chest radiograph helps identify chest abnormalities, though it cannot definitively diagnose TB. However, it is useful in ruling out pulmonary TB in individuals with a positive TST or TB blood test but no symptoms.

Treatment Options for LTBI

The decision to initiate treatment for latent TB infection is based on an individual's risk factors for developing TB disease. The following factors are considered:

1. Isoniazid Monotherapy: A recommended treatment for both adults and children involves isoniazid monotherapy administered over six months.
2. Alternative Approach for Children and Adolescents: Rifampicin plus isoniazid daily for three months is offered as an alternative to the six-month isoniazid monotherapy, specifically for children and adolescents under 15 years of age.
3. Weekly Regimen for Adults and Children Over 2 Years: An alternative to the standard six-month isoniazid monotherapy involves rifapentine and isoniazid weekly for three months, suitable for both adults and children over two years of age.

Preventive Treatment for Multidrug-Resistant TB Contacts

In certain high-risk household contacts of patients with multidrug-resistant tuberculosis (MDR-TB), preventive treatment may be considered based on individualized risk assessment and clinical justification. This targeted approach acknowledges the unique challenges posed by MDR-TB and underscores the importance of tailored interventions.