Latent Tuberculosis Infection Management

Diagnosis and Risk Stratification

• A positive PPD test with normal chest X-ray indicates latent TB infection when active TB has been excluded, with different cut-points for PPD positivity based on risk factors, including ≥5 mm for HIV-infected persons, recent contacts of TB cases, immunosuppressed patients, and persons with fibrotic changes on chest X-ray, ≥10 mm for recent immigrants from high-prevalence areas, injection drug users, residents of congregate settings, healthcare workers, and persons with certain medical conditions, and ≥15 mm for persons with no known risk factors 1, 2, 3, 4, 5, 6
• Clinical evaluation should include assessment for symptoms of active TB, and if any symptoms are present despite normal chest X-ray, collect three sputum specimens for AFB smear and culture 6, 7

• The following cut-off values for tuberculin skin test (TST) results are recommended based on a person's risk factors:

  Population	Induration Size
  HIV-infected persons, recent contacts of TB cases, persons with fibrotic changes on chest X-ray, and immunosuppressed patients	≥5 mm
  recent immigrants from high-prevalence areas, injection drug users, residents of congregate settings, and persons with certain medical conditions	≥10 mm
  persons with no known risk factors	≥15 mm [3, 4, 2, 5, 6]

• Key symptoms to evaluate include cough lasting ≥2-3 weeks, fever, night sweats, weight loss, hemoptysis, and history of TB exposure or risk factors, such as immigration from high-prevalence areas, HIV infection, homelessness, previous incarceration, close contact with active TB case, and immunosuppression 7

Treatment Regimens

• The Centers for Disease Control and Prevention recommends isoniazid (INH) for 9 months as the preferred regimen for most patients, with a dosing of 300 mg daily for adults or 10 mg/kg/day for children, and a rating of A (II) for both HIV-negative and HIV-positive patients 1, 2
• Alternative regimens include isoniazid for 6 months, with a rating of B (I) for HIV-negative and C (I) for HIV-positive patients, rifampin for 4 months, with a rating of B (II) for HIV-negative and B (III) for HIV-positive patients, and rifampin-pyrazinamide for 2 months, with a rating of B (II) for HIV-negative and A (I) for HIV-positive patients 2
• Extended therapy (12 months) is recommended for high-risk individuals, such as HIV-infected persons, those with fibrotic pulmonary lesions, and persons with silicosis, as suggested by the WHO and the CDC 8, 9

Monitoring and Adverse Effects

• Monitor for signs and symptoms of hepatotoxicity, and baseline liver function tests are recommended for patients with risk factors for hepatotoxicity, with regular liver function monitoring every 2-4 weeks for patients over 35 years of age, with pre-existing liver disease, history of alcohol abuse, taking other hepatotoxic medications, or pregnant or within 3 months postpartum 1, 3, 8
• Isoniazid should be withheld if transaminase levels exceed three times the upper limit of normal if associated with symptoms, or five times the upper limit of normal if the patient is asymptomatic 1
• Regular monitoring of liver function and symptoms is essential during treatment, as recommended by the FDA and the CDC 3, 8

Special Considerations

• The American Thoracic Society recommends considering directly observed therapy for high-risk patients or those with adherence concerns, and treatment should still be offered to high-risk individuals regardless of age 1, 2
• The decision to use preventive therapy during pregnancy should be made individually, and generally, therapy can be delayed until after delivery unless the woman was recently infected or has high-risk medical conditions, especially HIV infection 6
• Patients with HIV infection have higher rates of progression from latent to active TB, and require careful screening and prophylaxis, as recommended by the WHO and the CDC 3, 10
• Patients receiving immunosuppressive therapy, especially TNF blockers, require careful screening and prophylaxis before starting treatment, as suggested by the National Institutes of Health (NIH) and the American College of Rheumatology 3, 11
• Renal dialysis patients are at increased risk and should be screened with a designed prospective plan, as stated by the Kidney Disease: Improving Global Outcomes (KDIGO) foundation and the CDC 3, 8
• Thorough TB testing should be conducted in infertile women before assisted reproductive techniques to prevent congenital tuberculosis, as recommended by the American Journal of Respiratory and Critical Care Medicine 5
• Prior BCG vaccination can cause false-positive TST results, but this effect typically diminishes with time, and in healthcare workers with a history of BCG vaccination, it is usually prudent to consider positive reactions as indicating infection with M. tuberculosis, especially if they are from countries with a high prevalence of tuberculosis 4, 5, 6
• Consider IGRA testing (QuantiFERON-TB Gold) as a confirmatory test in BCG-vaccinated individuals, with higher specificity in BCG-vaccinated individuals, as recommended by the European Respiratory Society, the American College of Rheumatology, and the European Centre for Disease Prevention and Control (ECDC) 12, 13, 11, 6
• Failing to report TB cases can lead to delayed diagnosis and treatment, and all suspected or confirmed TB cases must be reported to the local health department, as required by law and recommended by the CDC 3, 8