Management of Latent Tuberculosis Infection

Interpretation of a Positive Mantoux Test

A positive Mantoux test represents a delayed-type hypersensitivity reaction to purified protein derivative (PPD), indicating the presence of memory T cells against M. tuberculosis antigens, according to the Centers for Disease Control and Prevention (CDC) 1
Interpretation of induration size depends on patient risk factors, with ≥5 mm considered positive in HIV-infected persons, recent contacts of TB cases, persons with fibrotic changes on chest radiograph, and immunosuppressed patients, as recommended by the American Thoracic Society 2, 3
≥10 mm is considered positive in recent immigrants from high-prevalence countries, injection drug users, residents of high-risk settings, and persons with certain medical conditions, according to the CDC 2, 4
≥15 mm is considered positive in persons with no known risk factors for TB, as stated by the American College of Chest Physicians 2, 5

All patients with a positive Mantoux test should undergo thorough symptom assessment (cough, fever, night sweats, weight loss) and chest radiography to rule out active pulmonary TB, as recommended by the CDC 1, 7, 8
Consider interferon-gamma release assays (IGRAs) as complementary tests, especially in BCG-vaccinated individuals, as they have higher specificity, according to the National Institute for Health and Care Excellence 4, 9

For latent TB infection (LTBI), isoniazid for 9 months is the recommended standard treatment for most patients, as stated by the Infectious Diseases Society of America 8
Alternative regimens include rifampin for 4 months, rifampin plus isoniazid for 3 months (3RH), and rifampin plus pyrazinamide for 2 months (2RZ), although the latter has higher hepatotoxicity, according to the British Thoracic Society 8, 10

HIV-infected patients have a higher risk of progression to active TB and may have false-negative Mantoux tests due to anergy, as reported by the CDC and the World Health Organization 1, 3, 4
Patients starting anti-TNF therapy should be screened for TB before starting treatment and complete LTBI treatment before starting anti-TNF therapy when possible, as recommended by the European Crohn’s and Colitis Organisation 9, 10

Monitor for hepatotoxicity, especially in older patients, women, those with pre-existing liver disease, and those consuming alcohol, as advised by the American Association for the Study of Liver Diseases and the CDC 4, 8, 10
Clinical monitoring for symptoms of hepatitis should be performed regularly, and adherence to the full course of therapy is crucial for effective prevention of TB disease, as emphasized by the Infectious Diseases Society of America and the CDC 8, 10