Chemoprophylaxis appears to reduce significantly the risk for progression from latent infection to active disease. In patients who have not received chemotherapy, a positive skin test result implies the presence of a few dormant but viable tubercle bacilli, which have the potential for reactivation. It has been demonstrated that the administration of INH daily for 6 to 12 months reduces the risk for reactivation by up to 80%. Because the risk for progressive disease is greatest soon after infection, recent converters to tuberculin reactivity are most likely to benefit from such therapy.
In 1999, the American Thoracic Society (ATS), the CDC, and the Infectious Disease Society of America revised the published guidelines for offering INH chemoprophylaxis of latent tuberculosis infection (LTBI). This revision was intended to sharpen the focus of tuberculin screening and chemoprophylaxis to those populations most likely to progress from latent infection to active pulmonary tuberculosis and to deemphasize the routine screening and chemoprophylaxis of persons at low risk of active TB. A person's candidacy for INH chemoprophylaxis should no longer depend on age, provided that other risk factors for progression to active disease are present.
Candidates for INH chemoprophylaxis (with the respective criterion for skin test positivity noted in parentheses) include the following:
- Patients with known or suspected HIV infection (5 mm).
- Close (especially household) contacts of patients with known active pulmonary TB (5 mm). Children and adolescent contacts of a person with TB should be offered INH regardless of PPD status until a PPD test can be repeated at 12 weeks.
- Patients with fibronodular disease on chest radiography compatible with old, healed TB (5 mm).
- Patients who have received solid-organ transplantation or who are receiving treatment with immunosupressive drugs, particularly TNF inhibitors (5 mm).
- Recent immigrants (<5 countries="" endemic="" from="" is="" li="" mm="" tuberculosis="" where="" years="">
- Native-born patients from medically underserved low-income areas, especially if homeless (10 mm).
- Patients with documented PPD conversion within the preceding 2 years (10 mm).
- Injection-drug users uninfected with HIV (10 mm).
- Patients with medical conditions predisposing to active TB, such as silicosis, diabetes, chronic renal insufficiency, leukemia or lymphoma, or cancer of the head or neck; persons who have undergone gastrectomy or jejunoileal bypass or whose weight is 10% or more below their ideal body weight; and children less than 4 years of age.
- Patients residing or employees working in long-term care facilities such as nursing homes, correctional facilities, and mental institutions (10 mm).
Persons without risk factors for acquiring TB and without medical conditions predisposing to active TB should not be considered candidates for INH chemoprophylaxis.