Screening for M. tuberculosis
Target groups and technique:
Tuberculin skin testing is performed to ascertain who is at high risk of latent
infection with M. tuberculosis and who would benefit from therapy to prevent
Current recommendations suggest that the following groups be screened
persons with HIV infection, close contacts of persons with infectious TB,
persons with immunocompromising medical conditions, users of injected drugs,
foreign-born persons from areas where TB is common, homeless persons,
low-income populations, and residents or workers in congregate settings, such
as correctional institutions, nursing homes, and mental institutions.
The Mantoux tuberculin skin test with 5 units of purified protein derivative
(PPD) is the standard method. The PPD is placed subcutaneously into the volar
aspect of the forearm, and the result is interpreted 48 to 72 hours later. A
positive reaction is determined by the size of the induration (not erythema) in
millimeters and varies depending on risk category. A two-step test, which consists
of a second test 1 to 3 weeks after an initially negative test result, is more
sensitive, because it may detect cases of latent infection in which the initial
immune response is muted but becomes evident owing to a booster phenomenon.
Therapy for latent infection: Persons with a positive tuberculin skin test
result should undergo chest radiography and clinical evaluation to exclude
active disease. If the findings are normal, latent infection is likely. The
decision to treat patients for latent infection depends on the person's
Treatment is recommended, regardless of age, for the following groups:
those who are known or are likely to have HIV infection, close contacts of a
person with TB, persons who inject drugs, persons with skin test results that
have recently (within 2 years) converted, persons with certain medical
conditions (such as diabetes mellitus, chronic renal failure, an organ
transplant, hematologic malignant disease, ongoing use of glucocorticoids, and
prior gastrectomy), and those who have chest radiographic findings that suggest
prior active TB but have not received adequate antituberculous therapy.
The following groups should be treated only if younger than 35 years:
foreign-born persons from areas where TB is common; medically underserved,
low-income populations; and homeless persons.
A 9-month course of daily INH therapy is now thought to be the most effective
regimen for eradication of latent TB infection. For persons with conditions in
which neuropathy is common, such as diabetes, uremia, alcoholism, and HIV
infection, pyridoxine also should be administered.