infectious diseases
Tuberculosis (TB)
Screening for TB
Screening for latent tuberculosis infection (LTBI) is done with a Skin testing or Close contact with a person who has active pulmonary TB Chest x-ray evidence of past TB infection Risk factors for exposure to TB (eg, people who have immigrated within 5 years from high-risk areas, indigent patients, IV drug users, selected health care practitioners such as respiratory therapists and practitioners working with high-risk populations) Risk factors for development of active TB (eg, HIV infection or other impaired immunity, gastrectomy, jejunoileal bypass surgery, silicosis, renal insufficiency, diabetes, head or neck cancer, age>70 years) Therapeutic immunosuppression with corticosteroids, tumor necrosis factor (TNF) inhibitors, or cancer chemotherapy In the US, most children and other people without specific TB risk factors should not be tested to minimize the number of false-positive results. A positive TST or IGRA result (see Skin testing for criteria) suggests latent TB infection (LTBI). Patients with a positive TST or IGRA result are evaluated for other clinical and epidemiologic risk factors and have a chest x-ray. Those with x-ray abnormalities suggesting TB require Updated guidelines for testing of LTBIare available from the CDC. Some patients with remote TB exposure, BCG vaccination, or infection with nontuberculous mycobacteria may have a negative TST or IGRA result; however, the TST itself may serve as an immune booster so that a subsequent test done as little as 1 week or as much as several years later may be positive (booster reaction). Thus, in people who are tested regularly (eg, health care workers), the second routine test will be positive, giving the false appearance ofrecentinfection (and hence mandating further testing and treatment). If recurrent testing for LTBI is indicated, a second TST should be done (on the opposite forearm) 1 to 4 weeks after the first to identify a booster reaction (because conversion due to infection during that brief interval is highly unlikely). Subsequent TST is done and interpreted normally. The new IGRAs for LTBI do not involve injection of antigens and thus do not cause boosting. They also are not influenced by preexisting hypersensitivity from BCG vaccination or infection with environmental mycobacteria other thanM. kansasii,M. szulgai, andM. marinum. Treatment of latent tuberculosis infection is indicated principally for People whose TST converted from negative to positive within the previous 2 years People with x-ray changes consistent with old TB but no evidence of active TB Other indications for preventive treatment include People who, if infected, are at high risk of developing active TB (eg, people with HIV infection, people with drug-induced immunosuppression) Any child<5 years old who is a close contact of a person with smear-positive TB, regardless of whether there was TST conversion Other people with an incidentally positive TST or IGRA result but without these risk factors are often treated for LTBI, but physicians should balance individual risks of drug toxicity against the benefits of treatment. Treatment generally consists ofisoniazid(INH) unless resistance is suspected (eg, in exposure to a known INH-resistant case). The dose is 300 mg once/day for 9 months for most adults and 10 mg/kg for 9 months for children. An alternative for patients resistant to or intolerant of INH isrifampin(RIF) 600 mg once/day for 4 months. INH plusrifapentinetaken once/week for 3 months is also effective. Current guidelines for treatment of LTBIare available from the CDC. The main limitations of treatment of LTBI are Hepatotoxicity Poor adherence When used for LTBI, INH causes clinical hepatitis in 1/1000 cases; hepatitis usually reverses if INH is stopped promptly. Patients being treated for LTBI should be instructed to stop the drug if they have any new symptoms, especially unexplained fatigue, loss of appetite, or nausea. Hepatitis due to RIF is less common than with INH, but drug interactions are frequent. Only about 50% of patients complete the recommended 9-month course of INH. Adherence is better with 4 months of RIF. Monthly visits to monitor symptoms and to encourage treatment completion are standard good clinical and public health practice. 