title: Diagnosing and treating asymptomatic tuberculosis infection.
abstract: OBJECTIVE
  To summarize relevant parts of the guidelines recommended by the Canadian and American Thoracic Societies for diagnosis and management of asymptomatic tuberculosis (TB) infection.
  
  
  METHODS
  The latest guidelines published by the Canadian and American Thoracic Societies were reviewed. Unfortunately, neither of these guidelines state explicitly how recommendations were derived. The references accompanying each set of guidelines, however, suggest that they were developed by extensive literature review of the subject and consensus among expert panels.
  
  
  RESULTS
  Only higher-risk patients should receive a TB screening test (Mantoux test) to minimize the possibility of false-positive test results. The cutoff points for positive tests vary to reflect the pretest likelihood of TB infection. An induration 5 mm or greater is considered positive in patients at highest risk of TB infection, that is, HIV-infected patients, close contacts of active TB cases, and patients with chest x-ray abnormalities suggestive of previous untreated TB. All other patients are considered positive if they have induration greater than 10 mm according to the Canadian guideline. A 15-mm cutoff point, however, is used for patients without risk factors in the American guideline. All patients with positive Mantoux test results should be considered infected with TB. Infected patients should be offered 6 to 12 months of isoniazid prophylaxis if they have HIV infection, if they have medical conditions that increase the risk of TB activation, or if they are younger than 35 years.
  
  
  CONCLUSIONS
  Prophylactic treatment of infected individuals effectively prevents the spread of TB infection. Family physicians, who most often see patients in the asymptomatic stage of TB infection, are uniquely situated to prevent secondary cases of TB by offering appropriate patients prophylactic treatment. Patients should be counseled about the risk and benefit of prophylactic treatment so they give informed consent for it.
authors.affiliation: Department of Family and Community Medicine, St Michael's Hospital, Toronto, Ont.
authors.forename: C T
authors.initials: CT
authors.lastname: Wang
mesh_terms: D000328:Adult; D019072:Antibiotic Prophylaxis; D002170:Canada; D003362:Cost-Benefit Analysis; D003937:Diagnosis, Differential; D006801:Humans; D017410:Practice Guidelines as Topic; D012307:Risk Factors; D014374:Tuberculin Test; D014376:Tuberculosis / Q000175:diagnosis* / Q000517:prevention & control; D014481:United States