Latent Tuberculosis Infection: A Guide for Primary Health Care Providers

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Targeted Testing for Tuberculosis

Targeted testing is an essential TB prevention and control strategy. This strategy entails finding and treating persons with LTBI who are at the highest risk for progressing to TB disease, and thus would benefit from treatment. Treatment of these high-risk individuals also benefits society by reducing the number of future TB cases. Unfocused population-based testing is not cost-effective or useful and leads to unnecessary treatment. TB testing activities should be conducted only among high-risk groups, with the intent to treat if LTBI is detected. Once TB disease has been excluded, treatment of LTBI should be offered to patients regardless of their age.

However, there may be instances in which health care providers are asked to test individuals who are not necessarily regarded as high risk (e.g., daycare center workers, teachers, and U.S.-born students). A few simple questions will help health care providers assess a patient’s risk for LTBI. Appendix A contains a sample risk assessment tool.

Currently, there are two testing methods available for the detection of M. tuberculosis infection in the U.S. The tests include:

• Mantoux tuberculin skin test (TST)
• Interferon-gamma release assays (IGRAs)

Three U.S. Food and Drug Administration (FDA) approved IGRAs are commercially available in the U.S.:

• QuantiFERON^®-TB Gold test (QFT-G)
• QuantiFERON^®-TB Gold-in-Tube test (QFT-GIT)
• T.SPOT^®.TB test

Identifying Persons at Risk for Developing TB Disease

Generally, persons at risk for developing TB disease fall into two broad categories: those who have an increased likelihood of exposure to persons with TB disease and those with clinical conditions or other factors associated with an increased the risk of progression from LTBI to TB disease.

Persons at risk for exposure to persons with TB disease include the following:

• Known close contacts of a person with infectious TB disease
• Persons who have immigrated from TB-endemic regions of the world (see Appendix B)
• Persons who work or reside in facilities or institutions with people who are at high risk for TB, such as hospitals that care for TB patients, homeless shelters, correctional facilities, nursing homes, or residential facilities for patients with AIDS

Also at risk are those with certain conditions and other factors associated with progression from LTBI to TB disease. These conditions and factors include:

• HIV infection
• Injection drug use
• Radiographic evidence of prior healed TB
• Low body weight (10% below ideal)
• Other medical conditions, such as:
  • silicosis
  • diabetes mellitus
  • chronic renal failure or on hemodialysis
  • gastrectomy
  • jejunoileal bypass
  • solid organ transplant
  • head and neck cancer
  • conditions that require prolonged use of corticosteroids or other immunosuppressive agents such as TNF-antagonists
• Recent TST converters (persons with baseline testing results who have an increase of 10 mm or more in the size of the TST reaction within a 2-year period. The risk of progression is greatest in the first 1 or 2 years after infection.)
• Infants and children under the age of five years who have a positive TB test result