Latent Tuberculosis Infection: A Guide for Primary Health Care Providers

Targeted Testing for Tuberculosis

Targeted testing is an essential TB prevention and control strategy that is used to identify, evaluate, and treat persons who are at high risk for latent tuberculosis infection (LTBI) or at high risk for developing TB disease once infected with M. tuberculosis. Identifying persons with LTBI is important to the goal of TB control and elimination because treatment of LTBI can prevent infected persons from developing TB disease and stop the further spread of TB. All testing activities should be accompanied by a plan for appropriate follow-up medical evaluation and treatment. Necessary medical evaluation and treatment resources need to be identified before testing activities begin. 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, unless medically contraindicated.

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 2 testing methods available for the detection of M. tuberculosis infection in the United States:

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

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

• 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 2 broad categories:

• Those who have an increased likelihood of exposure to persons with TB disease
• Those with clinical conditions or other factors associated with an increased 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 HIV infection/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 the following:

• 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 TNFα antagonists
• Recent TST converters (that is, 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).
• Infants and children under the age of five years who have a positive TB test result

*Of note, the risk of progression is greatest in the first 1 or 2 years after infection.