Tuberculosis, Latent (LTBI)

Tuberculosis, Latent (LTBI) is a topic covered in the 5-Minute Clinical Consult.

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Basics

Description

  • Latent tuberculosis infection (LTBI) is an asymptomatic, noninfectious condition following exposure to an active case of tuberculosis. LTBI is usually detected by a positive skin test (i.e., purified protein derivative [PPD]) or a positive interferon-γ release assay (IGRA) test. In LTBI, acid-fast bacilli smear and culture are negative, and chest x-ray (CXR) does not suggest active TB.
  • Active TB occurs in 5–10% of infected individuals who have not received preventive therapy. Chance of active TB increases with immunosuppression and is highest for all individuals within 2 years of infection; 85% of the cases are pulmonary, which is capable of person-to-person spread via aerosol route.
  • The majority (70% in 2017) of active TB cases in the United States occur in foreign-born persons. 78% are the result of reactivation of LTBI (1).
  • LTBI treatment is a key component of the TB elimination strategy for the United States.

ALERT
After 20 years of annual decreases in the number of active TB cases in the United States, the incidence has recently plateaued. Identification and treatment of LTBI is crucial to reverse this trend. Test for LTBI (PPD or IGRA) and treat latent infection in at-risk populations.

Epidemiology

  • TB is the leading cause of infectious disease mortality worldwide.
  • In the United States, high-risk groups include immigrants from Asia, Latin America, Africa, and the Pacific basin; blacks; homeless persons; persons with a history of drug use or history of incarceration; HIV-infected individuals; and health care workers.
  • Newly exposed (particularly children) are also at high risk.
  • In 2017, there were 9,093 new cases of TB in the United States, the lowest number of TB cases on record. Of these cases, 30% were U.S.-born and 70% foreign-born (1).
  • Among foreign-born persons, Asians have the highest active TB case rate (27 cases per 100,000) and non-Hispanic blacks (22/100,000) (1).
  • In 2017, the majority of foreign-born persons with TB came from five countries: Mexico (19%), Philippines (12%), India (9%), Vietnam (8%), and China (6%) (1).
  • In 2017, 6% of active TB cases in the United States were in HIV-positive individuals (1).
  • In 2017, the lowest state-specific incidence was 0.3 cases per 100,000 in Montana and the highest 8.1/100,000 in Hawaii.

Prevalence
  • 4% of the U.S. population has LTBI (~11 million).
  • ~1/3 of the world’s population harbors latent TB.

Etiology and Pathophysiology

Mycobacterium tuberculosis, Mycobacterium bovis, and Mycobacterium africanum

Risk Factors

  • HIV infection, immunosuppression
  • Immigrants (from Asia, Latin America, Pacific Islands, Africa, or areas with high rates of TB), including migrant workers
  • Close contact with infected individual
  • Institutionalization (e.g., prison, nursing home)
  • Use of illicit drugs
  • Lower socioeconomic or homeless status
  • Health care workers
  • Chronic medical disease such as diabetes mellitus (DM), end-stage renal disease, cancer, or silicosis; organ transplant (immunosuppression)
  • Persons with fibrotic changes on CXR consistent with previous TB infection
  • Recent TB skin test (tuberculin skin test [TST]) converters
  • Laboratory personnel working with mycobacteria
  • Organ donors should be screened. If donor is deceased, IGRA testing is still possible.

General Prevention

Screen for LTBI and treat individuals with positive tests.

Commonly Associated Conditions

  • HIV infection (see “Initial Tests (lab, imaging)”)
  • Immunosuppression

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