The diagnosis of latent tuberculosis infection in children in XXI century. Is tuberculin skin test still up to date?

Abstract

Tuberculosis morbidity rates in Poland have been gradually decreasing. Nevertheless, there are approximately 8 thousand cases being registered annually, which includes almost 3 thousand massively infectious patients. In the last 3 years, around 100 cases/year have been reported among children below 14 years of age. Infection with Mycobacterium tuberculosis should be considered in all patients who present symptoms suggesting tuberculosis, have had recent contact with a person suffering from lung tuberculosis or are planned to undergo an immunosuppressive treatment. HIV infected patients are also supposed to have screening tests for M. tuberculosis infection performed. For over a 100 years tuberculin skin test (TST) was the only test capable of confirming tuberculous infection. TST is based on the assessment of skin reaction to intracutaneous injection of tuberculin. Due to cross-reaction to the injected tuberculin in BCG vaccinated individuals, the correct interpretation of the test is difficult. Since 13 years new immunological assays have been available. They are based on detecting interferon gamma (Interferon Gamma Release Assay - IGRA) concentration in blood serum, which has previously been incubated with Mycobacterium tuberculosis antigens absent in the BCG strain. In infected individuals interferon gamma is intensively produced by memory cells in reaction to the contact with previously met Mycobacterium antigens. Many trials have proved IGRA's high sensitivity and, higher than TST, specificity. Recent guidelines promote the usage of IGRAs, even in children.

Is secretion of IFN‐gamma in response to Mycobacterium tuberculosis antigens in youngest children sufficient to play a role in TB diagnostics?

“…Despite a growing number of studies concerning IGRA's usefulness in children <5 years of age, including the meta‐analysis published in 2014, IGRA's sensitivity in this age group remains controversial . Following recent American Thoracic Society/Infectious Diseases Society of America/Centers for Disease Control and Prevention guidelines in children younger than 5 years of age, TST is recommended as a first line diagnostic tool rather than IGRA .…”