Risk for Tuberculosis among Children
Risk for Tuberculosis among Children
Contacts of adults with tuberculosis (TB) are at risk for infection. Tests based on interferon-γ (IFN-γ) expression in response to Mycobacterium tuberculosis antigens may be more sensitive than the tuberculin skin test (TST). Risk for infection was assessed by using TST and an IFN-γ-based assay (QuantiFERON Gold in Tube [QFT-IT] test) for 207 children in Nigeria in 1 of 3 groups: contact with adults with smear-positive TB, contact with adults with smear-negative TB, and controls. For these 3 groups, respectively, TST results were >10 mm for 38 (49%) of 78, 13 (16%) of 83, and 6 (13%) of 46 and QFT-IT positive for 53 (74%) of 72, 8 (10%) of 81, and 4 (10.3%) of 39 (p<0.01). Most test discrepancies were TST negative; QFT-IT positive if in contact with TB-positive persons; and TST positive, QFT-IT negative if in contact with TB-negative persons or controls. TST may underestimate risk for infection with TB in children.
Tuberculosis (TB) is the most important infectious cause of adult deaths, and persons with acid-fast bacilli (AFB) in their sputum are the most infectious group in the community. Children exposed to adults with smear-positive pulmonary TB have a high risk for infection, and this risk increases with the degree of contact. In countries with a high incidence of TB, risk for infection among children in contact with adults with TB is 30%50%, which is much higher than that reported by industrialized countries. However, these risk estimates were established with the tuberculin skin test (TST), which has several limitations. Children vaccinated with Mycobacterium bovis BCG or infected with mycobacteria other than M. tuberculosis can have false-positive TST reactions, and those with malnutrition, measles, and HIV or other infections often have false-negative reactions. In areas with a high incidence of TB, low sensitivity and specificity of the TST may result in either overestimation or underestimation of the risk for transmission.
New tests based on the expression of interferon-gamma (IFN-γ) by sensitized lymphocytes in response to specific M. tuberculosis antigens (e.g., early secretory protein 6 [ESAT-6] and culture filtrate protein 10 [CFP-10]) appear to be more specific and sensitive than the TST in identifying latent and active TB. Although a test with these characteristics could have enormous practical implications for improving management of children at high risk, most studies have focused on adults in countries with low incidence of TB.
This study assesses the risk for latent TB infection among young household contacts of adults with pulmonary TB in Nigeria, a country with a high incidence of TB. We compared the TST and the QuantiFERON TB Gold in Tube (QFT-IT) (Cellestis International, Carnegie, Victoria, Australia) test.
Abstract and Introduction
Abstract
Contacts of adults with tuberculosis (TB) are at risk for infection. Tests based on interferon-γ (IFN-γ) expression in response to Mycobacterium tuberculosis antigens may be more sensitive than the tuberculin skin test (TST). Risk for infection was assessed by using TST and an IFN-γ-based assay (QuantiFERON Gold in Tube [QFT-IT] test) for 207 children in Nigeria in 1 of 3 groups: contact with adults with smear-positive TB, contact with adults with smear-negative TB, and controls. For these 3 groups, respectively, TST results were >10 mm for 38 (49%) of 78, 13 (16%) of 83, and 6 (13%) of 46 and QFT-IT positive for 53 (74%) of 72, 8 (10%) of 81, and 4 (10.3%) of 39 (p<0.01). Most test discrepancies were TST negative; QFT-IT positive if in contact with TB-positive persons; and TST positive, QFT-IT negative if in contact with TB-negative persons or controls. TST may underestimate risk for infection with TB in children.
Introduction
Tuberculosis (TB) is the most important infectious cause of adult deaths, and persons with acid-fast bacilli (AFB) in their sputum are the most infectious group in the community. Children exposed to adults with smear-positive pulmonary TB have a high risk for infection, and this risk increases with the degree of contact. In countries with a high incidence of TB, risk for infection among children in contact with adults with TB is 30%50%, which is much higher than that reported by industrialized countries. However, these risk estimates were established with the tuberculin skin test (TST), which has several limitations. Children vaccinated with Mycobacterium bovis BCG or infected with mycobacteria other than M. tuberculosis can have false-positive TST reactions, and those with malnutrition, measles, and HIV or other infections often have false-negative reactions. In areas with a high incidence of TB, low sensitivity and specificity of the TST may result in either overestimation or underestimation of the risk for transmission.
New tests based on the expression of interferon-gamma (IFN-γ) by sensitized lymphocytes in response to specific M. tuberculosis antigens (e.g., early secretory protein 6 [ESAT-6] and culture filtrate protein 10 [CFP-10]) appear to be more specific and sensitive than the TST in identifying latent and active TB. Although a test with these characteristics could have enormous practical implications for improving management of children at high risk, most studies have focused on adults in countries with low incidence of TB.
This study assesses the risk for latent TB infection among young household contacts of adults with pulmonary TB in Nigeria, a country with a high incidence of TB. We compared the TST and the QuantiFERON TB Gold in Tube (QFT-IT) (Cellestis International, Carnegie, Victoria, Australia) test.
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