Use of T cell-based diagnosis of tuberculosis infection to optimize interpretation of tuberculin skin testing for child tuberculosis contacts.
BACKGROUND
Treatment of recent tuberculosis infection in children aged <2 years is essential, because of high risk of progression to disease, but diagnosis is hindered by the inaccuracy of the tuberculin skin test (TST). More-accurate T cell-based tests of infection could enhance diagnosis by optimizing interpretation of the TST results.


METHODS
A total of 979 child tuberculosis contacts in Istanbul underwent the TST and enzyme-linked immunospot assay. Using enzyme-linked immunospot test results as a reference standard, we assessed the effect of age and bacille Calmette-Guérin (BCG) vaccination on the sensitivity and specificity of the TST, and we computed the optimal TST cutoff points, using receiver operating characteristic curves.


RESULTS
With a TST cutoff point of >or=10 mm, the sensitivity of the TST was 66% for children aged <2 years, which was lower than that for older children (P= .006). Specificity was 75% for BCG-vaccinated children, compared with 92% for unvaccinated children (P= .001). Optimal cutoff points improved TST specificity for children with 1 BCG scar, with little loss of sensitivity. Despite the use of optimal cutoff points, TST sensitivity remained <70% for children aged <2 years, specificity remained <87% for BCG-vaccinated children aged >or=2 years, and overall accuracy was low for children with >1 BCG scar.


CONCLUSIONS
Negative results of the TST cannot exclude tuberculosis infection for child tuberculosis contacts aged <2 years, which supports the use of preventive therapy regardless of the TST results for this age group. In children aged >or=2 years, the accuracy of the TST can be improved by adjustment of cutoff points for BCG-vaccinated children but remains poor for children with >1 BCG scar. This methodology can define optimal TST cutoff points for diagnosis of tuberculosis infection tailored to target populations.
Bakir
Mustafa
M
Department of Paediatrics, Marmara University School of Medicine, Istanbul, Turkey.
Dosanjh
Davinder P S
DP
Deeks
Jonathan J
JJ
Soysal
Ahmet
A
Millington
Kerry A
KA
Efe
Serpil
S
Aslan
Yasemin
Y
Polat
Dilek
D
Kodalli
Nihat
N
Yagci
Aysegul
A
Barlan
Isil
I
Bahceciler
Nerin
N
Demiralp
Emel E
EE
Lalvani
Ajit
A
D000293:Adolescent; D001500:BCG Vaccine / Q000276:immunology; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D007223:Infant; D008297:Male; D012680:Sensitivity and Specificity; D013601:T-Lymphocytes / Q000276:immunology*; D014374:Tuberculin Test; D014376:Tuberculosis / Q000175:diagnosis*; D014421:Turkey
D001500:BCG Vaccine