another report.............COMPARISON OF WHOLE BLOOD...

another report.............

COMPARISON OF WHOLE BLOOD INTERFERON-GAMMA ASSAY
WITH TUBERCULIN SKIN TESTING IN HOUSEHOLD
CONTACTS OF PULMONARY TUBERCULOSIS PATIENTS IN
SALVADOR, BRAZIL
Almerio Machado Jr. MD* Krisztina Szabo MPH Theolis Barbosa PhD
Sergio M. Arruda MD Mitermayer G. Reis MD Lee W. Riley MD Iukary
O. Takenami Technician Fundacao Baiana para o Desenvolvimento das
Ciencias, Salvador, Brazil
PURPOSE: QuantiFERON TB-Gold In Tube (QFT) has emerged as
an alternative test to the tuberculin skin test (TST) to diagnose latent
tuberculosis infection (LTBI). Household (HH) contacts of TB patients
are at great risk for latent LTBI. We compared the performance of the
whole blood IFN- test with TST in HH contacts of hospitalized TB
patients in a Brazilian city with a high incidence of TB.
METHODS: Between November 2006-March 2007, HH contacts of
bacteriologically confirmed pulmonary TB patients were recruited in
Salvador, Brazil. All contacts underwent TST(2 UT), chest x-ray, and the
QFT assay. Patients with a previous history of pulmonary TB were
excluded from the study.
RESULTS: For 26 TB patients (15 males, 11 females with a median
age 31 years), 119 HH contacts were interviewed (45 males 37.8%;
median 4 contacts per household). However, 31 (26%) never returned for
their TST reading and were lost to follow-up. Among the 88 contacts
(median age 24; 31 males 35.2%,) 25 (28%) were children
; 15 years of
age. With a TST cut-off point of 10 mm, 58 (65.8%) were positive. With
a cut-off point of IFN- 0.35 IU/mL, 44 (50%) were QFT positive.
Overall, 39 (44%) were positive by both tests (95% CI 3.4-31) 25 (28%)
were negative by both tests and 24 (27%) had discordant results. Overall
concordance between QFT and TST was high (73%) with a fair agreement
(
0.46, standard error 0.09) between tests. The degree of sputum smear
positivity of tuberculosis patients was not predictive of IFN- (p0.15) or
TST positivity (p0.11) of the contacts.
CONCLUSION: TST and QFT assays produced comparable results
among HH contacts. Due to the small sample size the agreement between
tests was fair. There was a 26% loss to follow-up. This is an ongoing
investigation and further assessment is needed.
CLINICAL IMPLICATIONS: Assessing TST in such a population is
often difficult due to the need for the skin reaction to be examined
afterwards. QFT could become an important screening tool.
DISCLOSURE: Almerio Machado Jr., None.