Analysis of discordance between the tuberculin skin test and the interferon-gamma release assay.
OBJECTIVE
To analyze factors associated with discordance between tuberculin skin test (TST) and interferon-gamma release assay (IGRA) results among household contacts of pulmonary tuberculosis (PTB) patients.


METHODS
TST (purified protein derivative) and IGRA (QuantiFERON-TB Gold) were performed on household contacts of PTB patients diagnosed between 2006 and 2007 in Salvador, Brazil. Discordant test groups were compared with the TST-/IGRA- group.


RESULTS
Of 261 household contacts satisfactorily tested by TST, 145 (55.6%) had positive TST results; of 298 satisfactorily tested by IGRA, 127 (43.1%) had positive results. The test agreement was 0.76 (kappa = 0.53, 95%CI 0.43-0.63). Sixty-one (24%) were discordant: 44 (72%) with TST+/IGRA- and 17 (28%) with TST-/IGRA+ results. Compared to the TST-/IGRA- group, the TST+/IGRA- and TST+/IGRA+ groups were significantly more likely to have a chest X-ray showing old lung scars (OR = 6.8, 95%CI 1.3-35.0; OR = 7.4, 95%CI 2.2-24.4, respectively). The TST-/IGRA+ group was exposed to their index cases for significantly longer than the TST-/IGRA- group (OR = 7.2, 95%CI 1.7-29.3).


CONCLUSIONS
The TST+/IGRA- and TST+/IGRA+ groups shared more similar characteristics with each other than with the TST-/IGRA- group. In a setting endemic for TB, TST results appear to be more suitable in the decision to treat latent TB infection.
Machado
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Escola Bahiana de Medicina e Saúde Pública, Salvador, Bahia, Brazil; Hospital Especializado Octávio Mangabeira, Salvador, Bahia, Brazil. almeriojr@yahoo.com.br
Emodi
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K
Takenami
I
I
Finkmoore
B C
BC
Barbosa
T
T
Carvalho
J
J
Cavalcanti
L
L
Santos
G
G
Tavares
M
M
Mota
M
M
Barreto
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F
Reis
M G
MG
Arruda
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S
Riley
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