Evaluation of interferon-gamma release assays in the diagnosis of recent tuberculosis infection in health care workers.
BACKGROUND
Health care workers (HCWs) are a group at risk of latent tuberculosis infection (LTBI). The aims of this study were to determine IFN-gamma response by QuantiFERON-TB GOLD In Tube (QFN-G-IT) and T-SPOT.TB in HCWs, comparing the results with tuberculin skin test (TST); and to analyze the capacity of IFN-gamma tests to detect recent versus remote LTBI with a prolonged stimulation test (PST).


RESULTS
A total of 147 HCWs were enrolled; 23 of whom were BCG vaccinated. 95 HCWs (64.6%) had a previous positive TST and were not retested; and 52 HCWs had a previous negative TST or were tested for the first time. When we analysed individuals without previous positive TST, the number of positive results for T-SPOT.TB was 12/52 (23.1%); and for QFN-G-IT, 9/52 (17.3%). The global concordance (kappa) between T-SPOT.TB and QFN-G-IT with TST was 0.754 and 0.929 respectively. Of individuals with previous positive TST, T-SPOT.TB and QFN-G-IT were negative in 51.6% (49/95) and 62.1% (59/95) respectively, decreasing the concordance to 0.321 and 0.288, respectively. In non-BCG vaccinated HCWs with previous positive TST a positive IFN-gamma test was associated with degree of exposure and diameter of TST. PST was performed in 24 HCW with previous positive TST and negative IFN-gamma tests. PST was developed in 3 cell cultures stimulated with medium alone, ESAT-6 and CFP-10, respectively. In the third and sixth day of incubation period, part of the supernatants were replaced with complete medium supplemented with (rIL)-2. On day 9, ELISPOT assay was performed. In 14 samples PST was not valid due to not having enough cells. In 8 cases, the response was negative, and in 2 cases positive, suggesting that these patients were infected with Mycobacterium tuberculosis in some point in the past.


CONCLUSIONS
Both IFN-gamma tests showed a similar number of positive results, and concordance between the tests was excellent. None of the tests was affected by prior BCG vaccination. IFN-gamma tests are a useful tool for detecting recent infection in HCW population.
Casas
Irma
I
Servei de Medicina Preventiva, Hospital Universitari Germans Trias i Pujol Fundació Institut d'Investigació en Ciències de la Salut Germans Trias i Pujol, Badalona, Spain.
Latorre
Irene
I
Esteve
Maria
M
Ruiz-Manzano
Juan
J
Rodriguez
Dora
D
Prat
Cristina
C
García-Olivé
Ignasi
I
Lacoma
Alicia
A
Ausina
Vicente
V
Domínguez
Jose
J
D000293:Adolescent; D000328:Adult; D003430:Cross-Sectional Studies; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D006282:Health Personnel; D006801:Humans; D007156:Immunologic Memory; D017758:Infectious Disease Transmission, Patient-to-Professional; D007371:Interferon-gamma / Q000378:metabolism*; D055985:Latent Tuberculosis / Q000175:diagnosis* / Q000276:immunology / Q000635:transmission; D008297:Male; D008875:Middle Aged; D013030:Spain; D013601:T-Lymphocytes / Q000276:immunology; D055815:Young Adult
D007371:Interferon-gamma
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