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Open Access Research article

Prevalence of latent tuberculosis infection in Sudan: a case–control study comparing interferon-γ release assay and tuberculin skin test

Amani Osman Shakak1, Eltahir Awad Gasim Khalil27*, Ahmed Mudawi Musa2, Kawthar Abd Eljalil Mohamed Salih3, Abd Elgadir Ali Bashir4, Ala Hassan Ahmed5, Fath Elrahman Mohamed Idris6, Ahmed Mohamed Elhassan2 and Tuberculosis Research Group/Sudan

Author Affiliations

1 Faculty of Medical Sciences, University of Shendi, Shendi, Sudan

2 Department of Clinical Pathology & Immunology, Institute of Endemic Diseases, University of Khartoum, Medical Campus, Qasr Avenue, P.O. Box 45235, Postal code 11111, Khartoum, Sudan

3 Elneil Medical College, Khartoum, Sudan

4 Medical Commission, Khartoum State Ministry of Health, Khartoum, Sudan

5 Department of Medicine, Faculty of Medicine, University of Khartoum, Khartoum, Sudan

6 Khartoum North Teaching Hospital, Khartoum North, Sudan

7 Central Laboratory, Ministry of Science & Communications, Khartoum, Sudan

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BMC Public Health 2013, 13:1128  doi:10.1186/1471-2458-13-1128

Published: 5 December 2013

Abstract

Background

Most people exposed to M. tuberculosis show no evidence of clinical disease. Five to 10% of individuals with latent infection progress to develop overt disease during their life time. Identification of people with latent TB infection will increase case detection rates and may dictate new treatment policies to control tuberculosis. This study aimed to determine LTBI point prevalence in a population from Sudan using two different diagnostic methods: the tuberculin skin test (TST) and the IFN-γ release assay (IGRA).

Methods

This was a prospective, community-based and case-controlled study. Following informed consent, household contacts (HHCs; n = 98) of smear-positive index cases and Community controls (CCs; 186), were enrolled. Tuberculin skin test (TST), whole blood stimulation with ESAT-6/CFP-10 ± TB7.7 antigens or purified protein derivative (PPD) and IFN-γ levels determination with ELISA were performed. The levels of IFN-γ and TST induration between the CCs and the HHCs were compared using student t-test, Chi-square and Kappa coefficient. Pearson correlation test was used to compare TST and IFN-γ. P levels of <0.05 were considered significant.

Results

TST induration of ≥ 10 mm gave an LTBI point prevalence of 327 cases/1000 individuals among HHCs compared to 126 cases/1000 individuals among CCs (p = 0.000). PPD-induced IFN-γ release assay gave an LTBI point prevalence of 418 cases/1000 individuals among HHCs compared to 301 cases/1000 individuals among CCs (p =0.06). On the other hand ESAT-6/CFP-10 ± TB7.7-induced IFN-γ gave an LTBI point prevalence of 429 cases/1000 individuals among HHCs compared to 268 cases/1000 individuals among CCs (p = 0.01). IFN-γ productions levels induced by ESAT-6/CPF-10 ± TB7.7 antigens in HHCS and CCs were not significantly different from those induced by PPD (p = 0.7).

Conclusion

IFN-γ release assay (IGRA) gave higher LTBI point prevalence compared to TST in HHCs and CCs. PPD gave comparable results to ESAT-6/CFP-10 ± TB7.7 antigens in whole blood IFN-γ release, making it a cheap alternative to the recombinant antigens.

Keywords:
Latent Tb infection; IFN-γ release assay; TST; Sudan; Contact tracing