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Comparison of an In-house and a Commercial RD1-based ELISPOT-IFN- Assay for the Diagnosis of Mycobacterium tuberculosis Infection

Paola Mantegani, MSc, Clinic of Infectious Diseases, San Raffaele Scientific Institute, Milan, Italy
Federica Piana, MD, Emerging Bacterial Pathogens Unit, San Raffaele Scientific Institute, Milan, Italy
Luigi Codecasa, MD, Villa Marelli Institute, Lombardy Regional Reference Center for Tuberculosis Niguarda Hospital, Milan, Italy
Laura Galli, MSc, Clinic of Infectious Diseases, San Raffaele Scientific Institute, Milan, Italy
Paolo Scarpellini, MD, Clinic of Infectious Diseases, San Raffaele Scientific Institute, Milan, Italy
Adriano Lazzarin, MD, Clinic of Infectious Diseases, San Raffaele Scientific Institute, Milan, Italy and "Vita-Salute" San Raffaele University School of Medicine, Milan, Italy
Daniela Cirillo, MD, Emerging Bacterial Pathogens Unit, San Raffaele Scientific Institute, Milan, Italy
Claudio Fortis, MD, Clinic of Infectious Diseases, San Raffaele Scientific Institute, Milan, Italy

Reprint Requests: Claudio Fortis, MD, Clinic of Infectious Diseases, San Raffaele Scientific Institute, Via Stamira D’Ancona 20, 20127, Milano, Italy, Tel: +39-02-26437911, Fax: +39-02-26437989, E-mail: fortis.claudio{at}hsr.it

Objective: To compare a RD1-based in-house ELISPOT-interferon- (IFN-) assay with a commercial (T-SPOT.TB^TM) assay for the diagnosis of Mycobacterium tuberculosis (TB) infection and the efficacy of the tuberculin skin test (TST) and ELISPOT assay in detecting latent TB infection (LTBI).

Design: Eighty-six subjects (65 household contacts of contagious TB-infected patients, 13 subjects with active or previous TB infection, and 8 with suspected TB infection) were consecutively recruited in the context of a surveillance program.

Methods: Enrolled subjects underwent the Mantoux TST and two different ELISPOT-IFN- assays: an in-house assay using a pool of selected M. tuberculosis peptides (MTP) and the commercial T-SPOT.TB assay.

Results: The in-house and commercial ELISPOT-IFN- assays showed almost complete concordance (99%) in diagnosing acute or LTBI.When comparing the efficacy of the TST with the in-house ELISPOT assay in detecting TB infection, a small agreement was observed (k=0.344, P<0.0001): 36% of the subjects with a positive TST were ELISPOT-MTP negative and 12% with a negative TST were ELISPOT-MTP positive. Furthermore, 78% of the ELISPOT-MTP negative individuals were ELISPOT- Bacillus Calmette-Guérin (BCG) positive, most of whom had received BCG vaccination.

Conclusion: Our in-house ELISPOT assay based on a restricted pool of highly selected peptides is equivalent to the commercial T-SPOT.TB assay, is cheaper and is probably not confounded, unlike the TST, by BCG vaccination in our setting

Key Words: Bacillus Calmette-Guérin • CFP-10 • ELISPOT • ESAT-6 • Household contacts • IFN-g • PPD • Tuberculin skin test • Tuberculosis