Randomised clinical trial investigating the specificity of a novel skin test (C-Tb) for diagnosis of M. tuberculosis infection

PLoS One. 2013 May 14;8(5):e64215. doi: 10.1371/journal.pone.0064215. Print 2013.


Background: Tuberculin skin testing is simple and relatively inexpensive, but the specificity of PPD is affected by BCG vaccination.

Objective: Determine optimal dose and specificity of recombinant ESAT-6 and CFP-10 (C-Tb) produced in Lactococcus lactis for diagnosis of M. tuberculosis infection.

Methods: In a dose finding phase I trial 0.01 or 0.1 µg preserved and unpreserved C-Tb was injected by Mantoux technique in 38 patients with active tuberculosis and induration responses measured. In a phase II specificity trial in 151 uninfected, BCG vaccinated participants 0.1 µg C-Tb was compared to 2 TU PPD.

Results: 0.1 µg C-Tb gave a median induration of 15 mm after 2 days. Phenol preservation did not affect the response. The specificity of C-Tb was 99.3% (95% CI 96-100%) regarding indurations ≥5 mm as a positive outcome. This was higher than the specificity of PPD (63% using a cut-off of 5 mm or 92% using a cut-off of 15 mm to adjust for non-specific BCG responses). Local adverse reactions following C-Tb injection included transient itching and discomfort as expected components of the immune response.

Conclusion: C-Tb offers a simple and convenient skin test to diagnose M. tuberculosis infection using a single, universal cut-off unaffected by BCG vaccination.

Trial registration: ClinicalTrials.gov NCT01033929 and NCT01241188.

Publication types

  • Clinical Trial, Phase I
  • Clinical Trial, Phase II
  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Antigens, Bacterial / adverse effects
  • Antigens, Bacterial / chemistry
  • Antigens, Bacterial / immunology
  • Bacterial Proteins / adverse effects
  • Bacterial Proteins / chemistry
  • Bacterial Proteins / immunology
  • Dose-Response Relationship, Immunologic
  • Female
  • Humans
  • Male
  • Middle Aged
  • Mycobacterium bovis / immunology
  • Mycobacterium tuberculosis / immunology
  • Mycobacterium tuberculosis / physiology*
  • Phenol / chemistry
  • Sensitivity and Specificity
  • Tuberculin Test / adverse effects
  • Tuberculin Test / methods*
  • Tuberculosis / diagnosis*
  • Tuberculosis / immunology*
  • Vaccination
  • Young Adult


  • Antigens, Bacterial
  • Bacterial Proteins
  • CFP-10 protein, Mycobacterium tuberculosis
  • ESAT-6 protein, Mycobacterium tuberculosis
  • Phenol

Associated data

  • ClinicalTrials.gov/NCT01033929
  • ClinicalTrials.gov/NCT01241188

Grant support

The studies were sponsored by Statens Serum Institut, Copenhagen, Denmark (http://ssi.dk. Trial codes TESEC-02, Eudra CT No: 2009-012984-33 and TESEC-03, Eudra CT No.: 2009-017296-17). The funder supplied C-Tb and PPD and led monitoring. All authors had full access to the data. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.