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Clinical and Vaccine Immunology, August 2008, p. 1272-1276, Vol. 15, No. 8
1071-412X/08/$08.00+0 doi:10.1128/CVI.00114-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.
Appraisal of Interpretation Criteria for the Comparative Intradermal Tuberculin Test for Diagnosis of Tuberculosis in Cattle in Central Ethiopia
Gobena Ameni,1,2*
Glyn Hewinson,3
Abraham Aseffa,2
Douglas Young,4 and
Martin Vordermeier3
Aklilu Lemma Institute of Pathobiology, Addis Ababa University, P.O. Box 1176, Addis Ababa, Ethiopia,1 Armauer Hansen Research Institute, P.O. Box 1005, Addis Ababa, Ethiopia,2 TB Research Group, Veterinary Laboratories Agency, Weybridge, New Haw, Addlestone, Surrey KT15 3NB, United Kingdom,3 Department of Infectious Disease and Microbiology, Imperial College, South Kensinton Campus, London SW7 2AZ, United Kingdom4
Received 29 March 2008/ Returned for modification 22 April 2008/ Accepted 15 May 2008
Accurate detection and removal of infected cattle, using immunodiagnostic tests such as the comparative intradermal tuberculin (CIDT) test, are the basis of control strategies for bovine tuberculosis (TB). According to the Office des Internationale Epizooties recommendation, the cutoff point for positivity of the CIDT test, calculated as the difference between skin thicknesses after bovine tuberculin (B) and avian tuberculin (A) injections (B – A), is >4 mm. This cutoff point is used worldwide, although it is likely that local conditions influence test performance. Thus, this study was formulated to determine CIDT test cutoff points applicable to cattle in central Ethiopia. Receiver operating characteristic analysis was performed for the CIDT test, using data from 186 Bos indicus (zebu) and Bos taurus (Holstein) cattle. Detailed postmortem examination for the presence of TB lesions was used to define disease status. At a cutoff of >2 mm, CIDT test sensitivity was 69% (95% confidence interval [95% CI], 58.5 to 79%), while it was 59% (95% CI, 49 to 69%) at a cutoff of >4 mm. In contrast, specificities of the CIDT test at these two cutoff values were identical, at 97% (95% CI, 89 to 100%). Thus, the maximum sensitivity of the CIDT test can be realized using a >2-mm cutoff without affecting specificity. The apparent prevalence was significantly (
2 = 13.56; P < 0.001) higher at a cutoff of >2 mm (16.0%; n = 5,424) than at a >4-mm cutoff (13.5%; n = 5,424). Nonetheless, no significant difference (2 = 2.15; P = 0.14) in true prevalence was observed at a cutoff of >2 mm (19.6%) and at a cutoff of >4 mm (18.5%). Thus, our study demonstrates the importance of defining local, relevant cutoff values to maximize test sensitivity, and we suggest the application of the >2-mm cutoff for testing of cattle in central Ethiopia.
* Corresponding author. Mailing address: Aklilu Lemma Institute of Pathobiology, Addis Ababa University, P.O. Box 1176, Addis Ababa, Ethiopia. Phone: 251-1-911413073. Fax: 251-1-112755296. E-mail: gobenaameni{at}yahoo.com
Published ahead of print on 21 May 2008.
Clinical and Vaccine Immunology, August 2008, p. 1272-1276, Vol. 15, No. 8
1071-412X/08/$08.00+0 doi:10.1128/CVI.00114-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.
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