TB TEST PERFORMANCE

M A R K S C H O E N BAU MN AT I O N A L E P I D E M I O LO G I S T, C AT T L E H E A LT H C E N T E RU . S . D E PA R T M E N T O F A G R I C U LT U R EA N I M A L A N D P L A N T H E A LT H I N S P E C T I O N S E RV I C EV E T E R I N A RY S E RV I C E SO C TO B E R 1 5 , 2 0 1 7

11/15/2017 2

Performance measures for diagnostic testsSensitivity

Specificity

Predictive value positive

Predictive value negative

Likelihood estimates

Accuracy

Precision

ROC analysis

Examples showing variability and complexity of testing

▪ Caudal-fold tuberculin (CFT)

▪ Comparative cervical tuberculin (CCT)

▪ Gamma interferon, currently suspended

▪ Others occasionally used:

▪ IDEXX ELISA

▪ Cervical test (CT)

▪ On the horizon? I’d like to be optimistic, but am skeptical

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Antemortem tests in US TB program for cattle/bison

▪ SD beef herd in 2017▪ 657 cows/bulls

▪ Infection rate, 37/661 = 5.6%

▪ Texas dairy in 2015, depopulated 2016▪ 10,309 cows/heifers

▪ Infection rate first test, 149/10,309 = 1.4%

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Contrast of two depopulated US cattle herds

SD beef herd in 2017▪ 3 lesioned compatible cows found on depopulation among 578 skin-test

negative

▪ 37 lesioned compatible cows found among 87 CFT positives

▪ CFT detected 37 of 40 lesioned cattle, sensitivity of 92.5%

▪ Mean 18 days to postmortem on reactors, ~40 days on negatives

Texas dairy in 2015, depopulated in 2016▪ 33 lesioned compatible found on depopulation among 8,087 skin-test

negative

▪ 114 lesioned compatible found among 336 CFT positives

▪ CFT detected 114 of 147 lesioned cattle, sensitivity of 77.6%

▪ Mean 26 days to postmortem on reactors, mean 22 days on negatives

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Caudal-fold test

SD beef herd in 2017▪ 87 tested

▪ 37 negative

▪ 14 suspect

▪ 27 reactor zones

▪ Sensitivity – detection of TB

▪ Of CCT on CFT positive cattle, 29 of 37 visibly lesioned, 78.4%

▪ Of CFT/CCT combination, 29 of 40 visibly lesioned in the herd, 72.5%

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Comparative-cervical test

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Bovine Response (in mm)

CCT, Beef in SD, 78 tested, 2/24/17

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CCT, Beef in SD, 78 tested, 2/24/17

TX dairy herd in 2015, depopulated in 2016▪ 333 tested

▪ 267 negative

▪ 49 suspect

▪ 17 reactor zones

▪ Sensitivity – detection of TB

▪ Of CCT on CFT positive cattle, 49 of 113 visibly lesioned, 43.3%

▪ Of CFT/CCT combination, 49 of 147 visibly lesioned in the herd, 33.3%

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Comparative-cervical test

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Dairy Depopulation, CCT results on 333 cows, 113 TB-confirmed and 220 negative

Major interest is sensitivity in detecting TB in skin-test negative cattle

SD beef herd in 2017▪ 3 lesioned compatible cows found on depopulation among 578 skin-test

negative

▪ All 3 negative to IDEXX ELISA (0% sensitivity)

Texas dairy in 2015▪ 33 lesioned compatible found on depopulation among 8,087 skin-test

negative

▪ 27 had IDEXX ELISA results

▪ 19 positive (19/27 = 70% sensitivity), 7 of these were CFT positive 6 months earlier

▪ 8 negative, 1 of these was CFT positive 6 months earlier

▪ 19, Removing positives from earlier tests

▪ 12 positive (12/19 = 63% sensitivity)

▪ 7 negative

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IDEXX ELISA test

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SD beef TX dairy

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CFT CCT IDEXX ELISA*

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Contrast sensitivity performance in these two cattle herds

*Only tests on skin-test negative animals are included

TX Dairy had been tested 3 times prior to final test before depopulation▪ Desensitization phenomena

▪ Prior removal of best responding animals

▪ First test is the best test

Dairy/Beef differences▪ Production environments were very different

▪ Breed differences

Timing of testing

Tester difference?

Bacterial strain differences?

Add your own ___________________

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Why so different?

Mark SchoenbaumNational Epidemiologist, Cattle Health CenterU.S. Department of AgricultureAnimal and Plant Health Inspection ServiceVeterinary ServicesEmailAddress@aphis.usda.gov