Year of Publication

2018

College

Public Health

Degree Name

Master of Public Health (M.P.H.)

Committee Chair

Dr. Wayne T. Sanderson

Committee Member

Dr. Steve Browning

Committee Member

Dr. Craig N. Carter

Abstract

Objectives: To examine the inter-laboratory agreement between multiplex realtime quantitative polymerase chain reaction (qPCR) assay results and aerobic culture results on bovine lung samples for detection of Histophilus somni (HS), and to assess associations of laboratory-derived factors on test agreement.

Methods: A survey of records from the University of Kentucky Veterinary Diagnostic Laboratory (UKVDL) was conducted to evaluate test results from grossly pneumonic bovine lung samples submitted during the period April 1, 2015 through August 31, 2018. Cohen’s kappa coefficient with 95% confidence interval (CI) was calculated to describe the extent of agreement. Animal, environmental and laboratory factors were examined for associations to culture results using logistic regression analysis.

Results: Of the 417 cases analyzed, 56 were qPCR positive and culture positive for HS, 90 were qPCR positive and culture negative, 3 were qPCR negative and culture positive, and 268 were negative on both tests. Calculations yielded a Cohen’s kappa coefficient of 0.43 [CI: (0.35, 0.51)], considered moderate agreement, for the qPCR assay versus aerobic culture. Results from the final model revealed male gender and cycle threshold (Ct) value measured by qPCR were significantly associated with the probability of a positive HS culture result.

Conclusion: The specificity of qPCR for detection of HS, when evaluated against the gold standard of aerobic culture, is falsely low due to the challenges of growing this organism. Bacterial qPCR assays should be routinely performed 2 on all cases of bovine respiratory disease, in addition to aerobic culture, to enhance organism detection.

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