Modelling the probability and impact of false‐positive serology for Borrelia burgdorferi sensu lato: A case study

BACKGROUND: Serological screening tests for Lyme borreliosis have poor specificity, with potential for misdiagnosis and unnecessary antimicrobial treatment. OBJECTIVES: To evaluate the impact of Lyme borreliosis seroprevalence and serologic test characteristics on the probability of obtaining a false‐positive result and impact on antimicrobial use. STUDY DESIGN: Cross‐sectional serological survey and modelling. METHODS: Sera from 303 horses in southern Belgium were analysed by enzyme‐linked immunosorbent assay (ELISA). Apparent seroprevalence was derived from serological data and a Bayesian estimate of true seroprevalence was computed. These were a starting point to model the impact of test and population characteristics on the probability of obtaining false‐positive results and consequently unnecessary treatments and complications. RESULTS: Apparent and true seroprevalence were 22% (95% CI 18%‐27%) and 11% (credible interval with 95% probability 0.6%‐21%) respectively. We estimate that two‐thirds of positive samples are false positive in southern Belgium, with one in five of tested horses potentially misdiagnosed as infected. Around 5% of antimicrobial use in equine veterinary practice in Belgium may be attributable to treatment of a false‐positive result. MAIN LIMITATIONS: There was uncertainty regarding the ELISA's sensitivity and specificity. CONCLUSIONS: This study highlights the importance of appreciating the poor diagnostic value of ELISA screening for Lyme borreliosis as demonstrated by this case study of seroprevalence in southern Belgium where we demonstrate that a nontrivial number of horses is estimated to receive unwarranted treatment due to poor appreciation of screening test characteristics by practitioners, contributing substantially to unnecessary use of antimicrobials.