A Bayesian approach for the evaluation of six diagnostic assays and the estimation ofCryptosporidiumprevalence in dairy calves

Abstract

-The prevalence of Cryptosporidium in calves and the test properties of six diagnostic assays (microscopy (ME), an immunofluorescence assay (IFA), two ELISA and two PCR assays) were estimated using Bayesian analysis. In a first Bayesian approach, the test results of the four conventional techniques were used: ME, IFA and two ELISA. This four-test approach estimated that the calf prevalence was 17% (95% Probability Interval (PI): 0.1-0.28) and that the specificity estimates of the IFA and ELISA were high compared to ME. A six-test Bayesian model was developed using the test results of the 4 conventional assays and 2 PCR assays, resulting in a higher calf prevalence estimate (58% with a 95% PI: 0.5-0.66) and in a different test evaluation: the sensitivity estimates of the conventional techniques decreased in the six-test approach, due to the inclusion of two PCR assays with a higher sensitivity compared to the conventional techniques. The specificity estimates of these conventional assays were comparable in the four-test and six-test approach. These results both illustrate the potential and the pitfalls of a Bayesian analysis in estimating prevalence and test characteristics, since posterior estimates are variables depending both on the data at hand and prior information included in the analysis. The need for sensitive diagnostic assays in epidemiological studies is demonstrated, especially for the identification of subclinically infected animals since the PCR assays identify these animals with reduced oocyst excretion, which the conventional techniques fail to identify.Cryptosporidium / Bayesian / test evaluation / prevalence / calves

Occurrence and potential health risk of Cryptosporidium and Giardia in different water catchments in Belgium

“…Other studies have also reported an effect of land use on the contamination of water with Cryptosporidium and Giardia (Ongerth et al 1995;Ong et al 1996;Hansen and Ongerth 1991;Burnet 2012). The Blankaart catchment site is situated in an agricultural area, and high prevalences of Cryptosporidium and Giardia have been observed in cattle in Belgium (Geurden et al 2004(Geurden et al , 2006. However, we found no correlation between high concentrations of Cryptosporidium and Giardia in the surface water and rainfall prior to sampling.…”

Cryptosporidiumspecies causing acute diarrhoea in children in Antananarivo, Madagascar

“…Four children were antigen-positive but at an optical density close to the kit manufacturer's cut-off for positivity, and all four were negative by each of the other diagnostic tests and thus considered falsepositives. The specificity of the commercial antigen-detection ELISA in this study was therefore 98% (203/297), which is at the upper end of the range (89%-99%) reported by others (Rosenblatt and Sloan, 1993;Aarnaes et al, 1994;Geurden et al, 2006).…”

Detection of Cryptosporidium oocysts in fresh and frozen cattle faeces: comparison of three methods

“…A Bayesian approach has been implemented recently to evaluate six diagnostic tests for Cryptosporidium in dairy calves (Geurden et al. 2006).…”