Evaluation of a commercial ELISA kit for detection of antibodies against Toxoplasma gondii in serum, plasma and meat juice from experimentally and naturally infected sheep

Table 5 ROC-analysis: Relative accuracies of PrioCHECK ® Toxoplasma Ab SR ELISA (cut-off PP 20) in relation to IFAT, IHA and real-time PCR

			PrioCHECK® Toxoplasma Ab SR ELISA
Reference test	Sample	AUC/P*	Selected cut-off in ELISA	% relative sensitivity (95% confidence interval)	% relative specificity (95% confidence interval)
A
IFAT (cut-off 1:40)	serum	1.000/<0.000	19.79	100 (81.5 - 100.0)	100 (95.4 – 100.0)
IFAT (cut-off 1:80)	serum	1.000/<0.000	19.79	100 (81.5 - 100.0)	100 (95.4 – 100.0)
IHA (cut-off 1:80)	serum	1.000/<0.000	19.79	100 (81.5 - 100.0)	100 (95.4 – 100.0)
Real-time PCR	brain/muscle	0.959/<0.0001	19.79	100 (71.5 - 100.0) ^§	91.76 (83.8 - 96.6)^§
IFAT (cut-off 1:40)	meat juice 1:10**	0.999/<0.0001	20.29	100 (81.5 - 100.0)	98.72 (93.1 - 100.0)
IFAT (cut-off 1:80)	meat juice 1:10**	0.996/<0.0001	27.64	100 (78.2 - 100.0)	97.53 (91.4 - 99.7)
IFAT (cut-off 1:40)	meat juice 1:20**	0.999/<0.0001	15.83	100 (81.5 - 100.0)	98.72 (93.1 - 100.0)
IFAT (cut-off 1:80)	meat juice 1:20**	0.998/<0.0001	27.45	100 (78.2 - 100.0)	98.77 (93.3 - 100.0)
B
IFAT (cut-off 1:40)	serum	0.991/<0.0001	17.24	93.33 (88.1 - 96.8)	98.67 (95.3 - 99.8)
IFAT (cut-off 1:80)	serum	0.985/<0.0001	21.05	96.43 (91.9 - 98.8)	96.87 (92.9 - 99.0)
IHA (cut-off 1:80)	serum	0.998/<0.0001	21.05	97.87 (93.9 - 99.6)	98.74 (95.5 - 99.8)

A: Tests performed with samples from Swiss sheep (Group 2), B: Tests performed with samples from Austrian sheep (Groups 3 and 4).
*Significance level P (Area = 0.5); ** meat juice dilution; AUC: Area under curve.
^§ Note: The apparent low specificity of ELISA when real-time PCR is taken as reference test might be related to the low diagnostic sensitivity of PCR techniques linked to the small size of the analyzed sample. All real-time PCR positive animals were recognized as positive by ELISA (100% relative sensitivity), but some serologically positive animals in ELISA had negative PCR results accounting for a (potentially erroneous) relative lower specificity of the ELISA.