PRRS ELISA testing for Surveillance


May 2022

Adapting PRRS Oral Fluid ELISA to Surveillance

Swine oral fluids are an efficient sample type for detection of several swine pathogens including PRRSv by PCR and antibody by ELISA. Diagnostic tests for routine surveillance of PRRSv virus and antibody must have perfect, or nearly so, diagnostic specificity. Thus, researchers (Henao-Diaz et al., 2021) at the ISU VDL modified the cutoff of the PRRS Oral Fluid Antibody ELISA Test (IDEXX Laboratories) to accommodate surveillance testing of PRRSv antibody in the US swine industry. In summary, this study evaluated samples of known PRRS status (Panel 1), known PRRSV-negative status (Panel 2), and samples of unknown PRRSV status (Panel 3). A total 3350 oral fluid samples (Table 1) were tested according to the manufacturer (IDEXX Laboratories) instructions. Table 2 shows the performance of the oral fluid ELISA based on experimental samples (Panel 1) while Table 3 demonstrates the performance of the field samples (Panels 2 and 3). Increasing the cut-off from 0.4 to 1.0 minimally reduced diagnostic sensitivity in Panel 1 samples from 100% to 96.5% and increased diagnostic specificity in Panel 2 samples from ~95.2% to 99.2%. Thus, a sample to positive (S/P) cut-off ≥ 1.0 provided a diagnostic sensitivity of 96.5 (95% CI: 85.2, 99.2) and a diagnostic specificity of 99.2 (95% CI: 98.8, 99.7). Tables 2 and 3 show a range of cut-offs along with their associated performance. Thus, diagnosticians and veterinarians can choose the cut-off most appropriate to their specific application needs.

Table 1.  Oral fluid samples used to evaluate PRRSV oral fluid ELISA performance

Table 2.  PRRSV oral fluid ELISA1 performance based on experimental samples (Panel 1)2

Table 3. PRRSV oral fluid ELISA1 performance based on field samples (Panel 2 and 3)2,3

1  PRRSV OF Ab ELISA Test (kit lot KP950, IDEXX Laboratories, Inc., Westbrook, ME USA)
2  Panel 2 consisted of 1574 oral fluids collected from 94 PRRSV-negative production sites.        
3  Panel 3 consisted of 1380 field oral fluids samples from 211 commercial sites of unknown status.
4  Cut-off recommended by the assay manufacturer.
a,b,c,d  Different letters within a column indicate statistical differences in the proportion of positives (Cochran's Q, p < 0.05).


Henao-Diaz, A., Zhang, M., Giménez-Lirola, L., Ramirez, E., Gauger, P., Baum, D. H., . . . Zimmerman, J. (2021). Adapting a porcine reproductive and respiratory syndrome virus (PRRSV) oral fluid antibody ELISA to routine surveillance. Preventive Veterinary Medicine, 188, 105250. doi: