Figure 5个  Table 5个
    • SN titer* Number of samples Proportion
      ≥ 256 21 13.5% (21/156)
      128 20 12.9% (20/156)
      64 28 17.9% (28/156)
      32 24 15.4% (24/156)
      16 30 19.2% (30/156)
      8 20 12.8% (20/156)
      ≤ 4 13 8.3% (13/156)
      Note: * SN titers are expressed as the reciprocal dilution of the serum samples.

      Table 1.  SN titers for 156 sow serum samples from four major swine-rearing provinces in China.

    • Recombinant PEDV S proteins
      PEDV-S-SP1 PEDV-S-SP2 PEDV-S-SP3 PEDV-S-SP4 PEDV-S-SP5 PEDV-S-SP6 PEDV-S-SP7
      + – + – + – + – + – + – + –
      PEDV-positive sow sera (n = 123)a 16 107 15 108 49 74 85 38 26 97 32 91 32 92
      PEDV-negative sow sera (n = 33)b 1 32 1 32 3 30 2 31 3 30 1 32 1 32
      OD450 cutoff value for ELISA 1.448 1.365 1.106 0.774 0.717 1.123 0.9465
      Sensitivity (%)c 13.01 12.2 39.84 69.11 21.24 26.83 25.2
      Specificity (%)c 96.97 96.97 90.91 93.94 90.91 96.97 96.97
      Note: a 123 serum samples from sows that were diagnosed as PEDV-positive based on the SN titer. The cutoff value was 1:8; b 33 serum samples from sows that were diagnosed as PEDV-negative based on the SN titer. The cutoff value was 1:8;c The sensitivity and specificity for each recombinant protein was calculated based on an OD450 cutoff value determined using a ROC analysis.

      Table 2.  Comparison of the recombinant S fragment ELISA results using 156 field serum samples and SN titers

    • Samples Mean OD450 ± SD Intra-assay CV*(%) Inter-assay CV*(%)
      Intra-assay Inter-assay
      Negative sera 0.206 ± 0.005 0.226 ± 0.014 2.22 6.11
      0.308 ± 0.011 0.344 ± 0.038 3.48 11.09
      0.279 ± 0.014 0.267 ± 0.045 4.90 16.90
      0.381 ± 0.010 0.377 ± 0.047 2.55 12.43
      0.280 ± 0.007 0.302 ± 0.018 2.38 5.99
      0.250 ± 0.009 0.248 ± 0.017 3.46 6.94
      Positive sera 0.838 ± 0.040 0.877 ± 0.050 4.71 5.73
      0.673 ± 0.005 0.657 ± 0.047 0.73 7.22
      0.760 ± 0.032 0.750 ± 0.040 4.18 5.37
      1.065 ± 0.041 1.038 ± 0.115 3.82 11.063
      0.938 ± 0.023 0.955 ± 0.051 2.41 5.34
      0.548 ± 0.030 0.559 ± 0.047 5.39 8.46
      Note: CV*: Coefficient of variation.

      Table 3.  Repeatability of the SP4 ELISA for intra- and inter-assays (with three replications) using neutralizing antibody-negative and -positive serum samples

    •

      Table S1.  Primers used for polymerase chain reaction (PCR) involving the seven recombinant S peptides

    •

      Table S2.  Comparison of SP4 ELISA results with SN titers based on testing 156 field sow serum samples