Detection of extracellular factor-positive Streptococcus suis serotype 2 strains in tonsillar swabs of live sows by PCR

In this study, the sensitivity (Se) and specificity (Sp) of a PCR for the detection of EF-positive Streptococcus suis serotype 2 strains in tonsillar swabs of live sows were assessed. We sampled 471 sows originating from four farrow-to-finish farms by tonsillar swabbing and collected their tonsils after slaughter. On these specimens, a PCR, a bacterial examination (BE) or both were performed for the detection of EF-positive S. suis serotype 2 strains. Swab-PCR, Tonsil-PCR and Tonsil-BE were regarded as three integral tests. A Bayesian approach was used to calculate the Se and Sp of the tests. Se and Sp for Swab-PCR were 0.63 (95% credibility interval <0.52, 0.74>) and 0.96 (<0.92, 0.99>), respectively. Values for Se and Sp of Tonsil-PCR amounted to 0.88 (<0.75, 0.96>) and 0.94 (<0.87, 0.99>), respectively. For Tonsil-BE, Se was 0.65 (<0.51, 0.76>) and Sp was 0.97 (<0.91, 0.99>). Repetition of the swabbing procedure after 10 min resulted in a higher Se 0.85 (<0.67, 0.96>) than the Se of the first-Swab-PCR. Repetition of the PCR on the same sample did not result in any significant changes in the outcome of the analysis.