Verification and large scale clinical evaluation of a national standard protocol for Salmonella spp./Shigella spp. screening using real-time PCR combined with guided culture

Abstract

Salmonella spp./Shigella spp. are often associated with food poisoning and fecal-oral transmission of acute gastroenteritis that requires strict monitoring, especially among people who would handle food and water. In 2014, the National Health and Family Planning Commission of the P. R. China issued a national standard protocol (recommendatory) for the screening of Salmonella spp./Shigella spp.. However, its performance has not been fully studied. Whether it was suitable for use in our laboratory was still unknown. In the current study, the new protocol was first verified by various experiments and then its clinical performance was evaluated in about 20,000 stool samples over a three-year period. Verification results showed that the new protocol was highly specific and reproducible. Sensitivity (as defined as the lower limit of detection) of the new protocol at the PCR step was 10³CFU/mL and 10¹CFU/mL for Salmonella spp. and Shigella spp., while that at the guided culture step was 10⁴CFU/mL and 10³CFU/mL, respectively. The large scale clinical evaluation indicated that the new protocol could increase the positivity rate by two fold and decrease the workload/median turnaround time significantly. In conclusion, the protocol was verified and evaluated and was proven to be a valuable platform for the rapid, specific, sensitive and high-throughput screening of Salmonella spp./Shigella spp.

Keywords: Guided culture; Real-time PCR; Salmonella spp.; Shigella spp..