Feasibility of a Molecular Screening Method for Detection of Salmonella enterica and Campylobacter jejuni in a Routine Community-Based Clinical Microbiology Laboratory

Conventional diagnostic methods for the detection of Salmonella enterica and Campylobacter jejuni are laborious and time-consuming procedures, resulting in final results, for the majority of specimens, only after 3 to 4 days. Molecular detection can improve the time to reporting of the final results from several days to the next day. However, molecular assays for the detection of gastrointestinal pathogens directly from stool specimens have not made it into the routine clinical microbiology laboratory. In this study we have assessed the feasibility of a real-time PCR-based molecular screening method (MSM), aimed at S. enterica and C. jejuni, in the daily practice of a routine clinical microbiology laboratory. We have prospectively analyzed 2,067 stool specimens submitted for routine detection of gastrointestinal bacterial pathogens over a 7-month period. The MSM showed 98 to 100% sensitivity but routine culture showed only 77.8 to 86.8% sensitivity when an extended "gold standard" that included all culture-positive and all MSM-positive specimens, as confirmed by an independent secondary PCR of a different target gene, was used. An overall improvement in the rate of detection of both pathogens of 15 to 18% was observed. Both approaches performed nearly identically with regard to the specificity, positive predictive value, and negative predictive value, with the values for MSM being 99.7%, 93.1 to 96.6%, and 99.8 to 100%, respectively, and those for routine culture being 100%, 100%, and 97.6 to 99.5%, respectively. Finally, the final results were reported between 3 and 4 days earlier for negative specimens compared to the time of reporting of the results of routine culture. Positive specimens, on the other hand, required an additional 2 days to obtain a final result compared to the time required for routine culture, although preliminary MSM PCR-positive results were reported, on average, 2.9 to 3.8 days before the final routine culture results were reported. In conclusion, MSM can be incorporated into the daily practice of a routine clinical microbiology laboratory with ease. Furthermore, it provides an improvement in the screening for S. enterica and C. jejuni and substantially improves the time to the reporting of negative results.