Louissa Macfarlane-Smith

Molecular versus culture-based testing for gastrointestinal infection

Purpose of review Molecular-based diagnostic methods for the detection of gastrointestinal pathogens are becoming increasingly commonplace in microbiology laboratories. This review aims to summarize recent developments in this field and discuss the clinical application and limitations of implementing these techniques. Recent findings Recent evaluations of multiplex PCR assays show increased sensitivity whenever compared with standard microbiological culture-based methods. In addition to shorter turnaround times, assays can detect an increased repertoire of pathogens from a single specimen and provide useful information for infection prevention and control practices. There are many limitations, however, associated with their use, including clinical interpretation of results and lack of concordance between different test panels. Newer technologies, such as metagenomic analysis, can provide comprehensive information useful to both patient management and public health surveillance. Summary Molecular techniques are capable of replacing culture in the diagnosis of gastrointestinal infections. Whether all positive results, however, represent true infection is still debateable, as is the clinical significance of identifying more than one pathogen. As it currently stands, microbiological culture remains vital for public health surveillance, monitoring antibiotic resistance and managing outbreaks.

Evaluation of the novel artus C. difficile QS-RGQ, VanR QS-RGQ and MRSA/SA QS-RGQ assays for the laboratory diagnosis of Clostridium difficile infection (CDI), and for vancomycin-resistant enterococci (VRE) and methicillin-resistant Staphylococcus aureus (MRSA) screening

Clostridium difficile, methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE) are worldwide prevalent healthcare-associated pathogens. We have evaluated three Qiagen artus QS-RGQ assays for the detection of these pathogens. We examined 200 stool samples previously tested for C. difficile infection (CDI), 94 rectal swabs previously screened for VRE and 200 MRSA screening nasal swabs. With the routine diagnostic laboratory results being adopted as the gold standard, the sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of the artus C. difficile assay were 100%, for the artus VanR QS-RGQ assay, 95, 68, 44 and 98%, and for the artus MRSA/SA assay, 80, 94, 93 and 83%, respectively. The artus VanR assay detected the vanA and/or vanB genes in 32% of culture-negative VRE screens; in 71% of these cases, only vanB was detected. An over-estimation of the rate of faecal VRE colonisation could be due to a patient population with high rates of faecal carriage of non-enterococcal species carrying vanB. Based on our findings, we conclude that all three artus QS-RGQ assays could be a useful addition to a diagnostic laboratory, and that the optimal choice of assay should be determined according to user needs.