Evaluation of the performance of the QIAstat-Dx® Gastrointestinal Panel 2 for the detection of pathogens from stool at a diagnostic laboratory in South Africa

Results:In the retrospective arm a total of 32 isolates were tested on the ME panel which were all correctly detected by the QIAstat-Dx assay.In the prospective arm, 60 CSF specimens were evaluated.The positivity rate for bacterial and fungal pathogens was 10% for the ME panel, whereas culture had a positivity rate of 1.67% for on-panel pathogens.The culture-negative bacterial organisms detected by the QIAstat-Dx assay in the prospective arm included Streptococcus pyogenes(1), Streptococcus pneumoniae (1), Neisseria meningitidis(1) andStreptococcus agalactiae(1).Off panel targets detected by routine methods, which were not detected by the QIAstat-Dx assay included Staphylococcus epidermidis (in a neurosurgical patient) and cytomegalovirus.Fourteen of the prospective arm specimens underwent routine viral testing on request of the treating clinician.The QIAstat-Dx assay outperformed the labs routine PCR assay with a positivity rate of 14.3% compared to 7.14% for viral targets detected by both assays.Discussion: In the retrospective arm, the QIAstat-Dx displayed a sensitivity and specificity of 100%.In the prospective study, the QIAstat-Dx detected many more bacterial and fungal pathogens than culture.This was probably due to low numbers of organisms beyond the threshold of culture.Culture should still be performed on CSF specimens in parallel with these molecular tests, to detect significant off panel pathogens.The assay's detection rate of viral pathogens is double that of the current molecular assays detection rate.Discordant testing will reveal if the additional targets detected on QIAstat-Dx were false positives. Conclusion:Multiplex PCR assays provide a rapid evaluation of CSF for pathogens implicated in meningitis.This has implications for early initiation of appropriate therapy and institution of infection prevention and control practices.