Balancing Diagnostic Sensitivity and Operational Efficiency in MRSA Screening: A Study of Pooled Multi-Site Swabs With and without Viral Transport Media Using GeneXpert®

Methicillin-resistant Staphylococcus aureus (MRSA) remains a significant cause of healthcare-associated infections. Early identification of colonized individuals upon hospital admission is essential for effective infection control. This study aimed to evaluate the performance of pooled MRSA screening using the GeneXpert®system (Cepheid) under two conditions: with and without viral transport media (VTM). The goal was to assess the sensitivity of pooling strategies while minimizing reagent use, processing time, and laboratory workload. Swabs were collected from three anatomical sites, the axilla, groin, and nares, from newly admitted patients. Samples were pooled either with VTM or without VTM and then tested using the Xpert®MRSA assay. Experiments were conducted using three pooling configurations: (1) one positive and two negative swabs, (2) two positive and one negative swab, and (3) three positive swabs. The limit of detection (LoD) was also assessed for both VTM and non-VTM conditions through serial dilutions of known MRSA concentrations. In non-VTM pools, positive detection rates were 55%, 80%, and 100% for pools containing one, two, and three MRSA-positive swabs, respectively. In VTM pools, detection rates improved to 75%, 90%, and 100% for the same configurations. The LoD analysis confirmed that MRSA was detectable at low concentrations in both VTM- and non-VTM-pooled samples, with slightly higher sensitivity in the VTM group. No false negatives were observed in pools containing three positive samples under either condition. Pooling of MRSA screening samples using the GeneXpert®system is a viable strategy to reduce testing costs and workload. Detection sensitivity increases with bacterial load, and the use of VTM enhances performance, particularly in scenarios with low-prevalence. These findings support the implementation of pooled MRSA screening as an efficient and reliable method in hospital admission protocols.