Validation of a Rapid Loop-Mediated Isothermal Amplification-Based Test for the Detection of Shigella from Rectal Swab.

Abstract

The rapid loop-mediated isothermal amplification-based diagnostic test (RLDT) has been validated as a simple, sensitive, and rapid tool for detecting Shigella spp. from fresh or frozen stool. When stool is unavailable or difficult to transport, rectal swabs (RSs) in Cary-Blair medium, stool collected in buffered glycerol saline (BGS), or stool-dipped swabs (SDSs) in Cary-Blair medium offer alternatives that can be easily collected and transported without maintaining a cold chain. This study evaluated the performance of RLDTs for detecting Shigella spp. from RSs, stool collected in BGS, and SDSs compared with fresh stool (FS). Paired RSs and FS were collected from 105 children younger than 5 years old at two hospitals in Bangladesh. Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy were determined along with the agreement between assays using kappa statistics. The RLDTs detected Shigella in approximately 38-40% of samples across all sample types. Rectal swabs in Cary-Blair medium and SDS each showed 97.6% sensitivity and 100% specificity, with PPVs of 100% and NPVs of 98.5% (RSs) and 98.4% (SDSs) compared with FS; stool collected in BGS samples demonstrated the highest sensitivity (100%) and NPV (100%), with 98.4% specificity and 97.6% PPV. All alternative specimen types showed almost perfect agreement with FS. The RLDT performed well using RSs, indicating a practical alternative to stool for detecting Shigella. The assay was also reliable with stool collected in BGS and SDSs. Broader adoption of RLDTs could improve diagnostic capacity and strengthen surveillance and control efforts.