Rapid tests as a practical alternative to slide agglutination for the confirmation of O1.

Slide agglutination for serogroup and/or serotype identification is a crucial step for confirming cholera by culture. Rapid diagnostic tests (RDTs) are typically used directly on stool but are not considered sufficient for cholera confirmation. However, they may provide a practical alternative to the slide agglutination step of culture as they are easy to use, store, and require minimal training. This study evaluates the concordance of O1/O139 detection from presumptive colonies by slide agglutination with RDTs. Patients (≥1 year) with acute watery diarrhea at the icddr,b Dhaka hospital were enrolled. Stool samples were cultured on thiosulfate-citrate-bile salts-sucrose medium, and presumptive colonies were subcultured on Gelatin Agar medium. Isolates were then tested by slide agglutination and four commercial cholera RDTs. From 4 February 2024 through 24 May 2025, 1,638 patients with acute watery diarrhea were enrolled, 1,140 (70%) had presumptive colonies, and 482 (29%) were culture-confirmed as O1. We tested suspected colonies using Cholkit (n=1,140), SD Bioline (n=693), Crystal VC O1/O139 (n=693), and Crystal VC O1 (n=655) RDT kits. RDTs showed near-perfect concordance with slide agglutination. Using slide agglutination as the reference, the sensitivity of the RDT kits ranged from 99.3% to 99.6% and the specificity from 99.3% to 99.7%. RDTs offer a practical and potentially easier alternative to slide agglutination of presumptive colonies within typical cholera culture protocols. This may help to provide a pathway to quick confirmation of outbreaks in settings where lab facilities and reagents may be limited.IMPORTANCEThis study demonstrated that rapid diagnostic tests (RDTs) can effectively replace traditional slide agglutination methods to confirm suspected colonies belonging to the O1 serogroup, which are responsible for the current seventh cholera pandemic. Comparing four RDTs to slide agglutination, we found almost perfect agreement, with sensitivity and specificity exceeding 99%. Since RDTs are cheaper, easier to use and store, and require less technical training, adopting them could significantly speed up cholera outbreak confirmation, especially in areas with limited laboratory resources. This practical shift could lead to faster responses to cholera outbreaks, ultimately improving public health surveillance and disease control globally.