Cholera Rapid Test with Enrichment Step Has Diagnostic Performance Equivalent to Culture

Abstract

Cholera rapid diagnostic tests (RDT) could play a central role in outbreak detection and surveillance in low-resource settings, but their modest performance has hindered their broad adoption. The addition of an enrichment step may improve test specificity. We describe the results of a prospective diagnostic evaluation of the Crystal VC RDT (Span Diagnostics, India) with enrichment step and of culture, each compared to polymerase chain reaction (PCR), during a cholera outbreak in South Sudan. RDTs were performed on alkaline peptone water inoculated with stool and incubated for 4–6 hours at ambient temperature. Cholera culture was performed from wet filter paper inoculated with stool. Molecular detection of Vibrio cholerae O1 by PCR was done from dry Whatman 903 filter papers inoculated with stool, and from wet filter paper supernatant. In August and September 2015, 101 consecutive suspected cholera cases were enrolled, of which 36 were confirmed by PCR. The enriched RDT had 86.1% (95% CI: 70.5–95.3) sensitivity and 100% (95% CI: 94.4–100) specificity compared to PCR as the reference standard. The sensitivity of culture versus PCR was 83.3% (95% CI: 67.2–93.6) for culture performed on site and 72.2% (95% CI: 54.8–85.8) at the international reference laboratory, where samples were tested after an average delay of two months after sample collection, and specificity was 98.5% (95% CI: 91.7–100) and 100% (95% CI: 94.5–100), respectively. The RDT with enrichment showed performance comparable to that of culture and could be a sustainable alternative to culture confirmation where laboratory capacity is limited.

Evaluation of the SD bioline cholera rapid diagnostic test during the 2016 cholera outbreak in Lusaka, Zambia

“…PCR was performed using stool samples stored on Whatman 903 Protein Saver Card kept at ambient temperature following previously described methods . Total DNA extraction was performed by thermal shock method.…”

“…Although several immunochromatographic RDTs are commercially available, most of the recent diagnostic evaluations have focused on one product, Crystal VC (Arkray Health Care Private Limited, India; previously Span Diagnostics, India), which has shown high sensitivity of more than 90%, but moderate specificity (49–88%) when used directly on stools . In addition, relatively high proportions of false‐positive results with the O139 line have been reported by several teams . The specificity of this test can be improved by a 4‐ to 6‐h enrichment step in alkaline peptone water (APW), with the disadvantage of increasing the necessary logistics required and delaying the turn‐around time for results to be available .…”

“…In addition, relatively high proportions of false‐positive results with the O139 line have been reported by several teams . The specificity of this test can be improved by a 4‐ to 6‐h enrichment step in alkaline peptone water (APW), with the disadvantage of increasing the necessary logistics required and delaying the turn‐around time for results to be available . First data on two other tests, Artron Vibrio cholerae O139 and O1 Combo Test (Artron Laboratories Inc, Canada) and SD Bioline Cholera Ag O1/O139 RDT (Standard Diagnostics Inc., Korea), recently came from a retrospective analysis of routine data in Haiti comparing results of cholera RDTs to culture results .…”

Neighborhood-targeted and case-triggered use of a single dose of oral cholera vaccine in an urban setting: Feasibility and vaccine coverage

“…Due to limited human resources, cases coming from areas that had not been covered in the neighborhood-targeted OCV campaign and those testing positive to the, more specific [12], enriched RDT were prioritized. When possible, teams also conducted CTI in previously vaccinated areas where it appeared that cholera transmission may have continued.…”

Quantitative Dot Blot Assays to determine Vibrio cholerae O1 Lipopolysaccharide concentration using Monoclonal Antibody

“…Several methods have been developed for the rapid diagnosis of V. cholerae O1 and O139. Some methods are based on polyclonal antibodies that allow identifying the bacteria directly from the primary isolation in culture medium [7][8][9].…”