Evaluation of a Rapid Dipstick (Crystal VC) for the Diagnosis of Cholera in Zanzibar and a Comparison with Previous Studies

Abstract

BackgroundThe gold standard for the diagnosis of cholera is stool culture, but this requires laboratory facilities and takes at least 24 hours. A rapid diagnostic test (RDT) that can be used by minimally trained staff at treatment centers could potentially improve the reporting and management of cholera outbreaks.MethodsWe evaluated the Crystal VC™ RDT under field conditions in Zanzibar in 2009. Patients presenting to treatment centers with watery diarrhea provided a stool sample for rapid diagnostic testing. Results were compared to stool culture performed in a reference laboratory. We assessed the overall performance of the RDT and evaluated whether previous intake of antibiotics, intravenous fluids, location of testing, and skill level of the technician affected the RDT results.ResultsWe included stool samples from 624 patients. Compared to culture, the overall sensitivity of the RDT was 93.1% (95%CI: 88.7 to 96.2%), specificity was 49.2% (95%CI: 44.3 to 54.1%), the positive predictive value was 47.0% (95%CI: 42.1 to 52.0%) and the negative predictive value was 93.6% (95%CI: 89.6 to 96.5%). The overall false positivity rate was 50.8% (213/419); fieldworkers frequently misread very faint test lines as positive.ConclusionThe observed sensitivity of the Crystal VC RDT evaluated was similar compared to earlier versions, while specificity was poorer. The current version of the RDT could potentially be used as a screening tool in the field. Because of the high proportion of false positive results when field workers test stool specimens, positive results will need to be confirmed with stool culture.

Evaluation of enrichment method for the detection of Vibrio cholerae O1 using a rapid dipstick test in Bangladesh

“…However, Ley et al . () found no significant difference in cholera dipstick sensitivities between patients receiving and not receiving antibiotics.…”

“…However, a more recent evaluations in Zanzibar(Ley et al . ) and in India(Mukherjee et al . ) found no such association.…”

Use of a Cholera Rapid Diagnostic Test during a Mass Vaccination Campaign in Response to an Epidemic in Guinea, 2012

“…Rapid identification of initial cases of cholera in the early phase of an epidemic is critical for implementation of a timely public health response [4] to control the spread and duration of the outbreak. Currently, cholera diagnosis relies on the microbiological identification of the pathogen by stool culture, which remains the gold standard to confirm the diagnosis [5]. However, this procedure requires laboratory infrastructure, adequate transport procedures and trained staff [5].…”

“…Currently, cholera diagnosis relies on the microbiological identification of the pathogen by stool culture, which remains the gold standard to confirm the diagnosis [5]. However, this procedure requires laboratory infrastructure, adequate transport procedures and trained staff [5]. As rapid diagnostic tests (RDT) require less time, a minimum laboratory infrastructure and basic technical skills, they are used to confirm cholera outbreaks in places where high laboratory standards are difficult to obtain [6].…”

“…This cross-reactivity between O139 LPS and capsular polysaccharide explains that antibodies react with both encapsulated and non-encapsulated V. cholerae O139 strains [10]. The RDT is produced by Span Diagnostics (Surat, India) under the trade name Crystal VC [5]. Several evaluations have shown good sensitivity, ranging from 92% to 100% [7], [11]–[12].…”