Image: Two Cholkit dipsticks showing characteristic negative (left image) and positive (right image) results after 15 minutes sample run (Photo courtesy of International Centre for Diarrhoeal Disease Research).
Cholera is an acute watery diarrheal disease caused mainly by Vibrio cholerae serogroup O1 and less commonly by V. cholerae O139. Cholera can lead to severe diarrhea and death if untreated.
Recognizing cholera cases early, especially in the initial phase of an outbreak and in areas where cholera has not previously circulated, is a high public health priority and laboratory capacity in such settings is often limited. Globally, 3 to 5 million cases and over 100,000 deaths occur annually due to cholera.
An international team of scientists working with the International Centre for Diarrhoeal Disease Research (Dhaka, Bangladesh) collected fresh stools from 76 hospitalized adults and children at the Dhaka Hospital who presented with acute watery diarrhea. They performed conventional stool culture by streaking stool directly on selective TTGA (taurocholate-tellurite gelatin agar) plates, and incubated these plates overnight at 37 °C.
Colonies morphologically consistent with V. cholerae were analyzed by slide agglutination with monoclonal antibodies specific to V. cholerae serovar O1 (Ogawa or Inaba) and O139. The team compared their recently developed rapid diagnostic test (RDT) termed Cholkit that is based on an immunochromatographic lateral flow assay for the diagnosis of cholera cases using stool with the commercially available RDT, Crystal VC and a polymerase chain reaction (PCR) targeting the rfb and ctxA genes of V. cholerae.
The scientists reported that stool specimens from 76 patients were tested by all four of microbial culture, Cholkit, Crystal VC and PCR assays. Nineteen samples were positive by culture and all of them were confirmed as positive for V. cholerae O1 Inaba except one sample that was V. cholerae O1 Ogawa. Out of 19 stools positive by culture, all 19 (100%) were positive by both Cholkit and Crystal VC assays, and 15 (79%) were positive by PCR. Of all of the 57 patients with a negative stool culture Cholkit, Crystal VC and PCR were positive for 11 (19%), 12 (21%), and 6 (11%), respectively.
The authors concluded that the Cholkit dipstick is simple to use, requires no dedicated laboratory capacity, and has a sensitivity and specificity for V. cholerae O1 of 98% and 97%, respectively. The study was published on March 14, 2018, in the journal Public Library of Science Neglected Tropical Diseases.
International Centre for Diarrhoeal Disease Research