Diagnostic Limitations to Accurate Diagnosis of Cholera

ABSTRACTThe treatment regimen for diarrhea depends greatly on correct diagnosis of its etiology. Recent diarrhea outbreaks in Bangladesh showed Vibrio choleraeto be the predominant cause, although more than 40% of the suspected cases failed to show cholera etiology by conventional culture methods (CMs). In the present study, suspected cholera stools collected from every 50th patient during an acute diarrheal outbreak were analyzed extensively using different microbiological and molecular tools to determine their etiology. Of 135 stools tested, 86 (64%) produced V. choleraeO1 by CMs, while 119 (88%) tested positive for V. choleraeO1 by rapid cholera dipstick (DS) assay; all but three samples positive for V. choleraeO1 by CMs were also positive for V. choleraeO1 by DS assay. Of 49 stools that lacked CM-based cholera etiology despite most being positive for V. choleraeO1 by DS assay, 25 (51%) had coccoid V. choleraeO1 cells as confirmed by direct fluorescent antibody (DFA) assay, 36 (73%) amplified primers for the genes wbeO1 and ctxAby multiplex-PCR (M-PCR), and 31 (63%) showed El Tor-specific lytic phage on plaque assay (PA). Each of these methods allowed the cholera etiology to be confirmed for 97% of the stool samples. The results suggest that suspected cholera stools that fail to show etiology by CMs during acute diarrhea outbreaks may be due to the inactivation of V. choleraeby in vivovibriolytic action of the phage and/or nonculturability induced as a host response.