Question

There are several ways to diagnose cholera. Give three ways and explain each in detail.

Answer 1

1. Stool culture — A definitive diagnosis of cholera is based on isolation of the organism from clinical samples, which also permits a determination of the antibiotic susceptibility profile. V. cholerae can be isolated from stool using selective media such as thiosulfate citrate bile sucrose (TCBS) agar or taurocholate tellurite gelatin agar (TTGA). Once cultured, V. cholerae can be identified by biochemical tests; serogroup and serotype can be assigned by testing with specific antibodies [44]. In settings such as the United States, where cholera is a sporadic illness, the clinical microbiology laboratory should be informed of suspicion of cholera so that appropriate selective media can be used. These selective media are not routinely used for stool culture.

The recovery of viable V. cholerae from clinical specimens can be enhanced by enrichment in alkaline peptone water [44]. V. cholerae can also persist in a number of standard transport media, including Cary-Blair media while being transported to a central laboratory from field settings.

2. Rapid tests — There are several rapid tests that may be performed to make a presumptive diagnosis of cholera [45]. These include commercially available immunochromatographic lateral flow devices such as Crystal VC (Span Diagnostics), which detect the presence of the O1 or O139 antigen in rice water stool samples. While the sensitivity of Crystal VC is over 95 percent, the specificity of the test has ranged between 65 to 85 percent in field settings [46]. The low specificity of dipstick tests can limit their diagnostic utility in endemic areas, but a preponderance of positive tests in a small cohort of patients with diarrhea is useful in confirming a suspected outbreak in settings where cholera was not previously known to be endemic.

3. Dipstick rapid test - The Crystal® VC dipstick rapid test can provide an early warning to public health officials that an outbreak of cholera is occurring. However, the sensitivity and specificity of this test is not optimal.