Key points
- Testing a stool sample is usually needed to confirm if a single patient with acute watery diarrhea has cholera.
- Confirming if a patient has cholera is important since the disease can spread quickly and cause an outbreak.
Considerations
Testing a stool sample is almost always necessary to determine if a patient with acute watery diarrhea has cholera. Considering the clinical features of multiple patients who are part of a suspected outbreak of watery diarrhea also can be helpful.
About Vibrio cholerae O1 or O139
Serogroups O1 and O139, types of Vibrio cholerae bacteria, can produce a toxin that causes the disease known as cholera.
Only toxigenic strains of serogroups O1 and O139 cause widespread epidemics and are reportable to the World Health Organization (WHO) as cholera.
Vibrio cholerae O1 has two biotypes, Classical and El Tor. Each biotype has distinct serotypes: Inaba, Ogawa, and rarely Hikojima. The symptoms of infection are indistinguishable. A higher proportion of people infected with the El Tor biotype remain asymptomatic or have only a mild illness.
Infections with the Classical biotype of Vibrio cholerae O1 have become rare and limited to parts of Bangladesh and India.
Many other serogroups of Vibrio cholerae, both those with and without the cholera toxin gene, can cause cholera-like illness. Non-toxigenic strains of the O1 and O139 serogroups also can cause illness resembling cholera.
Diagnosing cholera
The most reliable way to diagnose cholera in the laboratory is to isolate and identify Vibrio cholerae serogroup O1 or O139 by culture of a stool specimen.
If you suspect cholera, notify your lab so they will culture on thiosulfate-citrate-bile salts-sucrose (TCBS) agar. TCBS is the preferred selective media for isolation and identification. However, if symptoms are severe, don't wait for a positive culture before starting aggressive treatment.
Cary Blair media is used to preserve and transport stool samples to the laboratory for testing. Reagents for serogrouping Vibrio cholerae isolates are available in U.S. state health department laboratories.
Commercially available rapid test kits are useful in epidemic settings. However, they don't yield an isolate for antimicrobial susceptibility testing and subtyping. They should not be used for routine diagnosis.
In countries where cholera occurs but access to diagnostic laboratory testing is difficult, WHO recommends the following clinical definitions:
Suspected case of cholera
- In areas where a cholera outbreak hasn't been declared:
- A suspected case is any patient 2 years and older presenting with acute watery diarrhea and severe dehydration.
- A suspected case is any patient 2 years and older dying from acute watery diarrhea.
- A suspected case is any patient 2 years and older presenting with acute watery diarrhea and severe dehydration.
- In areas where a cholera outbreak is declared:
- A suspected case is any person presenting with or dying from acute watery diarrhea.
- A suspected case is any person presenting with or dying from acute watery diarrhea.
Confirmed case of cholera
- A confirmed case is a suspected case with Vibrio cholerae O1 or O139 confirmed by culture or PCR (polymerase chain reaction).
- In countries where cholera isn't present or has been eliminated, a confirmed case is one in which the Vibrio cholerae O1 or O139 strain is toxigenic.
The Crystal® VC dipstick rapid test can provide an early warning to public health officials that a cholera outbreak is occurring. However, the sensitivity and specificity of this test is not optimal.
Fecal specimens testing positive for Vibrio cholerae O1 or O139 by the Crystal® VC dipstick rapid test should be confirmed using traditional culture-based methods suitable for the isolation and identification of Vibrio cholerae.
Reporting cases
Cholera is a nationally reportable disease in the United States. All isolates should be sent to CDC through state health department laboratories for cholera toxin-testing and subtyping.