Cholera laboratory tests

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editors-In-Chief: Priyamvada Singh, MBBS [2], Aysha Anwar, M.B.B.S[3]

Laboratory tests are not mandatory for diagnosis and treatment of cholera. In endemic areas when suspected, treatment should be started as early as possible with fluid replacement and antibiotics. In areas where cholera is uncommon, performing lab tests are worthwhile.Tests used for identification of organisms are: Direct microscopic examination of organism, dark field examination, gram staining, culture, antigen, polymerase chain reaction, and serotype tests.^{[1][2][3][4][5][6][7]}

Laboratory tests that may be helpful in diagnosing cholera infection include:^{[1][2][3][4][5][6][7][8]}

• Direct microscopic examination of organism (wet film)
• Dark field examination (helps visualize the motility of the organism)
• Gram staining

• Stool culture is the gold standard for Vibrio cholerae serotypes O1 and O139. A number of special media have been employed for the cultivation for Cholera vibrios. They are classified as follows:

1. Cary-Blair medium: This the most popular carrying media. This is a buffered solution of sodium chloride, sodium thioglycollate, disodium phosphate and calcium chloride at pH 8.4.
2. Venkataraman-ramakrishnan (VR) medium

1. Alkaline peptone water at pH 8.6
2. Monsur's taurocholate tellurite peptone water at pH 9.2

1. Alkaline bile salt agar: The colonies are very similar to those on Nutrient Agar.
2. Monsur's gelatin Tauro cholate trypticase tellurite agar (GTTA) medium: Cholera vibrios produce small translucent colonies with a greyish black centre.
3. TCBS medium: This the mostly widely used medium. This medium contains thiosulphate, citrate, bile salts and sucrose. Also in oysters and lobster in some cases. Cholera vibrios produce flat 2-3 mm in diameter, yellow nucleated colonies.

• Rapid tests which may help diagnose V. cholera infection in endemic areas with limited resources include Crystal VC® dipstick rapid test.^[1]
• Used for screening patients with suspected infection.
• Low sensitivity and specificity.
• Confirmation by culture required.

• Antigen, polymerase chain reaction
• Serotype tests
  • Quick method
  • Useful in epidemiological studies
  • Classic and El Tor both can be identified by using same method

Elevated serum specific gravity, protein, and hematocrit occurs due to dehydration caused by excessive fluid loss.

• Decreased sodium levels due to sodium loss in the stool.
• Serum potassium may remain normal for longer periods, which is a manifestation of the body's compensatory mechanism to deal with acidosis.
• Elevated blood urea nitrogen and creatinine (prerenal azotemia).
• Decreased pH, decreased bicarbonate (acidosis).

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  Agglutination test was used for the isolation and identification of Vibrio cholerae, the causal agent of cholera. From Public Health Image Library (PHIL). ^[9]
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  Heiberg Fermentation lab test used during the isolation and identification of Vibrio cholerae. From Public Health Image Library (PHIL). ^[9]
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  Hemolysis test tubes used for the purpose of isolation and identification of Vibrio cholerae. From Public Health Image Library (PHIL). ^[9]
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  Sensitivity test for Vibrio cholerae involving Group IV bacteriophage and Polymyxin B. From Public Health Image Library (PHIL). ^[9]
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  Typical "rice-water" stool from a cholera patient shows flecks of mucus that have settled to the bottom. From Public Health Image Library (PHIL). ^[9]

Gastroenterology

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