Cholera laboratory tests

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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]

## Overview

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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 Findings

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

### Stool Examination

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

### Stool Cultue

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* 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:

#### Holding or Transport Media

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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

#### Enrichment Media

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

#### Plating Media

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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

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* 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 and Antibody Tests

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

### Hemogram

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

### Serum Electrolytes

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* 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).

## Gallery

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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]

* Heiberg Fermentation lab test used during the isolation and identification of Vibrio cholerae. From Public Health Image Library (PHIL). [9]

* Hemolysis test tubes used for the purpose of isolation and identification of Vibrio cholerae. From Public Health Image Library (PHIL). [9]

* Sensitivity test for Vibrio cholerae involving Group IV bacteriophage and Polymyxin B. From Public Health Image Library (PHIL). [9]

* 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]

## References

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1. ↑ 1.0 1.1 1.2 http://www.cdc.gov/cholera/laboratory.html Accessed on October 7, 2016
2. ↑ 2.0 2.1 Alam M, Hasan NA, Sultana M, Nair GB, Sadique A, Faruque AS; et al. (2010). "Diagnostic limitations to accurate diagnosis of cholera". J Clin Microbiol. 48 (11): 3918–22. doi:10.1128/JCM.00616-10. PMC 3020846. PMID 20739485.CS1 maint: Explicit use of et al. (link) CS1 maint: Multiple names: authors list (link)
3. ↑ 3.0 3.1 Page AL, Alberti KP, Mondonge V, Rauzier J, Quilici ML, Guerin PJ (2012). "Evaluation of a rapid test for the diagnosis of cholera in the absence of a gold standard". PLoS One. 7 (5): e37360. doi:10.1371/journal.pone.0037360. PMC 3364251. PMID 22666350.CS1 maint: Multiple names: authors list (link)
4. ↑ 4.0 4.1 Rahman M, Sack DA, Mahmood S, Hossain A (1987). "Rapid diagnosis of cholera by coagglutination test using 4-h fecal enrichment cultures". J Clin Microbiol. 25 (11): 2204–6. PMC 269441. PMID 3693549.CS1 maint: Multiple names: authors list (link)
5. ↑ 5.0 5.1 BENENSON AS, ISLAM MR, GREENOUGH WB (1964). "RAPID IDENTIFICATION OF VIBRIO CHOLERAE BY DARKFIELD MICROSCOPY". Bull World Health Organ. 30: 827–31. PMC 2555074. PMID 14215188.CS1 maint: Multiple names: authors list (link)
6. ↑ 6.0 6.1 Lyon WJ (2001). "TaqMan PCR for detection of Vibrio cholerae O1, O139, non-O1, and non-O139 in pure cultures, raw oysters, and synthetic seawater". Appl Environ Microbiol. 67 (10): 4685–93. PMC 93220. PMID 11571173.
7. ↑ 7.0 7.1 Harris JB, LaRocque RC, Qadri F, Ryan ET, Calderwood SB (2012). "Cholera". Lancet. 379 (9835): 2466–76. doi:10.1016/S0140-6736(12)60436-X. PMC 3761070. PMID 22748592.CS1 maint: Multiple names: authors list (link)
8. ↑ Shirai H, Nishibuchi M, Ramamurthy T, Bhattacharya SK, Pal SC, Takeda Y (1991). "Polymerase chain reaction for detection of the cholera enterotoxin operon of Vibrio cholerae". J Clin Microbiol. 29 (11): 2517–21. PMC 270365. PMID 1774258.CS1 maint: Multiple names: authors list (link)
9. ↑ 9.0 9.1 9.2 9.3 9.4 "Public Health Image Library (PHIL)".

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