How Cholera Is Diagnosed

The symptoms of cholera often look a lot like other diarrheal diseases, making it tough to diagnose it on your own or with a physical exam.

While some medical teams in endemic areas will know cholera when they see it, the only real way to determine for certain you have cholera is through a lab test.

Self-Checks/At-Home Testing 

There currently aren't any diagnostic tests for cholera designed to take at home.

The only way the disease can be officially diagnosed is with the help of trained medical professionals.

That being said, there are ways individuals on their own can check for the biggest threat from cholera: dehydration. Self-checks for dehydration involve taking stock of what the body is doing by looking for a few key characteristics:

• Are you really thirsty? 
• Do you have to pee less frequently?
• When you do go, is your urine a dark yellow?
• Try pinching your skin. Does it go right back to where it was, or does it stay puckered and take a little bit to go back down?
• Are there any other signs of dehydration, such as ​dizziness, tiredness, or mood changes? 

In most cases, dehydration can be treated at home with over-the-counter or homemade oral rehydration solutions. If severe dehydration is suspected, however, it's important to see a doctor. 

Labs and Tests

Diarrhea can be caused by a lot of different things, including several different kinds of bacteria.

That's why medical teams rely on testing stool samples to spot Vibrio cholerae, the specific bacterium that causes cholera. Lab cultures and rapid tests are valuable tools for confirming cholera and spotting an outbreak early.

Lab Cultures 

Lab cultures to isolate and identify Vibrio cholerae are currently the gold standard for detecting and diagnosing cholera.

These tests are done by taking a small stool sample and spreading it on a special medium to see if the bacteria will grow.

The medium most commonly used for cholera cultures is thiosulfate–citrate–bile salts agar (TCBS)—a complex mixture of proteins, sugars, salts, and other ingredients that is ideal for growing Vibrio cholerae specifically. The sample is laid down on the medium in streaks so the bacteria are easier to identify, then placed in an incubator for 18 to 24 hours.

The moist nutrients and warm environment are nearly perfect conditions for the bacteria to spread, and if present, cholera bacteria will grow to form large, yellow-brown dots in just a matter of hours. When that happens, additional lab work is done to confirm the bacteria really is Vibrio cholerae, and then doctors use these test results to positively diagnose cholera.

Rapid Tests 

In areas where labs aren't readily available or where time is of the essence, rapid tests like the Crystal VC Dipstick Test can be used to spot cholera in the field.

Instead of hours or (more often) days waiting to see whether someone is positive for cholera, a rapid test can give a preliminary result in just minutes. The saved time can help public health and medical teams mobilize faster to more easily contain a cholera outbreak in its early stages.

In addition to speed, these tests have a few other advantages. Namely, they don't require refrigeration (or a "cold chain") to work, allowing them to be used in more places around the world. They're also cheap, clocking in at roughly half the cost of doing a lab culture, and require significantly less training to administer. These factors are all valuable in helping identify and respond to cholera outbreaks in impoverished areas without developed infrastructure—areas often hit hardest by cholera.

The biggest downside to the rapid tests, however, is that they aren't as accurate as lab cultures. Research shows them to be remarkably good at identifying people with cholera, giving a correct "positive" result nine times out of 10.

They aren't great, however, at accurately evaluating people without cholera, often giving false positives for people who didn't actually have the cholera bacteria. For this reason, rapid tests that come back positive for cholera should still be sent off for a lab culture to confirm the diagnosis.

In some instances, public health professionals might want to perform further tests to identify the bacterium strain or toxin assay. These, however, are more often used for surveillance and outbreak response, and not necessarily for diagnosis. 

Sources: 

Centers for Disease Control and Prevention. Cholera - Vibrio cholerae: Diagnosis and detection.

Centers for Disease Control and Prevention. Laboratory methods for the diagnosis of Vibrio cholerae.

Ley B, Khatib AM, Thriemer K, von Seidlein L, Deen J, Mukhopadyay A, et al. (2012) Evaluation of a Rapid Dipstick (Crystal VC) for the Diagnosis of Cholera in Zanzibar and a Comparison with Previous Studies. PLoS ONE 7(5): e36930. https://doi.org/10.1371/journal.pone.0036930