How Yellow Fever Is Diagnosed

It's Not Always an Easy Process

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Diagnosing yellow fever isn't easy. If your doctor suspects you have this disease, you should expect an array of lab tests.

Early in the illness, standard tests may not give you a definitive answer as to whether you have yellow fever or something similar to it. It gets easier to diagnose in the later stages, though, at the point when it can become life-threatening.

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Currently, we don't have an at-home test for yellow fever or the virus that causes yellow fever. That means, in order to be tested, you'll need to see your doctor.

Knowing the basic symptoms of yellow fever and whether you're at a heightened risk of complications is helpful if you have been to one of the 47 countries in Africa, South America, or Central America where yellow fever is prevalent. If you develop a flu-like illness a few days after being bit by a mosquito in any of those regions, don't delay getting medical treatment.

Doctor's Questions

You may be asked about travel to certain regions when going to your doctor's appointment. That's because the medical community goes on high alert when there's an outbreak of something serious like yellow fever. It's possible to catch this disease even when there's not an outbreak, though.

If there hasn't been a reported outbreak, it's possible that your doctor might not think to ask about travel when you go in with common symptoms such as a fever, nausea, and body aches. If you have been to an at-risk country, be sure to bring it up right away.

Labs and Tests

Once doctors suspect yellow fever, they generally run a test on the serum in your blood to look for markers that are specific to the virus that causes the illness.

Early on in the disease progression, the test may not be able to detect anything. That can be frustrating when you want to know why you're sick. Keep in mind that most cases of yellow fever do not ever progress past that point, meaning you'll be sick for a few days, then recover and be just fine.

Once a case has progressed to the later, toxic phase, the test is better able to detect it. Results, though, may take a few days to two weeks to come back.

Presumptive Diagnosis

Because 50 percent of people in the toxic stage could die within that time, doctors typically begin treatment right away based on what's called a presumptive diagnosis. That means they'll look at your symptoms along with where you've traveled to and when. Treatment involves managing the symptoms (i.e., hydration and lowering your fever) since no antiviral treatments are known to work on the virus.

Due to the risk of outbreaks, the CDC tracks cases of yellow fever in the United States. If you're at risk for it and become sick, it's important for you to be tested—otherwise, you could spread the disease to uninfected mosquitoes, who could then transmit it to other people.

You should not need any imaging tests for a diagnosis of yellow fever.

Differential Diagnoses

The symptoms that send you to the doctor with yellow fever are also common in a wide array of other illnesses. Your doctor may order additional blood tests for many other diseases with a similar presentation. These can include:

  • Severe malaria
  • Dengue fever (which is also caused by a member of the Flavivirus family)
  • Leptospirosis
  • Viral hepatitis
  • Jaundice (yellowing of the skin, from which the disease takes its name)
  • Other fevers that are hemorrhagic (involve the liver)
  • Poisoning

Your doctor may test you for any number of other things, as well, depending on your specific set of symptoms and other factors, such as lifestyle or recent travel.

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Article Sources
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  1. Centers for Disease Control and Prevention. Yellow Fever: Diagnostic Testing. Updated August 21, 2015.

  2. World Health Organization. Yellow Fever: Key Facts. Updated May 7, 2019.

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