Liz Szabo

USA TODAY

Urine is more accurate than blood in testing for the mosquito-borne Zika virus, a finding that may allow patients with the disease to be more easily diagnosed, the Centers for Disease Control and Prevention said Tuesday.

The Zika virus disappears from blood within about five days after symptoms appear. That means blood tests that look for genetic material from the virus, called PCR tests, can be negative after that time, even in infected people. Zika remains in urine for about a week longer.

In a study of 53 people whose urine, saliva and blood were collected on the same day, 92% urine samples tested positive for Zika, compared to 81% of saliva samples and 51% of blood samples, according to the CDC.

Based on the findings, the CDC now recommends doctors use urine tests less than 14 days after Zika-like symptoms begin. Doctors should use both urine and blood tests if symptoms began less than a week earlier, said CDC epidemiologist Marc Fischer.

Doctors testing patients whose symptoms appeared more than two weeks ago can run an alternative test, which looks for the presence of antibodies to Zika. This test takes longer to perform than PCR tests, Fischer said. This test also can produce inaccurate results in people who have dengue virus, a mosquito-borne illness that's similar to Zika.

Only about 20% of Zika patients experience symptoms, which include a rash, fever, headache, joint aches and pink eye.

The Food and Drug Administration approved the first commercial blood test for Zika, made by Quest Diagnostics, last month.

FDA approves first commercial test for Zika

Patients shouldn't expect quick answers, no matter what test is used.

"Given the current volume of samples, test results will not be available for at least three weeks after specimen receipt," according to the CDC. Getting results could take even longer in the summer, when mosquitoes are more active and more people ask to be tested.

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