To Find Zika, Test Urine, not Blood, CDC Says

(CN) — The Centers for Disease Control and Prevention updated its testing guidelines for the Zika virus on Tuesday, due to data showing that the virus can last longer and in higher levels in urine than blood.

Using blood samples to test patients for Zika has been difficult since they have to be analyzed using a nuanced technique that detects the virus' genetic material. Blood tests are also less effective if collected more than seven days after a person initially experiences symptoms.

The CDC reported on an analysis of 66 people in Florida who were tested for Zika using the agency's preferred diagnostic test, called Zika virus RT-PCR.

Roughly twice as many urine samples correctly tested positive compared with blood samples. The urine test was also able to identify the virus two week after the initial onset of symptoms, since Zika leaves the blood stream after about a week.

The CDC recommends testing both blood and urine samples from patients in the first week. If more than two weeks have passed, the CDC recommends a type of blood test that can detect a person's immune response to Zika, as opposed to the virus itself.

Zika generally causes only mild symptoms such as fever, rash and joint pain — and many people who are infected experience no symptoms at all.

Since only 20 percent of infected people demonstrate symptoms, the CDC says it is difficult for health officials to determine how many Zika infections have occurred in a given area.

The CDC confirmed Zika's connection to a series of birth defects in April.

Among the birth defects was microcephaly, a congenital disorder that results in babies born with a reduced head size and potential brain damage.

The virus has spread rapidly throughout Latin America and the Caribbean since local transmission was initially reported in Brazil last year.

Earlier this year, the World Health Organization declared Zika an international health emergency.

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