Getting tested for Zika

doctor and patient illustration

A doctor is your best adviser when determining whether to get tested for Zika, and what tests you need (CDC).

So you and your significant other are considering whether to get pregnant; but the summer’s headlines about Zika virus and its effect on developing babies has you worried.  Or maybe you’ve just returned from traveling to an area where Zika is active.  You’ve not experienced symptoms of Zika, but you’ve been around others with the disease and you know that 4 out of 5 people who get Zika show no symptoms.  You wonder if you might be infectious to your spouse or partner (Zika can be sexually transmitted). In both cases a test to see whether you might have Zika sounds like a good idea.

So are there tests for Zika?  And if so, which one is right for you?

It turns out that there are multiple kinds of tests for Zika, although no one test is consistently definitive.  The RT-PCR test (Real Time Polymerase Chain Reaction) test is the go-to test used by doctors to see if you have an active case of Zika.  It can be used to test blood serum, saliva or urine, but generally is sensitive only to viral levels present during active infections (first 5 days of illness for blood serum, 2-12 weeks for urine).  Its primary advantages are lower cost and speed, with results available as soon as the same day.

After illness has passed, doctors must rely on tests that look for the presence of antibodies left over after the body has fought off the infection.  A test called IgM-capture enzyme-linked immunosorbent assay (MAC-ELISA) can detect whether IgM and IgG antibodies are present in the blood serum for several months after infection.  Unfortunately, these tests can also react to antibodies from other mosquito-borne viruses, like dengue fever.  So additional dengue-specific tests (PRNT) may also be needed to confirm whether the person has been exposed to dengue or Zika.  These tests are more time consuming and expensive and may require up to a week to perform.

zika rash

An itchy rash is one of the symptoms of Zika infection brought on by a mosquito bite (Photo by Jackie Thornton).

Your doctor or public health office is the best authority to determine what type of test you might need.

So should you get tested?  Unless you live in south Florida, or unless you or your sex partner have recently traveled to an area of high Zika risk, the chances that you have been exposed to the Zika virus is extremely low.  In fact, the CDC does not recommend Zika testing for asymptomatic men, children or women who are not pregnant.

Zika testing is currently being provided free by the Centers for Disease Control and regional public health laboratories, but only for the following people:

  • Those with more than one Zika symptom who have traveled to an area with Zika infection or had unprotected sex with a partner who has traveled to such an area within the past 4 weeks;
  • Pregnant women who have traveled to a Zika area during their pregnancy, or 8 weeks before conception, or who had unprotected sex with a partner who spent time in such an area;
  • Those with Guillain-Barré syndrome with Zika exposure history;
  • Infants born to a woman with a positive or inconclusive Zika test;
  • Infant born with microcephaly by mother with Zika exposure history;
  • Those with Zika symptoms and who may have had an alternative mode of acquisition like a blood transfusion or organ transplant.

Women who think they may have been exposed to Zika, and who want to get pregnant but do not meet any of the above criteria, are not being tested now by the CDC or public health agencies.  Instead, if you fall into this category you are advised to avoid getting pregnant for two months and practice protected sex for six months.  One of the reasons for excluding non-pregnant women is that testing laboratories are currently backlogged with high priority cases.  Even if you meet one of the above criteria, test results may take up to 4 weeks to be received.

There are private laboratories (Viracor, LabCorps, and QuestDiagnostics) that will test blood and urine for Zika through your private physician, with costs ranging from approximately $165 for PCR testing to $700 for IgM and IgG testing.  If you opt for this route, you will bear the cost of testing and will have to proceed through your own physician.

As of 16 September 2016, there were 79 cases of locally acquired Zika in the U.S.  All of the locally acquired cases came from the south Florida/Miami/Dade County area.  So far there has been no local (non-travel related) transmission by mosquitoes of Zika in Texas.

[Thanks to Dr. Robert W. Haley, University of Texas-Southwestern, for some of the background information for this post.]

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