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What types of tests are available to detect Zika virus infection?
There are currently two testing methods available for detection of Zika virus infection:
- Detection of Zika virus genetic material (PCR testing): This test looks for evidence of the genetic material (RNA) of Zika virus. The test is most sensitive in the first 7 days after symptoms start when performed on blood, and in the first 14 days if performed on urine. The major limitation of this test is that genetic material can be detected for only a short time after the start of the illness. PCR may be more difficult to interpret in people without symptoms.
- Detection of antibodies against Zika virus (serology): This blood test measures antibodies against the virus that are developed as part of the human body's reaction to infection. Antibodies begin to form approximately one week after the start of symptoms. This means waiting an appropriate time following potential exposure to Zika virus before ordering the test. This test is usually done on 2 blood samples, taken 2 weeks apart, to show a rise in the level of antibodies from one sample to the next. The major advantage of a serology test is that it remains positive for several months or longer after infection. The major limitations are that it can be slow to perform and can cross-react with other viruses related to Zika virus. A positive result may represent a previous exposure to another virus, such as dengue, or past vaccination (e.g. to yellow fever). This can make interpreting the result difficult. Additional testing can be performed in specialist laboratories to clarify the result.
Further research is underway to support the needs of this outbreak.
Your usual pathology collection centre will collect the samples. They will then be sent to the most appropriate specialist testing centre as necessary.
Please give all relevant information to your health care provider. This will include mosquito bite exposure, past vaccinations or illnesses and recent (and past) travel history.
What do the Zika virus test results mean?
A positive PCR test for Zika virus genetic material means a current or very recent infection. Paired serology samples at least 2 weeks apart may be used to confirm this.
A negative PCR test for Zika virus genetic material may mean that there was no infection OR that the individual was infected but when the patient's sample was collected the virus was no longer present in the tested bodily fluid (blood or urine). Serology would then be used to decide if an infection was likely to have occurred.
A positive test for Zika virus by serology may be difficult to interpret or may require more extensive testing. Your health care provider in consultation with the pathologist will be able to assess if a Zika virus infection was likely.
A negative test for Zika virus by serology means either that the test was done too early in the disease course (no antibodies have yet been made and are not present in the collected sample), or that there was no infection. A negative serology test performed more than one to two months following return from travel indicates that there was no infection.
Who can get tested for Zika virus?
If you are worried about having been potentially infected with Zika virus during travel to areas at risk, please contact your health care provider.
Generally only people with symptoms of Zika virus infection need to be tested.
Zika virus infections in pregnant women may lead to serious outcomes for babies. Because of this, pregnant women who have travelled to areas with ongoing Zika virus transmission will also be offered testing. A positive test for Zika virus infection in a pregnant woman does not mean that her baby is infected or harmed; however she will need further specialist assessment.
Further information on testing for health professionals is available. Please refer to:
- Recommendations for assessment of pregnant women returning from Zika virus-affected areas
- Recommendations for reducing the risk of sexual transmission of Zika virus