Zika virus, a flavivirus originally found in Africa, has extended its range to southeast Asia, Pacific islands and recently caused an explosive epidemic in central and south America and the Caribbean. Mosquitoes are the primary vectors, although sexual transmission also occurs. Typical symptoms include fever, rash, headache, conjunctivitis, and arthralgia. The vast majority of infections are asymptomatic or mild and resolve without sequelae. However, Zika in pregnancy can result in congenital infection with severe birth defects, including microcephaly.

To date, more than 1,600 cases have been brought into the United States by returning travelers and mosquitoes capable of transmitting are present in much of the US. Four recent cases without travel or sexual exposure are now under investigation in southeast Florida, suggesting a Zika epidemic in the US may be underway. Therefore, it is critically important that clinicians caring for pregnant women screen for possible Zika virus infection. 

Recent studies show that Zika viremia may be more prolonged than initially thought, and may be detectable following asymptomatic infection. Based on this new information, CDC guidelines for screening have been updated.1 All pregnant women should be asked if they or their sexual partners have traveled to a Zika-endemic area, or if they have had symptoms suggestive of Zika. Those at risk should be screened for evidence of Zika infection, but the type of test varies depending on time of evaluation and history of symptoms. 

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Clinicians caring for pregnant women in the US should be familiar with the CDC testing algorithm. The new recommendation extends the use of the faster and more definitive PCR screening of blood and urine up to 14 days after onset of symptoms or possible exposure. Any positive PCR can be regarded as definitive evidence of Zika infection. Women evaluated at 2-12 weeks should be screened with Zika IgM serology, but the new guideline incorporates PCR as confirmatory test for those with detectable IgM. Because of potential false positives with IgM testing, including cross-reactivity with other flaviviruses, a positive IgM test with a negative PCR requires further confirmation and in most cases should be accompanied by testing for dengue IgM. 

Using this new approach to screening should help limit the impact of the Zika virus epidemic in the US. Further changes to the guidelines will undoubtedly follow, especially if Zika transmission becomes established within the US.


1. CDC. Update: Interim Guidance for Health Care Providers Caring for Pregnant Women with Possible Zika Virus Exposure — United States, July 2016.  MMWR. 2016; 65(29:;739–744.