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An Aedes aegypti mosquito, the chief vector of Zika virus. Photograph by James Gathany, CDC

CDC Recommendations for Pregnant Women Exposed to Zika

(This post has been updated twice.)

The Centers for Disease Control and Prevention has responded to growing alarm over the Zika virus epidemic in Central and South America with quickly published guidelines covering health care and tests for pregnant women who may have been exposed to the virus.

The guidelines come on the heels of the CDC’s recommendation last Friday night that US women who are pregnant, or planning to become pregnant, avoid traveling to the 13 countries where transmission of Zika has occurred, and also to the US territory of Puerto Rico.

Zika, which is transmitted by mosquitoes, arrived in South America in 2014 and ignited a pandemic. Most of the adult cases, which number more than 1 million, have been mild. (It is generally accepted that four out of five people infected with Zika do not develop symptoms; so the true number of those infected is likely more than 5 million.) But in Brazil, there has been an epidemic of a birth defect called microcephaly—smaller than usual brains and heads in newborns— that is associated temporally, and by some lab tests, with Zika infection. So far in Brazil there have been more than 3,500 cases of microcephaly. Zika has come to the United States as well, with local transmission in Puerto Rico and an imported case in the county surrounding Houston, and on Friday, a baby born in Hawaii to a woman who lived in Brazil while she was pregnant was diagnosed with Zika microcephaly. Today, the Illinois Department of Public Health disclosed that it is monitoring two pregnant women who traveled to Zika transmission areas.

(Update, Jan. 20: According to Florida media, that state’s department of health has announced three cases in Florida, all travel-related.)

The CDC’s guidelines today offer advice for pregnant women who traveled to a location where Zika is circulating, whether or not the woman reports symptoms of Zika infection: sudden fever, a rash, conjunctivitis, and joint pain. Broadly, women with a travel history and symptoms should have blood drawn to be tested for Zika infection—the test can be performed only by the CDC and some health departments—and if positive, should have regular ultrasounds to track fetal development and should be seen by one of several specialists. Pregnant women who traveled to a Zika area but did not experience symptoms are recommended to undergo ultrasounds first, and to seek a test to confirm infection if there are abnormalities in the imaging.

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The CDC’s advice for testing and treating pregnant women exposed to Zika virus, expressed as a flow chart. Graphic by the CDC; original here.

Within the text of the recommendations, which were published as an early release from the CDC’s weekly journal Morbidity and Mortality Weekly Report, there are hints of how complex this emerging situation has become. There is no vaccine for Zika, so as prevention the agency can recommend only “wearing long-sleeved shirts and long pants, using U.S. Environmental Protection Agency-registered insect repellents, using permethrin-treated clothing and gear, and staying and sleeping in screened-in or air-conditioned rooms.” There is no specific treatment, so it can recommend only “rest, fluids, and use of analgesics and antipyretics. Fever should be treated with acetaminophen.” (The CDC specifically rules out aspirin, because the mosquito-borne diseases chikungunya and dengue are also circulating in the areas where Zika is, and dengue can lead to hemorrhagic fever—so drugs that can increase bleeding are not recommended.)

The limited options for confirming Zika in a fetus are especially difficult, since amniocentesis—which could yield a sample for testing—also carries a risk of miscarriage. The CDC says:

Zika virus RT-PCR testing can be performed on amniotic fluid. Currently, it is unknown how sensitive or specific this test is for congenital infection. Also, it is unknown if a positive result is predictive of a subsequent fetal abnormality, and if so, what proportion of infants born after infection will have abnormalities. Amniocentesis is associated with an overall 0.1% risk of pregnancy loss when performed at less than 24 weeks of gestation…. early amniocentesis (≤14 weeks of gestation) is not recommended. Health care providers should discuss the risks and benefits of amniocentesis with their patients.

The CDC has also published guidance for health care professionals here, and explanations of how to send samples for testing here.

Update, Jan. 22: The CDC has added Barbados, Bolivia, Ecuador, Guadeloupe, Saint Martin, Guyana, Cape Verde, and Samoa to its “don’t travel if pregnant” list.

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