A small case study released today by the Centers for Disease Control and Prevention (CDC) supports the agency's suspicion that when pregnant women contract the Zika virus there is higher risk for adverse outcomes for the fetus, including microcephaly.
That risk appears especially associated with a Zika infection in the first trimester of pregnancy.
The discouraging news came on the same day that the CDC issued a new travel alert recommending that pregnant women not go to the Summer Olympics in Brazil, which is experiencing surges in both Zika infections and infants with microcephaly. The agency also announced that it is establishing a special registry for pregnant women in the United States who contract the virus to better understand this public health threat.
In the latest edition of the agency's Morbidity and Mortality Weekly Report (MMWR), CDC investigators outline the cases of nine pregnant women who became infected with the Zika virus after traveling to an area of active transmission. None of them died or were hospitalized. One woman who experienced Zika symptoms in her third trimester delivered a healthy infant, as did a woman whose symptoms appeared in the second trimester. The pregnancy of another woman with second-trimester symptoms is continuing.
For six women who reported Zika symptoms in their first trimester, the outcomes were mostly grim. Two of them miscarried, two aborted their pregnancies, and another delivered an infant with microcephaly. The sixth woman has yet to deliver her child.
One woman chose to end her pregnancy after an ultrasound suggested the absence of the corpus callosum, ventriculomegaly, and brain atrophy at the 20-week mark. A follow-up fetal MRI revealed severe brain atrophy. Reverse transcription polymerase chain reaction testing detected the RNA of Zika virus in the woman's amniotic fluid.
The MMWR article did not provide details about the other woman who had an abortion, or the health status of her fetus. Denise Jamieson, MD, MPH, a member of the agency's Zika response team, said at a news conference today that there was no additional information on the second terminated pregnancy. Dr Jamieson coleads a section of the team focused on pregnancy and birth defects.
The results of the case study, small as it was, were surprising, she said.
"We did not expect to see these brain abnormalities in this small case series of US pregnant travellers," Dr Jamieson said. "It is…greater than what we would have expected."
CDC Director Tom Frieden, MD, MPH, reiterated at the news conference that although the Zika virus is strongly suspected of causing microcephaly, based on a growing body of evidence, "there's no definite proof that it's the sole cause." The CDC and public health authorities in Brazil are conducting larger studies into the relationship, but the results could be months away.
The CDC hopes to glean insights from a voluntary registry it is launching on pregnant women here who contract the Zika virus. The CDC will collect data from public health agencies and individual clinicians. Dr Jamieson said details on the registry will soon appear on the CDC website.
In another move to prevent miscarriages and fetal abnormalities, the CDC is sending so-called Zika prevention kits to three US territories — Puerto Rico, American Samoa, and the US Virgin Islands — that are experiencing active virus transmission. The kits include educational literature, mosquito repellent, mosquito netting, condoms, an oral digital thermometer, and tablets that kill mosquito larvae in standing water
Sexual Transmission of Virus More Common Than Once Believed
Another study published today in MMWR confirmed that the Zika virus spreads through sexual relations, and does so more commonly than once believed.
The article reported on 14 cases of suspected sexual transmission. In each one, a man who had traveled to an area of active virus transmission developed symptoms within 2 weeks of his female sexual partner becoming ill. Study findings moved some of the cases beyond the realm of mere suspicion.
According to the MMWR article, lab tests confirmed Zika infections in two of the women, while four others had probably contracted the virus. The CDC eliminated the cases of two women based on additional information. The investigation into the six remaining cases continues.
"We did not…anticipate that we would see this many sexually transmitted cases of Zika," Dr Frieden said at today's news conference.
After a separate case of sexually transmitted Zika — not included in the MMWR study — surfaced in Texas earlier this month, the CDC advised men who have a pregnant partner to use a condom or practice abstinence for the duration of the pregnancy if they have visited, or live in, a Zika zone.
"Today's report underscores that recommendation," Dr Frieden said.
A Cloud Over the Summer Olympics
Concern about the suspected link between the Zika virus and microcephaly prompted the CDC last month to recommend that pregnant women postpone visiting areas of active virus transmission, which include most of Latin America and the Caribbean. In a significant expansion of its travel guidance, the agency today recommended that pregnant women consider not attending the Summer Olympics in Rio de Janeiro, Brazil, scheduled for August 5 through August 21, or the Paralympic Games, scheduled for September 7 through September 18.
If pregnant women decide to go, anyway, they should consult their clinician first and, along with their partner, strictly follow steps to avoid mosquito bites, such as applying mosquito spray and wearing long-sleeve shirts and long pants, according to the CDC.
The agency encourages women who are trying to become pregnant to talk to their clinician about the risks for a Zika virus infection and precautions against mosquito bites before traveling to the Summer Olympics.
The CDC also urges precautions for sexual relations. If men travel to the Olympics, and they have a pregnant partner, they should abstain from vaginal, anal, or oral sex, or else use condoms for the duration of the pregnancy.
The CDC travel alert included other recommendations for Olympic goers, such as getting up to date on routine vaccines, traveling with a companion for safety's sake, and only during the day; and steering clear of food sold by street vendors.
The travel guidance for the 2016 Summer Olympics is available on the CDC