The Centers for Disease Control and Prevention (CDC) on Friday issued new interim guidance for the prevention of sexual transmission of the Zika virus, as well as new interim guidance for health care providers to use in taking care of pregnant women and women of reproductive age. 

The sexual guidelines apply to “all methods” of sexual contact between males who have traveled to areas where active Zika transmission is taking place and pregnant women. This means oral, anal and vaginal sex. 

It does not apply to male sexual contact with other males.

The sexual guidelines come in the wake of a case in Dallas in which the virus was spread via sexual contact between a traveler returning from a Zika-affected country and a non-traveler. 

The new guidelines say that pregnant women who have traveled to a country where active Zika virus transmission is taking place should be tested for the virus between two and 12 weeks after returning from such travel. 

It also says pregnant women should use condoms to prevent the spread of Zika, or consider abstaining from sex for the duration of their pregnancy. 

According to the CDC:

“Men with a pregnant sex partner who reside in or have traveled to an area of active Zika virus transmission and their pregnant sex partners should consistently and correctly use condoms during sex (vaginal, anal, or oral) or abstain from sexual activity for the duration of the pregnancy. Consistent and correct use of latex condoms reduces the risk of sexual transmission of many infections, including those caused by other viruses.”

The CDC’s guidance does not specifically call for abstinence as the preferred or only option in situations involving pregnant or non-pregnant sexual partners, although it does say it should be “considered” along with consistent use of latex condoms for concerned couples.

There have only been three cases on record in the medical literature in which the Zika virus has been spread by sexual contact or blood transfusions, meaning that mosquitoes are most likely causing the vast majority of cases, said CDC director Tom Frieden in a press conference call. 

The virus is mainly spread by the widely distributed Aedes aegypti mosquito, which is an aggressive daytime biter and can be found in parts of North America as well as most of Central and South America. This mosquito species also carries other viruses, including Dengue and Chikungunya.

Frieden said there is increasing evidence that the Zika virus causes a devastating birth defect known as microcephaly, in which babies are born with smaller than average heads and incomplete brain development. In addition, the virus has been tied to Guillain Barré Syndrome in adults, which can cause temporary paralysis. The evidence on that, too, is mounting, but not yet conclusive, he said.

“With each passing day, the linkage between Zika and microcephaly becomes stronger,” he said, adding that the same is true for the tie between Zika and Guillain Barré Syndrome.

“I wish we knew more about Zika today. I wish we could do more about Zika today.”

“I wish we knew more about Zika today. I wish we could do more about Zika today,” Frieden said. 

A surge in microcephaly and Guillain Barré cases has been reported in Brazil, which is the epicenter of the Zika outbreak, since October of 2015. Outside of Brazil, there have been cases, including one microcephaly case involving a returning traveler from Brazil to Hawaii, but the time between infection and birth means that countries such as Colombia, where Zika transmission has recently been detected, have not yet seen an increase in such cases, Frieden said.

“We are quite literally discovering more about it each and every day.”

To illustrate how rare the Zika connection to microcephaly would be, Frieden said that if proven, Zika would be the first virus in more than 50 years to cause a birth-related abnormality. He also said he is unaware of any other mosquito-borne illness that is linked with birth defects such as microcephaly. 

Focus remains on mosquito transmission

Although sexual transmission of Zika virus infection is possible, mosquito bites from the widely distributed Aedes aegypti mosquito remain the primary way that Zika virus is transmitted. Because there is currently no vaccine or treatment for Zika virus, the best way to avoid Zika virus infection is to prevent mosquito bites.

While the CDC’s main focus is on preventing pregnant women from being infected with the virus, the new guidelines also include recommendations for non-pregnant women, and men with non-pregnant sexual partners who live in or have traveled to Zika-affected areas.

Here is the CDC’s advice for this category of people:

Couples in which a man resides in or has traveled to an area of active Zika virus transmission who are concerned about sexual transmission of Zika virus may consider using condoms consistently and correctly during sex or abstaining from sexual activity.

In the interim guidance issued Friday morning, the CDC admits that doctors do not know how long the risk of sexual transmission lasts. More specifically, doctors don’t know how long the virus can reside in bodily fluids, such as male semen. 

Call for testing all pregnant women or women of reproductive age who want to be tested

The updated guidelines recommend that pregnant women without symptoms of Zika virus disease can be offered testing for the virus at anytime between two to 12 weeks after returning from areas with ongoing Zika virus transmission. 

The CDC’s Frieden said that at least initially there will be a shortage of testing capacity that may be frustrating for some women, but that testing capabilities are being scaled up quickly. 

Here is the CDC’s advise for women of reproductive age who are not planning on getting pregnant, but are worried about Zika exposure:

For women of reproductive age, healthcare providers should discuss strategies to prevent unintended pregnancy, including counseling on family planning and the correct and consistent use of effective contraceptive methods, in the context of the potential risks of Zika virus transmission.

The CDC has issued travel advisories warning pregnant women to postpone travel to the majority of Central America and many South American nations and territories, from Costa Rica to Brazil, until more is known about the risks of contracting Zika and a resulting poor birth outcome such as microcephaly.