Clinical Guidance for Healthcare Providers for Prevention of Sexual Transmission of Zika Virus

What kind of sexual activity puts someone at risk for Zika if their partner is infected?
A person with Zika can transmit the virus to his or her partner(s) through vaginal sex, anal sex, and likely oral sex. The sharing of sex toys may also put someone at risk. Zika has been detected in semen, vaginal fluids, saliva, urine, and breast milk. There is no evidence at present that Zika can be transmitted through saliva during deep kissing.

There is documented evidence of sexual transmission of Zika from male-to-female, male-to-male, and female-to-male sex partners. Female-to-female sexual transmission has not yet been reported but is biologically plausible.

Are infections of same-sex partners being identified?
To date, there has been one case of male-to-male sexual transmission in the United States; none of the confirmed cases of sexual transmission have been female-to-female. However, because other diseases transmitted sexually can be passed between female sex partners, it is possible that Zika virus could be transmitted this way. Women with Zika may pass the virus to sex partners through vaginal fluids or menstrual blood.

The use of condoms or abstinence is recommended to protect sex partners concerned about Zika. The partners of people who live in or traveled to areas with risk of Zika should be tested if they had condomless sex and develop symptoms of Zika.

Can asymptomatically infected people have Zika in genital secretions and transmit it to their sex partners?
Sexual transmission from an asymptomatically infected male has been reported. Limited data suggest the incidence of Zika virus RNA shedding in semen and its persistence after infection are likely similar for symptomatic and asymptomatic men infected with Zika virus. People with symptomatic illness have transmitted Zika before they had symptoms, while they had symptoms, and after symptoms resolved.

Studies are underway to help us better understand when and under what circumstances Zika can be transmitted sexually. Specifically, scientists are studying semen and vaginal secretions to understand the incidence of viral shedding, the concentrations of virus, and the duration and pattern (e.g., steady decline, intermittent on/off) of viral shedding in genital secretions of symptomatic and asymptomatic individuals.

How long can Zika be transmitted to sex partners after initial infection?
Our knowledge is growing rapidly but we don’t yet know exactly how long infected people can transmit Zika sexually.

• Evidence of sexual transmission: Briefly, among the currently available reports of sexual transmission of Zika virus, the longest period from symptom onset in the index case to potential sexual transmission to a partner was between 32–41 days. However, most reports indicate shorter intervals.
• Potentially infectious Zika virus in semen: The longest reported period after symptom onset at which potentially infectious virus has been detected in semen by culture or cytopathic effect was 69 days. No other studies reported potentially infectious Zika virus in semen specimens obtained more than 40 days after symptom onset.
• Detection of Zika virus RNA in semen: A large number of publications have also reported on detection of Zika virus RNA in semen. However, this might not indicate presence of infectious virus at the time of sampling or correlate with the potential for sexual transmission of infectious virus. In the largest cohort study to date, Zika virus RNA shedding declined during the 3 months after symptom onset. At >90 after illness onset, semen of ≤7% of participants had detectable Zika virus RNA. The estimated mean time to clearance of Zika virus RNA from semen was 54 days. Similar findings have been observed in smaller cohort studies.

CDC recommends that pregnant couples use condoms or abstain from sex for the entire pregnancy, if the pregnant woman’s partner had a possible Zika virus exposure. Non-pregnant couples with a partner who traveled to an area with risk of Zika can follow the designated timeframes below to minimize their risk for sexual transmission of Zika virus.

• If a couple has a male partner and only he travels to an area with risk of Zika, the couple should consider using condoms or not having sex for at least 3 months after the male partner returns (even if he doesn’t have symptoms) or from the start of the male partner’s symptoms or date of diagnosis.
• If a couple has a female partner and only she travels to an area with risk of Zika, the couple should consider using condoms or not having sex for at least 2 months after the female partner returns (even if she doesn’t have symptoms) or from the start of the female partner’s symptoms or date of diagnosis.
• If a couple has both a male and female partner and they both travel to an area with risk of Zika, they should consider using condoms or not having sex for at least 3 months after their return or from the start of symptoms or date of diagnosis.

The longer precautionary period for males is because Zika virus can persist longer in semen than in other body fluids, including vaginal fluids, urine, and blood. Ongoing studies are systematically examining the incidence and duration of Zika virus shedding in the genital secretions of people with both symptomatic and asymptomatic Zika infection.

How common is it for people to transmit Zika to their sex partners?
We do not know. To date, the majority of documented cases of sexually transmitted Zika infection have been from men to their sex partners. The limited number of cases of sexual transmission from women to their sex partners suggests that it can occur but is less frequent than sexual transmission of Zika from men.

Should people who have been in areas with risk of Zika take precautions to prevent sexual Zika transmission to their partners?
Yes, especially if their partner is pregnant. Zika during pregnancy can cause microcephaly and other severe fetal nervous system defects.

Men and women who have traveled to or live in an area with risk of Zika and who have a pregnant sex partner should use a condom every time they have vaginal, anal, or oral sex or abstain from sex for the duration of the pregnancy. They should also avoid sharing sex toys throughout the pregnancy. This is important even for those who are asymptomatic. Most people who are infected do not have symptoms and it is possible that an asymptomatic person can transmit Zika through sex.

Men and women who have traveled to or live in an area with risk of Zika and who have partners who are not pregnant can also use condoms consistently and correctly to protect against infection or not have sex, if they are concerned about sexually transmitting Zika. The recommended length of time for using condoms or not having sex will depend on the person’s sex and where s/he lives. People considering condoms or abstinence should weigh the personal risks and benefits, which include:

• The likelihood that they have been infected with Zika, which will depend on the length of time spent in areas with risk of Zika and whether steps were taken to prevent mosquito bites while there
• The fact that for most adults, Zika is a short-lived illness with non-life-threatening, generally mild symptoms
• Plans for pregnancy (if applicable) and access to contraception
• Access to condoms (e.g., male and female condoms, dental dams)
• Desire for intimacy, including willingness to use condoms or not have sex
• Ability to use condoms (e.g. experience using them) or to not have sex
• The possibility of a partner becoming pregnant and infected with Zika (even if the pregnancy is not planned)

What should I tell patients concerned about getting Zika through sex?
Only people with sex partners who traveled to or live in an area with risk of Zika are at risk for getting Zika virus through sex. Sexual transmission of Zika is of greatest concern for pregnant women with partners who have had, or are at risk for, Zika virus infection.

• Pregnant women and women who could become pregnant should take the necessary precautions to prevent acquiring Zika sexually. Their partners should also be counseled to take the necessary precautions to prevent transmitting Zika sexually.
• All other patients should be informed that the chance of getting Zika from sex can be reduced by using condoms consistently and correctly, and eliminated through abstinence. To be effective, condoms must be used correctly from start to finish, every time during vaginal, anal, and oral sex.

When is Zika testing recommended to identify possible sexual transmission cases?
Zika virus testing has been recommended to establish a diagnosis of infection. Zika virus testing is recommended for people who may have been exposed to Zika through sex and who have Zika virus symptoms. Zika virus testing is also recommended for pregnant women who have symptoms of Zika and have recent exposure to Zika, for asymptomatic pregnant women with ongoing exposure to Zika, and for pregnant women whose fetus has birth defects potentially associated with Zika identified on ultrasound.

At this time, testing a person’s blood, urine, or genital secretions to determine their potential risk of sexually transmitting Zika virus is not recommended for the following reasons:

First, a negative blood test or antibody test could be falsely reassuring. This can happen when:

• The blood test is performed after the virus is no longer in the blood (detected by RNA NAT [nucleic acid testing]) but could still be present in other bodily fluids (e.g., semen).
• The antibody test is performed early after infection when the antibody levels are not yet high enough to be detected, or later after infection when the antibody levels have fallen to undetectable levels.
• The test is falsely negative.

Second, we have limited understandingExternal of Zika virus shedding in genital secretions, or of how to interpret the results of tests of semen or vaginal fluids. Zika shedding in these secretions may be intermittent, in which case a person could test negative at one point but still carry the virus and shed it again in the future.

For more information on diagnostic testing for Zika, see Testing for Zika.

What is the role for STD/HIV Programs in the Zika response?
STD and HIV programs have expertise in patient education, communication, and condom promotion and distribution efforts that may be relevant to preventing sexual transmission of Zika virus. CDC encourages state and local programs to work with their state health officials and connect concerned STD/HIV clients with possible sexual exposure to Zika to primary care or reproductive health providers who can offer counseling and follow up.