The Centers for Disease Control and Prevention (CDC) on Sunday changed its guidelines, suggesting that Ebola survivors avoid sex or use condoms to prevent spreading the virus “until more information becomes available.”

The guidelines had previously suggested that survivors wait three months before having unprotected sex. The change—which mirrors new guidelines from the World Health Organization (WHO)—highlights the confusion about the sexual transmission of this deadly virus.

Ebola, like other viruses, is present in all bodily fluids, including blood, feces, vomit, sweat, tears, and urine, as well as semen and vaginal fluids. The virus is transmitted through direct contact with infected fluids. Risk of transmission begins when a person starts showing symptoms, and is highest when the patient is the sickest because the virus causes vomiting, diarrhea, and unexplained bleeding.

Laboratory studies show that the virus is detectable at very low levels in a patient’s blood once she experiences fever, and increases logarithmically during the acute phase of infection. The bodies of people who die from Ebola are particularly infectious.

This is why so many health-care workers and family members become infected.

For those who survive, the level of virus in their blood drops during their clinical recovery. Few survivors have been studied in lab settings, but the longest that any study has found detectable levels of the virus in a survivor’s blood is 21 days after the onset of symptoms.

Even fewer studies have been done on sexual transmission of the virus, but those that have been conducted suggest the virus can be detected in vaginal fluids for up to 33 days after symptoms appear and in semen for 101 days.

These studies were the basis for the original suggestion that survivors abstain from sex or use condoms consistently for three months.

Those guidelines, however, have been called into question by a Liberian survivor who recovered in September but seems to have passed the virus on to his female partner just recently. A sample given to a lab found his semen contained the virus 175 days after he his symptoms first appeared.

Scientists have matched sequences of the virus in his semen to those found in his partner’s blood, suggesting sexual transmission. Still, they warn that the findings are preliminary and the virus in his semen may not have been infectious.

Very little is known about sexual transmission of Ebola, in part because the virus is so lethal. The current outbreak—which has been centered in Liberia, Sierra Leone, and Guinea—began in 2013 and has killed more than 10,600 people. The current epidemic has a fatality rate of about 50 percent—meaning that half of those who become infected die.

Given how little research there is on sexual transmission, this one case is enough to have experts question their knowledge and change their advice. For now, both the CDC and the WHO are urging survivors to abstain from sex or use condoms until further notice.

The CDC promises to update its web page on Ebola transmission as soon as information becomes available.