When it comes to the transmission of SARS-CoV-2, the virus that causes Covid-19, the focus has been on the droplets that spray from our mouths and out into the world. New findings from the Centers for Disease Control and Prevention suggest that focus was near-sighted. According to a new report SARS-CoV-2 can be possibly be transmitted through human feces as well.

Live, infectious SARS-CoV-2 was found in the stool sample of a 78-year-old severely sick Covid-19 patient. This finding was published this week in the CDC’s journal Emerging Infectious Diseases. This indicates “the need for appropriate precautions to avoid potential transmission of SARS-CoV-2 from feces,” the study team writes.

Brennan Spiegel is the editor-in-chief of the American Journal of Gastroenterology and a professor of medicine at Cedars Sinai. He tells that this study represents A shift in the way we think about the risk of spreading coronavirus through stool. Scientists have been tracing levels of viral RNA — genetic calling cards for coronavirus — in feces for several months. Previous studies conducted in China found viral RNA lingering on anal swabs, on toilet seats, and in fecal samples.

Viral RNA acts like a footprint: It tells scientists that SARS-CoV-2 was present in the person who made the feces. The presence of these genetic signatures is also the basis for the respiratory tests that also evaluate for Covid-19. But prior to now, scientists were not entirely convinced that the presence of SARS-Cov-2 in feces actually indicated that the virus COULD BE SPREAD through the feces.

“No one was saying ‘oh well, you’re just finding genetic material in the throat, that doesn’t mean the virus was alive,'” Spiegel tells. “But that’s what a lot of people said about intestines.”

THE CASE FOR POOP TRANSMISSION – The theory behind the poop-borne spread of SARS-CoV-2 begins where feces comes from — the gut. SARS-CoV-2 can live in the gastrointestinal system, because those tissues, like the lungs, are lined with cells containing ACE2 receptors. These are enzymes that the virus attaches to before it enters the cell.

Crucially, there’s far more surface area in the gut than in the lungs. “If you unfurl the intestines you have over a tennis court worth of surface for this virus to just replicate itself over and over,” Spiegel says. (The surface area of the gut has also been compared to that of a studio apartment.)

If the virus can adorn the walls of the gut, it’s reasonable to assume remnants of it would also end up in our stool. Early reports of this came mostly out of China, where stool testing happens more regularly for Covid-19 patients, says Spiegel.

For instance, a JAMA research letter from March found that 44 out of 153 fecal samples from Covid-19 patients contained RNA from the coronavirus. Another pre-print study (not peer-reviewed) from China found that signs of the virus continue to appear in patient stool samples even after respiratory swabs come back negative.

These studies primarily rely on PCR testing, which looks for signs of the virus and then amplifies them to find out how much is there. This CDC report performs a viral plaque assay. Simply put, that method tests to see whether the virus that is detected can actually infect other cells.

Still, some scientists are skeptical as to whether coronavirus can be transmitted, not just detected, through poo.

Rolf Halden is a professor and founder of the Human Health Observatory at Arizona State University. He says that research has revealed a “mixed bag” as to whether stool can consistently contain a live virus (Specifically, a study published in April in Nature didn’t find evidence of the infectious virus in stool samples).

That said, Halden isn’t ruling it out. “Fecal-oral transmission of the coronavirus is a new route to consider but it certainly is not a principal one, from what we know right now,” Halden tells.

If the virus definitively spreads through feces, that spread likely happens through the aerosolization of infected poop particles. Feces can become aerosolized when a toilet is flushed (this is called a toilet plume, and has consistently been an area of interest infectious disease research).

The CDC report did the extra legwork in the lab to demonstrate the live virus, as well as genetic signatures of it, exist in stool. “The bottom line is this case report raises the concern even higher,” says Spiegel.

It’s because of this that Spiegel recommends we exercise caution in the restroom.

The fact that infectious virus present warrants a change in the way you approach restrooms, Spiegel says. To be extra safe, he suggests you:

  • Put the seat down when you flush.
  • If someone is ill in your house, consider wearing a mask in the restroom.
  • Consider using different rolls of toilet paper if someone is ill.
  • Wash your hands after wiping (this may seem obvious, but the CDC estimates that only 31 percent of men and 65 percent of women actually do this).