COVID-19 is most commonly associated with respiratory illness, but a recent study reveals that the coronavirus can infect your intestine for weeks or months after you’ve cleared it from your lungs.

Researchers discovered that around one out of every seven COVID-19 patients continued to shed the virus’ genetic remnants in their feces for at least four months after their initial diagnosis, long after the virus had stopped shedding from their respiratory system.

According to senior researcher Dr. Ami Bhatt, an associate professor of medicine and genetics at Stanford University, this could explain why certain COVID-19 individuals have GI symptoms such as stomach pain, nausea, vomiting, and diarrhea.

“We found that people who had cleared their respiratory infection — meaning they were no longer testing positive for SARS-CoV-2 in their respiratory tract — were continuing to shed SARS-CoV-2 RNA in their feces,” explains Bhatt. “And those people in particular had a high incidence of GI symptoms.”

Bhatt and her colleagues hypothesized that a long-term gut infection could possibly lead to lengthy COVID symptoms in some persons.

“Long COVID could be the consequence of ongoing immune reaction to SARS-CoV-2, but it also could be that we have people who have persistent infections that are hiding out in niches other than the respiratory tract, like the GI tract,” Bhatt adds.

The researchers used an early clinical trial initiated in May 2020 at Stanford to explore a therapeutic therapy for mild COVID-19 infection for this work. More than 110 individuals were tracked to see how their symptoms progressed, and feces samples were taken on a regular basis to track virus shedding.

Many other studies have looked at viral shedding in individuals with severe COVID-19, but this is the first to look at viral RNA in feces from those with mild to moderate COVID, according to the researchers.

Researchers discovered COVID RNA remains in the feces of nearly half of the patients (49%) within the first week following diagnosis.

Nearly 13% of patients continued to shed viral RNA in their stools four months after diagnosis, when no more COVID remained in their lungs.

Researchers discovered that seven months after their initial diagnosis, almost 4% of people were still leaking viral RNA in their stools.

Bhatt was quick to point out that the RNA was made up of genetic leftovers of the coronavirus, not an actual live virus, implying that a person’s excrement is unlikely to be contagious.

“While there have been isolated reports of people being able to isolate live SARS-CoV-2 virus from stool, I think that that’s probably much less common than being able to isolate live virus from the respiratory tract,” Bhatt adds. “I don’t think that our study suggests that there’s lots of fecal-oral transmission.”

However, the presence of COVID-19 in the gut suggests one possible influence for long-haul disease, according to her.

“SARS-CoV-2 might be hanging out at the gut or even other tissues for a longer period of time than it sticks around in the respiratory tract, and there it can basically continue to kind of tickle our immune system and induce some of these long-term consequences,” Bhatt adds.

According to Dr. William Schaffner, medical director of the National Foundation for Infectious Diseases, long COVID has become such an established concern that several large medical institutes have established their own long COVID clinics to try to suss out symptoms and potential remedies.

“A very substantial proportion of individuals who recover from COVID acutely nonetheless have lingering symptoms, and they can involve an array of different organ systems,” Schaffner says.

“These data add to the notion that the cells in the intestine may themselves be involved with COVID viral infection, and they could potentially be contributors to some of the symptoms — abdominal pain, nausea, kind of just intestinal distress — that can be one aspect of long COVID,” he adds.

The findings, according to Bhatt and Schaffner, have implications for public health attempts to detect emerging COVID-19 outbreaks by analyzing a community’s wastewater for indications of the virus.

“If, as they say, about 4% of people seven or eight months later are still excreting viral remnants in their stool, it complicates the assessment of the density of new infections in a community,” Schaffner adds. “It’s another thing we have to take into consideration and start looking at going forward.”

However, Dr. Amesh Adalja, a senior scholar at the Johns Hopkins Center for Health Security, disagrees that long-term shedding in the stool should have an impact on the accuracy of wastewater COVID-19 surveillance.

“I don’t think that these findings change the value of wastewater surveillance, as we’ve already seen its value in real life,” Adalja says. “What’s valuable about wastewater surveillance is the trend if it is increasing or decreasing, which isn’t really impacted by this phenomenon.”

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