While doctors have focused on respiratory samples from pneumonia cases to identify coronavirus patients, they might have ignored a less apparent source of the spread: diarrhea.

The novel coronavirus was detected in the loose stool of the first U.S. case — a finding that hasn’t featured among case reports from Wuhan, China, the epicenter of the outbreak. However, that doesn’t surprise scientists who have studied coronaviruses, nor doctors familiar with the bug that caused SARS.

Diarrhea occurred in about 10 to 20 percent of patients afflicted with severe acute respiratory syndrome about 17 years ago and was the source of an explosive SARS outbreak in the Amoy Gardens residential complex in Hong Kong.

SARS and Wuhan viruses bind to the same distinctly shaped protein receptors in the body that are expressed in the lungs and intestines, making these organs the primary targets for both viruses, said Fang Li, an associate professor of veterinary and biomedical sciences at the University of Minnesota.

The discovery of the Wuhan virus, dubbed 2019-nCoV, in the fecal material of the 35-year-old man treated at the Providence Regional Medical Center Everett in Washington is “interesting,” said Scott Lindquist, the state epidemiologist for infectious disease at Washington’s Department of Health.

“That adds to the knowledge about this,” he told reporters on a conference call Friday. “It’s not only excreted in your respiratory secretions, it’s also secreted in your stool.”

Researchers don’t yet know how exactly 2019-nCoV spreads from person to person, but they suspect it is most likely from coming into contact with virus-containing droplets that could be emitted by an infected person’s cough and transferred to their hands or surfaces and objects.

That has led to a run on face masks. But those may be of limited benefit in the event the virus is being transmitted via the fecal-oral route, said John Nicholls, a clinical professor of pathology at the University of Hong Kong.

Squat latrines lacking covers, common in China, and hands that aren’t washed thoroughly with soap and water after visiting the bathroom could be a source of virus transmission, said Nicholls, who was part of the research team that isolated and characterized the SARS virus.

A virus-laden aerosol plume emanating from a SARS patient with diarrhea was implicated in possibly hundreds of cases at the Amoy Gardens housing complex in 2003. That led Hong Kong researchers to understand the importance of the virus’s spread through the gastrointestinal tract and to recognize both the limitation of face masks and importance of cleanliness and hygiene, Nicholls said in an interview.

“I think in Wuhan, that would be a very likely place where you might get the transmission” from fecal material, he said. “If it’s using the same receptor as for SARS, I can’t see why it shouldn’t be replicating in the gut.”

Nicholls and colleagues at the University of Hong Kong are testing laboratory models of human tissues and specimens to understand where and how the Wuhan virus replicates, he said.

Doctors have reported diarrhea infrequently in 2019-nCoV patients admitted to Wuhan hospitals, though it has been more prominent among reported cases outside the city, including members of a Shenzhen family infected in Wuhan, and more recently in the first U.S. case in Washington state. That patient experienced a two-day bout of diarrhea from which a sample tested positive.

The lab in Washington didn’t attempt to grow the virus from that specimen, said Lindquist, “because it wasn’t going to add anything to his care.”

Many of the emerging coronaviruses are so-called pneumoenteric viruses, meaning they can replicate both in the respiratory tract and the gastrointestinal system, said Ralph Baric, professor of microbiology and immunology at the Gillings School of Global Public Health at the University of North Carolina at Chapel Hill, who has studied coronaviruses for decades.

Overwhelmed by hundreds of severely sick pneumonia patients, doctors in Wuhan might not have focused on any gastric signs, Baric said in a phone interview.

“The Chinese are so overwhelmed at the moment and trying to do a combination of treating patients and dealing with the scope of the outbreak, and then trying to get out papers that describe what’s happening,” he said.

Any virus in stool is more likely to be present during the acute phase of an infection, occurring before hospitalized patients develop a life-threatening complication known as acute respiratory distress syndrome, Baric said.

“I have also spent most of my time focusing on the respiratory tract symptomology rather than the gut because of the relationship between these different emerging viruses and acute respiratory distress syndrome,” he said.

Zijian Feng, deputy director general of Chinese Center for Disease Control and Prevention, and colleagues released a report Wednesday on the first 425 Wuhan cases, and noted that early infections that didn’t appear to display typical signs — such as fever and viral pneumonia — or had mild symptoms might have been missed.

“The initial focus of case detection was on patients with pneumonia, but we now understand that some patients can present with gastrointestinal symptoms,” Feng and co-authors said in their report, which was published in the New England Journal of Medicine.

Emerging evidence of virus-containing diarrhea warrants further investigation, said Peter Collignon, a professor of clinical medicine at the Australian National University Medical School in Canberra, who advises the Australian government on infection control.

“This is something new,” Collignon said in an interview. “We presume it’s respiratory droplets, but with SARS there was evidence of other routes. We have to keep an open mind.”

RELATED PHOTOS Face masks may be of limited benefit if the new coronavirus is being transmitted via the fecal-oral route. | AFP-JIJI

Face masks may be of less benefit if the new coronavirus is additionally being transmitted via the gastrointestinal system. | AP