Virus World

Study suggesting virus spread through waste pipes in Chinese apartment building raises concerns. Coronaviruses wafting through a Chinese apartment building’s plumbing may have infected some residents, according to a new study, raising fears of yet another way that COVID-19 could spread. The case echoes a 2003 outbreak of severe acute respiratory syndrome (SARS) that spread through the pipes of a Hong Kong apartment building—and some worry that transmission via toilets might have contributed to the COVID-19 outbreak that shut down New York City early in the pandemic. The study adds to months of warnings that SARS-CoV-2, which causes COVID-19 and is thought to spread mainly through respiratory droplets and aerosols, could also infect via feces. “It’s not something that people like to talk about,” buildings expert Joseph Allen of the Harvard T.H. Chan School of Public Health wrote in a Washington Post op-ed this week.  Although fecal transmission of a pathogen is tricky to confirm—and proving that a virus spreads via building waste pipes is even more difficult—it is entirely possible, several researchers tell ScienceInsider. With their help, we try to answer some key questions about this unusual and still speculative risk.  

Can people catch COVID-19 from poop?

A number of studies have reported finding RNA from SARS-CoV-2 in fecal samples from COVID-19 patients. Some of those patients also had diarrhea, suggesting the virus had infected their intestinal tracts; the RNA could also come from swallowing saliva or respiratory tract fluids containing the virus. Such fecal samples inspired wastewater testing currently being used to watch for incipient COVID-19 outbreaks in cities around the world and at some U.S. universities. Some studies have also found abundant coronavirus RNA in hospital bathrooms, and one modeling study suggested that flushing a toilet can spew viral particles far above the seat. A person could therefore be exposed to SARS-CoV-2 by breathing aerosolized fecal matter, or by ingesting the virus after touching a contaminated surface. A key point often glossed over, scientists say, is the limited evidence that viral RNA in stool comes from live, infectious viruses—not just leftover material from “dead” or destroyed viruses. Only a few labs have reported culturing live virus from COVID-19 patient stool samples, which is challenging to do. One team has suggested that intestinal fluid neutralizes the virus. The U.S. Centers for Disease Control and Prevention says “it is unclear” whether virus in feces can cause COVID-19 and concludes the risk of spreading the virus this way is “low.” To date, there are no documented cases clearly indicating infection via fecal matter. But  Allen and other researchers say the risk should not be ignored. Many animal coronaviruses can be spread through feces, “so it isn’t a stretch to believe it might be possible with SARS-CoV-2,” says epidemiologist Susan Amirian of Rice University. But whether that risk is present in sewage is another question. By the time human waste reaches a typical sewer outfall or treatment plant, any potentially intact viruses are likely too diluted to be infectious, says environmental engineer Jordan Peccia of Yale University, who is testing wastewater for SARS-CoV-2 in Connecticut. To date, there is little to no evidence that COVID-19 spreads via sewage.

What about that 2003 SARS outbreak in Amoy Gardens?

Amoy Gardens, a Hong Kong housing complex with multiple apartment towers, saw 321 residents catch SARS in 2003; 42 of them died. Researchers traced the outbreak to a single visitor with SARS who had severe diarrhea. The bathrooms in the apartments had floor drains for cleaning, and when the U-shaped traps beneath these drains dried out, aerosolized SARS virus from the sick resident reached apartments through an air shaft. Typically, such wafting is blocked by water that has accumulated in the traps. Scientists suggested the wind even carried the aerosols to adjacent buildings. 

How does Amoy Gardens compare with the new COVID-19 cases in the Chinese apartment building?

Just nine people got sick from SARS-CoV-2 in Guangzhou, where the apartment building was located, and none died. But there are similarities, says University of Hong Kong mechanical engineer Yuguo Li, who studied both cases. Li’s group—along with teams from the Guangdong Provincial Center for Disease Control and Prevention and Guangzhou CDC—describe their new findings this week in the Annals of Internal Medicine. (China CDC mentioned the cases in less detail in a paper published late last month, as first reported by Bloomberg.)..

Scientists continue to investigate the role of toilets in the spread of coronavirus. The discovery of coronavirus in the bathroom of an unoccupied apartment in Guangzhou, China, suggests the airborne pathogen may have wafted upwards through drain pipes, an echo of a large SARS outbreak in Hong Kong 17 years ago. Traces of SARS-CoV-2 were detected in February on the sink, faucet and shower handle of a long-vacant apartment, researchers at the Chinese Center for Disease Control and Prevention said in a study published this month in Environment International. The contaminated bathroom was directly above the home of five people confirmed a week earlier to have COVID-19.  The scientists conducted “an on-site tracer simulation experiment” to see whether the virus could be spread through waste pipes via tiny airborne particles that can be created by the force of a toilet flush. They found such particles, called aerosols, in bathrooms 10 and 12 levels above the COVID-19 cases. Two cases were confirmed on each of those floors in early February, raising concern that SARS-CoV-2-laden particles from stool had drifted into their homes via plumbing.