COVID-19 is spread primarily through air, directly from human to human. Its secondary method of transmission is from contact with surfaces. A third possible method has emerged. For the first time, testing of patients showed a significant amount of SARS-CoV-2, the virus that causes COVID-19, in their feces.
In a research letter in Emerging Infectious Diseases, investigators of a cluster of COVID-19 cases linked to a shopping mall in Wenzhou, China, found viral RNA in the feces of 44 of 153 patients. The 72 urine specimens all tested negative.
Viral RNA is not the whole virus. It cannot infect another cell. It can do little more than indicate the patient had COVID-19. However, 5 of the patients did have whole viruses present.
The study suggests the spread of SARS-CoV-2 from contact surfaces (fomites) in public spaces like elevator buttons or restroom taps as well as aerosol transmission in the confined public space (restrooms and elevators). All patients (except on the 7th floor) were female including a restroom cleaner, pointing to restroom use as an infection source.
The virus, known to sicken and kill by fouling the respiratory system, now may have another way to spread.
Fecal contamination, usually associated with food poisoning, can also spread viruses if infected people don’t wash hands properly. The spread will be by contact with contaminated surfaces. It can also be spread through the air or by the effect of the toilet plume.
When you flush a toilet, the swirling water sends fecal particles into the air in the form of droplets, which should fall quickly to the floor or other surfaces. However, in a 1950s study first brought up the possibility of the toilet plume. Several types of flush toilets were filled with the Serratia marcescens bacteria, which went airborne as droplets and settled on and grew in Petri dishes placed all around the toilets. Droplet nuclei, the particles that remain after the water in a droplet evaporates, were detected as much as 8 minutes after the toilets were flushed.
The particles can be breathed in, a proven way that COVID-19 infect humans through nose and mouth. A 2013 study of toilets by the National Institute of Safety and Health (NIOSH) found up to 145,000 droplets were produced per flush.
We found no direct experimental evidence of a toilet plume responsible for an infection. But if you don’t want to worry about it, there is one easy solution to the toilet plume: Close the toilet lid! Closing the lid reduces aerosol fouling of the air by a factor of 12.
While that may work at home, on the office and on airplanes, most public toilets have no lids.