COVID-19 patients exhale millions of virus in early stages

COVID-19 patients carry particularly high viral loads during the early stages of the disease, with millions of virus exhaled in their breath per hour, reveals a study — which indicates that breath emission could possibly contribute to airborne transmission of the virus.

“Our study demonstrates that exhaled breath emission plays an important role in SARS-CoV-2 emission into the air, which could have contributed greatly to the observed airborne cluster infections and the ongoing pandemic,” said the researchers.

“Accordingly, measures such as enhanced ventilation and the use of face masks are essential to minimize the risk of infection by airborne SARS-CoV-2,” they highlighted.

The study also underscores the importance of wearing face mask, yet again, at all times when in contact with others — not just during activities such as talking or singing. 

Participants in the study were 76 subjects, comprising 57 COVID-19 patients, four hospitalized patients without COVID-19, and 15 healthy volunteers in Beijing, China. Among these patients, exhaled breath condensate (EBC) was sampled from 20 imported cases with COVID-19 and 29 local cases. Additionally, surface swabs and air samples were also collected from isolation rooms or personal items of the patients. [Clin Infect Dis 2020;doi:10.1093/cid/ciaa1283]

Among the environmental samples, EBC was most likely to be tested positive for SARS-CoV-2 (26.9 percent), compared with surface swabs (5.4 percent) and air samples (3.8 percent).

The rate of viral emission in EBC samples ranged from 1.03x10⁵ per hour to as high as 2.25x10⁷ viruses per hour.

“The SARS-CoV-2 breath emission rate is affected by many factors such as disease stage, patient activity, and possibly age,” explained the researchers.

“[A] significant discovery from this work is that SARS-CoV-2 emission was not, however, continuous at the same rate, but was rather a sporadic event,” they noted, based on the observation that two EBC samples collected on different dates from the same patient returned different test results. “We found that the SARS-CoV-2 breath emission rate into the air was the highest, up to 10⁵ viruses per min, during the earlier stages of COVID-19.”

On the other hand, surface swab samples revealed presence of the virus on various objects touched by the patients, including pillow case, mobile phones, and computer keyboards. Other surfaces such as toilets and hospital floor were also tested positive for SARS-CoV-2.

“The SARS-CoV-2 presence in the toilet room air might be due to the exhaled virus or the virus aerosolization from the toilet,” said the researchers.

In keeping with this notion, they found that SARS-CoV-2 was present in air samples of hospitals as well as quarantine hotel housing COVID-19 cases (estimated at 6.07x10³ viruses/m³).

In addition, surface sampling of air ventilation duct entrance also turned out positive for SARS-CoV-2.

“For the first time, we here report that the SARS-CoV-2 is released directly into the air via breathing by COVID-19 patients,” the researchers stated.

While respiratory droplets and direct contacts are the currently recognized major transmission routes of COVID-19, real-life airborne transmission has been documented in semi-enclosed areas, such as the choir cluster infection in Washington, US and a restaurant in Guangzhou, China, the researchers pointed out.

Accordingly, the WHO* has also recently updated its guideline to not exclude the possibility of airborne transmission in enclosed settings.     

*WHO: World Health Organization