The study found a few patients exhaled coronavirus into the air at an estimated rate of 1000-1,00,000 RNA copies/minute. Breath emission rate was the highest during the earlier stages of COVID-19. Virus emission was found to be a “sporadic event”.
Not just talking, singing or shouting, as the World Health Organization indicated on July 9, but even breathing can spread novel coronavirus into the air. A study published in Nature had earlier found airborne coronavirus in patient’s breath. A couple of more studies found airborne transmission of the virus during breathing and speaking. A new study posted on July 2 in preprint server MedRxiv has again found virus spread while breathing. Preprints are yet to be peer-reviewed and published in a scientific journal.
The study adds to the existing body of evidence that suggest airborne transmission of the virus can play a “major role” in virus spread. The study found that breath contained the virus “especially during the early stages of the disease”.
On July 9, WHO acknowledged that coronavirus can be airborne in closed settings that lack good ventilation and spread from one person to another in such settings on prolonged exposure.
Rate of virus exhalation
The study found that COVID-19 patients exhaled coronavirus into the air at an estimated rate of 1000-1,00,000 RNA copies/minute. The authors write that the virus levels in exhaled breath could reach 1,00,000 to 1,00,00,000 copies per metre cube at an average breathing rate of 12 litres per minute. This would mean that a COVID-19 patient can exhale millions of virus particles per hour. “Our data reveal direct evidence of airborne transmission of SARS-CoV-2 via breathing,” Maosheng Yao from Peking University who led the team writes.
The emission rate of virus was found to be influenced by a few factors such as disease stage, patient activity, and possibly age. “We found that the SARS-CoV-2 breath emission rate into the air was the highest, up to 1,00,000 viruses per minute, during the earlier stages of COVID-19,” they write.
However, the virus emission was not found to be continuous or at the same rate, but was rather a “sporadic event”. For instance, two breath samples collected from the same patient on different dates returned different test results.
The researchers collected exhaled breath condensate samples from 27 COVID-19 patients. The times from symptom onset to the sample collection were all less than 14 days. Of the 27 patients studied, they could detect the virus in the exhaled breath of five patients aged under 50. In these five patients, the emission rate in exhaled breath was 1000-100,000 RNA copies/minute.
Contamination of surfaces
While the hands of all the five patients did not have any virus, two of 22 phone samples tested positive, and toilet pit surface was tested positive for virus in the case of one patient. Virus in the exhaled breath could be “partially responsible” for the contamination on the surfaces, they say.
The researchers also collected samples from various surfaces and tested them for the presence of the virus. In all, 242 surface swab samples were collected and 13 tested positive for the virus. The virus was found on five categories of surfaces — toilet pits (16.7%, n=12), hospital floor (12.5%, n=16), other surfaces (7.4%, n=27), patient touching surfaces (4.0%, n=149), and medical touching surfaces (2.6%, n=38). No virus was found on handles.
“The overall SARS-CoV-2 positive rate for the surface swabs was 5.4% (n=242). These observations do not support the widely-held belief that direct transmission by contact with surfaces plays a major role in COVID-19 spread,” they write. Meanwhile, WHO classifies contact with contaminated surfaces as the second most common route of virus transmission.
Another route of transmission
Large respiratory droplets and direct contact with contaminated surfaces are currently considered as dominant routes of virus spread. But the present study has found that frequently touched surfaces like mobile phones have very low probability of virus presence.
“Evidences from our work show that exhaled breath emission may well be the most significant SARS-CoV-2 shedding mechanism, which could have contributed largely to the observed cluster infections and the ongoing pandemic. Accordingly, measures such as enhanced ventilation and the use of face masks are essential to minimise the risk of infection by airborne SARS-CoV-2,” they write.