Quantity of SARS-CoV-2 Exhaled During Normal Breathing
SARS-CoV-2, the causative agent of COVID-19, spreads through exhaled breath during breathing, coughing, talking, and singing. Olfactory scientists at Northwestern University Feinberg School of Medicine developed a portable device for the collection of exhaled breath and used it to measure how much SARS-CoV-2 RNA is exhaled during natural breathing.
A total of 294 specimens were collected twice a day at home from 43 patients with COVID-19 over the course of their illness. RT-qPCR was used to determine the number of SARS-CoV-2 RNA copies exhaled per minute.
Viral levels varied between and within individuals but on average participants breathed out 80 copies of SARS-CoV-2 RNA per minute for eight days after their symptoms began. Some participants shed as much as 876 copies of viral RNA per minute.
The average amount of viral RNA being exhaled into the environment did not statistically decrease until day 8 following symptom onset. Thereafter, exhaled viral RNA levels dropped precipitously to the threshold of detection.
Exhaled viral loads correlated with disease severity. They were significantly higher in samples collected when participants reported that their symptoms were severe compared to those collected when symptoms were reported as resolved, mild or, moderate.
The data set included 57 samples collected by 11 vaccinated individuals with breakthrough infections. Interestingly, vaccinated participants exhaled similar amounts of virus as unvaccinated participantst. Viral RNA levels from vaccinated individuals ranged from 0 to 549 exhaled copies per minute while viral loads for unvaccinated individuals ranged from 0 to 876 exhaled copies per minute.
The research team also sought to determine if different SARS-CoV-2 variants influenced the amount of exhaled viral RNA. The data set included individuals infected with early SARS-CoV-2 variants, delta, and omicron subvariants. Levels of viral shedding did not significantly differ between these three groups. Viral loads in the breath of individuals infected with early variants ranged from 0 to 876 RNA copies exhaled per minute; viral loads in individuals infected with the Delta variant ranged from 0 to 549 RNA copies exhaled per minute; and viral loads for individuals infected with the Omicron variant ranged from 0 to 264 RNA copies exhaled per minute.
Some other studies have suggested that an infectious dose of SARS-CoV-2 is 300 virions. If an infected person is exhaling 10 viral copies per minute could exhale an infectious dose in 30 minutes. However, a person who is exhaling 876 viral copies per minute could shed an infectious dose in approximately 20 seconds.
Reference
Lane G et al. Quantity of SARS-CoV-2 RNA copies exhaled per minute during natural breathing over the course of COVID-19 infection. medRxiv; posted September 08, 2023. doi: https://doi.org/10.1101/2023.09.06.23295138
