Infectiousness
Respiratory viruses spread through Infectious Respiratory Droplets, which are exhaled in breath. Various studies into SARS-CoV-2 have quantified the number of virus particles shed in the breath, finding anywhere from 64 – 27,000 viral particles shed each minute [1]. The rate of virus shedding in the breath tends to peak before the onset of symptoms, and before the virus can be detected in nasal swabs. While nasal swabs tend to have significantly higher viral loads overall, they do not reflect whether a person is actively spreading infection. Testing with nasal swabs gives negative results early in the infection when a person is most infectious, and gives positive results long after the person is no longer exhaling the virus.
Epidemiology
Research modeling the transmission of virus within the community relies on understanding rates of viral shed and uptake between individuals. Any effort to break the chain of transmission from one person to the next must take breath transmission into account.
Studies comparing samples from nasal swabs to exhaled breath condensate have demonstrated that even highly sensitive nasal swab tests are not appropriate for measuring infectiousness [2]. Testing that relies on nasal swabs fails to detect infectiousness in the critical early days when a patient is most infectious, and gives false positives after infectiousness has subsided. The only appropriate sampling method to break the chain of transmission from one person to another is rapid, widespread, non-invasive breath sampling, regardless of symptoms.
Figure adapted from: Raymenants J, Duthoo W, Stakenborg T, et al. Exhaled breath SARS-CoV-2 shedding patterns across variants of concern. Int J Infect Dis. 2022;123:25-33. doi:10.1016/j.ijid.2022.07.069
Conventional nasal swab-based testing does not directly test for infectiousness. All respiratory diseases spread through droplets exhaled from the breath. Therefore, breath sampling is the only true way to measure infectiousness. By testing the breath directly, we can test for infectiousness and track when and how long a person may spread disease. Conventional antigen testing is not sensitive enough to detect virus from breath samples, so it cannot accurately reflect infectiousness. Using our approach of sampling the breath and molecular testing gives us better insight into when disease may spread and gives valuable time to respond to an outbreak and minimize its spread.
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The importance of testing breath directly is highlighted when symptoms are taken into consideration. Research shows that a person is most infectious before they exhibit any symptoms. At these early stages of an infection, most people would not even think to take an antigen test, and if they did, it would give a negative result. Only sampling breath allows for testing of infectiousness using more sensitive detection methods.
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Researchers at Northwestern University have published important data exploring the rate of viral shed in EBC [3]. Their experimental design involved having volunteers collect breath samples at home and mail them to a central research facility for analysis by qPCR. The study demonstrates the importance of detecting infection through breath early in the course of the infection, as well as how simple the collection process can be.
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An in-house case study conducted by VosBio™ had similar results, showing a peak in viral shed rates in the breath, followed by a lingering detection of virus from nasal swabs after the subject was no longer contagious. The VosBio™ study demonstrated that it is not only possible to collect a breath sample rapidly with the VosCryo™ breath collector, but the results of the analysis can be ready within 20 minutes. This combination of speed and ease of use could allow widespread testing for infectiousness to lower the overall burden of communicable disease.
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1.Malik, M., Kunze, A.-C., Bahmer, T., Herget-Rosenthal, S., & Kunze, T. (2021). Sars-CoV-2: Viral loads of exhaled breath and oronasopharyngeal specimens in hospitalized patients with covid-19. International Journal of Infectious Diseases, 110, 105–110. https://doi.org/10.1016/j.ijid.2021.07.012
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2. Raymenants, J., Duthoo, W., Stakenborg, T., Verbruggen, B., Verplanken, J., Feys, J., Van Duppen, J., Hanifa, R., Marchal, E., Lambrechts, A., Maes, P., André, E., Van Den Wijngaert, N., & Peumans, P. (2022). Exhaled breath SARS-CoV-2 shedding patterns across variants of concern. International Journal of Infectious Diseases, 123, 25–33. https://doi.org/10.1016/j.ijid.2022.07.069
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3.Lane, G., Zhou, G., Hultquist, J. F., Simons, L. M., Redondo, R. L.-, Ozer, E. A., McCarthy, D. M., Ison, M. G., Achenbach, C. J., Wang, X., Wai, C. M., Wyatt, E., Aalsburg, A., Yang, Q., Noto, T., Alisoltani, A., Ysselstein, D., Awatramani, R., Murphy, R., … Zelano, C. (2024). Quantity of SARS-CoV-2 RNA copies exhaled per minute during natural breathing over the course of COVID-19 infection. https://doi.org/10.7554/eLife.91686.1