The prominence of asymptomatic superspreaders in transmission mean universal face masking should be part of COVID-19 de-escalation strategies
Chris Kenyon
Abstract
Beldomenico recently provided a convincing argument in this journal that superspreaders play an important role in the spread of SARS-CoV-2 (Beldomenico, 2020Beldomenico P.M. Do superspreaders generate new superspreaders? a hypothesis to explain the propagation pattern of COVID-19.Int J Infect Dis. 2020; Abstract Full Text Full Text PDF PubMed Scopus (43) Google Scholar). His argument is strengthened by recent evidence that a small proportion of individuals are ‘speech super-emitters’ who emit an order of magnitude more aerosol particles than their peers (Asadi et al., 2019Asadi S. Wexler A.S. Cappa C.D. Barreda S. Bouvier N.M. Ristenpart W.D. Aerosol emission and superemission during human speech increase with voice loudness.Sci Rep. 2019; 9: 2348Crossref PubMed Scopus (609) Google Scholar) and epidemiological evidence of the importance of superspreaders (Lloyd-Smith et al., 2005Lloyd-Smith J.O. Schreiber S.J. Kopp P.E. Getz W.M. Superspreading and the effect of individual variation on disease emergence.Nature. 2005; 438: 355-359Crossref PubMed Scopus (1607) Google Scholar). A study of SARS-CoV-1 transmission, for example, found that superspreaders played a greater role in its spread than in all the other respiratory viral infections evaluated (Lloyd-Smith et al., 2005Lloyd-Smith J.O. Schreiber S.J. Kopp P.E. Getz W.M. Superspreading and the effect of individual variation on disease emergence.Nature. 2005; 438: 355-359Crossref PubMed Scopus (1607) Google Scholar). If the same was true for SARS-CoV-2, then this could explain the apparent discrepancy between studies that typically find low secondary attack rates within homes (11.2% in one study in China (Bi et al., 2020Bi Q. Wu Y. Mei S. Ye C. Zou X. Zhang Z. et al.Epidemiology and transmission of COVID-19 in 391 cases and 1286 of their close contacts in Shenzhen, China: a retrospective cohort study.Lancet Infect Dis. 2020; Abstract Full Text Full Text PDF PubMed Scopus (1025) Google Scholar)) and high attack rates in specific clusters of transmission such as the Skagit County choir where 87% of choir attendees were infected by a single person following a single joint choir practice (Hamner et al., 2020Hamner L. Dubbel P. Capron I. Ross A. Jordan A. Lee J. et al.High SARS-CoV-2 attack rate followinge exposure at a choir practice—Skagit County, Washington, March 2020.MMWR Morbidity and mortality weekly report. 2020; 69: 606-610Crossref PubMed Scopus (27) Google Scholar). Likewise, one superspreading event linked to a single case in a church in South Korea, was reported to result in 3900 secondary cases (Shim et al., 2020Shim E. Tariq A. Choi W. Lee Y. Chowell G. Transmission potential and severity of COVID-19 in South Korea.Int J Infect Dis. 2020; 93: 339-344Abstract Full Text Full Text PDF PubMed Scopus (456) Google Scholar). These considerations are of added significance in the light of increasing evidence that a large proportion of SARS-CoV-2 transmissions occur whilst the transmitters have few or no symptoms (Arons et al., 2020Arons M.M. Hatfield K.M. Reddy S.C. Kimball A. James A. Jacobs J.R. et al.Presymptomatic SARS-CoV-2 Infections and Transmission in a Skilled Nursing Facility.N Engl J Med. 2020; Crossref PubMed Scopus (1443) Google Scholar) and evidence that SARS-CoV-2 is transmitted via airborne as well as contact and droplet routes (Setti et al., 2020Setti L. Passarini F. De Gennaro G. Barbieri P. Perrone M.G. Borelli M. et al.Airborne Transmission Route of COVID-19: Why 2 Meters/6 Feet of Inter-Personal Distance Could Not Be Enough.Int J Environ Res Public Health. 2020; 17Crossref Scopus (396) Google Scholar). As lockdown measures are eased it is worth considering that taken together these insights suggest that social distancing measures may not, by themselves, be sufficient to prevent large, new outbreaks of COVID-19 (Setti et al., 2020Setti L. Passarini F. De Gennaro G. Barbieri P. Perrone M.G. Borelli M. et al.Airborne Transmission Route of COVID-19: Why 2 Meters/6 Feet of Inter-Personal Distance Could Not Be Enough.Int J Environ Res Public Health. 2020; 17Crossref Scopus (396) Google Scholar). A single superspreader in an underventilated supermarket, for example, could infect a high number of individuals. Rather it is possible that universal face masking in public plus social distancing may be required to sufficiently reduce this risk (Setti et al., 2020Setti L. Passarini F. De Gennaro G. Barbieri P. Perrone M.G. Borelli M. et al.Airborne Transmission Route of COVID-19: Why 2 Meters/6 Feet of Inter-Personal Distance Could Not Be Enough.Int J Environ Res Public Health. 2020; 17Crossref Scopus (396) Google Scholar). Face masks have been shown to reduce the risk of transmission of a range of respiratory viruses including SARS-CoV-1 and other coronaviruses (Cheng et al., 2020Cheng V.C. Wong S.C. Chuang V.W. So S.Y. Chen J.H. Sridhar S. et al.The role of community-wide wearing of face mask for control of coronavirus disease 2019 (COVID-19) epidemic due to SARS-CoV-2.J Infect. 2020; Abstract Full Text Full Text PDF Scopus (519) Google Scholar, Howard et al., 2020Howard J. Huang A. Li Z. Tufekci Z. Zdimal V. van der Westhuizen H.-M. et al.Face masks against COVID-19: an evidence review.Preprints. 2020; (040203 (doi: 1020944/preprints2020040203v1). 2020)Google Scholar). Widespread use of face masks in public has also been associated with a lower incidence of COVID-19 at a population level (Cheng et al., 2020Cheng V.C. Wong S.C. Chuang V.W. So S.Y. Chen J.H. Sridhar S. et al.The role of community-wide wearing of face mask for control of coronavirus disease 2019 (COVID-19) epidemic due to SARS-CoV-2.J Infect. 2020; Abstract Full Text Full Text PDF Scopus (519) Google Scholar). Whilst gaps in the evidence for exactly how best to use face masks remain (Cheng et al., 2020Cheng V.C. Wong S.C. Chuang V.W. So S.Y. Chen J.H. Sridhar S. et al.The role of community-wide wearing of face mask for control of coronavirus disease 2019 (COVID-19) epidemic due to SARS-CoV-2.J Infect. 2020; Abstract Full Text Full Text PDF Scopus (519) Google Scholar), the evidence that superspreaders, who may have few or no symptoms, are responsible for large outbreaks provides further evidence to justify recommendations promoting universal face masking in public. No specific funding was received for this work.