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The prominence of asymptomatic superspreaders in transmission mean universal face masking should be part of COVID-19 de-escalation strategies

  • Chris Kenyon
    Correspondence
    Corresponding author.
    Affiliations
    HIV/STI Unit, Institute of Tropical Medicine, Department of Clinical Sciences, Antwerp 2000, Belgium

    Division of Infectious Diseases and HIV Medicine, University of Cape Town, Anzio Road, Observatory 7700, South Africa
    Search for articles by this author
Open AccessPublished:June 01, 2020DOI:https://doi.org/10.1016/j.ijid.2020.05.102
      Dear Editor,
      Beldomenico recently provided a convincing argument in this journal that superspreaders play an important role in the spread of SARS-CoV-2 (
      • Beldomenico P.M.
      Do superspreaders generate new superspreaders? a hypothesis to explain the propagation pattern of COVID-19.
      ). 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 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.
      ) and epidemiological evidence of the importance of superspreaders (
      • Lloyd-Smith J.O.
      • Schreiber S.J.
      • Kopp P.E.
      • Getz W.M.
      Superspreading and the effect of individual variation on disease emergence.
      ). 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 J.O.
      • Schreiber S.J.
      • Kopp P.E.
      • Getz W.M.
      Superspreading and the effect of individual variation on disease emergence.
      ). 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 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.
      )) 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 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.
      ). Likewise, one superspreading event linked to a single case in a church in South Korea, was reported to result in 3900 secondary cases (
      • Shim E.
      • Tariq A.
      • Choi W.
      • Lee Y.
      • Chowell G.
      Transmission potential and severity of COVID-19 in South Korea.
      ). 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 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.
      ) and evidence that SARS-CoV-2 is transmitted via airborne as well as contact and droplet routes (
      • Setti 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.
      ). 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 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.
      ). 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 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.
      ). 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 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.
      ,
      • Howard J.
      • Huang A.
      • Li Z.
      • Tufekci Z.
      • Zdimal V.
      • van der Westhuizen H.-M.
      • et al.
      Face masks against COVID-19: an evidence review.
      ). Widespread use of face masks in public has also been associated with a lower incidence of COVID-19 at a population level (
      • Cheng 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.
      ). Whilst gaps in the evidence for exactly how best to use face masks remain (
      • Cheng 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.
      ), 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.

      Funding

      No specific funding was received for this work.

      Ethical approval

      Not applicable

      Data availability

      Not applicable.

      Transparency declarations

      None to declare. All the authors declare that they have no conflicts of interest.

      Acknowledgements

      Nil.

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