MGH FLARE - May 31

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  • MGH FLARE - May 31 - How is #SARS-CoV-2 transmitted?
    https://us19.campaign-archive.com/?u=ef98149bee3f299584374540a&id=01f6d7d1ce

    Pas de preuve à ce jour d’une #transmission par #aérosols


    Illustration of different transmission routes (Wei and Li 2016).


    The “aerobiologic pathway” for the transmission of communicable respiratory diseases proposed by Roy and Milton (Roy and Milton 2004).

    The rapid spread of COVID-19 across the globe has prompted researchers and public health officials to revisit the age-old question: Is this virus spreading via the airborne route? A letter published in the NEJM reported the three-hour long viability of SARS-CoV-2 in aerosols that were experimentally generated with a nebulizer, though with marked exponential decay in virus titer (van Doremalen et al. 2020). A recent non-peer reviewed preprint from the University of Nebraska found that air sampled in patient rooms and hallways contained SARS-CoV-2 viral RNA; however, further testing did not identify any viable, infectious virus in these samples (Santarpia et al. 2020). Additionally, findings from the Korean CDC have shown that patients who have recovered are not infectious despite some continuing to have positive RT-PCRs (KCDC). These findings reinforce two important notions: 1) that viral RNA is not equivalent to infectious virus, and correspondingly, 2) that the presence of SARS-CoV-2 RNA in air samples does not necessarily imply that this pathogen can be effectively transmitted via the airborne route.

    Data thus far analyzing outbreaks and exposures during the care of patients with COVID-19 continue to support droplet and contact routes as the predominant modes of transmission for SARS-CoV-2
    , mirroring what was observed during the SARS epidemic (CDC: Cluster of Severe Acute Respiratory Syndrome Cases among Protected Health-Care Workers—Toronto, Canada, 2003). For example, an exposure investigation from Hong Kong did not identify any secondary cases among a group of 71 staff and 49 patients in contact with a confirmed COVID-19 patient who was initially admitted under standard precautions and spent thirty-five hours unmasked in an open cubicle (Wong et al. 2020). Investigators credited the lack of nosocomial transmission to the institution’s universal mask policy, aggressive hand hygiene, and environmental cleaning practices (Siegel et al. 2007). A case report from Singapore had similar findings: among 35 healthcare workers wearing surgical masks while in close contact with a COVID-19 positive patient during an aerosol-generating procedure, none tested positive for SARS-CoV-2 two weeks after exposure (Ng et al. 2020). A recently published MMWR report investigated high rates of secondary transmission of COVID-19 among attendees of a choir practice in Washington (Hamner et al. 2020). This superspreading event was heavily featured in media outlets nationwide, raising concerns of airborne spread of COVID-19. Nevertheless, although investigators did raise the possibility of aerosol emission via speech and singing, they concluded that the close and prolonged contact of attendees was highly conducive to disease spread via droplets and fomites.

    • What Is a Superspreader Event? - Mass General Advances in Motion
      https://advances.massgeneral.org/pulmonary/article.aspx?id=1285

      So Is It Airborne?

      The term “airborne transmission” is generally reserved for infections that are transmitted over large distances or times (Roy and Milton 2004). This is a key distinction: airborne transmission requires more than the demonstration of small particles containing viruses. The significance of airborne transmission can only be established by the frequent occurrence of infections across distance and time. A small number of pathogens—Mycobacterium tuberculosis, varicella-zoster virus, rubeola virus and the measles virus—transmit efficiently over large distances and times. These pathogens are characterized by high attack rates and distinct epidemiology that has, so far, not been observed with SARS-CoV-2 (CDC 2020).

      A number of examples have been cited in support of the existence of airborne transmission, including a now well-known outbreak at a restaurant in China (Lu et al. 2020). This example highlights the difficulty of making a rigid distinction between modes of transmission—all infections occurred in three adjacent tables (thus among people in close proximity), none of the wait staff were infected nor were any of the other patrons. Notably, the ventilation in the restaurant in question was relatively poor (0.6 to 0.8 air changes per hour). The same ambiguities apply to the types of spreading events discussed above—they are largely episodes in which people were interacting unmasked and could have been infected in multiple ways, including droplet and contact routes. From the existing epidemiology, it is clear that the primary mode of transmission of SARS-CoV-2 is by close contact and respiratory droplets. It is also clear, however, that transmission can occur over longer times and at distances greater than six feet in favorable circumstances, such as poor ventilation or aerosol-generating medical procedures (Yu et al. 2007).