• @kassem
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    #OMS 5 juin 2020 (page 2) : transmission du #sars-cov2 selon le statut symptomatique, pré-symptomatique, asymptomatique du sujet porteur
    ▻https://apps.who.int/iris/rest/bitstreams/1279750/retrieve

    Current evidence suggests that most transmission of #COVID- 19 is occurring from symptomatic people to others in close contact, when not wearing appropriate PPE. Among symptomatic patients, viral RNA can be detected in samples weeks after the onset of illness, but viable virus was not found after day 8 post onset of symptoms (19, 20) for mild patients, though this may be longer for severely ill patients. Prolonged RNA shedding, however, does not necessarily mean continued infectiousness.

    Transmissibility of the virus depends on the amount of viable virus being shed by a person, whether or not they are coughing and expelling more droplets, the type of contact they have with others, and what IPC measures are in place. Studies that investigate transmission should be interpreted bearing in mind the context in which they occurred.

    There is also the possibility of transmission from people who are infected and shedding virus but have not yet developed symptoms; this is called pre-symptomatic transmission. The incubation period for COVID-19, which is the time between exposure to the virus and symptom onset, is on average 5-6 days, but can be as long as 14 days.(21, 22) Additionally, data suggest that some people can test positive for COVID-19, via polymerase chain reaction (PCR) testing 1-3 days before they develop symptoms.(23) Pre-symptomatic transmission is defined as the transmission of the COVID-19 virus from someone infected and shedding virus but who has not yet developed symptoms. People who develop symptoms appear to have higher viral loads on or just prior to the day of symptom onset, relative to later on in their infection.(24)

    Some people infected with the COVID-19 virus do not ever develop any symptoms, although they can shed virus which may then be transmitted to others. One recent systematic review found that the proportion of asymptomatic cases ranged from 6% to 41%, with a pooled estimate of 16% (12%–20%), (25) although most studies included in this review have important limitations of poor reporting of symptoms, or did not properly define which symptoms they were investigating. Viable virus has been isolated from specimens of pre-symptomatic and asymptomatic individuals, suggesting, therefore, that people who do not have symptoms may be able transmit the virus to others.(26) Comprehensive studies on transmission from asymptomatic individuals are difficult to conduct, but the available evidence from contact tracing reported by Member States suggests that asymptomatically-infected individuals are much less likely to transmit the virus than those who develop symptoms.
    Among the available published studies, some have described occurrences of transmission from people who did not have symptoms.(21,25-32) For example, among 63 asymptomatically-infected individuals studied in China, there was evidence that 9 (14%) infected another person.(31) Furthermore, among two studies which carefully investigated secondary transmission from cases to contacts, one found no secondary transmission among 91 contacts of 9 asymptomatic cases,(33) while the other reported that 6.4% of cases were attributable to pre-symptomatic transmission.(32) The available data, to date, on onward infection from cases without symptoms comes from a limited number of studies with small samples that are subject to possible recall bias and for which fomite transmission cannot be ruled out.

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    • @kassem
      Kassem CC BY-NC-SA

      WHO Says Asymptomatic Spread “Rare,” Sparking Debate | Global Health NOW
      ▻https://www.globalhealthnow.org/2020-06/who-says-asymptomatic-spread-rare-sparking-debate

      The WHO called into question the extent that asymptomatic people are spreading COVID-19, launching a global debate, The Hill reports.

      “From the data we have, it still seems to be rare that an asymptomatic person actually transmits onward to a secondary individual,” said Maria Van Kerkhove, the WHO’s technical lead for COVID-19, citing unpublished data from detailed contact tracing reports at a briefing yesterday. She suggested that the focus should be on following symptomatic cases.

      If accurate, the implications would be huge—perhaps allowing some shutdown restrictions to ease. But if wrong, it could undo months of hard work, at a time people are chafing at the restrictions.

      Already, shutdown critics are pouncing on the news on social media.

      But Harvard Global Health Institute director Ashish Jha posited in a Twitter thread that the WHO could be using the term “asymptomatic,” when it really means “presymptomatic,”—an important distinction. Jha suggests that the agency should be more clear in its messaging, and notes that some models “suggest 40-60% of spread is from people when they didn’t have symptoms,” Forbes reports.

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