Asymptomatic infection

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COVID-19: What proportion are asymptomatic? • https://blogs.bmj.com/bmj/2020/05/04/... • • Between 5% and 80% of people testing positive for SARS-CoV-2 may be asymptomatic • Symptom-based screening will miss cases, perhaps a lot of them • Some asymptomatic cases will become symptomatic over the next week (i.e. pre-symptomatic) • Children and young adults can be asymptomatic • There is not a single reliable study to determine the number of asymptotics • • Population based antibody testing required • Diamond Princess • https://www.ncbi.nlm.nih.gov/research... • 3,711 people tested • 634 tested positive • 18% • Vo’Euganeo, (50Km west of Venice) • https://www.bmj.com/content/368/bmj.m... • All 3,000 people in village tested • 50 – 75% asymptomatic • Asymptomatics infectious • represented ‘a formidable source’ of contagion • 328 adults in Shanghai • https://www.clinicalmicrobiologyandin... • 328 adults were diagnosed with COVID-19 in Shanghai • Among them, 13 patients were asymptomatic at time of diagnosis • No subjective symptoms 2 weeks before admission • All of the 13 (4%) them were close contacts of the confirmed cases • • Japanese nationals evacuated from Wuhan • https://www.ijidonline.com/article/S1... • 565 citizens had been evacuated • 30.8% (7.7– 53.8%). • 30 days after evacuation • Asymptomatic and Pre-symptomatic SARS-CoV-2 Infections in Residents of a Long-Term Care Skilled Nursing Facility - King County, Washington • https://www.ncbi.nlm.nih.gov/research... • CDC 76 residents • categorized as asymptomatic or symptomatic at the time of testing and for previous 14 days • 23 (30%) residents, antigen positive and symptomatic • 13 (57%) were asymptomatic • 10 of these 13 previously asymptomatic residents developed symptoms within 7 days • Therefore 3 (4%) out of 76 truly asymptomatic • RT-PCR) values indicated large quantities of viral RNA in asymptomatic, pre-symptomatic, and symptomatic residents • Symptom based screening on a particular day could fail to detect half of positive cases • Iceland • https://www.nejm.org/doi/full/10.1056... • Population screening, 57% symptomatic, 43% asymptomatic • • CDC, Interim Clinical Guidance for Management of Patients with Confirmed Coronavirus Disease (COVID-19) • https://www.cdc.gov/coronavirus/2019-... • 13% of positive children asymptomatic • Risk of transmission is thought to be greatest when patients are symptomatic since viral shedding is greatest at the time of symptom onset and declines over the course of several days to weeks. • • WHO • 81% of infections show mild symptoms • 14% exhibit severe symptoms • 5% fall critically ill • Asymptomatic coronavirus infection: MERS-CoV and SARS-CoV-2 (COVID-19) • https://www.sciencedirect.com/science... • The extent of asymptomatic MERS-CoV (2012) cases is about 9.8% • • How much is covid-19 spreading via asymptomatic versus symptomatic infections? (4th May) • https://www.cebm.net/covid-19/covid-1... • Mathematical models SEIIR • Susceptible • Exposed • Infected, symptomatic • Infected, asymptomatic • Recovered • Therefore, need widespread antibody testing and contact tracing as soon as possible.

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