Following its emergence in Wuhan, China, in late November or early December 2019, the SARS-CoV-2 virus has rapidly spread globally. Genome sequencing of SARS-CoV-2 allows reconstruction of its transmission history, although this is contingent on sampling. We have analyzed 453 SARS-CoV-2 genomes collected between 20 February and 15 March 2020 from infected patients in Washington State, USA. We find that most SARS-CoV-2 infections sampled during this time derive from a single introduction in late January or early February 2020 which subsequently spread locally before active community surveillance was implemented.
Following its emergence in Wuhan,
We describe projections for the burden of infections and deaths in King and Snohomish Counties through April 7, as projections further out are strongly sensitive to assumptions about the scale of the local outbreak and importation dynamics from other regions that are not yet known. For the projections, we considered four scenarios for the increasingly effective impact of social distancing on COVID-19 incidence: • A baseline scenario assuming no change since January 15. • Scenarios with 25, 50, and 75 percent reductions in the rate of transmission assumed to take place starting March 10. The scenarios describe the generalized impacts of social distancing policies but do not currently speak to specific policy recommendations on issues like school closures, event cancellation, and work policies. We estimate that in the baseline scenario, on average across multiple simulations, there will have been roughly 25,000 people infected by April 7. Assuming mortality statistics will be like those seen in China, we expect that roughly 80 deaths will have occurred by April 7 and that roughly 400 total deaths will have been destined but not yet occurred. Effective social distancing slows the growth rate of the epidemic, and very effective interventions may stop the continued exponential growth. The table below illustrates the reductions in infections and deaths we expect with social distancing interventions. Social distancing intervention Estimated infections Destined deaths Business as usual 25,000 400 25% reduction 9,700 160 50% reduction 4,800 100 75% reduction 1,700 30 We do not yet know which scenario best represents current conditions in King and Snohomish counties, but previous experience in the region with weather-related social distancing and in other countries suggests to us that current efforts will likely land between baseline and 25% reduction scenarios. While we are not yet confident in our ability to estimate when the volume of new infections will overwhelm the health system, we discuss the issue below and believe it will be a critically important issue to address in the weeks to come. Thus, we believe more comprehensive non-pharmaceutical intervention policies in the region as soon as possible will be necessary to slow the onslaught of the disease, and we hope these are accompanied by policies to mitigate the broader societal impacts on the healthcare workforce and vulnerable populations.
IMPORTANCEThe association between COVID-19 symptoms and SARS-CoV-2 viral levels in children living in the community is not well understood. OBJECTIVE To characterize symptoms of pediatric COVID-19 in the community and analyze the association between symptoms and SARS-CoV-2 RNA levels, as approximated by cycle threshold (Ct) values, in children and adults. DESIGN, SETTING, AND PARTICIPANTS This cross-sectional study used a respiratory virus surveillance platform in persons of all ages to detect community COVID-19 cases from March 23 to November 9, 2020. A population-based convenience sample of children younger than 18 years and adults in King County, Washington, who enrolled online for home self-collection of upper respiratory samples for SARS-CoV-2 testing were included. EXPOSURES Detection of SARS-CoV-2 RNA by reverse transcription-polymerase chain reaction (RT-PCR) from participant-collected samples. MAIN OUTCOMES AND MEASURES RT-PCR-confirmed SARS-CoV-2 infection, with Ct values stratified by age and symptoms. RESULTS Among 555 SARS-CoV-2-positive participants (mean [SD] age, 33.7 [20.1] years; 320 were female [57.7%]), 47 of 123 children (38.2%) were asymptomatic compared with 31 of 432 adults (7.2%). When symptomatic, fewer symptoms were reported in children compared with adults (mean [SD], 1.6 [2.0] vs 4.5 [3.1]). Symptomatic individuals had lower Ct values (which corresponded to higher viral RNA levels) than asymptomatic individuals (adjusted estimate for children, −3.0; 95% CI, −5.5 to −0.6; P = .02; adjusted estimate for adults, −2.9; 95% CI, −5.2 to −0.6; P = .01). The difference in mean Ct values was neither statistically significant between symptomatic children and symptomatic adults (adjusted estimate, −0.7; 95% CI, −2.2 to 0.9; P = .41) nor between asymptomatic children and asymptomatic adults (adjusted estimate, −0.6; 95% CI, −4.0 to 2.8; P = .74). CONCLUSIONS AND RELEVANCEIn this community-based cross-sectional study, SARS-CoV-2 RNA levels, as determined by Ct values, were significantly higher in symptomatic individuals than in asymptomatic individuals and no significant age-related differences were found. Further research is needed to understand the role of SARS-CoV-2 RNA levels and viral transmission.
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