【文献Abstract】症状のない人からの新型コロナウイルス感染

〈要点〉

・症状のない人から発生する可能性が高いコミュニティにおけるSARS-CoV-2感染の割合を評価
・この研究においては無症候性の個人からの感染がすべての感染の半分以上を占めると推定。症候性COVID-19の人の特定と隔離に加えて、感染拡大を効果的に管理するには、症状のない感染者からの感染リスクを減らす必要がある。
・これらの調査結果は、安全で効果的なワクチンが利用可能になり広く使用されるまで、マスクの着用、手指衛生、社会的距離、病気でない人々の検査などの対策がCOVID-19の蔓延を遅らせるための基礎となることを示唆している。

〈雑感〉

・無症候性が半数！検査のキャパシティーを考えると全例PCRを実施できるわけでもないし、やはり今までの働き方（根性論や集まらないとダメみたいな）を変えていく必要があると改めて思った。そこから脱することでクリエイティブな働き方やビジネスを考えていかないと生き残れないんだろうな。。地域の方々がこぼれおちていかないように、我々もクリニックとしてできることをしながらフォローしていかなければ…。

〈文献〉

JAMA Netw Open. 2021 Jan 4;4(1):e2035057. doi: 10.1001/jamanetworkopen.2020.35057.
SARS-CoV-2 Transmission From People Without COVID-19 Symptoms
Michael A Johansson , Talia M Quandelacy , Sarah Kada , Pragati Venkata Prasad , Molly Steele , John T Brooks , Rachel B Slayton , Matthew Biggerstaff , Jay C Butler 
Abstract
Importance: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the etiology of coronavirus disease 2019 (COVID-19), is readily transmitted person to person. Optimal control of COVID-19 depends on directing resources and health messaging to mitigation efforts that are most likely to prevent transmission, but the relative importance of such measures has been disputed.

Objective: To assess the proportion of SARS-CoV-2 transmissions in the community that likely occur from persons without symptoms.

Design, setting, and participants: This decision analytical model assessed the relative amount of transmission from presymptomatic, never symptomatic, and symptomatic individuals across a range of scenarios in which the proportion of transmission from people who never develop symptoms (ie, remain asymptomatic) and the infectious period were varied according to published best estimates. For all estimates, data from a meta-analysis was used to set the incubation period at a median of 5 days. The infectious period duration was maintained at 10 days, and peak infectiousness was varied between 3 and 7 days (-2 and +2 days relative to the median incubation period). The overall proportion of SARS-CoV-2 was varied between 0% and 70% to assess a wide range of possible proportions.

Main outcomes and measures: Level of transmission of SARS-CoV-2 from presymptomatic, never symptomatic, and symptomatic individuals.

Results: The baseline assumptions for the model were that peak infectiousness occurred at the median of symptom onset and that 30% of individuals with infection never develop symptoms and are 75% as infectious as those who do develop symptoms. Combined, these baseline assumptions imply that persons with infection who never develop symptoms may account for approximately 24% of all transmission. In this base case, 59% of all transmission came from asymptomatic transmission, comprising 35% from presymptomatic individuals and 24% from individuals who never develop symptoms. Under a broad range of values for each of these assumptions, at least 50% of new SARS-CoV-2 infections was estimated to have originated from exposure to individuals with infection but without symptoms.

Conclusions and relevance: In this decision analytical model of multiple scenarios of proportions of asymptomatic individuals with COVID-19 and infectious periods, transmission from asymptomatic individuals was estimated to account for more than half of all transmissions. In addition to identification and isolation of persons with symptomatic COVID-19, effective control of spread will require reducing the risk of transmission from people with infection who do not have symptoms. These findings suggest that measures such as wearing masks, hand hygiene, social distancing, and strategic testing of people who are not ill will be foundational to slowing the spread of COVID-19 until safe and effective vaccines are available and widely used.