Research press release


Nature Medicine

Medical research: Modelling the timing of SARS-CoV-2 transmission

呼吸器疾患COVID-19の患者が感染性のSARS-CoV-2コロナウイルスを排出し始めるのは、最初の症状が現れる2~3日前からであるらしいことが、Nature Medicine に報告されたモデル化研究で示唆された。


今回、E Lauたちは、広州第八人民医院(中国)に入院した94人のCOVID-19患者でウイルス排出の時間的パターンを調べた。これらの患者からは、最初の症状が現れてから32日後まで、咽頭スワブが採取された。そして全部で414のスワブ検体の分析が行われ、患者のウイルス負荷が最も高かったのは、症状が出始めた時であったことが分かった。

その一方で、Lauたちは公開されたデータから得られた77対の「伝播ペア」 という別のサンプルを使って、COVID-19の感染力プロファイルをモデル化した。2人のCOVID-19患者からなる伝播ペアは、片方の患者がもう1人に疾患を感染させた可能性が非常に高く、2人の間の疫学的関連がはっきりしている。著者たちはここからスタートして、患者は症状出現の2.3日前から感染力を持ち始め、感染力がピークに達するのは症状が出る0.7日前であると推論した。そして、二次感染例の44%が症状出現前の段階の患者から感染したと見積もられ、感染力は7日以内に急速に低下すると予測された。


Patients with the respiratory disease COVID-19 may begin to shed, or excrete, infectious SARS-CoV-2 coronavirus 2–3 days before the first symptoms appear, suggests a modelling study reported in Nature Medicine.

Several factors can affect the efficacy of control measures designed to prevent the spread of SARS-CoV-2. These include the time between successive cases in a chain of transmission (serial interval) and the period between exposure to an infection and the appearance of symptoms (incubation period). If the serial interval is shorter than the incubation period, this would indicate that transmission may have happened before overt symptoms develop. As a result, control measures that take place at the point at which symptoms appear may have a reduced effect in controlling the spread of infection.

Eric Lau and colleagues investigated the temporal patterns of viral shedding in 94 patients with COVID-19 admitted to Guangzhou Eighth People’s Hospital in China. Throat swabs were collected from these patients from when symptoms first appeared until 32 days later. In total, 414 swabs were analysed, and the authors found that the patients had the highest viral load at the onset of symptoms.

Separately, they modelled COVID-19 infectiousness profiles from a different sample of 77 ‘transmission pairs’ from publicly available data. Each transmission pair comprised two patients with COVID-19 with a clear epidemiological link, with one patient highly likely to have infected the other. From here, the authors inferred that infectiousness started 2.3 days before symptoms appeared and peaked at 0.7 days before their appearance. They estimated that 44% of secondary cases were infected during the pre-symptomatic stage, with infectiousness predicted to decrease quickly within 7 days.

The authors note that the limitations of the study include the reliance of the research on patient recall of the onset of symptoms, which may have introduced bias, as there may be a delay in the recognition of the first symptoms.

doi: 10.1038/s41591-020-0869-5


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