SARS-CoV-2の安定性

SARS-CoV-2は

・低温で安定、高温で(70℃以上でかなり)失活

・酸やアルカリに強い。

・滑らかな表面で安定、ザラザラな表面で不安定

・滑らかでも伝導性の良い金属だと不安定で失活

・極端な乾燥(湿度20％以下)で不安定

・石けんは有効だが、消毒薬に劣る。

ドアノブやプラスチック製の玩具の消毒は十分行う必要がありそうです。

伝導性の低いステンレスは、伝導性の高い銅とは大きな違いが出ています。

ステンレス表面で結構長く活性が残ります。

これらは無風の状態で実験しているので、実際に風が吹いたり、紫外線が当たったり、高温、極度の湿度、極度の乾燥（20％以下の湿度）では、RNAが酸化されたり、分解されて、短い時間で失活します。

（※　管理者注）

以下は、NEJMからの報告です。

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SARS-CoV-2の半減期はエアロゾルで1.2時間、ステンレスで5.6時間、プラスチックで6.8時間。

指数関数的に減少します。

ベイズ型回帰モデルで推定したものです。

Aerosol and Surface Stability of SARS-CoV-2 as Compared with SARS-CoV-1

https://www.nejm.org/doi/full/10.1056/NEJMc2004973

A novel human coronavirus that is now named severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) (formerly called HCoV-19) emerged in Wuhan, China, in late 2019 and is now causing a pandemic.1 We analyzed the aerosol and surface stability of SARS-CoV-2 and compared it with SARS-CoV-1, the most closely related human coronavirus.2

We evaluated the stability of SARS-CoV-2 and SARS-CoV-1 in aerosols and on various surfaces and estimated their decay rates using a Bayesian regression model (see the Methods section in the Supplementary Appendix, available with the full text of this letter at NEJM.org). SARS-CoV-2 nCoV-WA1-2020 (MN985325.1) and SARS-CoV-1 Tor2 (AY274119.3) were the strains used. Aerosols (<5 μm) containing SARS-CoV-2 (105.25 50% tissue-culture infectious dose [TCID50] per milliliter) or SARS-CoV-1 (106.75-7.00 TCID50 per milliliter) were generated with the use of a three-jet Collison nebulizer and fed into a Goldberg drum to create an aerosolized environment. The inoculum resulted in cycle-threshold values between 20 and 22, similar to those observed in samples obtained from the upper and lower respiratory tract in humans.

Our data consisted of 10 experimental conditions involving two viruses (SARS-CoV-2 and SARS-CoV-1) in five environmental conditions (aerosols, plastic, stainless steel, copper, and cardboard). All experimental measurements are reported as means across three replicates.

Viability of SARS-CoV-1 and SARS-CoV-2 in Aerosols and on Various Surfaces.

SARS-CoV-2 remained viable in aerosols throughout the duration of our experiment (3 hours), with a reduction in infectious titer from 103.5 to 102.7 TCID50 per liter of air. This reduction was similar to that observed with SARS-CoV-1, from 104.3 to 103.5 TCID50 per milliliter (Figure 1A).

SARS-CoV-2 was more stable on plastic and stainless steel than on copper and cardboard, and viable virus was detected up to 72 hours after application to these surfaces (Figure 1A), although the virus titer was greatly reduced (from 103.7 to 100.6 TCID50 per milliliter of medium after 72 hours on plastic and from 103.7 to 100.6 TCID50 per milliliter after 48 hours on stainless steel). The stability kinetics of SARS-CoV-1 were similar (from 103.4 to 100.7 TCID50 per milliliter after 72 hours on plastic and from 103.6 to 100.6 TCID50 per milliliter after 48 hours on stainless steel). On copper, no viable SARS-CoV-2 was measured after 4 hours and no viable SARS-CoV-1 was measured after 8 hours. On cardboard, no viable SARS-CoV-2 was measured after 24 hours and no viable SARS-CoV-1 was measured after 8 hours (Figure 1A).

Both viruses had an exponential decay in virus titer across all experimental conditions, as indicated by a linear decrease in the log10TCID50 per liter of air or milliliter of medium over time (Figure 1B). The half-lives of SARS-CoV-2 and SARS-CoV-1 were similar in aerosols, with median estimates of approximately 1.1 to 1.2 hours and 95% credible intervals of 0.64 to 2.64 for SARS-CoV-2 and 0.78 to 2.43 for SARS-CoV-1 (Figure 1C, and Table S1 in the Supplementary Appendix). The half-lives of the two viruses were also similar on copper. On cardboard, the half-life of SARS-CoV-2 was longer than that of SARS-CoV-1. The longest viability of both viruses was on stainless steel and plastic; the estimated median half-life of SARS-CoV-2 was approximately 5.6 hours on stainless steel and 6.8 hours on plastic (Figure 1C). Estimated differences in the half-lives of the two viruses were small except for those on cardboard (Figure 1C). Individual replicate data were noticeably “noisier” (i.e., there was more variation in the experiment, resulting in a larger standard error) for cardboard than for other surfaces (Fig. S1 through S5), so we advise caution in interpreting this result.

We found that the stability of SARS-CoV-2 was similar to that of SARS-CoV-1 under the experimental circumstances tested. This indicates that differences in the epidemiologic characteristics of these viruses probably arise from other factors, including high viral loads in the upper respiratory tract and the potential for persons infected with SARS-CoV-2 to shed and transmit the virus while asymptomatic.3,4 Our results indicate that aerosol and fomite transmission of SARS-CoV-2 is plausible, since the virus can remain viable and infectious in aerosols for hours and on surfaces up to days (depending on the inoculum shed). These findings echo those with SARS-CoV-1, in which these forms of transmission were associated with nosocomial spread and super-spreading events,5 and they provide information for pandemic mitigation efforts.

一般の人には誤解があるかも知れませんが、RT-PCRというRNAを増幅する検査は感染性粒子が無くなった後も検出されます。

一方、ウイルス培養は実際に細胞に感染させて増殖するかを見るもので、こちらが実際の感染性を反映しています。

つまり培養結果の方が重要です。

NEJMの方が短く、Lancetのものが長く見えるのは決して矛盾ではありません。

以下は、Lancetからの報告です。

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以前に、さまざまな臨床サンプルにおける重症急性呼吸器症候群コロナウイルス2（SARS-CoV-2）の検出を報告しました。[1]

このウイルスは、汚染された場所のさまざまな表面で検出されます。[2]

ここでは、さまざまな環境条件でのSARS-CoV-2の安定性について報告します。

最初に、さまざまな温度でのSARS-CoV-2の安定性を測定しました。ウイルス輸送培地中のSARS-CoV-2（最終濃度〜6.8 log単位、50％組織培養感染用量[mL] / [TCID50]）を最大14日間インキュベートし、感染性をテストしました（付録p 1）。

ウイルスは4℃で非常に安定していますが、熱に敏感です。 4℃では、14日目には感染力価の約0.7ログ単位の減少しかありませんでした。インキュベーション温度を70℃に上げると、ウイルス不活化の時間が5分に短縮されました。

さらに、さまざまな表面でのこのウイルスの安定性を調査しました。簡単に言えば、ウイルス培養液の5μL液滴（1 mLあたりTCID50の〜7.8 log単位）を表面（付録p 1; 1個あたり〜cm2）にピペッティングし、相対湿度約65％で室温（22°C）に放置しましました。

所定の時点で回収された接種された物体は、ウイルスを溶出するために、200μLのウイルス輸送培地に30分間直ちに浸された。

したがって、このウイルスの回復は、不用意な接触からウイルスを拾う可能性を必ずしも反映していません。

3時間のインキュベーション後、印刷物およびティッシュペーパーから感染性ウイルスを回収できなかった。

そして2日後に処理された木材および布からは感染性ウイルスを検出できなかった。

対照的に、SARS-CoV-2は滑らかな表面でより安定していた。 4日後（ガラスおよび紙幣）または7日後（ステンレス鋼およびプラスチック）では、処理された滑らかな表面から感染性ウイルスを検出できませんでした。

驚くべきことに、7日目でも、検出可能なレベルの感染性ウイルスがサージカルマスクの外層にまだ存在している可能性があります（元の接種材料の〜0.1％）。

興味深いことに、感染性のSARS-CoV-2の二相性の崩壊は、これらの滑らかな表面から回収されたサンプルで見つかりました（付録pp 2–7）。

39の代表的な非感染性サンプルがRT-PCR [3]で陽性とテストされました（データは示していません）。

非感染性ウイルスが溶離液によってまだ回収できることを示しています。

また、15μLのSARS-CoV-2培養液（mLあたりTCID50の約7.8 log単位）をさまざまな消毒剤の135μLに加えて、消毒剤の殺ウイルス効果をテストしました（付録p 1）。

ハンドソープでの5分間のインキュベーションを除いて、室温（22°C）で5分間のインキュベーション後、感染性ウイルスは検出されませんでした。

さらに、SARS-CoV-2は、室温で幅広いpH値（pH 3〜10、付録p 1）で非常に安定していることもわかりました。

全体として、SARS-CoV-2は良好な環境で非常に安定している可能性があります4が、標準的な消毒方法の影響も受けます。

この研究は、国立衛生研究所のアレルギーおよび感染症研究所（契約HHSN272201400006C）によってサポートされていました。

Stability of SARS-CoV-2 in different environmental conditions

Lancet Microbe 2020

Published Online

April 2, 2020 https://doi.org/10.1016/ S2666-5247(20)30003-3

We previously reported the detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in different clinical samples.[1]

This virus can be detected on different surfaces in a contaminated site.[2]

Here, we report the stability of SARS-CoV-2 in different environmental conditions.

We first measured the stability of SARS-CoV-2 at different temperatures. SARS-CoV-2 in virus transport medium (final concentration ~6·8 log unit of 50% tissue culture infectious dose [TCID50] per mL) was incubated for up to 14 days and then tested for its infectivity (appendix p 1).

The virus is highly stable at 4°C, but sensitive to heat. At 4°C, there was only around a 0·7 log-unit reduction of infectious titre on day 14. With the incubation temperature increased to 70°C, the time for virus inactivation was reduced to 5 mins.

We further investigated the stability of this virus on different surfaces. Briefly, a 5 μL droplet of virus culture (~7·8 log unit of TCID50 per mL) was pipetted on a surface (appendix p 1; ~cm2 per piece) and left at room temperature (22°C) with a relative humidity of around 65%.

The inoculated objects retrieved at desired time-points were immediately soaked with 200 μL of virus transport medium for 30 mins to elute the virus.

Therefore, this recovery of virus does not necessarily reflect the potential to pick up the virus from casual contact.

No infectious virus could be recovered from printing and tissue papers after a 3-hour incubation, whereas no infectious virus could be detected from treated wood and cloth on day 2.

By contrast, SARS-CoV-2 was more stable on smooth surfaces. No infectious virus could be detected from treated smooth surfaces on day 4 (glass and banknote) or day 7 (stainless steel and plastic). Strikingly, a detectable level of infectious virus could still be present on the outer layer of a surgical mask on day 7 (~0·1% of the original inoculum).

Interestingly, a biphasic decay of infectious SARS-CoV-2 could be found in samples recovered from these smooth surfaces (appendix pp 2–7).

39 representative non-infectious samples tested positive by RT-PCR[3] (data not shown), showing that non-infectious viruses could still be recovered by the eluents.

We also tested the virucidal effects of disinfectants by adding 15 μL of SARS-CoV-2 culture (~7·8 log unit of TCID50 per mL) to 135 μL of various disinfectants at working concentration (appendix p 1).

With the exception of a 5-min incubation with hand soap, no infectious virus could be detected after a 5-min incubation at room temperature (22°C).

Additionally, we also found that SARS-CoV-2 is extremely stable in a wide range of pH values at room temperature (pH 3–10; appendix p 1).

Overall, SARS-CoV-2 can be highly stable in a favourable environment,4 but it is also susceptible to standard disinfection methods.

This work was supported by National Institute of Allergy and Infectious Diseases, National Institutes of Health (contract HHSN272201400006C).

LLMP was supported by the Croucher Foundation. We declare no competing interests.

Alex W H Chin, Julie T S Chu, Mahen R A Perera, Kenrie P Y Hui, Hui-Ling Yen, Michael C W Chan, Malik Peiris, *Leo L M Poon llmpoon@hku.hk

School of Public Health, LKS Faculty of Medicine, The University of Hong Kong, Hong Kong Special Administrative Region, China.

1 Pan Y, Zhang D, Yang P, Poon LLM, Wang Q. Viral load of SARS-CoV-2 in clinical samples. Lancet Infect Dis 2020; published online

Feb 24. https://doi.org/10·1016/S1473– 3099(20)30113–4.

2 Ye G, Lin H, Chen L, et al. Environmental contamination of the SARS-CoV-2 in healthcare premises: an urgent call for protection for healthcare workers. medRxiv 2020; published online March 16. DOI:10·1101/2020·03·11·20034546 (preprint).

3 Chu DKW, Pan Y, Cheng SMS, et al. Molecular diagnosis of a novel coronavirus (2019-nCoV) causing an outbreak of pneumonia. Clin Chem 2020; published online Jan 31. DOI:10·1093/ clinchem/hvaa029.

4 van Doremalen N, Bushmaker T, Morris DH, et al. Aerosol and surface stability of SARS- CoV-2 as compared with SARS-CoV-1.

N Engl J Med 2020; published online March 17. DOI:10·1056/NEJMc2004973.