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【HEALTHOGRAPHICS】新型冠狀病毒要多久才失去感染力?

2020/4/15 — 17:26

香港大學醫學院製圖

香港大學醫學院製圖

【文:香港大學醫學院】

港大醫學院公共衞生學院公共衞生實驗室科學分部主任潘烈文教授的團隊,早前研究新型冠狀病毒(SARS-CoV-2)在不同環境的感染力。這些研究結果能幫助我們以正確方法保持個人衞生和家居清潔。

Q1:高溫可否殺死病毒?

廣告

病毒在溫暖地方仍具感染力,這是不爭的事實。不過研究發現溫度會影響病毒的穩定性,團隊在實驗室量度病毒在不同溫度下減少速度。在愈高溫的環境下,病毒越快失去感染力。以下是病毒在不同溫度下失去感染力的所需時間:

■ 4 ℃:14 日後病毒仍然穩定
■ 22 ℃:14 日
■ 37 ℃:2 日
■ 56 ℃:30 分鐘
■ 70 ℃:5分鐘

廣告

如果市民擔心自己衣物曾接觸病毒,例如曾接觸患者,或要照顧家居隔離人士,可將衣物用 60 ℃ 的熱水浸泡半小時再洗。

Q2:病毒在不同物料表面的穩定性有分別嗎?

團隊測試過病毒停留在不同物料表面的穩定性,整體來說病毒在平滑表面上比較穩定。以下是病毒在各種物料上失去感染力的所需時間:

■ 紙張、紙巾:3 小時
■ 木材、布料:2 日
■ 玻璃:4 日
■ 不鏽鋼、塑膠:4 至 7 日
■ 外科口罩表面:7 日後仍驗出病毒

要注意的是,病毒在外科口罩的表面多日後仍能被檢測,因此不建議大家重用口罩,而每次佩戴、除下或觸碰口罩,必須徹底清潔雙手。

病毒在紙張只存留三小時,那麼在口罩外層加張紙巾是否可以令口罩更耐用?這方法亦不建議,因會令佩戴者更加不舒服,可能會更頻密觸摸口罩而沾污雙手。

Q3:清潔劑能有效殺死病毒嗎?

雖然病毒在室溫下、在不同物料的感染力仍能維持一段時間,但使用清潔劑能夠有效殺死病毒,減少傳播。我們測試過以下清潔劑 ,全部在 5 分鐘後檢測不出病毒:

■ 1:49 家用漂白水
■ 1:99 家用漂白水
■ 70% 乙醇(酒精)
■ 7.5% 聚維酮碘(含碘消毒劑的常見成份)
■ 0.05% 氯二甲酚(滴露的有效成份)
■ 0.05% 氯己定(粉紅色消毒藥水的常見成份)
■ 0.1% 苯扎氯安(消毒濕紙巾的常見成份)

至於在 1:49 的肥皂水內,部分病毒 5 分鐘內仍具感染力;但 15 分鐘後已驗不出病毒。

因此大家無須過於恐慌,其實將家居和物品表面以清潔劑清洗一段時間,均能殺死新冠病毒,減少感染風險。


Q1. Are higher temperatures more likely to cause loss of infectivity in viruses?

Common knowledge says higher temperature are generally not ideal for viruses; our study further examines how different temperatures can have varying effects on the amount of time it takes for the virus to lose its infectivity. To test this hypothesis, our team incubated the virus and observed how long it would take for it to lose infectivity at different temperatures.

■ At 4°C, the virus remained stable after 14 days
■ At 22°C, the virus lost infectivity after 14 days
■ At 37°C, the virus lost infectivity after 2 days
■ At 56°C, the virus lost infectivity after 30 minutes
■ At 70°C, the virus lost infectivity after 5 minutes

For those concerned about having exposed their clothes to the virus (i.e. you had come in contact with a confirmed patient), or if you are taking care of someone currently under self-quarantine, you may want to first soak your clothes in hot water (60°C) f or 30 minutes before washing them in order to thoroughly disinfect.

Q2. Do different surfaces have an effect on the amount of time it takes for viruses to lose infectivity?

In addition to testing the impact of temperature on the infectivity of the virus, our team also tested how long it would take for the virus to lose infectivity on different surfaces. In summary, it seems the virus took a longer period of time to lose infectivity while on smoother surfaces, and less time on coarser ones:

■ Printed paper and tissue paper: the virus lost infectivity after three hours.
■ Wooden surfaces and fabric: the virus lost infectivity after two days.
■ Glass surfaces: the virus lost infectivity after 4 days.
■ Stainless steel surfaces and plastic: the virus lost infectivity after 4 to 7 days.
■ Surgical mask: the virus still detectable after 7 days

It is worth noting that the outer layer of surgical masks told a different story, as the virus remained infective and detectable even after 7 days. Knowing this, we once again stress that face masks should not be re-used; one should also wash their hands thoroughly before and after putting on the mask.

Q3. Are disinfectants effective in causing viruses to lose infectivity?

Although the coronavirus may take longer to lose infectivity when under room temperature, disinfectants may be used to shorten this duration, thereby reducing chances of transmission and infection. Our team tested a wide variety of different disinfectants and found that all the following were effective in causing viruses to lose infectivity after five minutes of use:

■ Household Bleach (1:49)
■ Household Bleach (1:99)
■ Ethanol (70%)
■ Povidone-iodine (7.5%)
■ Chloroxylenol (0.05%)
■ Chlorhexidine (0.05%)
■ Benzalkonium chloride (0.1%)

One point of note in the study: when hand soap was used at a ratio of 1:49, only half the number of the virus lost infectivity after five minutes; after 15 minutes however, all traces of the virus had lost its infectivity.

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