立場新聞 Stand News

新型冠狀病毒疫情系列之九 — 輕症患者或無病徵受感染者

2020/3/26 — 7:56

新型冠狀病毒與2003年的沙士(同是冠狀病毒,至今已知的冠狀病毒有8種)的最大不同之處是,新型冠狀病毒患者存在大量隱性患者,他們在社區的播毒能力成了重大關注。

3月20日的《自然科學》期刊的一篇文章,估算它們約佔所有受感染者的六成,而又因為這種病毒對兒童的危害較小,估計有56%的受感染兒童只有輕微,甚至無感染病癥。(註一)

有7百人受感染的鑽石公主號遊輪個案研究也提出類似數據,他們估算乘客中的無病癥受感染者的比率為17.9%,相對於從武漢撤日僑民的比率為33.3%。(註二)

廣告

3月19日《柳葉刀》期刊的一篇文章研究了76個大陸案例,大陸將嚴重個案定義為:

(一)呼吸困難,每分鐘喘氣超過30次;
(二)血氧濃度低於93%;
(三)動脈分壓氧氣和吸氧分數低於水銀壓力300mmHg(急性呼吸窘迫綜合症指標);
(四)出現嚴重併發病。

廣告

在76個案例中,他們將61宗案例定義為輕症。在較症病例中,病毒的播放密度比重症低於60倍。(註三)

據一份綜合研究指出,在中國發出旅遊限制之前,只有14%的受感染者被確診。(註四)

3月16日的《科學》期刊的一篇文章指出,86%的受感染者沒有被發現,他們的傳染能力可以是確診者的55%。(註五)

有文章指出輕症(醫學術語)患者不一定病得輕微,受苦小。全球約8成新型冠狀病毒患者被醫學斷為輕症,他們一般表現為發燒和乾咳,也可以同時出現肺部積水、呼吸困難、頭痛、肌肉病、乏力和腹瀉。

研究指出,病毒的潛伏期為5天,約98%的患者11.5日後發病,1%的患者在14天後發病。(註六)

大部份國家建議輕症患者家居隔離,世衛對家居隔離提出19點建議,特別是要求清潔共用廁所。但香港的大部份家居條件不符合世衛指標。(註七)

歐洲研究組織指出新型冠狀病毒基本上沒有變異。(註八)

哥大愛滋病研究中心學者何大衛指出,新型冠狀病毒有些特癥可能與愛滋病差不多,病毒對人的影響因人而異,各人體質不同,由於遺傳基因,有些人就算受了感染,也不足以致命或重病。(註九)

 

備註

註一

Covert coronavirus infections could be seeding new outbreaks

Nature 20 March 2020  

what proportion of infected people have mild or no symptoms and might be passing the virus on to others. Some of the first detailed estimates of these covert cases suggest that they could represent some 60% of all infections.

To gauge the extent of covert infections, a team of researchers in China and the United States developed a model using clinical data from 26,000 laboratory-confirmed cases reported to the health commission of Wuhan, the epicentre of the outbreak, in the Chinese province of Hubei.

Chowell’s modelling study3, published on 12 March in Eurosurveillance, shows that about 18% of some 700 infected individuals on Diamond Princess never showed symptoms.

“You have to keep in mind that this was a special population” with lots of elderly people, says Chowell. Older people tend to fare badly when infected with the new coronavirus, so he suspects the rate of asymptomatic infections in a general population might be closer to the 31% that the Japanese team reported.

Taking the results from several studies into account, Chowell thinks that asymptomatic or mild cases combined represent about 40–50% of all infections.

Many scientists fear that this might also have led to an underestimate of kids’ susceptibility to the virus. A study of more than 700 infected children in China found that 56% had mild or no symptoms6.

註二

Estimating the asymptomatic proportion of coronavirus disease 2019 (COVID-19) cases on board the Diamond Princess cruise ship, Yokohama, Japan, 2020

Currently, there is no clear evidence that COVID-19 asymptomatic persons can transmit SARS-CoV-2, but there is accumulating evidence indicating that a substantial fraction of SARS-CoV-2 infected individuals are asymptomatic

Our estimated asymptomatic proportion is at 17.9% (95%CrI: 15.5–20.2%), which overlaps with a recently derived estimate of 33.3% (95% confidence interval: 8.3–58.3%) from data of Japanese citizens evacuated from Wuhan [13

註三

Viral dynamics in mild and severe cases of COVID-19

Lancet

March 19, 2020

76 patients admitted to the First Affiliated Hospital of Nanchang University (Nanchang, China) from Jan 21 to Feb 4, 2020, were included in the study.

Patients who had any of the following features at the time of, or after, admission were classified as severe cases: (1) respiratory distress (≥30 breaths per min); (2) oxygen saturation at rest ≤93%; (3) ratio of partial pressure of arterial oxygen to fractional concentration of oxygen inspired air ≤300 mm Hg; or (4) severe disease complications (eg, respiratory failure, requirement of mechanical ventilation, septic shock, or non-respiratory organ failure). 46 (61%) individuals were classified as mild cases and 30 (39%) were classified as severe cases.

The mean viral load of severe cases was around 60 times higher than that of mild cases,

註四

Mild Cases May Be Driving Coronavirus Spread

WebMD Health News

The study, which was an international collaboration between researchers in China, Hong Kong, London, and the U.S., estimates that in the period before travel restrictions were announced in China, only 14% -- or about 1 out of 7 -- of infections were recognized.

註五

Substantial undocumented infection facilitates the rapid dissemination of novel coronavirus (SARS-CoV2)

Science  16 Mar 2020:

The results for 10–23 January 2020 delineate the characteristics of the SARS-CoV2 moving through a developed society, China, without major restrictions or control. These findings provide a baseline assessment of the fraction of undocumented infections and their relative infectiousness for such an environment. However, differences in control activity, viral surveillance and testing, and case definition and reporting would likely impact rates of infection documentation. Thus, the key findings, that 86% of infections went undocumented and that, per person, these undocumented infections were 55% as contagious as documented infections, could shift in other countries with different control, surveillance and reporting practices.

註六

There is a wide misconception of what a 'mild' case of COVID-19 looks like. It can be ugly and brutal.

Cases in general are categorized as "asymptomatic," "mild," "severe," or "critical." Studies have suggested that about 80% of infections by the novel coronavirus are mild, but that simply refers to people who don't need to be hospitalized. Mild cases can also develop into severe cases if the viral infections worsen.

Mild COVID-19 cases are often worse than a cold or flu — they're usually marked by fevers and dry coughs. Less common but still possible are a handful of other symptoms including fluid in the lungs, shortness of breath, headaches, muscle soreness, fatigue, and gastrointestinal symptoms.

Recent research suggests that on average, the virus' incubation period is about five days. Nearly 98% of patients develop symptoms within 11 1/2 days, though about 1% start showing symptoms after 14 days.

註七

Home care for patients with COVID-19 presenting with mild symptoms and management of their contacts

Clean and disinfect bathroom and toilet surfaces at least once daily. Regular household soap or detergent should be used first for cleaning, and then, after rinsing, regular household disinfectant containing 0.1% sodium hypochlorite should be applied

註八

People With Mild Symptoms Can Spread Coronavirus, European Researchers Warn

And regarding the concern that the virus could mutate, Koopmans says that genetic analysis by her lab shows that the virus is not mutating much and not in ways that would make it even more harmful. "There's no real obvious changes that would be of concern," she says.

註九

The Tip of the Iceberg: Virologist David Ho (BS '74) Speaks About COVID-19

Caltech trustee David Ho (BS '74) of the Aaron Diamond AIDS Research Center, Columbia University,

RNA viruses all replicate with low fidelity. Mutations occur at pretty similar rates and these viruses typically don't have proofreading functions. In contrast, we replicate our DNA with high fidelity and we have a proofreading function to fix the errors. So, every time they replicate, there's a fixed rate of mutation. This virus is mutating but it has mutated very little so far. There are differences but probably they are functionally not important, so that's not the explanation for why you see different disease courses among the infected.

For HIV it's the same thing: 10 people could be infected by the same strain but you have very different outcomes. With HIV, genetics and environmental factors play a role. Some of the genetics has been worked out; we know that there are certain tissue types that would protect and others that would harm. I suspect it's the same here

全文完

發表意見