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新型冠狀病毒疫情系列之十一 — 測試

2020/3/31 — 18:14

如何進行病毒測試成了不少政府的頭疼的事。日本厚生省在疫症早期甚至認定測試不是醫療問題而是學術問題(註1);英國政府也曾提出類似於放任的方法,讓巿民自行產生免疫能力;美國的特朗普被指責不重視測試,但一經開始廣泛測試,美國的被確診人數就火箭式上升。由於試劑緊缺,德國仍然只願意測試在過去14天內曾出現病例的地區中的帶流感病癥狀人士或在14天內的緊密接觸者 (註5)。

日本和英國政府雖然已改變了態度,但其早期說法未必全無道理,既然這個病毒至今沒有特效藥,是否確診可能都是同一治療方法,從一份英國的深切治療室報告中看到的,重症死亡率達5成。而且,對大部份的輕症患者來說,到醫院求診可能是更加危險的作法。正如那批湧回香港的英國留學生,在機倉內緊密接觸13小時,只要當中有一個超級帶菌者,其情節遠比滯留在倫敦危險。但是,廣泛的病毒測試有助人們了這個病毒的特性,從而有助於控制疫情

廣告

英國

廣告

在中國於1月12日公佈了病毒的核糖核酸(遺傳)基因圖譜後,英國是最早的國家之一研製出測試方法,它被醫學界質疑政府為何反應遲鈍。(註2)

《柳葉刀》期刊主編Richard Horton甚至撰文指英國國民保健NHS的做法是英國的醜聞(註3)。NHS的一名員工寫下:「當這場疫情完結之後,整個NHS管理局成員應該辭職。」

PCR Test (核糖核酸測試)

從患者的上呼吸道或下呼吸道取唾液樣本,對比其中的核糖核酸的某一小段是否對應已知病毒的核糖核酸,是目前醫學廣泛使用的方法。孟加拉目前有1500套測試件,每個測試成本450港元,相當於它的工人平均工資(註3)。PCR Test需要極之清潔的試劑,美國疾控中心在2月5 日派發的試劑因為受了污染而產生了大量假陰性,阻礙了美國的測試進度(註4)。中國的大部份醫院也進行了大量PCR Test,但它也因同樣問題,導致疫情數字不準確(註5)。

在這方面,香港有一定國際地位,它是世衛公佈的七種PCR Test之一,各PCR Test針對的核糖核酸片段有所不同。(註6)

PCR Test的問題是成本高,測試結果的時間較長,樣本帶有病毒,不能由一般化驗室處理(註8),醫院不能自行測試。不過,美國藥檢處已對相關制品的要求大幅度降式。美國已有大型醫療儀器公司(Roche)進出了FDA批核的商用產品,也有公可推出可用於醫院的新產品。位於世界前列的醫療服務公司(LibCorp) 推出其自行開發的PCR Test服務(註9)。

抗體測試

抗體測試類似於我們日常的驗孕測試,人們將滴血放在試紙上,再加上試劑,在一個小型套件上以目測方式,觀看兩條色帶的顯現以決定是否曾受感染。它的成本很低,可以控制在每個測試在2美元之下,中國和新加坡首先採用。中國在大型爆發疫症之下,沒有足夠的PCR測試,很多測試是以滴血方式進行。但是它的缺點是準確度低。就以10%的假陽性為例,在一個大城巿廣泛使用下,可以出現數萬個假陽性向政府求救,場面可能不受控制。同時,這種測試大多都是事後測試,因為抗體可能在受感染後的5天、10天或20天後出現,而且,抗體在受感染後殘留多久也未有科學數據參考。(註10)盟疾控中心估計抗體測試可能要在病發後的2周至4周後才有效(註11)。這種由亞洲開始使用的廉價方法成了全球的救命草(註12),英國政府準備訂購350萬套,但沒有人知道它向誰訂購(註13),美國多家私營公司大量生產這些套件,Chembio Diagnostics Inc 接了巴西的400萬美元訂單(註14)。愛爾蘭也參與研發(註15),這不奇怪,因為它本身不是什麼高科技。日本也向中國採購這些套件。

醜聞

抗體測試的第一宗醜聞是西班牙退回向深圳一家公司購買的測試套,因為它只有3成的準確度,而專家要求準確度至少為8成。中國外交部解釋那間深圳公司並非中國交給西班牙的可採購供應商的名單之內,這個羅生門可能雙方都有些問題(註16)。

英國的一家小型醫療服務供應商,在網頁上聲稱可以提供定價125英鎊的測試套件,可是這些套年並非這家公司所研製的。這則廣告是一家美國公司,BioMedomic製作的,而這些套件的成本只值2美元,採購價格不會超出9美元(註17)。

美國公司也不遑多讓,一間名為Biomerica的公司在未得到美國藥檢處FDA通過,不能在美國本土出售其抗體測試套之前,已向中東、歐洲和其他國家輸出樣本和接訂單。它的股票在一天之內由2美元升至16美元,再跌至6.96美元。(註18)

有人可能說,買美國產品有保證,總有過買大陸。況慢,看看一則美國廣告。它是一家名為 Safecare Bio-tech 的公司, 在美國和加拿大設有辦事處。但它的制品來自大陸杭州的。

後記

英國準備把這種抗體測試套讓私人採購有一定問題。因為,抗體測試的原意不是用作治療而是用作研究。它在2012年的中東呼吸綜合症中制作病毒地圖時的主要工具。(註19)

 

備註

註1

Coronavirus: Why Japan tested so few people

The National Institute of Infectious Diseases, which has been in charge of PCR tests, published a statement by chief Takaji Wakita on its website March 1.

It rebutted accusations of trying to make the number of infections look small by curbing tests, saying such claims are based on factual errors.

The medical term "active epidemiological investigation" repeatedly appears in the statement. This bit of jargon is key to understanding the go-slow approach of the health ministry and the NIID.

註2

Up to 30% of coronavirus cases asymptomatic

In South Korea, nationwide testing, comprehensive isolation of Covid-19 patients and strict rules on social interaction have shown results. The measures have proved effective in slowing the spread of the coronavirus.

Germany's Federal Ministry of Health says people will only get tested if they present with flu-like symptoms AND were in a region with known cases of coronavirus cases in the past 14 days OR if they had contact with a person who had tested positive for Covid-19 in the past 14 days.

Germany mulls mass testing for coronavirus immunity: report

註3

https://bdnews24.com/health/2020/03/07/what-is-the-test-for-coronavirus-and-how-does-it-work

But the entire process is dependent on receiving a sample. Each RT-PCR test costs more than Tk 5,000 but the government is currently bearing the expenses.

ARE THERE ENOUGH TESTING KITS?

At present, the IEDCR has about 1,500 test kits with more on the way, according to Alamgir.

註4

Why the CDC botched its coronavirus testing

On February 5 the CDC began to send out coronavirus test kits, but many of the kits were soon found to have faulty negative controls (what shows up when coronavirus is absent), caused by contaminated reagents. This was probably a side effect of a rushed job to put the kits together. Labs with failed negative controls had to ship their samples to the CDC itself for testing.

The first thing to know is that PCR is a very sensitive test. You need extremely clean reagents, and the smallest contaminants can ruin it completely

What is a coronavirus test like? How are CDC kits handled? Here are the details

The CDC website indicated at one point Thursday that only 445 tests had been conducted nationwide. As of late Friday morning, that number had increased by six to 451 total across the U.S.

註5

https://biology.stackexchange.com/questions/90095/how-does-a-coronavirus-test-kit-work

Unfortunately, most hospital labs in China are not qualified enough to perform tests of this level and that's why it takes so long to truly diagnose a patient with nCoV, even if tons of test kits are already sent to the infected area

註7

Summary table of available protocols

註8

CDC 2019-Novel Coronavirus (2019-nCoV)  Real-Time RT-PCR Diagnostic Panel

Specimens must be packaged, shipped, and transported according to the current edition of the International Air Transport Association (IATA) Dangerous Goods Regulation.

註8

https://www.roche.com/media/releases/med-cor-2020-03-13.htm

The widely available Roche’s cobas 6800/8800 Systems, which are used to perform the cobas SARS-CoV-2 Test, provide test results in three and half hours and offer improved operating efficiency, flexibility, and fastest time-to-results with the highest throughput providing up to 96 results in about three hours and a total of 384 results for the cobas 6800 System and 960 results for the cobas 8800 System in 8 hours. The test can be run simultaneously with other assays provided by Roche for use on the cobas 6800/8800 Systems.

註9

https://www.labcorp.com/coronavirus-disease-covid-19

註10

What are serologic tests?

 

註11

European Centre for Disease Prevention and Control

serum, acute and convalescent (possibly 2 to 4 weeks after acute phase) for when serological testing becomes available

註12

The next frontier in coronavirus testing: Identifying the full scope of the pandemic, not just individual infections

The serological tests, which are being deployed in some countries in Asia and are starting to be used at one New York hospital,

註13

United Kingdom pledges to roll out extensive antibody testing

On 25 March, a UK government official said that the country had ordered 3.5 million ‘finger-prick’ tests and planned to order millions more.

 “I would expect the false-positive rate to be very high because of this prior exposure — unless they figured out how to make the serological test very specific,” he says. Garry says that for a validated test, he would expect a false-positive threshold of less than 5% — meaning fewer than 5 out of 100 people without the antibodies test positive — although he could see that being relaxed to 10%. Even with ready access to clinical samples, understanding false-positive levels on this timescale would require a massive effort, says Garry.

註14

U.S. companies, labs rush to produce blood test for coronavirus immunity

Several private companies have begun selling blood tests for COVID-19 antibodies outside the United States, including California-based Biomerica Inc (BMRA.O) and South Korean test maker Sugentech Inc (253840.KQ). Biomerica said its test sells for less than $10 and the company already has orders from Europe and the Middle East. Chembio Diagnostics Inc CMI.O of New York said it received a $4 million order from Brazil for its COVID-19 antibody test, and it plans a study of the test at several sites in the United States.

註15

https://www.irishpost.com/news/irish-company-create-coronavirus-testing-kit-can-confirm-infection-15-minutes-181738

Will Japan's virus testing policy be enough to flatten the curve?

BY MAGDALENA OSUMI

MAR 16, 2020

A spokeswoman for textile and chemical product company Kurabo Industries Ltd., which sells the 15-minute test kits developed by a Chinese firm, said it has the capacity to supply 10,000 tests per day and may increase production should the need arise.

註16

Unreliability of new tests delays effort to slow coronavirus spread in Spain

Chinese embassy in Spain had issued a statement on Twitter saying that Shengzhen Bioeasy Biotechnology does not have a license to sell its products and that it was not on the “list of classified suppliers” that China showed to Spain.

註17

Coronavirus: Can I get tested to see if I have Covid-19?

A private healthcare clinic in London defended its decision to charge £375 for a test.

Shortage of Virus Tests in U.K. Lures Profiteers and Con Artists

Three days earlier, AlphaBioLabs — which has since stopped marketing the test to the public — had announced that it would be selling its kit for £125. One newspaper hailed the news with the headline: “Brit lab’s new finger-prick test can ‘detect virus in 15 minutes.’”

But the British lab did not create the test. The one advertised on its website was made by an American company, BioMedomics. Each kit costs around $2 to manufacture and no more than $9 to buy wholesale.

註18

Biomerica has begun shipping samples of this COVID-19 test to multiple Ministries of Health and government agencies that have requested the product through the Company’s distributors in the Middle East, Europe, and other countries

https://finance.yahoo.com/news/biomerica-begins-shipping-samples-10-001634145.html

In addition, Biomerica has begun the application process with the FDA under the COVID-19 Emergency Use Authorization (EUA), aimed at the possible clearance and eventual use of the test in the US. At this time, the product is not available for sale or use in the US.

https://www.reuters.com/companies/BMRA.O

註19

https://www.biocompare.com/pfu/110447/soids/2326315/Antibodies/MERS-CoV

Anti-MERS-CoV antibodies are available for research in infectious disease. The Middle East respiratory syndrome (MERS)-related corona virus (CoV) is a species within the Coronaviridae is a family of enveloped, single-stranded RNA viruses. The pathogen was first identified in Saudi Arabia in 2012 and is believed to be transmitted from camels. Visit the antibody supplier page for further details, including target antigen, tested applications, and more.

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