COVER STORY • 0Expansion of PCR Testing Is the Key to an
Exit Strategy, But Which Is More Important– Sensitivity or Frequency of Tests?

By Kazumasa Oguro

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Awareness of the Issue
The spread of Covid-19 is having a grave impact on our society. For
example, in the Cabinet Office’s “Quarterly Estimates of Jan.-March
2020 GDP (Second Preliminary)” the real GDP growth rate for theperiod was an annual negative 2.2% (year-on-year), but the average
forecast of 12 private think-tanks puts the estimated growth rate for
the April-June period at an annual negative 27% (year-on-year), andthe Japanese economy looks set to sink to its worst level since the endof World War II.
On May 25, 2020, the Japanese government lifted the State ofEmergency Declaration on the spread of Covid-19 across Japan, butwith the reopening of social activities and economic activities,
infections are once again spreading, especially around Tokyo.
Depending on the spread of infections, the government may once
again issue restrictions on going out, or ask for voluntary restraint on
business activities, but in this instance the economic loss will beimmeasurable and the number of small and medium enterprises(SMEs) going bankrupt will likely rise sharply. In fact, the 2020 versionof the White Paper on Small and Medium Enterprises (approved by the
Cabinet on April 20, 2020) points to the “likelihood of concerns overfinancing difficulties in the accommodation and food service industry
deepening for the next six months.” According to the Financial
Statements Statistics of Corporations by Industry (Ministry of Finance)
for Fiscal 2018, cash deposits held by SMEs with capital of 10 million
yen to 50 million yen only amount to around three months’ worth ofoperating costs.
Is there a way to continue near-normal social and economic
activities by utilizing the knowledge of economics? Addressing thisissue requires collecting and putting together various kinds ofexpertise, but the most important requirement looks to be resolving“information asymmetry”.
Currently, the number of confirmed cases in Japan is 42,098 people(as of Aug. 5, 2020), and this means that to begin with there are more
people who are not infected. Yet why are the vast majority of people
restricted from going out or asked to refrain from social and economic
activities? This is because there is an “information asymmetry”. For
our part also, there are many cases where we ourselves cannot
determine whether we have been infected or not. This is why we aim
to lower the number of times we interact with other people byrestricting ourselves or refraining from going out. Japan has thus far
been successful in placing the so-called cluster control as its main
1 Japan SPOTLIGHT • November / December 2020

Author Kazumasa Oguro

strategy, but because the focus was on targeting the test subjects andtracing their contacts, the number of tests has been extremely low
compared to other countries. But when normal economic activities
re-open, if we are able to determine ourselves whether we have been
infected or not by utilizing technology, the situation will change
drastically.
This is why Professor Paul Romer of New York University, who is aNobel Prize winner in Economics and a heavyweight of the American
Economic Association, is recommending 20 million tests be conducteda day (https://roadmap.paulromer.net/). An infectious disease team in
the United Kingdom is also recommending 10 million tests a day(https://ephg-covid-19.org/), while the Rockefeller Foundation
proposes 30 million a day (https://bit.ly/2wWIxTC) and the Center for
Ethics of Harvard University 50 million a day (https://ethics.harvard.
edu/Covid-Roadmap). Quite coincidentally, from very early on (May 9,2020), I and others constructed an online “Emergency
Recommendation: Covid-19 V-shaped Recovery Project”, and in the“Exit strategy” addressing expansion of Covid-19 we released an
emergency recommendation to conduct 10 million tests a day.
The main message of the emergency recommendation is that “themost important aspect of balancing containment of the expansion of
infections with social and economic activities is for all citizens to beable to regularly (around once every two weeks) find out, if so they
desire, whether they have been infected with coronavirus, thereby
creating a system, within six months at the latest, where people who
continuously test negative feel safe to resume going out and work, andthis is most crucial in going forward to the next step.” Later, the Canon
Institute for Global Studies and others released similar
recommendations on expanding the testing system.

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Is False Positive Really an Issue?
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But expansion of the testing system in Japan is slow to move. One
33of the obstacles is the domestic debate on the “false positive issue”.
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False positive refers to “testing positive when in fact the patient is not 35
infected with novel coronavirus” and an index called “specificity” exists 36
as a concept that demonstrates its accuracy (Table 1).
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Specificity refers to “the percentage of accurately testing negative
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when not infected with the novel coronavirus”, and the relationship39“specificity = 1-the percentage of false positive” generally holds. If
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specificity is close to 100%, false positive is generally zero. If
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specificity is 99.99%, false positive is a mere 0.01%. But when42
https://www.jef.or.jp/journal/

COVER STORY 0
TABLE 1

False positive, false negative & theconcept of sensitivity & specificity
Confirmed cases(A+B)

Non-confirmed cases(C+D)

PositiveA

C False positive

Negative

B False negativeD

Sensitivity = A/(A+B)

Specificity = D/(C+D)

Source: Compiled by the author

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For example, let us look at a scenario where 20,000 tests are
conducted twice a day, and suppose that there were 116 infectedpatients for the first test during a period when infections werespreading, and four infected patients for the second test when
infections are being contained. The average rate of positivity is 0.3% (=120 ÷ 40,000), but the rate of positivity for the first test is 0.58% (=116 ÷ 20,000), and the rate of positivity for the second test is 0.02%(= 4 ÷ 20,000), and if specificity is to be estimated, including for thosetests during periods when infections were spreading, true infectedpatients will also be counted and there is a possibility of mistaking
specificity or judging false positive. In fact, it is desirable to estimate
specificity from data when infections are being contained, and that canbe read from data in Chart 2.
This chart shows the trends in the positivity rate of PCR testing inAustralia for a given period (May 23 to June 18), and even when
20,000 tests, give or take, were conducted every day, there were manydays when the number of confirmed cases was in single digits. If false
positive exists around 1%, it means that it would not have beensurprising to see around 200 false positive patients alone every day,but that was not the case. On the other hand, if the positivity rate wasto be calculated using data in Chart 2, it is around 0.03%, and from ※1 and ※2 the specificity of PCR tests is generally around more than
99.97%.
Thus, “unless there are human errors such as sample
contamination, the specificity of PCR tests is generally 100% (false
positive is generally zero)” is the real truth, and politically opposing the
expansion of the testing system based on the “false positive issue”
basically does not hold.

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specificity is 99%, it causes major issues.
For example, when specificity of PCR tests is 99%, false positive
exists by 1%, and if 14 million people (equivalent to the population
size of Tokyo) are tested, even if the number of those infected is in factzero, 140,000 people (= 1% of 14 million people) will test positive inthe form of false positive cases. Even if they are false positive, if
140,000 cases are confirmed, it will exceed the medical capacities
such as hospital beds and medical doctors who can treat the patients,
and thereby will be highly likely to cause a collapse in the healthsystem.
Therefore, in Japan, there are still voices that oppose the expansionof PCR tests citing the “false positive issue” as one of the reasons, but
unless there are human errors such as sample contaminations, thespecificity of PCR tests will never be 99% (false positive at 1%), and it
is basically 100% (false positive at basically zero). PCR tests areoutside the author’s expertise, but this is a fact that came out of aseries of study groups that were held with experts.
Several case studies that justify this will be introduced
briefly. First is the case of Wuhan city in China. Infections
CHART 1in Wuhan had been contained for a while, but because
Positive rate for low cumulative confirmed
newly infected patients were discovered between May 9
deaths by region (as of July 1, 2020)
and May 10, 2020, after about five weeks of no new
Cumulative
cases, all citizens in each of the districts of Wuhan were
Cumulative
Cumulative
Positive
confirmed
deaths
PCR tests
ratetested over the course of 10 days. Of roughly 9.9 million
cases
(②)
(③)
(=①÷③)
people, those infected with symptoms were zero, and 300(①)
were asymptomatic. “Specificity = 1-percentage of false
Uganda889
01704120.5%
positive”, and it shows that even if all of the
Fiji
18
0
5105
0.4%
asymptomatic patients are false positive, the percentage
Rwanda1025
21479040.7%
of those that are false positive is less than 0.0031%, andMyanmar
299
6
79072
0.4%
therefore the specificity of PCR tests turned out to be
more than 99.9969%.
Taiwan
447
7
77025
0.6%
Chart 1 lists the rates of positivity in regions with low
Malta
670
9
99198
0.7%
numbers of cumulative deaths (as of July 1, 2020), but
New Zealand
1178
224053290.3%
false positives are part of the confirmed cases andSlovakia
1667
28
211813
0.8%
therefore “percentage of false positive ≦ rate of
Latvia1118
301527780.7%
positivity” holds (※1). As previously stated, “specificity =1-percentage of false positive” (※2), and for example, theLithuania
1817
78
4282380.4%
rate of positivity in Australia is 0.3%, and therefore from
Australia
7834
1042505923
0.3%※1 and ※2 the specificity of PCR tests can be shown toSouth Korea
12850
282
12644221.0%
be more than 99.7%. But included in the 0.3% rate of
Japan
18723
974
4674444.0%
positivity must be those that are truly positive, and hence
Source: Compiled by the author based on “Coronavirus Pandemic (Covid-19) – the data” in Our World in Datathe specificity of PCR tests may be higher.
Japan SPOTLIGHT • November / December 2020

2

COVER STORY 0with sensitivity of 40%? Chart 3 shows theresults of a simplified simulation analysis
using the SIR model, assuming a basic
Confirmed
Number of
Number of
Positive
Positive
Confirmed
cases
tests
reproduction number R0 of 2.5, infectious
tests
rate
rate
Date
cases
(7-day rolling (7-day rolling(②)(=①÷②)(=③÷④)(①)
period of 14 days, and specificity of 100%.
average, ③)
average, ④)
The horizontal axis shows “the number of2020-05-23
14
21580
0.06%
11
25230
0.04%
days since the initial condition” and the2020-05-24
11
32533
0.03%
10
26096
0.04%
vertical axis shows “cumulative number of2020-05-25
3
19405
0.02%
9
26024
0.04%
confirmed community transmissions”.
2020-05-26
9
44023
0.02%
8
28908
0.03%
The chart also compares four scenarios:
2020-05-27
15
50098
0.03%
9
32393
0.03%
“Basic scenario”, “Test expansion 1”, “Test2020-05-28
6
29123
0.02%
9
32823
0.03%
expansion 2”, and “Test expansion 3”.
“Basic scenario” sees infections expanding
2020-05-29
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30178
0.04%
10
32420
0.03%
with no tests being conducted, while “Test2020-05-30
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30916
0.07%
11
33754
0.03%
expansion 1” shows a scenario where PCR
2020-05-31
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26030
0.05%
11
32825
0.03%
tests with 70% sensitivity are conducted2020-06-01
10
17652
0.06%
12
32574
0.04%
for a population of 10 million in 10-day
2020-06-02
9
18167
0.05%
12
28881
0.04%
intervals. Testing 10 million residents at
2020-06-03
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22313
0.08%
13
24911
0.05%
10-day intervals indicates building a testing2020-06-04
8
33629
0.02%
13
25555
0.05%
system for 1 million tests per day.
2020-06-05
11
32863
0.03%
13
25939
0.05%
“Test expansion 2” shows a scenario
where PCR tests with 70% sensitivity are
2020-06-06
11
11396
0.10%
11
23150
0.05%
conducted for 10 million residents at five2020-06-07
4
26874
0.01%
10
23271
0.04%
day intervals, and “Test expansion 3”
2020-06-08
5
16053
0.03%
9
23042
0.04%
shows a scenario where PCR tests with
2020-06-09
5
17169
0.03%
9
22900
0.04%
40% sensitivity are conducted at five-day
2020-06-10
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29270
0.01%
7
23893
0.03%
intervals. Testing residents of 10 million at
2020-06-11
9
31269
0.03%
7
23556
0.03%
five-day intervals indicates building a
2020-06-12
9
34327
0.03%
6
23765
0.03%
testing system of 2 million tests per day.
2020-06-13
5
37101
0.01%
6
27438
0.02%
Simulation analysis has been done
based on these scenarios, and the2020-06-14
12
29702
0.04%
7
27842
0.02%
overview is as follows. First, since the2020-06-15
18
15796
0.11%
9
27805
0.03%
initial infectious rate is 0.1% and the2020-06-16
15
20198
0.07%
10
28238
0.04%
population is 10 million, the number of2020-06-17
12
27770
0.04%
11
28023
0.04%
confirmed cases in the initial stage is
2020-06-18
23
51380
0.04%
13
30896
0.04%
10,000 people (= 10 million people ×Source: Compiled by the author based on “Coronavirus Pandemic (Covid-19) – the data” in Our World in Data0.1%), and the non-infected are 9.99
million people (= 10 million – 10,000
Sensitivity or Frequency of Tests?
people). From the initial stage to day one, infected patients at the initialstage randomly transmit the virus at a basic reproduction number ofIf false positive is not a major issue, the next issue that comes is
R0=2.5 to non-infected people assuming a certain level of group“false negative”. False negative refers to “testing negative when in fact
immunity functionality. In this case, when infected patients are
the patient is infected with the novel coronavirus”, and an index called
confirmed through regular PCR tests (sensitivity = 70% or 40%,“sensitivity” exists as a concept to demonstrate its accuracy.
specificity = 100%) conducted for the residents in the region via an
Sensitivity refers to “the percentage of accurately testing positive
expansion of testing, these confirmed patients are assumed to bewhen a patient is infected with the novel coronavirus”, and generally
quickly quarantined. Similarly, the number of confirmed cases on day“sensitivity = 1-percentage of false negative” holds. If sensitivity is
two and forward is estimated based on data such as the number ofgenerally 70%, false negative is generally 30%, but if sensitivity is
confirmed cases on day one.
40%, false negative becomes 60%.
The results of this simulation analysis are shown in Chart 3. What
Let us suppose there is a region with a population of 10 million andwe can learn from the results is that as trends in the number of
an initial infectious rate of 0.1%, how different will the trends be in theconfirmed cases show for “Test expansion 1”, “Test expansion 2”, andnumber of confirmed cases when tests are expanded for PCR tests“Test expansion 3”, the higher the “sensitivity” and “frequency” ofwith sensitivity of 70% and when tests are expanded for PCR tests
testing, the lower the number of long-term cumulative confirmed
CHART 2

Positive rate of PCR tests in Australia

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3 Japan SPOTLIGHT • November / December 2020

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COVER STORY 0

income due to the current Covid-19 pandemic,
and secure the necessary human resources to(population of 10 million, initial infectious rate 0.1%)
expand testing. In addition, in order to resolve(Vertical axis unit: number of people)
the bottlenecks that prevent securing(Horizontal axis unit: day)necessary materials, a “Network for Emergency
3000000
Measures for Covid-19 Testing” should be built
Basic scenario (R0 = 2.5, infectious period = 14 days)
with relevant ministries, prefectures, andTest expansion 1 (10-day interval, 70% sensitivity)
2500000
Test expansion 2 (5-day interval, 70% sensitivity)
collaborative organizations coming together
Test expansion 3 (5-day interval, 40% sensitivity)
around the Prime Minister’s Office. It will also
2000000
be worth considering whether this body cancome together and have the functionality of
1500000
resource procurement, implementation, andaggregation and analysis of test results.
1000000
To date, many research institutions and500000pharmaceutical companies have been working
to develop vaccines, but no matter how
0
enormous the capital investment, successful
vaccine development in 10 years is not
Source: Compiled by the author
guaranteed. Of course, it is important that theworld work together and invest in vaccine
cases. On the other hand, cumulative confirmed cases showeddevelopment, perhaps more than it has up to now, and aim for urgent
progressive increase for the “basic scenario” where no tests wereand speedy vaccine development, and such efforts should continue,
conducted. This indicates the importance of the “sensitivity” andbut coming up with an “exit strategy” that relies solely on a successful“frequency” of the tests.
outcome comes with huge risks. Thus, developing “treatment”, notWhich, then, is more important, the “sensitivity” (70% or 40%) orjust new vaccines, is vital.
the “frequency” (10-day interval or five-day interval)? This can also be
In other words, once infected with the novel coronavirus, if proper
read from Chart 3. The chart shows that the number of confirmed
treatment can be developed at various stages of its symptoms throughcases during each peak at “Basic scenario” > “Test expansion 1” >usage of effective existing medication or a combination of medications“Test expansion 3” > “Test expansion 2”, but the relationship “Testand prescribed quantities or frequency, and if the mortality rate can be
expansion 1” > “Test expansion 3” is particularly important.
brought down to a level equivalent or less than regular influenza, the“Sensitivity” for “Test expansion 1” is 70% and “sensitivity” for “Testissue of a trade-off between life and economy can be resolved andexpansion 3” is 40%, and while the sensitivity of PCR tests for “Testnormal economic activities can be restored.
expansion 3” is inferior to “Test expansion 1”, by increasing the test
Regardless, what is important in addressing the expansion of Covid“frequency” from the 10-day interval to five-day interval, the number
19 is the final goal and a flexible strategy. To begin with, it is notof confirmed cases on the 50th day for “Test expansion 3” is at a lower
appropriate to aim for 100% containment of the virus in a short period
level compared to “Test expansion 1”. This indicates the possibilityof time; rather, it is impossible. To uphold the mechanism ofthat “frequency” of PCR tests is more important than “sensitivity”.
democracy and universal values such as freedom and basic humanIn preparing a mass PCR testing implementation system, the driverights, and to gradually restore economic activities, it will bethrough method of South Korea, the “regional PCR centers” of theappropriate to aim for a 90% to 95% containment of Covid-19 by
Tokyo Medical Association, utilizing laboratories of dental doctors andgathering public and private knowledge and expertise, and utilizing
medical doctors, and permission for pharmacies to do PCR testing as
science and the latest technology led by the private sector.
adopted in New York may all be utilized, but organizing PCR testing for
As Chart 3 shows, the key to an exit strategy lies with “expansion of
voters at polling stations in the event of a House of Representative
PCR tests”. An incomplete strategy indeed is the worst, and it isGeneral Election may also be useful. In addition, in order to conduct
important to be fully aware that aiming for a balance under such an
mass testing, there is naturally a need to secure a great number ofincomplete strategy will, in the end, cause great harm to both.
human resources and materials.
For human resources, medical experts such as doctors and nurses
alone are insufficient in numbers to serve as testing personnel, andtherefore there will be a need to allow testing to be conducted by nonmedically licensed personnel also, who have gone through proper
training, under the supervision of doctors or others. In this instance,
Kazumasa Oguro is a professor of the Faculty of Economics at Hosei
University and consulting fellow at the Research Institute of Economy, Trade &the recommendation is to treat expansion of testing as part of public
Industry at METI.
works, thereby prioritizing employing those who have lost jobs and

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CHART 3

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Simplified simulation analysis

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Japan SPOTLIGHT • November / December 20204