The story behind mass testing is just not so easy, however may cause nice waste for the inhabitants, so a distinct technique must be considered.
For many exterior the medical career, the story is straightforward: testing the complete inhabitants, detecting contaminated individuals, treating and offloading the well being system. But the story behind mass testing is just not so easy, which may trigger nice waste for the inhabitants. Need to consider one other technique.
The downside of mass testing might be summarized as follows: (1) false positives and false negatives; (2) it’s fairly costly to detect 1 case; and (3) post-test penalties. We will talk about every concern under to see the overall ‘image’ of testing.
1. False positives and false negatives
By now, most of us most likely know that no take a look at is ideal, within the sense of 100% accuracy. PCR testing is taken into account the ‘gold normal’, nevertheless it nonetheless has flaws. There are two foremost flaws (see abstract desk):
• The individual is just not truly contaminated, however the take a look at is optimistic. This is a ‘false optimistic’ case. PCR checks usually have a false-positive charge of about 5% (common), however the take a look at is speedy [dựa vào kháng nguyên] just one% of false positives.
• The individual is definitely contaminated, however the take a look at is unfavorable. This is a ‘false unfavorable’ case. PCR checks normally have a false unfavorable charge of about 13% (on common), and speedy checks are very excessive, as much as 50%.
This makes it tough for a person that in the event that they get a optimistic outcome, it’s unlikely that they’re contaminated, as it could simply be a false optimistic. There are many the explanation why false positives, together with the rationale the virus is ‘useless’, however as a result of PCR is so delicate it nonetheless detects it!
2. How many individuals are contaminated?
Is there a method to quantify false positives and false negatives in the neighborhood? The reply is sure, however with an assumption. Assumptions concerning the true variety of infections in the neighborhood. So far, nobody is aware of how many individuals in the neighborhood are contaminated, however that quantity is actually greater than what we detect.
So how many individuals are estimated to be contaminated in the neighborhood? According to an evaluation that I ‘favourite’ (as a result of they use good strategies), the variety of individuals contaminated within the European group ranges from 2.6% to 16.1%, and the common is 6.2% (even 6%) . Very excessive.
The diagram under illustrates a program mass testing over 10 million individuals. With a inhabitants of 10 million, we’d count on 600,000 individuals to be contaminated (assuming a 6% an infection charge as within the literature). PCR technique with 87% sensitivity will assist us detect 522,000 optimistic individuals, that’s, we miss 78,000 individuals (false unfavorable). With a specificity of 95%, PCR will yield 5% false positives, equal to 470,000 individuals.
Thus, PCR will yield 522,000 + 470,000 = 992,000 individuals with optimistic outcomes. But out of those solely 522,000 are true (contaminated). In different phrases, out of each 100 individuals who take a look at optimistic, solely 53 are literally contaminated, and 47 are false.
3. Cost to the group
These easy calculations result in the query: how a lot will it price the group to detect 1 case?
According to the press, the price of PCR testing is about 734,000 VND/pattern . But in case you do extra, the associated fee might be decrease. We attempt to calculate based mostly on the price of 500,000 VND / pattern or 25 USD.
Because mass testing must be carried out on 10 million individuals (hypothetical inhabitants), the full price is 10 million x 25 = $250 million.
With $250 million, we discover 522,000 true positives. Thus, the associated fee to detect 1 case is 479 USD, or 9.58 million VND. That is, individuals need to spend practically 10 million dong simply to detect 1 true optimistic case!
4. After the take a look at
But after all the story would not cease there. After testing optimistic once more, you might want to check once more to make certain, as a result of the preliminary take a look at will not be correct. Some individuals need to take the take a look at all 3 instances to verify. Therefore, the group price is way bigger than the 250 million USD little one.
The assumption behind is that people who find themselves optimistic and confirmed to be contaminated have to be handled. The program detected 522,000 instances, so the query is can the well being system deal with this quantity?
However, the speed of extreme instances requiring hospitalization might be 20%. Twenty % of 522,000 instances are 104,400 requiring hospitalization. Still a reasonably large quantity for the well being system.
5. Another Strategy
The calculations above present that mass testing is pricey and never a ‘good concept’. Need to consider one other technique, and I name it ‘targeted testing’ technique. In this manner, solely individuals ought to be examined for which the outcomes will likely be extra correct and the ‘diagnostic yield’ greater. It ought to be added that testing strategies, even antigen checks, are extremely correct in individuals with signs (however in asymptomatic individuals, their accuracy is poor). Therefore, I feel to check solely those that:
• Symptomatic — no matter whether or not the individual is vaccinated or not. “Symptoms” right here embody cough, shortness of breath, fatigue, muscle aches, headache, lack of style, sore throat, vomiting, diarrhea, and so on.
• Having contact with contaminated individuals: these are high-risk individuals, so testing these individuals is more practical;
We can assume that the quantity of people that meet the above two standards is about 10% of the hypothetical inhabitants, or about 1 million individuals. Therefore, specializing in these teams will assist cut back the associated fee burden on the group but additionally improve the effectiveness of screening.
In reality, the above dialogue turns into meaningless when the Delta variant is current. The Delta variant has a transmission coefficient of as much as 6-7, so the thought of herd immunity to testing is meaningless. According to Professor Andrew Pollard (the inventor of the AstraZeneca vaccine), mass testing for the Delta variant is pointless and there’s no method to cease this virus in the neighborhood. We have to simply accept and alter to dwell with it.
Robust estimates of the true (inhabitants) an infection charge for COVID-19: a backcasting method
Delta variant has wrecked hopes of herd immunity, warn scientists (The Telegraph)
How a lot does a COVID-19 take a look at price underneath the brand new laws? (Tuoi Tre Newspaper)
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