Shedding new light on the "covid" PCR test - Journal of Infection

[OlsSalt]

Learning as we go along in this new world of "covid testing" and applications for cruising. Letter to the editor of the Journal of Infection:

https://www.journalofinfection.com/article/S0163-4453(21)00265-6/fulltext

 

Data and efficacy should be rapidly increasing now one year out from the first early 2020 Diamond Princess cruise "covid" shut down, including what was learned from that very first incident itself that sent shock and alarm bells ringing for the entire cruise industry. We continue to learn more about: testing, incidence, transmission,  prevention, therapeutics and treatment. 

 

My fingers are crossed for my own committed  SS cruise in March 2022.

 

 

 

[cruiseej]

Here's the key statement from the letter @OlsSalt posted:

 

"In light of our findings that more than half of individuals with positive PCR test results are unlikely to have been infectious, RT-PCR test positivity should not be taken as an accurate measure of infectious SARS-CoV-2 incidence. Our results confirm the findings of others that the routine use of 'positive' RT-PCR test results as the gold standard for assessing and controlling infectiousness fails to reflect the fact that 50-75% of the time an individual is PCR positive, they are likely to be post-infectious.”

 

Nonetheless, many travel safeguards implemented around the world are based on PCR tests. For our upcoming cruise from Barbados, for instance, we'll need a RT-PCR test before leaving home, plus a rapid PCR test upon arrival. I wonder how long it will take the medical community to amplify what this and other researchers have said, and get government regulators to understand that other tests for viral load might be the better standard to use going forward.

[jpalbny]

On 6/19/2021 at 3:08 PM, cruiseej said:

I wonder how long it will take the medical community to amplify what this and other researchers have said, and get government regulators to understand that other tests for viral load might be the better standard to use going forward.

 

Me too. This is what I've thought all along. The problem is, there is no other "gold standard" out there.

 

When you use PCR only on a population of patients who are sick with a viral syndrome, then a positive result likely means that they are infected with COVID-19 and they are sick and infectious. The test (like all tests) performs well when used appropriately.

The problem is that the PCR test is too sensitive and can pick up viral fragments that aren't infectious, as well as intact virus particles that are infectious, and can't tell the difference. So when you test people who aren't sick at all, the false-positive rate goes up (Baye's theorem for those who are interested; as the pre-test probability falls, the positive predictive value falls as well).

 

But - we have no better test out there. So we're stuck with PCR until we either (1) realize that previously vaccinated asymptomatic people are unlikely to be contagious and stop testing them; or (2) we get a better test that can differentiate between intact contagious virus, and inactive RNA fragments. The former is likely to happen first I think, but it will take some time.

[frantic36]

27 minutes ago, jpalbny said:

So we're stuck with PCR until we either (1) realize that previously vaccinated asymptomatic people are unlikely to be contagious and stop testing them; or (2) we get a better test that can differentiate between intact contagious virus, and inactive RNA fragments. The former is likely to happen first I think, but it will take some time.

 

Over on the Aus/NZ board someone just posted this link to an article posted in a paper for local general doctors. I know more studies have to be done but it is sounding positive about vaccinations reducing transmission.

 

https://www1.racgp.org.au/newsgp/clinical/mounting-evidence-suggests-covid-vaccines-do-reduc

[OlsSalt]

Thanks for the Aus/NZ article link. Raises the question I have right now, since many of us are planning cruises that will not depart until well into 2022.  Will a current vaccination for this one specific virus still be valid when the cruise actually departs a year from now?

 

A question that obviously has no answer, just one more of the known unknowns. 

 

An evolving field of  multiple uncertainties, leading to varying regulatory responses: Prevention -Testing-Therapeutics - Cure........ and cruising!

 

From the link:   What about the limits of vaccines?
Reducing the risk of transmitting the coronavirus relies on developing strong immunity against the virus. But immunity, even from the vaccines, fades over time. Scientists are actively monitoring people who have received COVID-19 vaccines to understand how long vaccine immunity is likely to last, and if and when booster shots will be required.

[Host Jazzbeau]

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