Update: Antigen Tests & Omicron, Home Tests Not Getting Reported

 


Two updates on testing.

Antigen Tests Less Sensitive to Omicron

On Wednesday I blogged about the challenges the new Omicron variant is posing for testing. Essentially, you can have antigen tests that are fast and inaccurate or PCR tests that are slow and accurate. 

Antigen tests are just barely satisfactory for symptomatic cases (false negatives in 1 of 4 to 1 of 8 tests), and they are basically useless for asymptomatic cases (false negatives in 1 of 2 to 1 of 3 tests). Even that assumes the tests work for Omicron.

Well yesterday the FDA announced that antigen tests are less sensitive to Omicron than other variants. They don't have information on how much less sensitive they are but are working to get that info. They are also trying to learn why and think the tests can be adjusted to compensate once they know.

Dr. Fauci is quoted in this article: "What the FDA is saying today is that when you look at Omicron and its ability to detect Omicron, some of the tests have a diminution, further, of the sensitivity, but they still say the tests are useful and should be used."

But exactly how are they useful if they now possibly have more than a one in four chance of giving a false negative for symptomatic people, and are already essemtially useless for asymptomatic people?

The average person isn't going know anything about test sensitivity. They will just assume whatever the test tells them is correct, and go about their business if they have a false negative. 

One reason the home tests might not work as well is that they are not swabbing the areas where the virus lives. Lots of people in the know say the thing to do is swab your throat instead of your nose.  One pre-print study (not yet peer reviewed) in South Africa found that throat swab antigen tests had 100% agreement with PCR tests.

Home Testing Calls Case Data into Question

An unintended consequence of home testing is that it is interfering with case counting. A NY Times article says this is "wreaking havoc with the accuracy of official positivity rates and case counts."

The article quotes Dr. Marcus Plescia, chief medical officer at the Association of State and Territorial Health Officials as saying: "Our entire approach to the pandemic has been case-based surveillance: We have to count every case, and that’s just not accurate anymore" because of the increasing use of at-home antigen tests.

The problem is that people may not know whether they should report the results of their at- home test. If they know they should they may not know how. 

I follow these things very closely. I have no idea whether or how I could report the result of a self-administered test to AzDHS.  

This problem can only get worse with the Biden Administration's plan to distribute 500 million at-home tests starting in January. Some public health officials say that because of this we're going to have to focus on some other metric, like hospitalizations or deaths, in evaluating our response to the la demi.




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