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Missouri May Greatly Undercount COVID-19 Cases By Omitting Antigen Test Results

Julie Denesha
COVID-19 testing events have become common in Missouri but the state isn't reporting results for one type of test.

Antigen tests now comprise about a third of COVID-19 tests conducted in Missouri but their results are not included in case counts.

Updated: February 10, 2021 at 9:19 AM CST
Missouri health officials added data from antigen tests to the state’s COVID-19 dashboard on Wednesday following reporting by several news outlets, including KCUR, that it had not included results from those tests in the state’s COVID-19 case tallies.

Positive antigen tests are now listed in a new “probable case” field on the website. Cases are considered “confirmed” and included in the state’s confirmed case count if they are confirmed through PCR testing.

A total of 2,966 probable cases have been identified through antigen testing in the last seven days, according to the new dashboard data. Another 6,223 confirmed cases have been identified through the more widespread PCR testing.

The percentage of recent PCR tests that are positive has declined to 7.7%, while the positivity rate for antigen tests, which are considered less accurate, stands at 7.1%.

The pervasiveness of COVID-19 in Missouri may be much larger than the state’s public data show.

The nearly half a million confirmed cases listed on Missouri’s dashboard do not include tens of thousands of positive tests found through antigen tests administered in the state, a new analysis by CNN found.

Most states have included cases found through antigen testing in their case tallies, according to CNN’s report. By excluding antigen tests, Missouri’s case numbers may appear artificially low compared with other states.

A spokeswoman for the Missouri Department of Health and Senior Services did not respond to inquiries from KCUR on Tuesday.

Almost 470,000 COVID-19 cases have been identified in Missouri through PCR (polymerase chain reaction) tests, which are the most commonly administered tests used to diagnose COVID-19. More than 4 million such tests have been administered in Missouri.

This state’s confirmed case count does not include the 75,308 cases identified through the 708,780 antigen tests that have been conducted in Missouri. Antigen tests, which detect proteins found in the virus, are not as reliable as PCR tests but can be done more quickly and cheaply.

It’s unclear whether the positive antigen tests represent cases that also may have been identified through PCR testing.

A total of 301,641 individuals have been tested in Missouri through antigen testing. Some have been tested more than once, accounting for the more than 700,000 that have been administered.

Antigen tests have been used in Missouri since last March, although the number of antigen tests performed during much of the pandemic has been small compared to the PCR test numbers.

Since late November, however, the use of antigen tests has increased sharply, and they now make up roughly a third of all COVID-19 tests administered in Missouri. Meanwhile, the numbers of PCR tests administered in the state in January has dropped to its lowest level since June of 2020.

As a health care reporter, I aim to empower my audience to take steps to improve health care and make informed decisions as consumers and voters. I tell human stories augmented with research and data to explain how our health care system works and sometimes fails us. Email me at alexs@kcur.org.
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