CNN analysis shows that Covid-19 antigen tests were not counted among the cases in some countries

CNN analysis shows that Covid-19 antigen tests were not counted among the cases in some countries

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Five states – California, Colorado, Maryland, Missouri and Nevada – publicly report only cases confirmed with PCR tests in their online scores, according to a CNN analysis of the Department of Health’s dashboards in all 50 state.

Some states only report the results of polymerase chain reaction tests in their Covid-19 case numbers and exclude the results of antigen tests, as antigen tests are generally considered less accurate. But as antigen testing arrives in the United States, this exclusion could lead to possible miscalculations.

In California, for example, CNN was told that the antigen Covid-19 test results should be reported to local health departments and the California Department of Public Health. However, publicly reported Covid-19 test data only reflect the results of diagnostic tests that detect the coronavirus’ genetic material, such as PCR – polymerase chain reaction – tests.

CNN requested antigen test data from the state’s Department of Public Health, but in an email was told that “the results of antigen tests are not currently being reported publicly in the country.”

Across the four remaining states, the data they shared with CNN represents about 10,000 positive Covid-19 antigen test results shown in January over just a few samples.

If it is added to the number of cases reported, the positive antigen test results will increase the Covid-19 cases, which were reported to be between 5% and 50% at that time, according to CNN’s analysis.

In Maryland, 3,522 positive antigen tests were reported to the Maryland Department of Health between Jan. 23 and Jan. 29, the department emailed CNN. That is an average of 503 positive antigen tests per day that are not included in the state’s daily dashboard.
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In Nevada, a total of 7,764 antigen tests were reported to the Nevada Department of Health and Human Services between Jan. 21 and 27, according to a document from the department’s analysis office. Among these tests, 623 were positive. In Nevada, statements are based on ‘molecular tests only’, with the exception of the Nevada Department of Corrections, which uses the BinaxNOW antigen test among people currently locked up.

In Colorado, between Jan. 25 and 31, there were 10,203 total antigen test encounters per day, of which 527 were positive, according to the Colorado State Emergency Operations Center. The department emailed CNN saying the average seven-day positivity for antigen testing last week was 5.17%.

In the week of Jan. 10, a total of 50,113 antigen tests were reported to the Department of Health in Missouri, according to data obtained by CNN. Among these tests, 5,285 were positive.

‘We are going to see an underestimation’

Public health officials have noted that although antigen tests are usually faster and cheaper than typical PCR tests, antigen tests are likely to miss an active Covid-19 infection compared to PCR tests. Because of this difference in accuracy, some states choose to report only Covid-19 cases confirmed by PCR tests.
In June, at least 28 states did not follow CDC recommendations to report antigen test results as ‘likely’ cases in Covid-19 cases. Although the number is now much smaller, some experts are concerned that in the future a distorted picture of the actual spread of diseases for residents in a state, if one does not reveal ‘probable’ cases.
“Antigen-based testing is not necessarily the majority of all tests performed everywhere, so it is unlikely that we will get a dramatically incorrect estimate at the moment – also because most states report it. But there is the risk ahead. , “the dr. David Dowdy, an epidemiologist at Infectious Diseases at the Johns Hopkins Bloomberg School of Public Health, told CNN last week.

“I think more and more of these antigen-based tests are being used,” he said. “So there is definitely a risk that if it is not reported consistently, we are going to see an underestimation of the number of Covid cases in the country, and especially in the countries that do not report it.”

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Faster antigen testing is expected in the United States, as last week, the Biden government announced that the Department of Defense and the Department of Health and Human Services are working with Australian company Ellume to make more of its full-fledged home Covid-19- present tests. the United States. The test is a fast, non-prescription self-test that detects SARS-CoV-2 antigen. SARS-CoV-2 is the name of the virus that causes Covid-19.

While antigen tests work by detecting a protein that is part of the new coronavirus, PCR tests work by detecting genetic material from the virus called RNA.

For antigen tests, “proteins have a shorter lifespan in the body, so there may be more false negatives from these tests,” said Dr. Elizabeth McNally, director of the Center for Genetic Medicine at Northwestern University Feinberg School of Medicine, in an email written to CNN.

“Antigen tests are frequently used to detect other viruses, and we know that they also have false positives and false negatives,” she added.

Since PCR tests are usually very accurate, they do not need to be repeated.

For antigen tests, “positive results are usually very accurate, but false positives can occur, especially in areas where very few people have the virus,” according to the U.S. Food and Drug Administration. Negative results may need to be confirmed with a PCR test.
“Because antigen tests are more likely to report false negative results than false positive results, the problem is more that there may be people who have Covid who are missed by these antigen – based tests, but not that they are false positive,” Dowdy said. He added that it is estimated that antigen tests will be positive in about 80% to 90% of people who have Covid-19.
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“If the percentage of your tests that are positive is primarily tracked, there is a risk of underestimating the percentage positive, if you include antigen-based tests,” Dowdy said. “But if you look at the total number – who generally see more people – then there are people who have confirmed Covid-19 who are not testing positive.”

In some states, the results of antigen tests may be included in the total number of cases as ‘probable cases’, but not in the percentage of positivity of the tests, which follows the percentage of all coronavirus tests that are in a positive state.

In Hawaii, for example, “antigen tests are counted as probable cases, rather than confirmed cases,” Brooks Baehr, a spokesman for the Hawaii Department of Health, said in an email to CNN. But “for the test of percentage positivity, antigen tests are not included in our scores because we lack accurate scores of the total number of antigen tests performed in our condition.”

“The more testing we do, the better”

‘It seems strange’ not to include the results of antigen tests in the Covid-19 effects across the country, McNally, North-West University, said in her email.

In the scores, “the combination of PCR and antigen may improve the sensitivity and specificity of the test, but overall the test we do works pretty well, so I don’t think it’s really necessary,” McNally said. “We know there are far more cases of Covid-19 than have been reported.”

The most important take-away, Dowdy said, is that Covid-19 testing should continue and remain an important tool for responding to the pandemic.

“The more we do it, the better,” Dowdy of Johns Hopkins University said.

“It’s better for people to know if they have this disease or not,” he said. “It’s also important for public health authorities to know how many people have Covid-19 in a given location – and therefore we should try to increase PCR testing and antigen testing, and to make sure we report it. as fully as possible. ‘

Virginia Langmaid and CNN’s Deidre McPhillips contributed to this report.

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