The latest dashboard from coronavirus disease control and prevention centers combines data on two different types of tests that experts say could swell the key statistics used by epidemiologists to monitor the epidemic.
The agency’s recently released Covid-19 Data Tracker test dashboard combines the results of diagnostic tests, which identify current infections, and serological tests, which detect whether someone has ever been infected. Epidemiologists warn that tests are not designed for the same purpose and that mixing the data could mask reality.
The CDC says it aims to separate data on the two types of tests soon.
“[Le tableau de bord] includes diagnostic and serology results, which include repeat tests for individuals, as well as the number of serological tests and additional information on commercial laboratory serological tests, “CDC spokeswoman Kristen Nordlund said , in a press release to CNBC. “We hope that the test data will be shared equally between the PCR [ou les tests de diagnostic] and serological tests in the coming weeks. “
The CDC did not respond to CNBC’s question on why the data was released combined. The Atlantic first reported data from the CDC.
Since serological tests are intended to be used for both asymptomatic and symptomatic people while diagnostic tests or PCR tests are currently used often to confirm suspected infections, people are less likely to give a positive result with a serological test than with a PCR test, said Robert Bednarczyk, assistant professor of global health and epidemiology at Emory University.
“If we test more people and don’t find as many cases, it would be a sign that things are getting better,” he told CNBC. “But if it happens because we artificially inflate the number of tests, then we don’t see the real picture.”
Diagnostic tests, most of which require a sample taken with a swab, are crucial for contact tracing and for stopping the spread of the virus, said Bednarczyk.
Serological tests, which use a blood sample, are used by epidemiologists to estimate how much the population has already been exposed to the virus, said Bednarczyk. He added that it is useful from a research perspective, but should not be used to determine the state of the epidemic.
“Without a clear comparison between apples of the number of tests per capita, it is difficult to compare disease rates between states,” he said. “The types of tests should be separated.”
Instead of federal guidelines on data collection, several state public health departments have also released their test data in this combined way.
Georgia, which took one of the first and most ambitious decisions to reopen much of its economy, is currently combining data from the two tests, the Macon Telegraph reported for the first time. The Georgian Department of Public Health confirmed to CNBC on Thursday that it is working to update its website to separate the data. A spokesperson added that 57,000, or about 14%, of the 407,000 tests performed by the state were serological tests.
Virginia and Vermont confirmed to CNBC that they had previously combined the data for the two tests, but have since updated their websites to separate the two data sets.
Delimiting the data has had “minimal” impact, Vermont Department of Public Health spokesman Ben Truman said, but said the state had made the decision to avoid inflating the rate of test positivity, a key data point that indicates the number of people being tested who turn. positive for the virus. Some states have linked their reopening plans to specific test positivity milestones.
“To be a case, you must be laboratory confirmed by molecular testing,” reads an explanation for the decision to separate data from the Vermont epidemiological data team, provided by Truman. “To allow a calculation [en pourcentage] positive, we should only include tests that could potentially make you a case, so only molecular tests. If we include serology, we inflate the denominator. “