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Coronavirus and CDC: Test count error leaves epidemiologists “Really Baffled”

WASHINGTON – As it traces the spread of coronavirus, the Centers for Disease Control and Prevention combines active infection detection with those who detect recovery from Covid-19 – a system that teaches the image of the pandemic but raises the proportion of Americans tested as President Trump boasts of testing .

Stunned epidemiologists say that data from antibody tests and active virus tests should never be mixed because diagnostic testing aims to quantify the amount of active disease in the population. Serological testing can also be unreliable. And patients who have done both diagnostic and serological tests would be counted twice in the total.

“It just doesn’t make sense; we’re all really puzzled, says Natalie Dean, a biostatist at the University of Florida.

Epidemiologists, state health officials and a spokeswoman for C.D.C. said there was no ill intent; they attributed the erroneous reporting system to confusion and fatigue in overworked states and local health departments that usually track infections – not tests – during outbreaks. C.D.C. relies on states to report their data.

A spokeswoman for C.D.C., Kristen Nordlund, said that viral testing was much more common than antibody testing in the early days of the pandemic, and some states combined the virus tests with the few antibody results they had.

State health officials in Virginia, Texas, Georgia and Vermont also said they began splitting their test data.

“This is not an intentional misuse of information – it’s part of the fog of the war on infectious diseases,” said Michael T. Osterholm, a University of Minnesota professor and former state epidemiologist, who was heavily critical of the disease control centers early in the pandemic. . “We have been monitoring cases and now we are all trying to test and this presents unique challenges.”

“We’re like the blind epidemiologists trying to understand the elephant,” said Michael Levy, a professor of epidemiology at the University of Pennsylvania. Health officials, he said, need good reporting to “understand the relationship between the epidemic we can’t see and the data we can see.”

Scott J. Becker, executive director of the Association of Public Health Laboratories, said there was another reason why states tracked tests: Trump wants the numbers.

“We never had to capture test volume. That was what the White House wanted to know, how many tests were done,” Becker said, adding, “Usually everything works through the public health system, but in this response it has been a driving force to have data numbers, on several levels. “

Like Nordlund at C.D.C., health officials throughout the country say that diagnostic tests, which detect the presence of the virus, had initially outperformed antibody tests, so agencies grouped them together. Although both figures are helpful in assessing the extent of the outbreak, only viral test numbers can indicate a state’s ability to identify individuals who currently have the virus.

Bill Hanage, an epidemiologist at Harvard T.H. Chan School of Public Health, said that the mix of the two figures would distort the image of the coronavirus outbreak in different parts of the country. In most locations outside New York City, the center of the outbreak in the United States, the percentage of people who have been exposed to the virus and who would produce a positive result on an antibody test is likely to be lower than 10 percent.

“What this means is that these tests are more likely to come back negative, which means you can end up with a misleading picture overall,” he said. “You think there are fewer illnesses than it actually is. It’s not something that will certainly be helpful.

Clark Mercer, chief of staff of Ralph Northam, a Democrat, Virginia, initially defended the strategy last week at a news conference, saying it was important for the state to report totals that included antibody tests to be able to rank properly compared to other states.

“If we’re going to be compared to all 50 states,” he said, “I want to make sure it’s apples to apples.”

But a few days later Mr. Northam, a doctor, said he had only recently been told that the data was combined and had since directed the health department to split the results. Serology, or antibody, tests accounted for 9 percent of tests in Virginia, said Northam – a figure that Dr. Lilian Peake, the Virginia epidemiologist, said would not have drastically changed the state’s overall performance.

“In the 20 years that I have been a public health leader, we have never focused on testing, and this is a new virus, so we are still learning about it,” Dr. Peake Friday. “The tests are evolving, and we are still learning how to interpret them.”

“If we include serology, we inflate the denominator,” said Erik W. Filkorn, spokesman for Vermont’s health surgery center, in a statement on Friday, adding that the effect had been minimal. Serology tests accounted for 4 percent of all tests in Vermont, he said, and including them may have increased the percent positive rate by “a fraction of a percentage point.”

“The integrity of our data is definitely our first priority,” Dr. Kathleen Toomey, commissioner for the Georgia Department of Public Health, at a news conference on Thursday.

The Pennsylvania Department of Health is still using a small number of positive antibody tests to inform the state’s overall case number, a spokeswoman, Nate Wardle, said on Friday. But he said the antibody tests were not skewed results – they represent less than 1 percent of the total cases in the state, he said – and were not used to decide if regions should reopen.

Wardle said that patients who had a positive antibody test as well as symptoms or a high-risk exposure were included in the state’s “probable” test count, based on guidance from the CDC, which allowed the state to track whether patients who had symptoms early may have had the virus.

“We believe that the way we report the data is correct,” he said, adding that the probable cause falls out and was kept separately from confirmed cases. “We do not use our likely cases in any of our decision-making.”

Sheryl Gay Stolberg reported from Washington, Sheila Kaplan from New York and Sarah Mervosh from Canton, Ohio. Apoorva Mandavilli contributed with reporting from New York.

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