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Coronavirus and CDC: Errors in test count leave epidemiologists “really amazed”

WASHINGTON – While monitoring the spread of the coronavirus, the disease control and prevention centers combine tests that detect active infection with tests that detect recovery from Covid-19 – a system that blurs the picture of the pandemic, but the percentage of Americans tested increases President Trump boasts of testing.

Astonished epidemiologists say that data from antibody tests and active virus tests should never be mixed, as diagnostic tests attempt to quantify the amount of active diseases in the population. Serological tests can also be unreliable. And patients who had both diagnostic and serological tests would be counted twice in the total.

“It just doesn’t make sense. We’re all really stunned,” said Natalie Dean, a biostatist at the University of Florida.

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

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

State health agencies in Virginia, Texas, Georgia, and Vermont also said they were beginning to disaggregate their test data.

“This is not a deliberate misuse of information – it is part of the fog of the infectious disease war,” said Michael T. Osterholm, a professor at the University of Minnesota and a former state epidemiologist who sharply criticized the disease control centers at the start of the pandemic. “We have been monitoring cases and now we are all trying to run tests. This presents unique challenges.”

“We are like the blind epidemiologists trying to understand the elephant,” said Michael Levy, professor of epidemiology at the University of Pennsylvania. Health officials, he said, need good coverage 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 is another reason why states are tracking tests: Mr. Trump wants the numbers.

“We never had to record the test volume. The White House wanted to know how many tests were carried out,” said Becker, adding: “Normally, all of this works through the public health system, but in that response there was an effort to have data numbers on several levels. “

As Ms. Nordlund of C.D.C. Health officials across the country say that diagnostic tests that detect the presence of the virus initially far exceeded the antibody tests, so the authorities summarized them. While both numbers are helpful in assessing the extent of the outbreak, only viral test numbers can indicate a state’s ability to identify people who currently have the virus.

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

“That means these tests tend to be negative, which means you get a misleading picture overall,” he said. “You will think that there are fewer diseases there than there really are. That will not be helpful, to say the least.”

Clark Mercer, the chief of staff of Virginia Democratic Governor Ralph Northam, defended the strategy at a press conference last week and said it was important that the state reported sums with antibody tests to be classified correctly compared to other states.

“If we’re compared to all 50 states,” he said, “I want to make sure they’re apples for apples.”

A few days later, Mister Northam, a doctor, said he had only recently learned that the data was being combined and had since instructed the health department to disaggregate the results. Serology or antibody tests accounted for 9 percent of the tests in Virginia, said Northam – a number that, according to Dr. Lilian Peake, the epidemiologist of the state of Virginia, would not have changed the overall results of the state drastically.

“In the 20 years that I’ve been a leader in public health, we’ve never focused on testing. This is a new virus, so we’re still learning about it,” said Dr. Peake on Friday. “The tests are being developed and we are still learning how to interpret them.”

“If we include serology, we increase the denominator,” said Erik W. Filkorn, a spokesman for the Vermont Health Center, in a statement on Friday, adding that the effect was minimal. Serology tests accounted for 4 percent of all tests in Vermont, and the inclusion of these tests could have increased the percentage positive rate by “a fraction of a percentage point.”

“The integrity of our data is absolutely our top priority,” said Dr. Kathleen Toomey, the commissioner of the Georgia Department of Public Health, at a press conference on Thursday.

The Pennsylvania Department of Health is still using a small number of positive antibody tests to determine the total number of cases in the state, a spokesman, Nate Wardle, said on Friday. But he said that these antibody tests were not biased results – they account for less than 1 percent of all cases in the state, he said – and were not used to decide whether regions should be reopened.

Mr. Wardle said that patients who had a positive antibody test, as well as symptoms or high-risk exposure, were included in the state’s “likely” test count based on the CDC’s instructions that allowed the state to track patients Symptoms early on might have had the virus.

“We believe that the way we report the data is correct,” he said, adding that the cases with probable causes were broken out and kept separate from confirmed cases. “We don’t use our probable cases in any of our decisions.”

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

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