New data on Louisiana’s coronavirus cases has confirmed what many public health experts have long expected: the virus was widespread in the state much earlier than initially limited testing was able to show.

The data, released by the state Department of Health on Tuesday, sheds new light on the march of COVID-19 through Louisiana, providing a valuable tool to researchers as they seek to gain a better understanding of its rapid spread.

By tracking coronavirus cases by the date patients experienced their first symptoms, the newly released information provides a more accurate picture of the curve the state is on than by the daily release of new cases, a metric complicated by the often-long waits for tests to be processed.

A similar set of data released by the department at the same time also provides a more accurate picture of the tragic toll the virus has taken by backdating deaths attributed to the coronavirus to the date they occurred, as opposed to the date they were reported to the state.

By March 27, the most recent date for which the new data is available, more than 13,300 people who would later test positive for the virus saw the first indications they were infected. That's almost five times the number of people confirmed as positive for coronavirus by that point.

It would take more than a week before the state's official tally caught up.

Similarly, 193 Louisianans had succumbed to the virus on March 27, but it would be four days before those deaths were reflected in the daily counts.

“The goal of this data is to give a more accurate representation to the public of what that curve actually looks like,” said Alex Billioux, assistant secretary for the state’s Office of Public Health.

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The announcement that more details are available related to when patients first noticed symptoms was met with glee from at least one researcher.

“Yay, finally! It’s about time,” Tulane University epidemiologist Susan Hassig said. “I was getting real irritated.”

The data will accompany, but not replace, the now sadly familiar daily reports on newly identified cases and deaths the Department of Health provides on its website at noon.

The reports on the onset of symptoms and dates of death will be several days behind the current numbers owing to the work needed to track down the information, though Billioux said they will continue updating the data going forward.

But even with that lag, the new information provides an illuminating picture of the virus’s progress.

The difference between the time symptoms first appear and the time a case is confirmed can be dramatic, and the new data paints a picture of a far higher infection rate in the weeks after the first case was confirmed than was available when looking at when tests came back positive.

Billioux said the new counts will provide a clearer picture of what was happening in the state on various dates by clearing away external factors. For example, both Louisiana and other states have seen numbers ease up when weekends cause lags in testing, only to see those figures surge in subsequent days.

“On Sunday we announced 68 new individuals who died, of which nine had actually happened in the last 24 hours,” Billioux said. “The reality is that it’s not a fair representation, we were learning of deaths that may have occurred days before.”

Dating the cases from when symptoms first appeared also helps address the differing rates at which labs process tests and variations in when people decide to get themselves checked out.

Information on the actual date of death of victims of the virus, along with admissions data from hospitals, had already been used internally by the Department of Health to help produce a state model of what resources will be needed going forward. That model has been looking more promising in recent days, though officials are still trying to determine why the deaths from the virus have not abated and why 70% of its victims are African-American.

“The COVID-19 outbreak in Louisiana is of grave concern, even as we’re starting to see the curve bend,” Billioux said. “We were concerned and talking about it before we had a case in the state.”

For those seeking to better understand the virus’s growth in the state, the new data will provide a wealth of information, Hassig said.

“It’s a really important thing because it gives us a much better time frame in terms of what these numbers actually mean,” she said.

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Knowing the date a test was processed and came back positive is “not meaningful” for those looking for markers or indicators of the state’s progress, Hassig said.

“It’s far more important to know how they were distributed among the days they were drawn and captured,” she said. “That tells us far more than whatever date they were reported.”

And more-detailed information could also be used to get a better handle on exactly when the outbreak in Louisiana began by working backwards from the infection data, she said.

Even with the additional data, Billioux warned there are still many things that are unknown about how widely the virus spread through the state and how quickly. A key gap in the understanding of researchers and officials is how many people may have contracted the virus but were asymptomatic or suffering mild symptoms that didn’t prompt them to get a test.

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The state is now working to start testing people for antibodies to the virus, which would indicate whether they had contracted it without ever seeking medical attention.

“That’s going to give us even more information about what we think is the actual level of COVID in the state,” he said.

Editor's note: This story was updated on April 8, 2020 to reflect an update to the data released by the Louisiana Department of Health.