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Why do coronavirus case counts differ from one website to another? Curious Texas investigates

Health experts say counties have the most accurate information, and different methods of reporting can create discrepancies.

For Texans trying to find the number of COVID-19 cases in their area, the total may depend on where they look.

Dallas County, for example, reported 247 cases on the county health department’s website earlier this week. But on the same day, the Texas Department of State Health Services’ site showed only 169.

One reader asked Curious Texas: Why are these numbers different depending on where you look? Where should you go to find the most accurate count? Here’s what you need to know.

Reporting methods matter

Some of the difference between state and county totals is attributable to different methodologies.

For example, the Dallas County health department doesn’t include people who test positive but reside outside the county. So even if people test positive in Dallas, they are included in the count only if they live in Dallas County.

But Austin’s health department, among others, includes anyone who is tested or treated in Austin-Travis County, said Jen Samp, public information and marketing manager for Austin Public Health.

Chris Van Deusen, director of media relations for the Department of State Health Services, said the department recently changed its methodology for reporting statewide totals to speed up its online reports.

Previously, the department waited for official reports to come in from local jurisdictions, creating a discrepancy between county and statewide totals. Now the department is using the totals that counties report publicly. The Texas Tribune reported that the change happened Tuesday.

“We’re collecting those in the evening and updating our data the next morning, so they could get off again once the local jurisdictions update their numbers,” Van Deusen said in an email.

The change led to the addition of 305 cases to the state’s total.

It’s also important to note that some sites, including the state health department’s, don’t include people who returned from China or who returned from a cruise ship on a chartered flight to San Antonio.

It’s also possible that some sites include presumptive positive cases — cases the Centers for Disease Control and Prevention hasn’t confirmed — while others do not.

A popular interactive map created by Johns Hopkins University pulls from several public health databases and includes presumptive positive cases. Earlier this week, the map showed more cases in Texas than the state health department’s website did.

The state health department’s site warns that other sites may be using news reports to count cases, making it possible that some cases have been counted twice.

Counties probably have the best data

Dr. John Carlo, former Dallas County medical director and CEO of Prism Health North Texas, said local governments generally have the most accurate information.

“Probably the most up to date and current is going to be the lowest jurisdictional entity,” he said. “It’s easier and more timely when you’re in a smaller segment of the population.”

Van Deusen said the state also recommends looking to counties for case information.

Be careful about city counts

Some cities have been issuing news releases or reporting cases within city limits. But that can create confusion when a city lies in more than one county.

Frisco, for example, lies in Collin and Denton counties. When a Frisco family tested positive for the disease earlier this month, the cases were confirmed by Collin County.

As of Thursday, 19 cases had been reported in Frisco, but they were split between the two counties. Trying to separate cases by city may create confusion or errors.

Counts may change as the virus is better understood

Health experts say it’s possible case definitions could change as scientists and health officials learn more about the disease.

In China, where the outbreak originated, the criteria for what constituted a case changed several times, which some experts believe led to significant changes in the numbers reported.

In mid-February, the country said it would count people who were clinically diagnosed with the disease even if they hadn’t been tested. That caused a spike in numbers.

But later that month, China went back to counting only lab-confirmed cases, causing what appeared to be a huge decline.

“It does happen from time to time where we might change the definition or case definition to what we consider a case depending on multiple factors,” Carlo said.

Still, some health experts, noting how quickly the numbers changed in China, have raised questions about how reliable the information is at the epicenter of the outbreak.

Overall, cases are probably undercounted

Health experts say testing abilities across the country have lagged, making it likely that there are more cases of COVID-19 in communities than officially reported.

Texas especially has lagged behind other states in testing people for the infection. The Washington Post reported this week that New York — one of the states hit hardest by the outbreak — has processed seven times as many tests as Texas, even though Texas has 9 million more people.

Public health officials have emphasized that the case count is likely to increase significantly as Texas increases testing and gets a better understanding of the outbreak.

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