Texas Expands and Improves Measures of COVID-19 Positivity Rate
News Release
Sept. 14, 2020
The Texas Department of State Health Services today will begin reporting two additional measures of theCOVID-19 positivity rate, the percentage of tests that are positive in a given period. The update is the result of DSHS’s work to enhance the state’s COVID-19 data in partnership with the Governor’s Strike Force.
While DSHS will continue to post the data in the form Texans are used to, DSHS will primarily rely on the positivity rate calculated according to when people were tested, the specimen collection date, which provides the most accurate view of the pandemic’s effect over time. Because all test results received will be counted by when the test occurred, the rate for previous days will change as that information become more complete, and it will not be skewed by delays in reporting test results to the state.
“These enhancements are part of our continuous effort to improve the information we present,” said Dr. John Hellerstedt, DSHS commissioner. “As the COVID-19 pandemic evolves, so must the data we share. Our information must provide the clearest possible picture of what is happening now and what has occurred in the past. The trends in this and other data shape our understanding of what to expect in the future.”
As an additional point of reference, DSHS will post a rate based on when lab results were reported to the state. Both new methods will use positive and total molecular test results reported in NEDSS, the National Electronic Disease Surveillance System, and be calculated as a seven-day average. They will also exclude duplicate or other erroneous lab results. Recent upgrades to NEDSS now allow DSHS to clean up the testing data more quickly to be used in the positivity calculations.
The state’s legacy positivity rate used the number of new confirmed COVID-19 cases over seven days divided by the number of new molecular test results over the same seven days. That method served as a reliable proxy for the overall COVID-19 trend for most of the pandemic. However, an influx of older test results in August caused new cases and new test results to get out of sync, leading to large swings in the positivity rate and the need to reevaluate methods to calculate it.
The positivity rate by specimen collection date shows a peak in late June and July as Texas saw a dramatic increase in the number of COVID-19 cases reported in the state. The other methods mirror the same overall trend until diverging when the older test results began to be reported in August. DSHS will post all three methods for a time to allow for a continued comparison.
Each day, more than 600 clinical laboratories and other testing providers, 600 hospitals, 57 local health entities and the eight DSHS public health regions submit data about COVID-19 to DSHS where it is quickly analyzed and reported to the public to provide the most up-to-date information possible. DSHS will continue to work with the Strike Force on further improvements.
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(News Media Contact: Chris Van Deusen, DSHS Director of Media Relations)