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