UDOH changes COVID-19 transmission index measurements

Feb 12, 2021, 12:24 PM | Updated: 5:44 pm
UDOH changes transmission index...
Photo: Utah Department of Health

SALT LAKE CITY — The Utah Department of Health (UDOH) announced changes to the COVID-19 transmission index in the state.  At first glance, it may look like the positivity rate has taken a huge drop, but state health workers say you need to take a closer look at the data.  



Beginning Thursday, Feb. 18, UDOH will transition to the “test over test” method to track positivity rates.

When it comes to measuring the number of positive cases, there are three different ways to look at the numbers.  Until now, UDOH has been using something called the “people over people” method.  That means they take the number of people who test positive and divide that by the total number of people who get tested.  That method has one drawback… duplicates.  Executive Director Rich Saunders says they’ve been weeding out the results from people who have come in for multiple tests in a short period of time.

However, the “test over test” model would change that.

“It’s just allowing us to capture all of the tests that are being done instead of having to sort out or de-duplicate people,” he says.

‘People over people’ v. ‘Test over test’: What’s the difference?

The “test over test” model looks at the total number of positive results and divides that by the total number of tests performed.  Saunders says this method is being used by the CDC, and switching to it will help health officials better align Utah with national figures.

Saunders says, “It also helps us to better compare to other states because most states are using this method of ‘test over test’ instead of ‘people over people.’”

They anticipate the transmission index will skew lower when the switch is made.  For instance, the rolling seven-day average positivity rate is 14.7% percent under the POP method, but it’s only 6.6% if you use TOT.  Is one number more accurate than the other?  Not necessarily.

Saunders says, “When we did the layover of the two methods, the trends were precisely the same.”

Which method’s will be posted to the state’s COVID-19 website?  Both.  If someone wants to compare Utah’s rate to what it used to be, the POP numbers would be best to measure that.  If they want to compare Utah to other states, TOT is the number to look for.

Changes to the state’s official transmission risk tables

However, since the numbers will skew lower, UDOH has made some adjustments to their transmission risk tables.  A 7-day average percent positivity of greater than 10% will belong to the “high” transmission category; a percent positivity between 5.1%-9.9% will belong to the “moderate” transmission category; and a percent positivity of 5% or less will belong to the “low” transmission category,” according to UDOH. 

A transmission level (high, moderate, low) is determined if a county has two of the three metrics in the designated level of transmission.  The other two are case rate per 100 thousand people, and hospital bed utilization.

Additionally, public gathering requirements in areas of “moderate” transmission will be changed.  The department added actions and precautions for businesses and individuals to take in areas of “low” to “moderate” transmission. 

In these areas, public gatherings may occur with side-by-side seating as long as the event host completes the event template and all patrons are wearing masks, are assigned seating and attest to not having any COVID-19 symptoms or exposures in the past 14 days.

UDOH said, “concessions stands must be closed in “moderate” due to increased risk that occurs with more people in attendance and when masks are removed to eat or drink.

Physical distancing between household groups is still strongly recommended at these venues as a precaution. 

In areas of “low” transmission, masks will be required, but no other restrictions are placed on these events.

Even though the positivity rates have been dropping, Saunders says none of Utah’s 29 counties, none of them would be dropped to a lower transmission risk level when this change takes place.

“It doesn’t look like it would be any time soon,” Saunders says.

As of today, the report stated 489,716 total vaccines have been administered, which is 26,996 more than Thursday.

How To Prevent the Spread of COVID-19 Coronavirus

COVID-19 coronavirus spreads person to person, similar to the common cold and the flu. So, to prevent it from spreading:

  • Wash hands frequently and thoroughly, with soap and water, for at least 20 seconds.
  • Don’t touch your face.
  • Wear a mask to protect yourself and others per CDC recommendations.
  • Keep children and those with compromised immune systems away from someone who is coughing or sneezing (in this instance, at least six feet).
  • If there is an outbreak near you, practice social distancing (stay at home, instead of going to the movies, sports events, or other activities).
  • Obtain a flu shot.

Local resources

KSL Coronavirus Q&A 

Utah’s Coronavirus Information 

Utah State Board of Education

Utah Hospital Association

The Church of Jesus Christ of Latter-day Saints

Utah Coronavirus Information Line – 1-800-456-7707

National Resources

Centers for Disease Control and Prevention

Commonly asked questions, World Health Organization

Cases in the United States

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UDOH changes COVID-19 transmission index measurements