Utah is changing the way it measures the rate of positive COVID-19 tests. Here is what it means.

The state of Utah is changing the way it reports to the public on one of the statistics following the spread of COVID-19.

The test positivity rate is the percentage of tests that come back positive for COVID-19 – and Utah health officials have been explaining for months that a 3-5% rate indicates the virus is under control .

It hit 32.71% on Jan. 7, during the state’s post-holiday surge, but it has recently fallen, hovering around 16%.

The new method that the Utah Department of Health will use will make the percentage appear lower. This will help public health officials “see the benefits of our increased screening capacity” and make comparisons with other states more valid, state epidemiologist Dr Angela Dunn recently told reporters. explaining the change.

In its daily report on Monday, the ministry listed both the previous measure – a seven-day moving average of 15.4%, and the new one, which has a seven-day moving average of 7.3%.

Here’s how these methods differ.

What does the test positivity rate show?

The percentage of tests for COVID-19 that come back positive is “a leading indicator of the spread of COVID,” Dunn said. “In addition, it also measures the amount of testing we do.”

How did Utah calculate it?

Since the start of the pandemic, Utah has used a method called “people rather than people,” Dunn said. This means the number of people who have tested positive divided by the number of people who have been tested.

As people were tested, the state would count their first positive test in a 90-day period – or, if they never were, their first negative test. All other test results in this window have not been included. Health officials use a 90-day window, Dunn said, because it is the period of immunity for someone after catching the coronavirus.

So, under this method, a person who is tested multiple times in three months is counted once – subsequent results are “deduplicated” in the health department’s count of the number of people tested during that 90-day period.

What is changing in the way Utah calculates it?

The new method is called “test after test”. It takes the number of positive tests in a day or a week, and divides it by the number of tests performed during the same period.

“Each test reported to [Utah] The Department of Health is included in that calculation, ”Dunn said.

The number of tests performed in Utah is now considerably higher, as testing has grown with the addition of rapid tests and regular testing is prevalent among employees, students, nursing home residents and others.

These tests are usually carried out on healthy people; they have no symptoms and do not believe they have the virus. They are tested to stay in class or continue working.

So counting all the results, when so many presumably healthy people are tested, will lower the positivity rate.

The new method, said Dunn, “will allow us to see the benefits of our increased testing capacity.”

With all of these tests, people who catch the virus will know it quickly, she said. Health officials can respond with contact tracing and act faster to stop the spread. And the positivity rate will reflect that environment.

The “people over people” method made sense at the start of the pandemic, she said. At the time, the federal Centers for Disease Control and Prevention required that a COVID-19 patient undergo two consecutive negative tests before they could be considered cured of the virus.

A person could rack up a lot of positive tests before they get two negative tests, artificially inflating the “test-to-test” calculation, she said. The CDC later changed its guideline, but Utah continued to use the “people rather than the people” method.

The CDC uses both methods and a third, she noted.

Public health officials are looking at the two calculations, Dunn said. The “people rather than people” method, she said, “reflects our growing cases”.

The phrase ‘test by test’ “is really helpful because it allows us to see our increase in testing and how much that helps us reduce our cases.”

What is the difference in practical terms?

The new statistic for the positivity rate will be smaller.

Monday’s report showed the difference, with 15.4% versus 7.3% for a seven-day moving average by both methods.

The “people rather than people” method, said Dunn, “skews the percentage of positivity a bit more.” The “test-to-test” method “skews the percentage of positivity a bit,” she said. “The truth is somewhere in the middle.”

“You’re going to notice that the trends for these two methods are actually very similar,” Dunn said. Looking at the graphs for the two calculations, over time they are virtually parallel.

Is it a political decision, to improve the figures?

Dunn downplayed this perception. She noted that at least 37 other states use the “test on the test” – and taking the test makes it easier to compare apples to apples with other states.

If the daily figure seems lower, will people let their guard down?

“We have to change the scale in our heads,” Dunn said.

The post-Christmas test positivity rate of over 30% “was high because that was the scale we were using,” Dunn said. “Now 15% will be really high, 10% will be really high.”

How should people read the data?

“We know that no measurement is going to tell us how bad it is or when it is going to end,” Dunn said. “We have to watch everything.”

She recommends people look at three key statistics: the test positivity rate, the number of new cases, and the number of hospitalizations or remaining capacity.

“All of these three metrics give us a really nice picture of where we are now in the pandemic and where we are going,” Dunn said.