Complications arise due to different ways to measure the proportion of people who test positive for COVID-19

Different ways to calculate important pandemic number causing confusion

Health experts say the positivity rate for COVID-19 can be calculated differently, which means agencies are having a tough time calculating the number.

PHOENIX - According to experts, the percent positive rate for COVID-19 can be the best way to identify community spread, but as it turns out, not all organizations, including the Arizona Department of Health Services, are using the same method.

Percent positive is the percentage of people who test positive for the virus, of those overall who have been tested.

"That percent positive metric is a really important one that is going to make a big difference in the decisions being made," said former AZDHS Director Will Humble.

Different ways to calculate percent positive rate

Humble says there are different ways to track the percent positive rate. The first can be by division, or taking the number of positive tests reported each day, divided by the total number of reported positive and negative tests. This is used by the ASU Biodesign Institute and Johns Hopkins University.

Humble, however, says a more accurate reading is with the epi curve. The samples are back filled, and it is a way to track the results on the date the sample was collected. Humble says AZDHS uses this method, but excludes tests that are not reported electronically.

"The approach they have selected is a good one, the problem is that not all labs are turning in their analyses in electronic format, and the state is only using the data coming back electronically to calculate the percent positive. Now, they are backdating it, which is good," said Humble.

The difference in calculations explain the difference in percentages for positive rates in the same state.

In order to fix this, Humble hopes the AZDHS starts using data from labs across the entire state. This will help come up with a better metric that leaders can use to make policy decisions.

"The reason that is so important now is that we are using that metric to make realy important decisions on when to open in person learning in the K-12 system. We are using those metrics to think through and when we allow bars night clubs," said Humble.

According to Humble, tracking has been a challenge not only here in Arizona, but across the country. FOX 10 has reached out to officials with AZDHS for comment.

Tune in to FOX 10 Phoenix for the latest news

Get the latest coronavirus news by downloading the FOX 10 News App. Our promise is that our alerts are there to inform you - not scare you.

On CoronavirusNOW.com, you'll find extensive coverage about COVID-19, including breaking news from around the country, exclusive interviews with health officials, and informative content from a variety of public health resources.

COVID-19 symptoms

Symptoms for coronavirus COVID-19 include fever, coughing, and shortness of breath. These, of course, are similar to the common cold and flu.

Expect a common cold to start out with a sore or scratchy throat, cough, runny and/or stuffy nose. Flu symptoms are more intense and usually come on suddenly, and can include a high fever.

Symptoms of COVID-19 may appear more slowly. They usually include fever, a dry cough and noticeable shortness of breath, according to the World Health Organization. A minority of cases develop pneumonia, and the disease is especially worrisome for the elderly and those with other medical problems such as high blood pressure, obesity, diabetes or heart conditions.