Last week, the Arizona Department of Health Services announced it had updated its guidance on when schools should transition to virtual learning. The agency recommended the move be made if a county’s COVID-19 benchmarks are in the red. But one of those indicators could be flawed.

The benchmarks include case count, percent positivity and COVID-like illness. But COVID-like illness has Will Humble, the former head of DHS, concerned. 

"It’s essentially a soft reporting method of some subjective symptoms that can be observed in hospital and emergency department settings," he said. 

Like cough, fever or shortness of breath. But in the early days of COVID: "Testing was so limited that COVID-like illness observations had some value, because it's all we had," Humble explained.

But now testing is widely available and results come fairly fast. Something else: not everyone develops those classic COVID symptoms.

"So, why would you still put weight on something as flimsy as COVID-like illness, which is subjective and poorly reported? So that's the issue that I have is that we're using a metric from the Stone Ages."

Saskia Popescu is an epidemiologist at the University of Arizona's College of Public Health.

"So, I think that the challenge is that when we're using COVID-like illness as a surveillance mechanism, it's inherently limited," she said. "And that's really what we're doing in the U.S. with the CDC is they mix it with influenza-like illness so that that data gets pulled together. So they're really using two syndromic surveillance networks to start to see, because we know sometimes the symptoms are similar, If you are starting to see these massive influx of people with a fever, and a cough and difficulty breathing, that is an indication that, sure, it might be seasonal influenza, it might just be normal respiratory viruses, but it also could be COVID-19."

So, while syndromic surveillance provides some information, it doesn't paint a complete picture of what's happening. Still, Popescu says more data is good. 

“So it does help in some ways, but my concern is also that, you know, it's  inherently flawed," she said. "So using it as a critical piece to help determine if schools should stay open worries me, you know. I don't think it's the strongest pillar to stand on.”

To illustrate the issue, look at Yuma or Graham counties on the DHS website. Their case count per 100,000 and percent positivity are in the red. But COVID-like illness is in the green.