Both entities use the same thresholds for the rate of new virus infections and to calculate the percent of tests that are positive. But because of Wyoming’s small population, the state made a few customizations to the formulas.
The Centers for Disease Control time-lapse map shows how COVID-19 transmission levels changed during July.
“Instead of calculating case rates and percent positivity over a 7-day period the way CDC does, we calculate those over a 14-day period,” Harrist explained via email. “This helps stabilize the metrics. We also take into account the number of active cases, which is especially important for smaller counties where just a few cases can have a large impact on case rates.”
She added, “Our metrics may be slower to change than CDC’s metrics, but do provide more stability.”
In practice, this can result in contradictory guidance from the state and the CDC. For example, the new masking recommendations are based on a community’s transmission category, but Wyoming’s counties fall into vastly different groups depending on the metrics.
The Wyoming Department of Health’s metrics have eight counties experiencing low virus transmission rates, while the CDC would say not a single Wyoming county falls below moderate transmission, with all but four counties seeing a high degree of spread.
Conversely, Wyoming’s metrics say just one county — Sublette — has experienced high transmission rates over the last 14 days.
