Nearly 150 outbreaks in Colorado were resolved over the past week, a significant bite taken out of the clusters that have plagued the state for more than a year.

As of Wednesday, when new data by the state was published, there are 352 current outbreaks statewide. That’s down from 488 reported as of June 9 and is far below the 859 that were active at the beginning of May, when Colorado was in the throes of a fourth pandemic wave. 

There are likely two explanations for the decrease in outbreaks.

First, the presence of COVID-19 in Colorado has declined significantly over the past month, as the fourth wave abated and vaccination levels continued to improve, albeit at a slower rate. As of Wednesday afternoon, for instance, the state had averaged 345 new cases each day over the previous seven days. That’s the lowest average since Sept. 13. The average positivity rate stands at just 2.3%, which is the lowest level ever during the pandemic.

Even hospitalizations, which have proved to be the most stubborn metric to improve this spring, have improved of late. There are a total of 372 confirmed and suspected COVID-19 patients currently hospitalized in Colorado. That’s down from a recent peak of 731 on May 8 and 601 on May 26. 

The other explanation is that the state changed its definition of outbreaks earlier this month. Now, the state counts outbreaks at five or more confirmed cases in a facility or non-household group within 14 days. The previous definition of outbreaks – two or more cases – still stands for residential car facilities. 

The definition change didn’t result in outbreaks with fewer cases being deemed resolved; if the clusters pre-dated the change, they will still be counted as active outbreaks until they resolve, said Jessica Bralish, the director of communications for the state Department of Public Health and Environment.

But the change will mean fewer outbreaks will be reported each week.

“We updated the definitions on June 1 to better reflect the risk of COVID-19 in a variety of settings across Colorado,” Bralish said in an email.

The number of K-12 outbreaks climbed steadily during the fourth wave and became a dominant cause of clusters. But they’ve fallen off dramatically of late. As of Wednesday, there were 118 listed as active, some of which date back to 2020. That’s down from 157 reported on June 9, 205 on June 2 and 258 on May 5. 

There are fewer outbreaks in nursing homes, assisted-living facilities, restaurants and child care centers, among other declines.