The first COVID-19 cluster linked to the Colorado wildfires was reported Wednesday by the Colorado Department of Public Health and Environment.

Four firefighters have tested positive and 23 others have been exposed, according to Kris Eriksen, public information officer with the Portland National Incident Management Organization.

Three firefighters in the same engine tested positive for COVID-19 after fighting the Cameron Peak fire on Aug. 24 and 25. One remains in the hospital, while the other two were released from isolation Friday.

A fourth firefighter was tested Tuesday after complaining about respiratory issues. The test came back positive and the firefighter is self-isolating.

The fourth firefighter had been in close contact with at least 23 others, 19 being members of the firefighter’s crew and the other four being helpers. Those 23 were tested for COVID-19 on Thursday and are awaiting results in quarantine.

Eriksen said NIMO has taken drastic measures to prevent the spread of COVID-19 within the team.

“We’re doing everything we can,” Eriksen said.

Preventative measures include mandatory mask use and social distancing, separating staff from different units, focusing on smaller groups and using thermal imaging to check temperatures before entering the incident command post.