There have been four COVID-19 outbreaks in Colorado churches in two weeks, with Garfield County experiencing at least 22 positive cases, CPR reports.

The transmission largely occurred before Gov. Jared Polis issued a statewide face covering mandate on July 16. The cases in Garfield County involved insufficient distancing and masking. Both churches, Iglesia de Dios Pentacostal and Iglesia Misionera Pentecostes casa del pan de vida, also allowed group singing.

“Singing releases smaller infectious particles that can hang in the air and circulate in enclosed spaces, and the risk increases when there are large numbers of people indoors,” the Colorado Department of Public Health and Environment told CPR. “Our guidance related to houses of worship strongly discourages choirs and singing by parishioners.”

Other cases of COVID-19 occurred among employees at Springs Journey Church in Colorado Springs and at The Heights Church in Denver. Corbin Hobbs, a pastor at The Heights Church, explained that the cases related to his facility were not the result of worship services, which have been virtual since March.

The danger of crowded worship services became more stark when Ohio revealed that a single man who went to church while COVID-19 positive was responsible for more than 90 infections. The transmissions occurred in June, CNN reports, before Ohio’s governor issued a mask mandate. The man infected 56 people at the church, and 18 of them spread the virus to others.

This article has been updated to include comments from Corbin Hobbs.