Colorado tied its own daily high of new COVID-19 cases earlier this week, clocking more than 900, and the count of deaths from the disease recently climbed above 2,000.

If a pair of rallies in Denver’s Civic Center park on Saturday contributed to the disease’s spread, the effects would be starting to manifest themselves now.

Photos from inside a “Patriot Muster” rally, published by Colorado Public Radio, show attendees standing in close quarters and few wearing face coverings. Most attendees at a counterprotest that took place the same afternoon, called a “BLM-Antifa Soup Drive,” wore face coverings, but social distancing was scarce at that event as well.

Spokesperson Tammy Vigil for the Denver Department of Public Health and Environment told The Denver Gazette in an emailed statement that any spread of COVID-19 as a result of attendance at the rallies would start to show up in communities between two and 14 days after exposure.

“We are always worried about COVID-19 spread when public health orders are not followed, as you mentioned: few face coverings, no social distancing, people shouting,” she said in the statement. “The fact it was outdoors is better than if it were inside.”

She did not immediately respond to a follow-up inquiry about the ability of contact tracing to track multiple infections back to a particular event.

Gov. Jared Polis in July put in place a statewide requirement for people to wear face coverings while in public indoor spaces and while using public or non-personal transportation, which he extended this month for another 30 days.

Lisa Miller, a medical doctor and professor of epidemiology at the Colorado School of Public Health, said while the risk of COVID-19 transmission is much lower outdoors than inside, said precautions such as mask wearing and social distancing are still relevant. 

“One way to think about it is to think about the worst possible situation outdoors. So what would be the most extreme, high-risk situation outdoors?” she said.

“And it would be one in which no one’s wearing a mask, people are densely compacted together, people are circulating around so you’re exposed to multiple people. … People are talking loudly or shouting or singing, and this occurs for a long period of time.”

In response to an inquiry from The Denver Gazette about whether the state is concerned attendance at last weekend’s rallies could lead to a rise in COVID-19 cases, the Colorado State Emergency Operations Center also provided a statement.

“In general, we are always concerned when people gather in large gatherings without masks or distancing. Mask wearing and physical distancing can greatly reduce the risk in these situations,” says the statement.

“It’s a good reminder that it shouldn’t be about what public health guidance we can skirt — it should be about what we can do to keep ourselves, our families, and our communities as safe as possible.”

It’s unknown how far from around Denver people traveled to attend Saturday’s rallies, but not everyone came from the area. An organizer of the Patriot Muster rally, John Tiegen, is from El Paso County.

State and local public health agencies in Colorado have worked to monitor the spread of COVID-19 through contact tracing, in which people known to have been infected are interviewed about their recent activity and people they have come in contact with are notified about their possible exposure.

But Miller said the ability to trace a person’s infection back to a particular event isn’t straightforward. People may not accurately remember every place they went and every person they came in contact with several days previously.

Contact tracing may not link together separate infections to make a pattern visible. 

She added social events are often related, meaning a person could have been exposed at several points: Someone might go to an outdoor festival and then go to a restaurant, for example.

“People often think that that’s an easy thing to do, but it’s actually very difficult to connect back to one specific event when you’re thinking about the long period of time may have been exposed and to pin it on one thing.”