Nearly half of all new COVID-19 cases in Colorado have a telltale genetic marker of the omicron variant, a top state health official said Wednesday, the latest sign of the strain’s escalating presence here.

Positivity and case rates in Colorado have turned upward again, after weeks of declines. They’re still far below the peaks of early and mid-November, however. In Eagle and Pitkin counties, where omicron is already making its presence known, rates have shot upward; in Eagle alone, the positivity rate is 30%, a health official said Wednesday.

Statewide, nearly 10% of all positive cases last week were a result of omicron. As of a couple of days ago, 45% of all positive samples sequenced in the state lab had a genetic marker for omicron, state epidemiologist Rachel Herlihy told reporters Wednesday.

“We could infer that potentially half of what we’re seeing in the state, at least as of a couple of days ago, was potentially — or is potentially — the omicron variant,” she said.

She added that the strain had been identified in all 21 wastewater systems, scattered across the state, that health officials monitor for signs of what diseases are circulating within certain communities.

“At this point we believe that omicron is widespread across the state,” Herlihy continued, “and there is likely local transmission occurring in many of our communities, if not most of our communities, now.”

Put more simply by Beth Carlton, epidemiologist with the Colorado School of Public Health: “This variant spreads like wildfire.” It’s moving faster than the delta variant, she continued, which emerged here in early summer and has for months accounted for nearly every case in the state. Omicron is expected to displace it in the coming days and weeks, officials said this week.

The standard two-dose vaccines of Pfizer and Moderna have diminished protection against omicron, Herlihy said, emphasizing the need for booster dose uptake. Additional doses have been shown to give more protection against infection and severe disease and death from omicron. Information on where you can get inoculated, including locations of mass vaccination sites, can be found on the state’s website.

Leaders in Eagle County, where the per-100,000 incidence rate has more than tripled in the span of a week, instituted a mask order Wednesday that went into effect immediately. The state has sent an additional vaccine team to the area to support uptake, and it’s also deployed 18 nurses to Eagle County to help with staffing at the local hospital. Testing capabilities have been strained there, officials said, and are also receiving state support.

Summit County officials said in a statement Tuesday that omicron is likely to blame for a “drastic” surge in cases and testing there. Nearby Pitkin County has seen a similarly “huge spike” in the last seven days, said deputy county manager Phylis Mattice.

She said the state Department of Public Health and Environment had taken almost two weeks to confirm a sample as having the omicron variant present.

“Of course it’s going to be here,” she said of omicron. “It’s the beginning of the season, and you’ve got people coming from everywhere.”

There have been mixed signals about how severe omicron is, Herlihy told reporters. But even if the strain is less severe, its ability to spread rapidly would still strain hospitals. Heath Harmon, who leads Eagle County Public Health, told officials there Wednesday morning that even if omicron is 50% less severe than delta, but is twice as transmissible, “it’s a wash.”

“Even if this virus is one-tenth the strength of delta,” added Chris Lindley, the chief population officer for Vail Health, “looking at the numbers we have today, there’s no question we’ll be operating at the highest capacity in our hospital that we’ve ever operated.”

Carlton, of the Colorado School of Public Health, said it’s still unclear if omicron is more severe than other variants.

“Early evidence is that it might be less virulent,” she wrote in an email. “But, to be clear, we saw increases in COVID hospitalizations in South Africa following the growth of Omicron, and are now seeing increases in hospitalization in the U.K. A highly infectious variant that is less virulent can still strain our hospital capacity.”

Though the numbers are starting to trend back up, Carlton said every day of improvement in hospitalizations is critical now.

“Every day that we see declines in COVID hospital demand and in cases, puts us in a better position to respond to Omicron,” she wrote, adding that Colorado is in a different position than other areas of the country. “Hospitalizations are declining and Omicron is a little more slow to arrive here. That means we have a little more time to prepare: get people vaccinated and boosted, get surge testing capacity in place, underscore the urgency of masking.”

But, she added, “it’s only a matter of days before Omicron is here in full force in Colorado.”