As many as 31 million Americans now receive healthcare through an accountable care organization (ACO), according to a recent report from industry consulting firm Oliver Wyman.

The report, “The ACO Surprise,” contends that while many believe that ACOs have had little impact on the market to date, the sheer numbers of patients getting healthcare via an ACO tells a different story.

In its analysis, Oliver Wyman researchers determined that about 2.4 million Medicare beneficiaries were receiving care via the different Medicare ACO programs run by the Centers for Medicare & Medicaid Services; another 15 million non-Medicare patients received care at these Medicare ACOs; and 8 million to 14 million are part of ACOs run by large national and regional insurers for their non-Medicare populations.

In total, the research indicates that nearly 45 percent of the population live in a primary care service area (PCSA) served by at least one ACO, and 17 percent live in a PCSA that is served by two or more, a number that is likely to rapidly increase in the coming years, according Richard Weil, co-author of the report.

“What we found is that when an ACO shows up in a market it changes the way other providers in the market think about their ACO strategy,” Weil said. “In a competitive market, when an ACO shows up other competitors feel like they need to become ACOs as well.”

And, Weil noted, the competition for primary care doctors that has been occurring for the past few years is likely to intensify as more PCSAs have multiple ACO competitors.

“Patients are going to be attributed to primary care physicians and primary care physicians have to chose one, and only one, ACO – they can’t be a part of more than one ACO,” Weil said.

Oliver Wyman researchers found a significant number of patients in ACOs, even when eliminating for the purposes of this study organizations that are doing such things as piloting bundled payments since they are not population-based programs, or those that receive pay-for-performance and care coordination payments since they are not value-based programs. That said, they still provide a significant caveat to the state of the ACO market. Namely, even those included in the study still fall short of being a “true” ACO, one that shares both upside and downside risk.

“Of the 89 providers approved as ACOs in the most recent round, only five are taking on both upside and downside risk. The remaining 84 could simply tweak their current models, run as predominantly fee-for-service enterprises, and hope for the best,” the report stated. “If they create any savings, they get to share in them; if not, there’s no penalty. And it has to be acknowledged that though many ACOs have made progress in transforming their clinical processes, incentive models, and data tools and infrastructure, almost none have transformed all of them.”

But that shouldn’t be a surprise Weil added, as organizations that have embarked on this path have found the process of transforming their current delivery systems to be a much larger task than many have anticipated.

“The actual costs to get these programs up and running and to be successful are bigger than people think – and it’s not just technology,” Weil said. “Yes, you are going to spend a lot of money on technology, but when you talk about this being a transformative change to the way that your clinical enterprise works, as well as how you are paid and how your business works, means there is this one-time outlay of change management and business process changes. People are underestimating how much work there is there and how critical it is to their success.”