FAIRFIELD -- Partnership HealthPlan of California will expand into Lake County, giving the nonprofit managed Medi-Cal plan a foothold in all six North Bay counties and more than 200,000 enrollees throughout Northern California.

The Fairfield-based health plan has seen significant growth over the past two years and could grow further still as provisions of the Affordable Care Act are implemented in coming years, particularly expansion of eligibility for Medicaid and Medi-Cal.

The addition of Lake County will add roughly 18,000 Medi-Cal enrollees out of a total patient population of 64,000, according to spokesman Dave McCallum. Partnership's plan there will go live in on June 1, 2013.

Currently, the health plan contracts with Solano, Yolo, Napa, Marin, Sonoma and Mendocino county government agencies. Partnership’s reimbursement to physicians includes a fee-for-service payment, capitation and additional incentives for taking on Medi-Cal recipients, versus a predetermined, non-negotiable state reimbursement. The plan contracts with just about every major provider -- from Kaiser Permanente to Sutter Health -- and with most private practices.

The health plan is also eying additional counties to the north, possibly expanding into Humboldt, Trinity, Shasta and other counties, particularly as the state looks to eliminate a number of health programs that will be shifted to Medi-Cal rather than remain stand-alone programs, such as Healthy Families.

Some advocates of such programs oppose that transition, noting that reimbursement rates may be less and patients may have to switch doctors. But, Mr. McCallum said, if Partnership HealthPlan or other similar plans take over for the counties, the managed Medi-Cal will provide for better integration and essentially create medical homes, versus the more disparate current Medi-Cal system.

Partnership HealthPlan is one of six not-for-profit county-organized health systems operating in the state.

"Our primary focus is to get all Medi-Cal recipients to choose a primary care provider, or 'medical home,'" Mr. McCallum said. "In addition to our managed care model being able to contract more physicians and ensure better overall care for our members, it's an exciting time of change in the way we deliver health care in this country."

As a result of the growth, the health plan expects to double its 300-person workforce over the next two years, according to Mr. McCallum.

Already, the health plan is outgrowing its current space in the former Copart building in Fairfield. The new employees will be based in Santa Rosa, where Partnership HealthPlan shares offices with the Sonoma County Department of Health and Human Services, and Fairfield. As much as 20 percent of the workforce will telecommute from the rural Northern California counties.

Another office may open in Redding, depending on expansion to the north, according to Mr. McCallum.

Mr. McCallum noted the challenge with coordinating with providers and patients in rural counties, but said that outreach efforts will continue.

"Lots of challenges, sure, but we work well with the state, our medial partners, community stakeholders and our members," Mr. McCallum said.