In its first month since getting state approval for expansion last fall, Sacramento-based HMO Western Health Advantage said it has enrolled some 750 persons into new employer health plans across Sonoma, Marin and Napa counties.

The new enrollees are spread across about 20 employer groups, with the majority -- about 400 -- coming from Sonoma Valley Hospital, according to Rick Heron, chief marketing and brand officer of Western Health.

So far, the HMO views that as positive growth and expects to add more employers and individuals at a steady clip through 2013.

"We're pretty pleased with that," Mr. Heron said, considering how early it is since the product has been available to employers.  "It's gotten a great response from brokers and agents in the region, and we're constantly quoting new business." Western Health began marketing the product during 2012 enrollment season late last year.

While the 750 new enrollees are from employer-sponsored groups, Western Health does anticipate on drawing a good deal of its North Bay business from the individual market, where it hopes to capitalize on the California Health Benefit Exchange, or Covered California, that is the result of health care reform.

"From here, it's a constant sales effort," Mr. Heron said. "A lot of WHA's efforts are on the exchange. We just completed the exchange bid -- the solicitation of qualified health plans -- this week, so a lot of our focus is there."

The HMO filed and obtained approval for an expansion into the North Bay counties last fall, forming a network around the Meritage Medical Network and most of the area's hospitals, except Sutter Health and Kaiser Permanente facilities.

In its initial application with the California Department of Managed Health Care, Western Health listed Marin General and Santa Rosa Memorial hospitals as potential subscriber groups to the plan. Both facilities are in the HMO's provider network, Sonoma Valley, Palm Drive, Healdsburg District and Petaluma Valley, which like Memorial is operated by St. Joseph Health.  The Annadel Medical Group, also affiliated with St. Joseph Health, is also part of the provider network.

Also in the initial state application were projections of how many members Western Health anticipated enrolling, estimating that it could add some 3,900 new enrollees. That estimate was before the HMO amended its initial filing to include Napa County. Initially, only Marin and Sonoma counties were included.

The arrival of Western Health is viewed by many as a critical point for the region's providers, particularly independent district hospitals that  have  struggled for their share of insured patients without a viable health plan for employer groups. Brokers and providers also hope that the injection of new competition into the region might lead to lower cost increases on employer premiums, which have spiked as the cost of health care steadily increased.