Major medical enrollment at the eight largest U.S. health insurers fell 2.5% at insured, “at risk” plans in 2009, a market data firm says.

“Administrative services only” enrollment at self-insured employers fell just 0.9%, but overall enrollment fell by 2.2 million people, according to Mark Farrah Associates, Kennebunk, Maine.

“The difficult economy continues to take a toll in terms of rising medical expenses and declining membership for most plans,” the firm says.