The American Medical Association finds a sharp drop in competition in the U.S. health insurance business.

In the combined HMO and PPO markets, 95% of metropolitan areas have few competing health insurers, according to the AMA, Chicago.

In 95% of markets, a single insurer had 30% or more of the business, the physician group says, and in 56% of markets, a lone insurer had 50% or more of the business.

Between 1995 and 2005, there were more than 400 mergers involving health insurers and managed care organizations, the AMA notes.

Near monopolies don’t help patients, asserts AMA board member James Rohack.

“Health insurers are posting historically high profit margins, yet patient health insurance premiums continue to rise without an expansion of benefits,” he says.