NEW YORK_Fitch Ratings said Friday it is downgrading to a negative outlook for several health insurers, citing concerns over the potential impact of health care reform.

The new outlook covers Aetna Inc., Blue Cross Blue Shield of Florida, Blue Cross Blue Shield of Idaho Health Service Inc., Cigna Corp., Coventry Health Care Inc. and Health Care Service Corp.

The revision means Fitch holds a negative outlook for all 12 health insurers it covers. Negative outlooks remain for Health Insurance Plan of Greater New York, Health Net Inc., Healthmarkets Inc., Humana Inc., UnitedHealth Group Inc. and WellPoint Inc.

"The negative outlook reflects the strong potential for national health care reform and its possible adverse implications on each company's financial strength and creditworthiness," Fitch said, in s statement. "Though no bill has been finalized yet, and multiple policy schemes are possible, most of the alternatives being debated could weaken health insurers' financial profiles in Fitch's view."

One key concern expressed by insurers is the potential for a government health insurance plan taking customers, and revenue, away from private plans. President Obama hoped for Congressional action on a plan before the August recess, but Democrats have signaled that any bill will likely be delayed until after the recess.