The four largest U.S. for-profit health insurers on average denied policies to one out of every seven applicants based on their prior medical history, according to a congressional investigation released Tuesday.

Two top House Democrats said the findings covered 2007 to 2009 for Aetna Inc., Humana Inc., UnitedHealth Group Inc. and WellPoint Inc. In total, the carriers denied coverage to more than 651,000 people due to pre-existing medical conditions over the three-year period.

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