Health insurer stocks dropped sharply on Wednesday after UnitedHealth Group (UNH.N) said costs were on the rise for the largest U.S. healthcare provider by market value due to an increase in surgeries among older adults.

Shares of industry bellwether UnitedHealth fell 7.3% to $455.11, wiping out roughly $42 billion from the company’s market capitalization in the current trading session.

Medicare-focused insurer Humana Inc (HUM.N) fell 14%, and a broader index of managed care providers (.SPLRCHMO) lost 8%, hitting a 17-month low in Wednesday’s trading.