The health insurance company Anthem Blue Cross is coming under intense pressure for deciding to raise rates by as much as 39 percent for individual policyholders. Anthem is a California-based subsidiary of the health insurance giant WellPoint, which earned $2.7 billion in the last quarter of 2009. In a letter released Monday, Health and Human Services Secretary Kathleen Sebelius asked the company to explain the rate increase. She wrote, “These extraordinary increases are up to 15 times faster than inflation and threaten to make health care unaffordable for hundreds of thousands of Californians, many of whom are already struggling to make ends meet in a difficult economy.”