Nov. 24 (Bloomberg) — A "culture of increased transparency" is needed at the U.S. Health and Human Services Department, Secretary Sylvia Mathews Burwell said, after Obamacare enrollment data were padded with dental plan customers in what she has called an error.

The mistake was "unacceptable," Burwell said in a memo sent to her senior managers this week, obtained by Bloomberg News. As an first step, she told them to convene meetings with staff to solicit suggestions to increase "transparency, ownership and accountability" at the 77,000- employee agency she runs.

The number of people signed up for health insurance is a key measure of success for the Patient Protection and Affordable Care Act. The health department acknowledged Nov. 20 that it had double-counted about 393,000 people in dental plans when it announced that 7.3 million Americans were enrolled in August. Enrollment was revised downward as a result, to 6.9 million in August and 6.7 million in October.