Six million procedures a year are performed at outpatient surgical centers in the United States.

These centers are popular for minor surgery and other procedures that don't require a hospital stay.

Some of the centers are part of a hospital system. Others are not. And that is the problem, say experts like Dr. William Schaffner.

"They are not being regulated with anywhere near the thoroughness and completeness and frequency that large hospitals are," says Dr. Willaim Schaffner of the Vanderbilt Medical Center.

Little was known about infection control in these facilities. So, Dr. Melissa Schaefer at the U.S. Centers for Disease Control and other researchers, reviewed practices at 70 ambulatory surgical centers that were certified by the government.

"We found that, you know, two thirds or about 67 percent of facilities had a least one lapse in infection control," says Schaefer.

Nearly half were not sterilizing or disinfecting instruments correctly.

Almost 20 percent were careless in cleaning surfaces and operating areas after procedures.

Among the most serious: improper hand washing.  

Other lapses included improper handling of blood glucose monitoring equipment.

"Twenty-eight percent of facilities were using medications that are packaged and labeled for single patient use, for multiple patients," says Schaefer.

The study suggests mistakes in infection control may be extensive.

"With a large medical center or a large community hospital, I think there is greater assurance that their infection control procedures are indeed at a very high level," says Schaffner. "Beyond that, it's kind of difficult."

Experts say the risks are unacceptable. Some lawmakers are calling for tighter regulation of outpatient surgery centers.

The study was published in the Journal of the American Medical Association.