CHICAGO -- The nation's most influential health care regulator frequently serves the interests of the hospital industry over those of the public, giving its seal of approval to medical centers riddled by life-threatening problems and underreporting of patient deaths caused by infections and hospital errors.

The Joint Commission on Accreditation of Healthcare Organizations, based in Oakbrook Terrace, Ill., has been empowered by Congress to ensure the quality and safety of hospitals. Operating as a virtual monopoly for monitoring public health care, the commission promotes its surveys as an assurance that hospitals are clean, adequately staffed and provide superior care.

But the Chicago Tribune found the commission often fails in its role. Among the findings:

Less than 1 percent of hospitals failed to receive accreditation from the commission in the last 17 years, and some hospitals received high accreditation scores even in the midst of a public health crisis. In Florida this month, Palm Beach Gardens Medical Center retained its high accreditation ranking from the Joint Commission even after federal public health investigators swooped into the hospital and found that patients were in "immediate jeopardy" of harm because of infection-control deficiencies.

Hospital inspection dates are announced up to three months in advance, allowing medical centers to quickly upgrade conditions and obtain accreditation.

Using a voluntary system of reporting, the Joint Commission vastly underestimates the number of avoidable patient deaths.

Joint Commission officials said that the survey process is not flawless. "We have missed things," acknowledged the commission president, Dr. Dennis O'Leary. "These are fallible systems."

Michael J. Berens and Bruce Japsen are reporters for the Chicago Tribune, a Tribune Publishing newspaper.