WASHINGTON — Hospitals and regulators fail to record at least 90 percent of patient injuries, infections, and other safety issues, a study found.

A review uncovered 354 so-called adverse events, such as pressure sores, bloodstream infections, and medication errors, at three teaching hospitals. A system designed by the federal Agency for Healthcare Research and Quality identified 35 cases at the same facilities while the hospitals’ voluntary reporting programs found four, according to the study, published in the journal Health Affairs.

An incomplete picture of how often patients are harmed undermines public and private efforts to improve the quality of medical services in the United States, David Classen, a professor at the University of Utah School of Medicine in Salt Lake City, and his coauthors conclude.

Voluntary reporting by hospital operators and the US-sanctioned method for tracking adverse events failed to provide accurate insights into the safety of US hospitals, the study found. The report doesn’t disclose the names of the hospitals because of confidentiality agreements.

Adverse events occurred during one-third of admissions at the hospitals, according to the researchers. Classen and his colleagues studied 795 patient records using the Cambridge, Mass.-based Institute for Healthcare Improvement’s Global Trigger Tool. The institute’s method involves reviews of patient charts by nurses, pharmacists, and physicians. The researchers didn’t try to establish whether the harm could have been prevented.

Efforts to track patient safety intensified after a 1999 report by the Institute of Medicine found that medical errors caused as many as 98,000 deaths and more than 1 million injuries each year.

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