WASHINGTON — Hospital employees recognize and report only one out of seven errors, accidents and other events that harm Medicare patients while they are hospitalized, federal investigators say in a new report.

Yet even after hospitals investigate preventable injuries and infections that have been reported, they rarely change their practices to prevent repetition of the “adverse events,” according to the study, from Daniel R. Levinson, inspector general of the Department of Health and Human Services.

In the report, being issued on Friday, Mr. Levinson notes that as a condition of being paid under Medicare, hospitals are to “track medical errors and adverse patient events, analyze their causes” and improve care.

Nearly all hospitals have some type of system for employees to inform hospital managers of adverse events, defined as significant harm experienced by patients as a result of medical care.