Only one in seven hospital errors that harm Medicare patients are reported by employees, federal investigators report.

Yet, in exchange for receiving money under Medicare, hospitals are required to track “adverse patient events” in an effort to identify their causes and improve patient care. Harmful events may include medication errors, bedsores, infections acquired while in the hospital.

Investigators estimate that more than 130,000 patients experience such adverse events in a single month.

“Despite the existence of incident reporting systems, hospital staff did not report most events that harmed Medicare beneficiaries,” said Daniel R. Levinson, inspector general of the Department of Health and Human Services.

Fear doesn’t seem to motivating the under-reporting, Levinson says. Rather, hospital employees don’t appear to recognize “what constitutes patient harm” or they assumed that someone else would report the incident.

In addition, Levinson reported, “hospitals made few changes to policies or practices” after reported incidents, saying that the errors did not reveal any systemic issues.