Skip to main content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it's official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you're on a federal government site.


The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Adverse Events in Hospitals: A Quarter of Medicare Patients Experienced Harm in October 2018


In 2010, OIG reported the first national incidence rate of patient harm events in hospitals—27 percent of hospitalized Medicare patients experienced harm in October 2008. During that month, hospital care associated with these events cost Medicare and patients an estimated $324 million in reimbursement, coinsurance, and deductible payments. Nearly half of these events were preventable.

OIG conducted a new study to update the national incidence rate of patient harm events among hospitalized Medicare patients in October 2018. This work included calculating a new rate of preventable events and updating the cost of patient harm to the Medicare program.

The Department of Health and Human Services (HHS) leads national efforts to promote quality health care and prevent patient harm. Several agencies share this responsibility, including AHRQ, which leads HHS's efforts to improve health care quality, and CMS, which is the Nation's largest health care payer and oversight entity.

Although HHS agencies have reported progress during the past decade toward improving patient safety, protecting the health and safety of HHS beneficiaries remains one of HHS's top management and performance challenges. An increased understanding of the prevalence and nature of patient harm will further assist efforts to reduce patient harm events and the factors contributing to these events.


We reviewed medical records for a random sample of 770 Medicare patients who were discharged from acute-care hospitals during October 2018. We conducted a two-stage medical record review to estimate a national incidence rate of adverse events and temporary harm events. Our review included all causes of patient harm regardless of whether the harm was preventable.

Stage 1: Nurses screened the records for possible patient harm events using a "trigger tool" method. A "trigger" is a clinical clue (e.g., documentation of a fall) that may indicate harm. From the Medicare claims data, nurses also reviewed present-on-admission indicators to identify harm that developed after the patient was admitted. We automatically referred records to Stage 2 when patients were readmitted within 30 days of discharge, regardless of whether the nurse identified harm (these include readmissions in October and November).

Stage 2: Physicians reviewed the records flagged during Stage 1 as containing possible harm events. Physician-reviewers identified harm events and assessed the severity of events, whether events were preventable, and factors that contributed to events.

We calculated the potential cost incurred by Medicare and patients as a result of these events. We also determined whether events were on CMS's lists of hospital-acquired conditions. Finally, we compared the results of this report to our 2010 report and explained the limitations of this comparison.


Twenty-five percent of Medicare patients experienced patient harm during their hospital stays in October 2018. Patient harm includes adverse events and temporary harm events.

Twelve percent of patients experienced adverse events, which are events that led to longer hospital stays, permanent harm, life-saving intervention, or death. In addition to the patients who experienced adverse events, 13 percent of patients experienced temporary harm events, which required intervention but did not cause lasting harm, prolong hospital stays, or require life-sustaining measures. Temporary harm events were sometimes serious and could have caused further harm if providers had not promptly treated patients.


Given the scale and persistence of patient harm in hospitals in the decade since our last report, HHS leadership and agencies must work with urgency to reduce patient harm in hospitals. Although HHS agencies took steps to improve patient safety in hospitals, including implementing many of our prior recommendations, substantial efforts are still needed. We made seven recommendations and received concurrences from CMS and AHRQ on all: