Adverse events during hospitalization: results of a patient survey.

Background: A two-stage probability sample of patients recently discharged from 16 general acute care hospitals in Massachusetts were interviewed to determine the rates at which patients experience what they considered to be adverse events, to describe the kinds of events they reported, and to identify the correlates of those reports.
Methods: Eligible respondents were adults, 18 years of age or older, who were medical or surgical patients overnight or longer between April 1 and October 1, 2003, and who were discharged to their homes in Massachusetts. Questions covered perceptions of adverse events during hospitalizations and possible correlates of those events. Telephone interviews were carried out an average of nine months after discharge with 2,582 patients (response rate, 53%-60%).
Results: Twenty-nine percent of respondents reported at least one unexpected "negative" event during their hospitalization. After physician review, the revised estimate was that 25% perceived that they had experienced at least one event that met our definition for an adverse event. The most common reported events were reactions to newly prescribed drugs (40%) and the effects of surgery (34%). Physician reviewers coded 57% of the adverse events as "significant" and 18% as "serious" or "life-threatening." The physician reviewers also rated 31% of the reported adverse events as likely to be preventable.
Discussion: The estimate that one in four hospital patients experienced an adverse event is considerably higher than the published rates based on hospital record review, indicating the potential value of surveys for studies of patient safety. Because of nonresponse among older patients, that estimate is probably an underestimate. Designs that would reduce lags between discharge and interviews and decrease hospital nonresponses would reduce two key threats to confidence in the survey results.