Any injury caused by medical care.

Examples:

• pneumothorax from central venous catheter placement
• anaphylaxis to penicillin
• postoperative wound infection
• hospital-acquired delirium (or "sundowning") in elderly patients

Identifying something as an adverse event does not imply "error," "negligence," or poor quality care. It simply indicates that an undesirable clinical outcome resulted from some aspect of diagnosis or therapy, not an underlying disease process. Thus, pneumothorax from central venous catheter placement counts as an adverse event regardless of insertion technique. Similarly, postoperative wound infections count as adverse events even if the operation proceeded with optimal adherence to sterile procedures, the patient received appropriate antibiotic prophylaxis in the perioperative setting, and so on. (See also iatrogenic).