The analysis, published Dec. 19 in the journal Surgery, used malpractice records to find instances in which surgeons operated on the wrong patient or part of the body, or left objects inside the patient after surgery.

Compared to other medical errors, the rate of such of such mistakes in the United States is very low. Still, the study found doctors leave towels, cotton balls, sponges and other surgical equipment inside patients’ bodies about 39 times a week, on average. Doctors operate on the wrong body part 20 times a week and the wrong patient, also 20 times a week. …

The study’s findings likely underestimate the actual occurrence, however. “What we describe in a study is the low end of the range. There are definitely more of these occurring,” said study co-author Dr. Marty Makary, a surgeon at Johns Hopkins Medical Center and the author of a book about hospital dysfunction called “Unaccountable” (Bloomsbury Press, 2012).