Despite the efforts to improve patient safety, medical errors and unavoidable mistakes in US hospitals have not improved over time, according to a six-year study involving ten North Carolina hospitals.

The study, conducted between 2002 and 2007, tracked medical errors in the hospitals by analysing data from more than 2,341 randomly selected admissions in the ten hospitals.

Researchers looked for mistakes including the presence of bedsores, readmissions within 30 days and medication dosage mistakes.

The study results showed that harm to the patients as a result of medical errors was common and the number of incidents did not decrease over the study period.

There were about 588 instances of patient harm such as surgical errors, medical dosage mistakes, hospital-acquired infections. Among them, 50 were life-threatening, 17 caused permanent problems and 14 resulted in death.