Determining risk factors for methicillin-resistant Staphylococcus aureus carriage after discharge from hospital.

At the University Medical Center, Utrecht, methicillin-resistant Staphylococcus aureus (MRSA) patients are considered lifelong MRSA carriers and potentially contagious when readmitted. The purpose of this study was to determine whether patients who become MRSA carriers while in hospital remain colonized after discharge, and whether risk factors for prolonged carriage exist. Thirty-six patients colonized with MRSA during three outbreaks at University Medical Center, Utrecht (group I: 1986-1989), and twenty patients already colonized with MRSA on, or during, admission to the hospital (group II: 1990-1995) were screened for MRSA in two studies. The patients had been discharged from the hospital for periods varying from 15 days to 4.6 years. MRSA was found in five (9%). Four of these patients had skin lesions (wounds), one with an external fixture. The presence of skin- and underlying diseases differed significantly between carriers and non-carriers, supporting the hypothesis that wounds are a major risk factor for long-term MRSA carriage. This study led us to revise our policy concerning readmission of former MRSA patients. We now consider that patients who contracted MRSA in the past no longer need isolation if the following two criteria are met. Absence for at least six months of open wounds, skin lesions, tracheostomy, infections and sources of infection such as abscesses and furuncles, orthopaedic implants, drains, catheters, or tubes. Three MRSA-negative sets of swabs from nose, throat, perineum, urine, and sputum taken at least one hour apart after this six-month period.