Clonotypes of Staphylococcus aureus isolated from continuous ambulatory peritoneal dialysis patients: what is the vector between nares and infection site?

Staphylococcus aureus is frequently isolated from patients with infections related to continuous ambulatory peritoneal dialysis (CAPD). In many cases, the organism is also isolated simultaneously from the anterior nares. To clarify the transmission trail of S. aureus, we used DNA analysis to identify clonotypes of clinical strains. The nares and exit sites of 32 CAPD patients were swabbed, and PD fluid samples were taken for pathogen culture. Genome DNA of S. aureus was digested with restriction enzyme Sma I for pulsed-field gel electrophoresis. We also asked the patients how they usually performed the PD procedure. S. aureus was isolated from 4 patients, including 3 who hosted two strains isolated separately from different sites. The DNA patterns of the strains isolated from these latter 3 patients were identical. However, the clonotypes from all 4 patients were different. Most of the patients did not wash their hands and wear masks while exchanging PD bags and caring for their exit sites. After the patients were disinfected and re-educated in proper procedures, S. aureus was not detected in any of them. These data suggest that no outbreak occurred in our hospital and that the vectors of endogenous infection were the patients themselves, probably their hands. A bacteriological study presents an efficient opportunity to re-educate patients in PD procedure.