Analysis of A Nosocomial Methicillin-Resistant Staphylococcus aureus Outbreak by Using Arbitrarily-Primed Polymerase Chain Reaction (AP-PCR)

In the past decade, methicillin-resistant Staphylococcus aureus (MRSA) has become a major nosocomial pathogen, causing severe morbidity and mortality at many hospitals worldwide. Because of frequent nosocomial outbreaks of MRSA, this organism has been a focus of epidemiologic studies. Currently, there is no definitive typing system for distinguishing individual strains of MRSA. Most typing methods are based on either phenotypic or genotypic differences among MRSA strains. Arbitrarily primed-polymerase chain reaction (APPCR) is a technique for generation of characteristic fingerprints from complex genomic DNA. In this study, it was planned to identify the source of an MRSA outbreak in a surgical ward at Hacettepe University Hospital and to demonstrate the clonal relationship among MRSA isolates by using AP-PCR. In October 1995, an increase was noticed in the number of MRSA isolates from this surgical ward. All MRSA isolates obtained from clinical specimens of this ward were collected prospectively for 10 weeks (14 MRSA isolates from wound cultures of 10 patients). Surveillance cultures were taken from ward personnel (nose cultures fom 4 physicians, 7 nurses, 1 secretary, 1 waiter), 2 surgical dressing containers and nebulizer. MRSA was isolated from one of the surgical dressing containers, nebulizer and nose cultures of 3 physicians, 3 nurses and the secretary. AP-PCR analysis showed that most MRSA isolates belonged to 2 major clones (pattern A, pattern B). Pattern A was the most frequent one and was present in 4 clinical isolates and the surgical dressing container. Pattern B was identified in 3 clinical isolates and nose culture of a physician. Patterns closely resembling pattern A (pattern A’) and pattern B (pattern B’) were detected in a clinical isolate and nose culture of another physician; another clinical isolate and nose culture of a nurse, respectively . AP-PCR analysis revealed that this mini-MRSA outbreak was originated from the contamination of common container with MRSA and nasal MRSA carriage in ward staff