Characterisation of staphylococcus aureus bacteraemia at Tygerberg hospital

Abstract

To elucidate the local epidemiology of Staphylococcus aureus bacteraemia, we characterised blood culture isolates using molecular methods and prospectively collected clinical data to determine the occurrence of community-acquired, methicillin-resistant S. aureus (MRSA). Consecutive S. aureus blood culture isolates were collected over a one-year period from patients who were admitted to Tygerberg Academic Hospital in the Western Cape. A multiplex polymerase chain reaction (PCR) was used for the detection of spa, mecA and lukS/F-PV genes. Strain typing was performed using spa typing. Multiplex PCR for staphylococcal cassette chromosome mec (SCCmec) typing was also performed, as well as multilocus sequence typing (MLST) on selected isolates. Cases were categorised by clinical data as either hospital-acquired, healthcare-associated or community-acquired. One hundred and thirteen S. aureus isolates (30% MRSA) were collected from 104 cases of bacteraemia. According to clinical data, all community-acquired infections, 54% of hospital-acquired cases and the majority of healthcare-associated cases were due to methicillin-sensitive S. aureus (MSSA). Furthermore, all Panton-Valentine leukocidin (PVL)-positive isolates (15.9% of all S. aureus) were MSSA. MRSA strains were isolated from hospital-acquired cases (with a minority of healthcare-associated cases) and clustered mainly in spa-CC701 and CC012. SCCmec type IV was predominant. MLST clones included ST239-MRSAIII, ST36-MRSA-II and ST612-MRSA-IV. The predominant source for S. aureus bacteraemia was catheter-related infection (39%). Community-acquired S. aureus infections in our setting remain sensitive to methicillin and current treatment guidelines suffice. The majority of hospital-acquired and healthcare-associated infections were catheter-related. Prevention and treatment should be targeted accordingly.