Enhanced surveillance of Staphylococcus aureus at Gauteng Academic Hospitals

Abstract

Background: Bloodstream infections (BSI) are significant cause of mortality in patients worldwide. Among Gram-positive bacteria, Staphylococcus aureus (SA) is the most common pathogen that expresses virulence factors, develops resistance to antimicrobial agents and is prevalent in the hospital and the community settings. These features explain the need to monitor and report SA trends and patterns of antimicrobial resistance. We aimed to determine the characteristics of S. aureus bacteremia cases during one year study period and to describe the proportion of methicillin-susceptible Staphylococcus aureus (MSSA) and methicillin-resistant Staphylococcus aureus (MRSA) cases by site. Methods & Materials: The surveillance was based on a cross- sectional study design. Bacteraemia cases were reported through an active, enhanced antimicrobial resistance surveillance programme and SA was initiated in September 2012. The data for a one year period was analyzed. Susceptibility testing was performed on MicroScan® using PB28 panels for SA. We established MIC50 and MIC90 breakpoint values and the percentage of susceptibility. CLSI standards were applied for susceptibility breakpoints. We investigated the presence of β-lactamases and mecA genes by PCR. Molecular typing was done using conventional typing methods. Results: During the study period, a total of 307 SA isolates were recorded, equally from each site, of which 254 isolates were received. From susceptibility testing performed, 95 (37%) isolates were MRSA. The proportion of MRSA decreased from 47% in 2012 to 33% in 2013. The most prevalent SCCmec type identified was SCCmec type III (67%) followed by types IV (33%). Clinically, the outcome of patients with MRSA did worse 22 (42%) died (p = 0.0042), had a hospital stay longer than 21 days (p = 0.022) and received antimicrobial treatment two months prior to admission (p = 0.016) compared to patients with MSSA. Empirical treatment of MRSA bacteraemia was appropriate in 24% of cases. Conclusion: There is a high percentage of MRSA at sentinel sites in Gauteng. The majority of isolates have been identified as SCCmec typeIII. A greater proportion of patients with MRSA had received previous antimicrobial agents and had a longer duration of hospitals stay. Infection control measures and appropriate use of antimicrobial agents are critical for the prevention of MRSA.