Ward-specific clustering of methicillin-resistant Staphylococcus aureus spa-type t037 and t045 in two hospitals in South Africa: 2013 to 2017

Methicillin-resistant Staphylococcus aureus (MRSA) is a highly clonal pathogen causing bacteraemia in various settings. The aim of the study was to determine if the MRSA isolates with the same spa-type originating from two hospitals in South Africa were genetically-related. Staphylococcus aureus isolated from blood cultures were submitted to CHARM as part of the GERMS-SA surveillance program. The identified MRSA isolates underwent further molecular characterization (SCCmec and spa-typing). Isolates with the same spa-type underwent PFGE. Twenty-one MRSA isolates were selected for WGS. Eighteen percent (n=95/529) and 33% (n=234/710) of isolates submitted from Gauteng and the Western Cape were methicillin-resistant, respectively. Spa-type t037 (23.5%, n=55/234) and t045 (23.1%, n=54/234) were the dominant spa-types in the Western Cape and were associated with SCCmec type III and I, respectively. Spa-type t037 (43.2%; n=41/95) were the predominant spa-type in Gauteng and were associated with SCCmec type III. The Gauteng (GAU)-t037-MRSA-III cases (73.2%; n=30/41) occurred in three different paediatric wards, whereas the Western Cape (WC)-t037-MRSA-III cases (69%, n=38/55) occurred in the adult surgical ICU and burns unit. The WC-t045-MRSA-I cases (72.2%; n=39/54) occurred in four different paediatric wards. PFGE showed that the GAU- and WC-t037-MRSA-III isolates, as well as the WC-t045-MRSA-I isolates, were almost genetically indistinguishable. WGS showed that the Vienna/Hungarian/Brazilian clone (ST239-MRSA-III) (WC- and GAU-t037-MRSA-III) and British EMRSA-3 clone (ST5-MRSA-I) (WC-t045-MRSA-I) were in circulation and a low frequency of SNP differences was observed among isolates with the same spa-type in similar wards.