Community-acquired, non-multiresistant oxacillin-resistant Staphylococcus aureus (Norsa) in South Western Sydney

Community-acquired oxacillin-resistant Staphylococcus aureus (ORSA) infections are an emerging problem in the 1990s in Sydney, Australia. Laboratory data pertaining to all specimens that grew S. aureus between 1/1/1990 and 31/12/1999 were analysed. A total of 12,909 isolates of S. aureus were obtained. The proportions that were non-multiresistant oxacillin-resistant S. aureus (NORSA) increased from 0.09% in 1990 to 5.5% in 1999. Resistance of NORSA strains to erythromycin was 8.5%, ciprofloxacin 8.4%, tetracycline 13%, rifampicin 0.7%, and fusidic acid 5.3%. A chart review was performed for cases of NORSA infection which occurred 1/1/1998-3/5/1998. Isolates from these cases underwent E-test oxacillin MIC testing, mecA determinant PCR, phage typing and pulsed-field gel electrophoresis. All nine of the patients with NORSA were Polynesians, and all had serious soft tissue infections. Bacteraemia was not seen. Only one patient received vancomycin yet all recovered. Isolates from all nine patients contained the mecA determinant. Oxacillin MICs were 1-8mg/l. Strain differentiation with phage typing and pulsed-field gel electrophoresis showed isolates from eight patients were closely related and were similar to New Zealand WSPP1 and WSPP2 strains. Medical practitioners should take specimens for culture and sensitivity from lesions where infection with S. aureus is likely. Empirical treatment of staphylococcal infections in Polynesians needs to cover NORSA. Methods to detect oxacillin resistance need to be robust.