Methicillin-resistant Staphylococcal aureus evolution in Australia over 35 years.

Australia has a long association methicillin-resistant Staphylococcus aureus (MRSA). Its unique geographic and demographic features have led to the emergence and spread of three types of MRSA over 35 years. Classical multiresistant hospital-acquired MRSA were first noted in Australia in 1965. By the end of the 1970s, strains of this type of MRSA were well established in the complex tertiary care hospitals in the capital cities on the eastern seaboard of mainland Australia. Characterized by resistance to beta-lactams, erythromycin, tetracycline, gentamicin, and trimethoprim-sulfamethoxazole, these strains have persisted and diversified genetically and have acquired a variety of new resistances. They have proven pathogenicity and are a prominent cause of hospital infection in the endemic institutions. More recently they have become endemic in some central state tertiary care hospitals. Community-acquired strains of MRSA first appeared in the north of Western Australia in the mid-1980s. Strains have subsequently appeared in the south of the state and in the two adjacent central states, and are more frequently isolated from Aboriginal patients. Although harboring few or no additional resistances apart from resistance to beta-lactams initially, these strains are also accumulating additional resistances. A different variety of community-acquired MRSA has recently been noted in eastern Australia. It has a similar antibiogram to the western strains, but an entirely different epidemiology, resembling that currently being experienced in parts of New Zealand, and associated with patients of south Pacific island origin.