An international multicenter study of antimicrobial resistance and typing of hospital Staphylococcus aureus isolates from 21 laboratories in 19 countries or states

During 1996, 4065 consecutive Staphylococcus aureus strains from different patients were collected in 21 worldwide hospital laboratories. The strains, their resistance pattern, and hospital demographic data were forwarded to Statens Serum Institut where the strains were typed and data analyzed. Resistance patterns varied by region and resistance to other antibiotics than methicillin were mainly related to the occurrence of methicillin resistance, except for mupirocin, rifampicin, and fusidic acid. Methicillin-resistant S. aureus (MRSA) occurred with low levels in hospitals in Northern Europe (<1%), increasing levels in middle-European countries, United States, New Zealand, and Australia (6-22%), and very high levels in Southern European countries as well as in parts of the United States, Asia, and South Africa (28-63%). MRSA found in large hospitals were more resistant to other antibiotics than MRSA found in smaller hospitals serviced by the same laboratory. No difference in resistance levels was seen for methicillin-susceptible S. aureus (MSSA) isolated in large or small hospitals. Intensive Care Units had the highest level of MRSA. Strains from the lower respiratory tract showed the highest resistance levels and blood isolates the lowest. A dominating MRSA clone was found in hospitals with an MRSA frequency of more than 10%. Pulsed-field gel electrophoresis (PFGE) typing recognized several of these clones as international epidemic MRSA (E-MRSA). All MSSA isolates were phage typed (typeability 85.4%) and divided in seven major phage patterns. Isolates of all patterns were found in all hospitals except one, indicating that the MSSA seldom represented the spread of clones within the hospital. The comparison should evaluate the prevalence of community-acquired MRSA and identify internationally E-MRSA. The present study gives a snapshot of the MRSA situation, but it is important to build up a continuous national and international surveillance, because MRSA is a global socioeconomic problem. Global infection control procedures, including rational antibiotic use, should be agreed on. The accompanying paper will address the issue of antibiotic consumption and MRSA.