B. M. WILLEY, G. RUZO, B. SHOPSIN, B. N. KREISWIRTH, A. FAMIGLIETTI, C. VAY, A. McGEER, D. E. LOW.

Mount Sinai Hospital, University of Toronto, Toronto, Ontario, Canada; Nuestra Senora De Lujan and Hospital de Clinicas, Buenos Aires, Argentina; and PHRI, New York, New York, US.

Background: MRSA rates in the province of Ontario (ON) increased from <500 cases/year prior to 1995 to 8610 in 1998. In 1996, Argentina reported 65% of hospital/clinical S. aureus to be MRSA. This study determined the genetic relationship between MRSA identified in the two countries.

Methods: 56 MRSA from Buenos Aires (BA) (14/1995, 2/1996, 21/1997, 19/1998) were compared to 1083 ON strains (289/1996, 557/1997, 237/1998) using SmaI pulsed field typing (PFGE). All BA and 92 ON MRSA were sub-typed by computerized alignment of proteinA gene repeat sequences (SPA).

Results: PFGE identified 4 major clones: 160 isolates of clone A (143 ON, 17 BA), 142 clone B (109 ON, 33 BA), 784 clone C (all ON), 35 clone D (32 ON, 3 BA), and 18 of other/uncertain clonality (15 ON, 3 BA). The 92 ON MRSA SPA typed included 12/clone A, 25/B, 69/C, 12/D, and 7 of uncertain type. SPA confirmed the PFGE clonal delineation and further divided these clones. PFGE clone A was divisible into 8 SPA types (4 ON, 5 BA); B into 10 types (7 ON, 5 BA); C into 4 types (4 ON only), D into 7 types (4 ON, 3 BA). SPA types 2 (PFGE clone A), 3 and 33 (both clone B) were found among ON and BA MRSA. These SPA types predominated among clones A and B in both countries, and were observed at a constant rate between 1995 and 1998. SPA typing confirmed clone C to be newly emergent in ON and associated with the provinces dramatic increase in MRSA cases. This clone was not found among BA MRSA.

Conclusions: Characterization of MRSA from ON and BA using two validated molecular methods has elucidated the global nature of their dissemination and demonstrated the existence of only a limited number of distinct epidemic clones.

Presented at:

Abstract submitted to the 9th International Congress on Infectious Diseases, Buenos Aires, Argentina, April 10-13, 2000