Characteristics of USA500/Iberian Methicillin-Resistant Staphylococcus aureus (MRSA) Invasive Disease
Methods: Population-based surveillance for invasive MRSA disease was conducted in the 8-county metropolitan Atlanta area from 1-1-2005 to 12-31-2011 through the Active Bacterial Core surveillance program of the Georgia Emerging Infections Program. Isolates were typed by pulse-field gel electrophoresis (PFGE) and/or screened for SCCmec (SM) types II and IV and categorized as non-USA300 with SM IV, USA300, USA100 or other. SM IV isolates were subtyped and spa typed; clonal complex (CC) was inferred by spa type. CC8, non-USA300 that were SM IV but not IVa, were classified as USA500/Iberian. Medical records were reviewed.
Results: Among a total of 2,006 invasive MRSA infections, 36% were due to USA300, 31% USA 100, 27% (540/2,006) USA500/Iberian, and 7% other. Most invasive USA500/Iberian cases (99%) were bacteremias. Clinical syndromes included: bacteremia without focus (38%), central line-associated bloodstream infection (24%), pneumonia/empyema (12%), skin and soft tissue (9%), urinary tract (9%), bone or joint infections (7%), and endocarditis (3%). Most were healthcare-associated community-onset (72%), in men (63%) of black race (73%); 24% were in persons with HIV/AIDS. Trimethoprim-sulfamethoxazole resistance was high (97%). In-hospital mortality was 21% (110/532) for USA500/Iberian, compared to 21% (126/608) for USA100 and 14% (98/712) for USA300. On multivariable analysis, invasive USA500/Iberian infections had similar risk of in-hospital mortality as USA300 (aOR 1.34; 95% CI 0.96 – 1.87) and USA100 (aOR 0.97; 95% CI 0.70 – 1.35).
Conclusion: USA500/Iberian MRSA was a common cause of invasive disease in Atlanta. The association with healthcare exposure, HIV/AIDS and trimethoprim-sulfamethoxazole resistance was strong. In-hospital mortality for invasive USA500/Iberian MRSA infections was similar to USA100 and USA300 after adjusting for confounders.
A. G. Melendez,
E. K. Crispell, None
M. M. Farley, None