Decreasing methicillin-resistant Staphylococcus aureus (MRSA) infections is attributable to the disappearance of predominant MRSA ST239 clones, Shanghai, 2008-2017

A consistently decreasing prevalence of MRSA infections in China has been reported, however, the underlying mechanism of molecular processes responsible for this decline in MRSA infections has been poorly understood. We conducted an epidemiologic investigation to determine the dynamic changes of Staphylococcus aureus infections. A total of 3695 S. aureus isolates was recovered from 2008 to 2017, and subsequently characterized by infection types, resistance profile, and clone types. The frequency of respiratory infection decreased over the study period from 76% to 52%. The proportion of MRSA remarkably decreased (from 83.5% to 54.2%, 2008-2017) (p < .0001). The prevalence of predominant healthcare-associated MRSA (HA-MRSA) clones, ST239-t030 and ST239-t037, significantly decreased (from 20.3% to 1% and 18.4% to 0.5%, 2008-2017, respectively); both of them were replaced by the continually growing ST5-t2460 clone (from 0% to 17.3%, 2008-2017). Epidemic community-acquired MRSA (CA-MRSA) ST59 and ST398 clones also increased (from 1.0% to 5.8% and 1.8% to 10.5%, 2008-2017, respectively). These results demonstrated a significant decrease in the previously dominant HA-MRSA ST239 clones, leading to a marked decrease in the prevalence of MRSA over the past decade, and shed new light on the complex competition of S. aureus clones predominating within the health-care environment.