Epidemiological And Etiological Characteristics Of Methicillin-Resistant Staphylococcus Aureus Infections

Methicillin-resistant Staphylococcus aureus(MRSA) is a major pathogen capable of causing nosocomial and community infection and difficult to treat for the feature of multi-drug resistant. With the widespread transmission in the world, MRSA strains had caused outbreak of epidemic and brought serious economic losses and adverse effects to the communities.To understand the variability in the molecular and clinical features of MRSA in Shenzhen, we implemented a study at nine sentinel hospitals in 2014. MRSA infections were classified, according to epidemiological information and standard epidemiological definitions established by U.S. Centers for Disease Control and Prevention(CDC). Epidemiological information was analyzed and real-time PCR methods were established to analyze the isolates for the presence of virulence genes, such as pvl and sixteen enterotoxin genes(sea-see and seg-seq). Genotypic analysis included SCCmec typing, spa typing, agr typing, MLST and PFGE.In 2014, a total of 107,406 clinical specimens were cultured for bacteria at the 9 sentinel hospitals, of which 812(0.8%) were identified as MRSA. Of these 812 strains, we excluded 527 colonizing MRSA strains isolated from sputum or throat swab samples of the patients. We also excluded another 102 MRSA strains due to incomplete demographic and clinical information. In the end, a total of 183 MRSA infections and 26 MRSA colonization were included into this study. The group of MRSA infection and colonization was comprised of CA-MRSA infections(33.5%), HA-MRSA infections(21.5%), HACO-MRSA infections(32.5%) and MRSA colonization(12.4%). Demographic characteristics showed that the median age of patients infected with HA-MRSA was older than the other two categories. The clinical characteristics in CA, HA, and HACO-MRSA were different, and CA-MRSA was most frequently involved in SSTI(52.9%); HA-MRSA was most frequently identified from respiratory tract(22.2%), surgical site(20.0%) and traumatic wound infections(20.0%), while MRSA colonization was most frequently identified from respiratory tract infections(57.7%); HACO-MRSA strains were most commonly isolated from patients infected with mastitis(47.1%). Etiological characteristics was different from the early studies, but CA-MRSA, HA-MRSA, HACO-MRSA and MRSA colonization showed no significant difference, and the major clone was CC59-t437-SCCmec IV/V-agr I-USA1000?Our findings suggest that CA-MRSA, HA-MRSA, HACO-MRSA and MRSA colonization share the same major molecular characteristic but differ by demographic and clinical characteristics; the predominant clone is CC59-t437-SCCmec IV/V-agr I-USA1000.We speculate that this phenomenon was caused by strain transmission and genetic feature. High-risk patients and healthcare personnel in high-risk departments, as department of general surgery, internal medicine, mastitis, orthopaedics and intensive care units, should be considered as part of prevention efforts to reduce MRSA transmission in the future.