Background: To control the spread of methicillin-resistant Staphylococcus aureus (MRSA) in hospitals, infection control measures such as hand hygiene practices were introduced into the teaching hospitals in Shanghai, China, in 2008. Currently, there is limited information characterizing the latest hospital-acquired S. aureus infections in this area. Therefore, we sought to determine the prevalence, molecular characteristics, and genotype-phenotype correlation of hospital-acquired S. aureus infections in Huashan Hospital, one of the largest teaching hospitals in Shanghai.
Results: Among 608 hospital-acquired S. aureus clinical isolates obtained from January to December of 2011 in Huashan Hospital, 68.1% were MRSA. The predominant MRSA clones were ST239-SCCmecIII and ST5-SCCmecII. ST239 was mainly recovered from respiratory specimens and sterile body fluids, ST5 was associated with respiratory specimens and blood, and ST1 was most prevalent in urine samples. In this study, 31 dispersed sequence types (STs) of methicillin-susceptible S. aureus (MSSA) were identified, most of which caused skin/soft tissue infection and bacteremia. The frequencies of pvl-, muPA-, and qacA/B-positive isolates were 1.6, 9.9, and 11.8% respectively. MuPA was more frequently identified in ST1 and ST5, and qacA/B was more prevalent in ST239 and ST5. Most of the pvl-positive isolates were MSSA, whereas the majority of muPA- and qacA/B-positive isolates were MRSA. ST239 and ST5 had higher resistance rates to multiple antibiotics. In Huashan Hospital, the infection rate in the intensive care unit (ICU) was 3.9 per 1000 hospitalized days, but only 1.2 per 1000 hospitalized days in the other wards. Each ward harbored its own dominant STs. Pulsed-field gel electrophoresis showed diversity within the same epidemic S. aureus clones originating from the same wards.
Conclusion: There is still a high prevalence of MRSA infections in the teaching hospital in Shanghai. There were also differences in the major infection types caused by MRSA and MSSA, and hospital-acquired S. aureus infections in the ICU of Huashan Hospital pose a greater threat to patient safety than in other wards. The high proportion of multiple antibiotic and chlorhexidine-based antiseptic-resistant clones in this hospital underscores the need for more effective infection control measures to help curtail dissemination of MRSA to hospitalized patients.