Distribution And Risk Factors Of Nosocomial Meticillin Resistant Staphylococcus Aureus(MRSA) Infections

ObjectiveTo investigate the prevalence and risk factors of meticillin-resistant Staphylococcusaureus (MRSA) among nosocomial infections, so as to provide a scientific referencefor developing inpatients prevention and treatment of MRSA nosocomial infections.MethodsThe MRSA infections, in the year of2012, were surveillianced in a Tertiaryhospital of Guangzhou. Both the MRSA and MSSA strains were tested forsusceptibility using Kirby-Bauer disc diffusion method. Two toxic genes, pvl and tst,were examined by PCR method. SCCmec typing, among MRSA isolates, was carriedout by multiplex PCR, and the products were sent to sequencing and its sequenceswere submitted to the GenBank database for comparison. The homology analysisbetween the SA strains was conducted by Pulsed Field Gel Electrophoresis (PFGE)typing. A non-matched case-control study was carried out for analysis of risk factorsand the MRSA patients and MSSA patients were enrolled as cases and controls. Inaddition, a1:2matched case-control study, matched for hospitals, gender, age (±5years) and dates of hospital admission time((±15days) was applied and MRSApatients and SA-negative patients were regarded as cases and controls. Data ofrelevant exposure factors was extracted by self-made questionnaire. Univariate andmultivariate analysises were using nonconditonal logitistic regression model fornon-matched case-control study and conditional logistic regression model for1:2matched case-control study.Results1.Sample Size:57MRSA infectors,116MSSA infestors and114non-infectedpatients were enrolled in the study.2.Susceptibility profile:The antimicrobial resistant results showed that all of the tested antibiotics, except for vancomycin and linezolid. MRSA resistance rates of18kinds of antimicrobial agents were: PEN (100.00%),OXA(100.0%),AMP(100.0%)＞ERY(92.98%)＞LEV(85.96%)＞AMC(82.46%),CZO(82.46%),IMP(82.46%)＞TCY(78.95%)＞CIP(77.19%)＞QDA (73.68%)＞GEN(66.67%)＞SXT(26.32%)＞CHL (24.56%)＞VAN(0.0%), LNZ (0.0%).3.Virulence genes:MRSA strains carrying pvl was5.26%(3/57), MSSA strainscarrying pvl was18.97%(22/116), two rate difference was statistically significant (P=0.016); MRSA strains tst carrier rate8.77%(5/57), MSSA strains carrying tst was4.31%(5/116), the two rates was no significant difference (P=0.237).4.SCCmec typing:57strains of MRSA SCCmec genotyping of case: the detection11strains SCCmec type Ⅱ,21strains SCCmec Ⅲ type,9strains SCCmec Ⅳ typeand14strains SCCmec Ⅴ type, the two MRSA strains can not detect; according toSCCmec typing judgment55MRSA containing HA-MRSA32strain andCA-MRSA23strain.5.PFGE typing:The57MRSA and116MSSA strains were classified into13and32clusters at the level of80%in Dice ratio, respectively.2MRSA strains were found100%similarity,no MSSA strains were found100%similarity.6.Risk factors: Univariate analysis of risk factors for MRSA bacteraemia usingMSSA bacteraemia controls show that older(≥65year)(OR﹦3.215,95%CI:1.607－6.430),having more than three times of hospitalization(OR﹦3.747,95%CI:1.912－7.343),ICU treatment history(OR﹦3.313,95%CI:1.189－9.230), antibioticsuse(OR﹦2.639,95%CI:1.289－5.401), β-lactamase inhibitor(OR﹦5.309,95%CI:1.747－16.134),cardiovascular and cerebrovascular diseases (OR﹦6.943,95%CI:3.338－14.443), COPD(OR﹦8.273,95%CI:2.558－26.752), suctioned(OR﹦3.096,95%CI:1.396-6.866), mechanical ventilation(OR﹦5.920,95%CI:1.972－17.772),drainage tube(OR﹦5.056,95%CI:2.262－11.298), catheter(OR﹦2.310,95%CI:1.130－4.722), nasogastric feeding tube(OR﹦2.553,95%CI:1.220－5.341)andarteriovenous cannula (OR﹦3.378,95%CI:1.583－7.209); Having cardiovascular andcerebrovascular diseases (OR﹦5.817,95%CI:2.290－14.774) and COPD(OR﹦4.924,95%CI:1.149－21.093) were the risk factors of MRSA infections whencompared with MSSA patients. While, having more than three times of hospitalization(OR﹦2.212,95%CI:1.099－4.453), ICU treatment history(OR﹦4.853,95%CI:1.294－18.201), suctioned(OR﹦7.446,95%CI:2.481-22.344),mechanical ventilation(OR﹦4.000,95%CI:1.383－11.566), tracheostomy/intubation (OR﹦8.293,95%CI:1.777 －38.692),drainage tube(OR﹦3.281,95%CI:1.559－6.908) and catheterization(OR﹦5.074,95%CI:1.998－12.882). Having more than three times of hospitalization(OR﹦2.273,95%CI:1.065－4.849）are independent risk factors of MRSA when comparedwith those non-infected.ConclusionsNo vancomycin and linezolid resistant strains were detected. While, other drugresistant and multidrug resistant strains were founded. In the hospital, both PVL andtst genes were uncommon. CA-MRSA and HA-MRSA strains were coexistence innosocomial infections. which demonstrates that the the strains were spread in sporadicmethod.