Prevalence and Characteristics of qacA/B-positive Methicillin-resistant Staphylococcus aureus (MRSA) Bloodstream Infection Isolates in a Tertiary Hospital

Abstract

BackgroundThe increasing use of chlorhexidine (CHG) for MRSA decolonization has raised concerns about the emergence of resistance or tolerance to these agents.MethodsWe evaluated the frequency and characteristics of qacA/B chlorhexidine tolerance genes among MRSA bloodstream infection (BSI) isolates at a tertiary hospital in Korea. MRSA BSI isolates collected from 2011 to 2016 was examined for carriage of qacA/B and smr genes and high-level mupirocin resistance. Staphylococcal cassette chromosome mec (SCCmec) and spa typing was also performed.ResultsOf the 203 MRSA BSI isolates, 57 (28.1%) were positive for qacA/B, 6 (3.0%) were positive for smr, and 15 (7.4%) were mupirocin resistant. Table 1 shows characteristics of qacA/B-positive vs. qacA/B-negative MRSA BSI. Patients with qacA/B-positive isolates were more often diagnosed with nosocomial BSI and catheter related BSI, but were less often diagnosed with bone and soft-tissue infections. The qacA/B-positive isolates were more often resistant to mupirocin, clindamycin, and ciprofloxacin and more often had a CHG MIC of >= 4mg/L. The qacA/B-positive isolates were more likely to belong to SCCmec II or III (84.2% vs. 38.5%, P < 0.001), which are common healthcare-associated (HA) MRSA strains in Korea. Most common spa types in qacA/B positive isolates were t2460 (64.9%) and t9353 (14.0%).ConclusionThe qacA/B carriage among MRSA BSI isolates are not uncommon in this study and showed the features of HA-MRSA BSI.Table 1.Characteristics of qacA/B-positive vs. qacA/B-negative MRSA BSI.Characteristics qacA/B (+) (n = 57) qacA/B (-) (n = 146) P Age, median years(IQR)72 (60–84)69 (56–75)0.062Nosocomial BSI44 (77.2)61 (41.8)< 0.001Catheter-related BSI35 (61.4)41 (28.1)< 0.001Primary BSI14 (24.6)38 (26.0)0.999Bone and soft-tissue infections4 (10.8)33 (22.6)0.009Pneumonia2 (3,5)12 (8.2)0.358Other infections2 (3.5)13 (8.9)0.242Clindamycin resistant56 (98.2)96 (65.8)<0.001Ciprofloxacin resistant56 (98.2)56 (38.4)<0.001Vancomycin MIC >= 2mg/L17 (29.8)26 (17.8)0.084Chlorhexidine MIC >= 4mg/L54 (94.7)50 (34.2)<0.001SCCmec II37 (64.9)39 (27.3)<0.001SCCmec III11 (19.3)16 (11.2)0.168SCCmec IV9 (15.8)88 (61.5)<0.00130 day mortality14 (24.6)35 (25.0)0.999Data are no. (%) of casesDisclosures All authors: No reported disclosures.