Abstract
BackgroundStaphylococcus aureus is one of most common pathogens in humans. Methicillin-resistant S. aureus (MRSA) accounts for 64 % of S. aureus bacteremia isolated in intensive care units (ICUs), and heteroresistant vancomycin-intermediates S. aureus (hVISA) is a phenotype of MRSA. However, studies focusing on the hVISA impact on critically ill patients are scarce.MethodsThis was a retrospective study conducted in a tertiary medical center from January 2009 to December 2010. All adult patients in ICUs with MRSA bloodstream infection were eligible. A modified population analysis profile and area under the curve method was applied to all isolates to confirm hVISA phenotype. Multilocus sequence typing (MLST), staphylococcal cassette chromosome mec (SCCmec) and the accessory gene regulator (agr) typing were performed individually. Clinical outcomes including in-hospital mortality, length of stay in intensive care unit and hospital after MRSA bacteremia of the patients were also analyzed.ResultsA total of 48 patients were enrolled and 14 patients were confirmed to have the hVISA phenotype. The prevalence of hVISA was 29.2 %. There was no difference in the age, sex, comorbidity, Charlson’s comorbidity score and previous vancomycin therapy between the hVISA and VSSA groups. The hVISA group had a significantly higher in-hospital mortality than the VSSA group (13/14 versus 22/34; p = 0.046). All of the 14 hVISA patients had an MIC = 2 mg/L by E-test and this represented a significant association between high MIC and the development of hVISA (p < 0.001). MLST analysis showed all the isolates in the hVISA group were ST239, while ST239 (14/34; 41.2 %) and ST5 (12/34; 35.3 %) were predominant in the VSSA group (p = 0.007). A comparison of the survivor and non-survivor group showed that the hVISA phenotype (OR 11.8; 95 % CI 1.1–126.99; p = 0.042) and sequential organ failure assessment (SOFA) score (OR 1.39; 95 % CI 1.07–1.81; p = 0.014) were independent factors significantly associated with in-hospital mortality.ConclusionsPatients in ICUs with MRSA bacteremia may have a higher in-hospital mortality if they have the hVISA phenotype. SOFA score is also predictor of mortality.
Highlights
Staphylococcus aureus is one of most common pathogens in humans
The sequential organ failure assessment (SOFA) score represented the severity of illness when Methicillin-resistant S. aureus (MRSA) bacteremia developed and there was no differentce between the heteroresistant vancomycin-intermediates S. aureus (hVISA) and vancomycin susceptible S. aureus (VSSA) groups
The primary site of infection was different among the two groups, and we were unable to located the origin of infection for 7 patients (50 %) in the hVISA group while pneumonia was predominant (18/34; 52.9 %) in the VSSA group
Summary
Methicillin-resistant S. aureus (MRSA) accounts for 64 % of S. aureus bacteremia isolated in intensive care units (ICUs), and heteroresistant vancomycin-intermediates S. aureus (hVISA) is a phenotype of MRSA. Methicillin-resistant S. aureus (MRSA) emerged several decades ago and is still a concern worldwide, especially in critical ill patients because of higher treatment costs and mortality rates [5]. Since heteroresistant vancomycin-intermediates S. aureus (hVISA) has been considered a phenotype of MRSA and has been reported throughout the world. These hVISA isolates are resistant subpopulations that are present in fully vancomycin susceptible S. aureus (VSSA) at a rate of 1 per 105–106 organisms [8, 9]. They are considered as the stage preceding the development of VISA and frequently occur in isolates with a minimum inhibitory concentration (MIC) within the susceptible range (≧2 mg/L by E-test) [10]
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