Prevalence and clinical prognosis of heteroresistant vancomycin-intermediate Staphylococcus aureus in a tertiary care center in China

Background The emergence of heteroresistant vancomycin-intermediate Staphylococcus aureus （hVISA） is increasingly challenging the methods for detection in diagnostic microbiology laboratories. However, the report of hVISA is rare in China. This study summarizes the prevalence and clinical features associated with hVISA infections at our institution and the local impact they have on clinical outcome. Methods A total of 122 methicillin-resistant Staphylococcus aureus （MRSA） isolates which were of the causative pathogens were collected. One hundred and two patients for whom we had full information of MRSA pneumonia were included. Isolates of MRSA were collected using PCR to detect the mecA gene. Both Etest and macro Etest were performed to screen for hVISA. The Staphylococcal chromosome cassette mec （SCCmec） types were determined by multiplex PCR strategy. Logistic regression analysis was used to determine the risk factors. Results Among the 122 MRSA isolates collected, 25 （20.5%） strains were identified as hVISA. There were 119 （97.5%） SCCmec III isolates, two （1.6%） SCCmec II isolates, and one （0.8%） SCCmec V isolate. The 30-day mortality of MRSA-hospital acquired pneumonia （HAP） was 37.3%, and 62.5% for hVISA-HAP. Vancomycin treatment was the independent risk factor of hVISA. Factors independently associated with 30-day mortality in all patients were acute physiology and Chronic Health Evaluation （APACHE） II score 〉20, multiple lobe lesions, and creatinine clearance rate （CCR） 〈15 ml/min. Conclusions The prevalence of hVISA is 20.5% at our institution, hVISA-HAP patients had a poor clinical outcome. Vancomycin treatment was the independent predictors for hVISA infection. Factors independently associated with 30-day mortality in all patients were APACHE II score 〉20, multiple lobe lesions and CCR 〈15 ml/min.

Treatment of methicillin-resistant Staphylococcus aureus infections:Importance of high vancomycin minumum inhibitory concentrations

Staphylococcus aureus(SA) infections remain a major cause of morbidity and mortality despite the availability of numerous effective anti-staphylococcal antibiotics.This organism is responsible for both nosocomial and community-acquired infections ranging from relatively minor skin and soft tissue infections to life-threateningsystemic infections.The increasing incidence of methicillin-resistant strains has granted an increasing use of vancomycin causing a covert progressive increase of its minimum inhibitory concentration(MIC)(dubbed the MIC "creep").In this way,the emergence of vancomycinintermediate SA(VISA) strains and heteroresistantVISA has raised concern for the scarcity of alternative treatment options.Equally alarming,though fortunately less frequent,is the emergence of vancomycin-resistant SA.These strains show different mechanisms of resistance but have similar problems in terms of therapeutic approach.Ultimately,various debate issues have arisen regarding the emergence of SA strains with a minimum inhibitory concentration sitting on the superior limit of the sensitivity range(i.e.,MIC = 2 μg/mL).These strains have shown certain resilience to vancomycin and a different clinical behaviour regardless of vancomycin use,both in methicillin-resistant SA and in methicillin-sensitive SA.The aim of this text is to revise the clinical impact and consequences of the emergence of reduced vancomycin susceptibility SA strains,and the different optimal treatment options known.