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.