PVL(+) MRSA causing infections in hospitalised patients

Abstract number: P650

Wong-Beringer A., Lee M., Yamaki J., Shriner K.

Objectives: Concerns for Panton-Valentine leukocidin (PVL) producing community-associated (CA) MRSA strains overtaking healthcare-associated (HA) infections and the potential for severe infections in association with PVL expression level have led us to determine 1) molecular epidemiology, 2) disease spectrum, and 3) correlation of disease severity with PVL gene expression level in hospitalised patients infected with PVL(+) MRSA strains.

Methods: 186 MRSA isolates obtained from patients during 7/05–6/07 were saved for molecular characterisation while medical charts of patients were reviewed for relevant demographic, laboratory, and clinical data. We screened all isolates for the presence of lukS-F gene by PVL Evigene® test (AdvanDx, Woburn, MA: a qualitative nucleic acid hybridisation assay for research use only). Using published protocols, PCR typing for SCCmec types (I-IV), USA300;ST8 and PVL transcripts by reverse transcriptase-PCR using SYBR green with primer specific for lukF gene were performed on a subset of strains. MRSA NRS384 (PVL(+) USA300;ST8, SCCmec IVa) and NRS22 (PVL(-), USA600;ST45, SCCmec II) strains served as positive and negative controls respectively.

Results: PVL(+) strains caused 45% (83/186) of MRSA infections in hospitalised adults; 54% were HA per clinical criteria. 96% of PVL(+) strains (52/54) belong to USA300 and 85% (46/54) carried SCCmec type IV cassette. CA-infections were 92% cellulitis +/- abscess plus 1 necrotising fasciitis. HA-infections were more likely to be invasive (pneumonia, bacteraemia) than CA (53% vs 5%, p < 0.05), with 60% from nursing home residents. Patients with HA compared to CA infections were older (mean age: 68 vs 48y, p < 0.0001) with higher APACHE II score (12.3 vs 3.4, p < 0.0001). Of the PVL(+) isolates tested (n = 61), pvl transcript levels ranged from 0 to 8.9 fold higher than control strain. When grouped based on level of pvl gene expression, strains with 2-fold higher mRNA levels vs 0–2 fold relative to control strain were more frequently CA (57% vs 43%) and less likely to cause invasive infections (43% vs 55%) such as pneumonia (7% vs 32%).

Conclusion: Over half of the USA300, SCCmec IV, PVL(+) strains caused healthcare rather than community-associated MRSA infections in adults, with the predominant place of acquisition in the nursing home. PVL expression levels vary widely among clinical isolates; high PVL expression levels do not predict invasive disease.

Session Details

Date: 19/04/2008
Time: 00:00-00:00
Session name: 18th European Congress of Clinical Microbiology and Infectious Diseases
Location: Barcelona, Spain
Presentation type:
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