Epidemiology of Enterococci with Acquired Resistance to Antibiotics in Sweden: Special emphasis on Ampicillin and Vancomycin

The first hospital outbreak of vancomycin-resistant enterococci (VRE) and carriage rates of VRE and ampicillin-resistant enterococci (ARE) in Sweden were investigated. Clonal relationships and mutations in fluoroquinolone resistance determining regions among ARE collected nation-wide were studied. Risk factors for ARE infection, shedding of ARE and the presence of the virulence gene esp in ARE isolates and patients on a hematology unit and other units at Uppsala University Hospital were further investigated. The first Swedish hospital VRE outbreak was due to clonal spread of E. faecium, vanA . The nation wide carriage rates of ARE and VRE were 21.5% / 1% and 6% / 0%, among hospitalized patients and non-hospitalized individuals respectively. All ARE and VRE were E. faecium and >90% resistant to ciprofloxacin. All VRE carried vanB . Carriage of ARE was independently associated with >5 days of antibiotic treatment. Phenotypic and genetic typing showed a significantly higher homogeneity among ARE compared to matched ASE E. faecium isolates. Mutations conferring high-level ciprofloxacin resistance were found only in ARE. Risk factors for ARE infection included long duration of hospital stay and exposure to antibiotics. Skin carriage was associated with ARE shedding. ARE bacteremia was independently associated with prior ARE colonization and hematopoietic stem cell transplantation. Death was more common in ARE septicemia cases compared to controls. Esp was significantly more common in ARE surveillance compared to ARE blood isolates from patients on the hematology ward. In conclusion, VRE were rare but clonally related multi-resistant ARE E. faecium were highly prevalent in Swedish hospitals. Spread of ARE in hospitals during the 1990s is suggested to be the main explanation for the emergence of ARE in Sweden. Spread was facilitated by use of antibiotics and probably by the presence of virulence genes in E. faecium isolates.