Risk factors for community-onset bloodstream infection with extended-spectrum β-lactamase-producing Enterobacteriaceae: national population-based case-control study

OBJECTIVES

The aim was to investigate risk factors for community-onset bloodstream infections with extended-spectrum β-lactamase-producing Enterobacteriaceae (EPE BSI).

METHODS

It is mandatory to report EPE BSI to a national register at the Public Health Agency of Sweden. Using this register, we performed a population-based case-control study from 2007 to 2012 of 945 cases and 9390 controls. Exposure data on comorbidity, hospitalization, in- and outpatient antibiotic consumption and socio-economic status were collected from hospital and health registers.

RESULTS

The overall incidence of EPE BSI was 1.7 per 100 000 person-years. The 30-day mortality was 11.3%. Urological disorders inferred the highest EPE BSI risk, adjusted odds ratio (aOR) 4.32 (95% Confidence Interval (CI) 3.41-5.47), followed by immunological disorders, aOR 3.54 (CI 2.01-6.23), haematological malignancy, aOR 2.77 (CI 1.57-4.87), solid tumours, aOR 2.28 (1.76-2.94) and diabetes, aOR 2.03 (1.58-2.61). Consumption of fluoroquinolones or mostly non-EPE-active antibiotics with selective Gram-negative spectrum of activity within the previous 3 months was associated with EPE BSI, aORs 5.52 (CI 2.8-11.0) and 3.8, CI 1.9-7.7) respectively. There was a dose-response relationship in EPE BSI risk with increasing number of consecutive regimens. Antibiotic consumption >3 months before EPE BSI was not associated with increased risk. Higher age, malignancies and education ≤12 years (aORs >2) were associated with increased 30-day mortality.

CONCLUSIONS

Targeted interventions should be directed towards improving care for patients with immunosuppression, urological disorders and subjects with lower socio-economic status. Antibiotic stewardship should focus on reduction of fluoroquinolones.

Epidemiology of extended-spectrum β-lactamase-producing Escherichia coli in Sweden 2007-2011

Extended-spectrum β-lactamase (ESBL) -producing Enterobacteriaceae have been notifiable according to the Swedish Communicable Disease Act since 2007. A major increase in the number of cases has been observed, with 2099 cases in 2007 and 7225 cases in 2012. The majority of the isolates are Escherichia coli. Additionally, Swedish data on the prevalence of ESBL-producing invasive isolates of E. coli are available through EARS-Net, and through biannual point prevalence studies, where molecular characterization of isolates from the entire country is carried out. This paper describes major trends in the Swedish epidemiology of ESBL-producing E. coli in the period 2007-2012. Isolates from the point prevalence studies were subjected to antimicrobial susceptibility testing, ESBL genotyping, pulsed-field gel electrophoresis, multi-locus sequence typing and phylogenetic grouping with PCR. The distribution of sequence types, resistance genes and susceptibility levels were all stable over the three study periods. The dominating resistance gene conferring ESBL was blaCTX -M-15 , found in 54-58% of the isolates. ST131 represented 34-38% of the isolates. Other major sequence types were ST38, ST69, ST405, ST617 and ST648, each representing 2-6% of the isolates. Phylogenetic group B2 was the most common, and was observed in 41-47% of the isolates. However, among ST131 isolates the B2 phylogenetic group represented 90-98% of the isolates. The most important epidemiological difference seen over time was that the median age of infected women decreased from 62 to 52 years (p <0.0001) and infected men from 67 to 64 years. A potential explanation might be the shift towards a higher proportion of community-acquired infections in individuals lacking comorbidities.

Phenotypic detection of plasmid-acquired AmpC in Escherichia coli--evaluation of screening criteria and performance of two commercial methods for the phenotypic confirmation of AmpC production

The phenotypic detection of plasmid-acquired AmpC (pAmpC) in Escherichia coli is challenging, and molecular methods are required for confirmation. In addition to cefoxitin resistance, multiresistance and high-level resistance to cephalosporins have both been suggested as criteria for targeting isolates with pAmpC, but data to support these proposed criteria are lacking. A Swedish collection of 378 isolates with either putative chromosomal hyperproduction of AmpC (cAmpC) or pAmpC were subjected to disk diffusion and minimum inhibitory concentration (MIC) determination with the Etest. The frequency of resistance to gentamicin, ciprofloxacin, and trimethoprim among cAmpC and pAmpC was compared to elucidate the issue of multidrug resistance. Lastly, methods for the phenotypic confirmation of pAmpC were compared. One in-house disk diffusion method, one method employing NeoSensitabs (Rosco), and one Etest method (bioMérieux) were compared. The analysis of histograms based on both disk diffusion and the Etest showed that resistance [according to the European Committee on Antimicrobial Susceptibility Testing (EUCAST)] to cefotaxime and/or ceftazidime occurred in almost all isolates. By coining resistance instead of non-susceptibility, the number of isolates required to subject to phenotypic testing/genotypic confirmation dropped by more than 40 %, without compromising the sensitivity substantially. Further, almost 70 % of isolates with pAmpC were non-multidrug resistant, clearly indicating that this is an inappropriate criterion for further investigation. The phenotypic tests all had more than 90 % sensitivity, and the best sensitivities were obtained with the in-house method and with the ceftazidime ± cloxacillin NeoSensitab. In conclusion, clinical resistance to cefotaxime and/or ceftazidime seems to be an appropriate criterion for pAmpC screening, and several phenotypic methods perform well for the phenotypic confirmation of AmpC production prior to genotypic confirmation.