Quantifying Hospital-Acquired Carriage of Extended-Spectrum Beta-Lactamase-Producing Enterobacteriaceae Among Patients in Dutch Hospitals

BACKGROUND

Extended-spectrum β-lactamase–producing Enterobacteriaceae (ESBL-E) are emerging worldwide. Contact precautions are recommended for known ESBL-E carriers to control the spread of ESBL-E within hospitals.

OBJECTIVE

This study quantified the acquisition of ESBL-E rectal carriage among patients in Dutch hospitals, given the application of contact precautions.

METHODS

Data were used from 2 cluster-randomized studies on isolation strategies for ESBL-E: (1) the SoM study, performed in 14 Dutch hospitals from 2011 through 2014 and (2) the R-GNOSIS study, for which data were limited to those collected in a Dutch hospital in 2014. Perianal cultures were obtained, either during ward-based prevalence surveys (SoM), or at admission and twice weekly thereafter (R-GNOSIS). In both studies, contact precautions were applied to all known ESBL-E carriers. Estimates for acquisition of ESBL-E were based on the results of admission and discharge cultures from patients hospitalized for more than 2 days (both studies) and a Markov chain Monte Carlo (MCMC) model, applied to all patients hospitalized (R-GNOSIS).

RESULTS

The absolute risk of acquisition of ESBL-E rectal carriage ranged from 2.4% to 2.9% with an ESBL-E acquisition rate of 2.8 to 3.8 acquisitions per 1,000 patient days. In addition, 28% of acquisitions were attributable to patient-dependent transmission, and the per-admission reproduction number was 0.06.

CONCLUSIONS

The low ESBL-E acquisition rate in this study demonstrates that it is possible to control the nosocomial transmission of ESBL in a low-endemic, non-ICU setting whereEscherichia coliis the most prevalent ESBL-E and standard and contact precautions are applied for known ESBL-E carriers.

TRIAL REGISTRATION

Nederlands Trialregister, NTR2799,http://www.trialregister.nl/trialreg/admin/rctview.asp?TC=2799; ISRCTN Registry, ISRCTN57648070,http://www.isrctn.com/ISRCTN57648070

Infect Control Hosp Epidemiol2018;39:32–39

Whole-Genome Multilocus Sequence Typing of Extended-Spectrum-Beta-Lactamase-Producing Enterobacteriaceae

Molecular typing has become indispensable in the detection of nosocomial transmission of bacterial pathogens and the identification of sources and routes of transmission in outbreak settings, but current methods are labor-intensive, are difficult to standardize, or have limited resolution. Whole-genome multilocus sequence typing (wgMLST) has emerged as a whole-genome sequencing (WGS)-based gene-by-gene typing method that may overcome these limitations and has been applied successfully for several species in outbreak settings. In this study, genus-, genetic-complex-, and species-specific wgMLST schemes were developed for Citrobacter spp., the Enterobacter cloacae complex, Escherichia coli, Klebsiella oxytoca, and Klebsiella pneumoniae and used to type a national collection of 1,798 extended-spectrum-beta-lactamase-producing Enterobacteriaceae (ESBL-E) isolates obtained from patients in Dutch hospitals. Genus-, genetic-complex-, and species-specific thresholds for genetic distance that accurately distinguish between epidemiologically related and unrelated isolates were defined for Citrobacter spp., the E. cloacae complex, E. coli, and K. pneumoniae wgMLST was shown to have higher discriminatory power and typeability than in silico MLST. In conclusion, the wgMLST schemes developed in this study facilitate high-resolution WGS-based typing of the most prevalent ESBL-producing species in clinical practice and may contribute to further elucidation of the complex epidemiology of antimicrobial-resistant Enterobacteriaceae wgMLST opens up possibilities for the creation of a Web-accessible database for the global surveillance of ESBL-producing bacterial clones.

Rectal Carriage of Extended-Spectrum-Beta-Lactamase-Producing Enterobacteriaceae in Hospitalized Patients: Selective Preenrichment Increases Yield of Screening

This study evaluated the added value of selective preenrichment for the detection of rectal carriage of extended-spectrum-beta-lactamase-producing Enterobacteriaceae (ESBL-E). ESBL-E rectal carriage was identified in 4.8% of hospitalized patients, and 25.9% of ESBL-E rectal carriers were identified with selective preenrichment only.

Impact of contact isolation for multidrug-resistant organisms on the occurrence of medical errors and adverse events

Contact isolation of infected or colonised hospitalised patients is instrumental to interrupting multidrug-resistant organism (MDRO) cross-transmission. Many studies suggest an increased rate of adverse events associated with isolation. We aimed to compare isolated to non-isolated patients in intensive care units (ICUs) for the occurrence of adverse events and medical errors.

METHODS

We used the large database of the Iatroref III study that included consecutive patients from three ICUs to compare the occurrence of pre-defined medical errors and adverse events among isolated vs. non-isolated patients. A subdistribution hazard regression model with careful adjustment on confounding factors was used to assess the effect of patient isolation on the occurrence of medical errors and adverse events.

RESULTS

Two centres of the Iatroref III study were eligible, an 18-bed and a 10-bed ICU (nurse-to-bed ratio 2.8 and 2.5, respectively), with a total of 1,221 patients. After exclusion of the neutropenic and graft transplant patients, a total of 170 isolated patients were compared to 980 non-isolated patients. Errors in insulin administration and anticoagulant prescription were more frequent in isolated patients. Adverse events such as hypo- or hyperglycaemia, thromboembolic events, haemorrhage, and MDRO ventilator-associated pneumonia (VAP) were also more frequent with isolation. After careful adjustment of confounders, errors in anticoagulant prescription [subdistribution hazard ratio (sHR) = 1.7, p = 0.04], hypoglycaemia (sHR = 1.5, p = 0.01), hyperglycaemia (sHR = 1.5, p = 0.004), and MDRO VAP (sHR = 2.1, p = 0.001) remain more frequent in isolated patients.

CONCLUSION

Contact isolation of ICU patients is associated with an increased rate of some medical errors and adverse events, including non-infectious ones.

Secular trends in nosocomial bloodstream infections: antibiotic-resistant bacteria increase the total burden of infection

BACKGROUND

It is unknown whether rising incidence rates of nosocomial bloodstream infections (BSIs) caused by antibiotic-resistant bacteria (ARB) replace antibiotic-susceptible bacteria (ASB), leaving the total BSI rate unaffected.

METHODS

We investigated temporal trends in annual incidence densities (events per 100 000 patient-days) of nosocomial BSIs caused by methicillin-resistant Staphylococcus aureus (MRSA), ARB other than MRSA, and ASB in 7 ARB-endemic and 7 ARB-nonendemic hospitals between 1998 and 2007.

RESULTS

33 130 nosocomial BSIs (14% caused by ARB) yielded 36 679 microorganisms. From 1998 to 2007, the MRSA incidence density increased from 0.2 to 0.7 (annual increase, 22%) in ARB-nonendemic hospitals, and from 3.1 to 11.7 (annual increase, 10%) in ARB-endemic hospitals (P = .2), increasing the incidence density difference between ARB-endemic and ARB-nonendemic hospitals from 2.9 to 11.0. The non-MRSA ARB incidence density increased from 2.8 to 4.1 (annual increase, 5%) in ARB-nonendemic hospitals, and from 1.5 to 17.4 (annual increase, 22%) in ARB-endemic hospitals (P < .001), changing the incidence density difference from -1.3 to 13.3. Trends in ASB incidence densities were similar in both groups (P = .7). With annual increases of 3.8% and 5.4% of all nosocomial BSIs in ARB-nonendemic and ARB-endemic hospitals, respectively (P < .001), the overall incidence density difference of 3.8 increased to 24.4.

CONCLUSIONS

Increased nosocomial BSI rates due to ARB occur in addition to infections caused by ASB, increasing the total burden of disease. Hospitals with high ARB infection rates in 2005 had an excess burden of BSI of 20.6 per 100 000 patient-days in a 10-year period, mainly caused by infections with ARB.

Genome-wide identification of ampicillin resistance determinants in Enterococcus faecium

Enterococcus faecium has become a nosocomial pathogen of major importance, causing infections that are difficult to treat owing to its multi-drug resistance. In particular, resistance to the β-lactam antibiotic ampicillin has become ubiquitous among clinical isolates. Mutations in the low-affinity penicillin binding protein PBP5 have previously been shown to be important for ampicillin resistance in E. faecium, but the existence of additional resistance determinants has been suggested. Here, we constructed a high-density transposon mutant library in E. faecium and developed a transposon mutant tracking approach termed Microarray-based Transposon Mapping (M-TraM), leading to the identification of a compendium of E. faecium genes that contribute to ampicillin resistance. These genes are part of the core genome of E. faecium, indicating a high potential for E. faecium to evolve towards β-lactam resistance. To validate the M-TraM results, we adapted a Cre-lox recombination system to construct targeted, markerless mutants in E. faecium. We confirmed the role of four genes in ampicillin resistance by the generation of targeted mutants and further characterized these mutants regarding their resistance to lysozyme. The results revealed that ddcP, a gene predicted to encode a low-molecular-weight penicillin binding protein with D-alanyl-D-alanine carboxypeptidase activity, was essential for high-level ampicillin resistance. Furthermore, deletion of ddcP sensitized E. faecium to lysozyme and abolished membrane-associated D,D-carboxypeptidase activity. This study has led to the development of a broadly applicable platform for functional genomic-based studies in E. faecium, and it provides a new perspective on the genetic basis of ampicillin resistance in this organism.

Enterococcus faecium has emerged as an important nosocomial pathogen around the world. Clinical E. faecium isolates are often resistant to multiple antibiotics, thereby complicating therapeutic interventions. However, the molecular mechanisms that contribute to the recent emergence of E. faecium as a nosocomial pathogen of major importance are only poorly understood, which is, at least partially, due to the lack of appropriate genetic tools for the study of this organism. Here, we developed a systematic genome-wide strategy, based on transposon mutagenesis and microarray-based screening, to identify E. faecium genes that contribute to ampicillin resistance. We also adapted the Cre-lox recombination system to construct targeted, markerless mutants in E. faecium. These tools enabled us to perform both high-throughput genome-wide analysis and specific targeted investigations in a clinical E. faecium isolate. We comprehensively identified, confirmed, and characterized a compendium of genes affecting the sensitivity to ampicillin in E. faecium. The identified intrinsic ampicillin resistance determinants are highly conserved among E. faecium, indicating that this organism has a high potential to evolve towards ampicillin resistance. These ampicillin-resistance determinants may serve as targets for the development of novel antimicrobial therapeutics.

Incidence densities in a competing events analysis

Epidemiologists often study the incidence density (ID; also known as incidence rate), which is the number of observed events divided by population-time at risk. Its computational simplicity makes it attractive in applications, but a common concern is that the ID is misleading if the underlying hazard is not constant in time. Another difficulty arises if competing events are present, which seems to have attracted less attention in the literature. However, there are situations in which the presence of competing events obscures the analysis more than nonconstant hazards do. The authors illustrate such a situation using data on infectious complications in patients receiving stem cell transplants, showing that a certain transplant type reduces the infection ID but eventually increases the cumulative infection probability because of its effect on the competing event. The authors investigate the extent to which IDs allow for a reasonable analysis of competing events. They suggest a simple multistate-type graphic based on IDs, which immediately displays the competing event situation. The authors also suggest a more formal summary analysis in terms of a best approximating effect on the cumulative event probability, considering another data example of US women infected with human immunodeficiency virus. Competing events and even more complex event patterns may be adequately addressed with the suggested methodology.

Diagnostic techniques in bloodstream infections: where are we going?

Rapid and early detection of bacteria in blood has an important role in the diagnosis of a febrile patient for at least three reasons: to establish the presence of an infection, to reassure the clinician about the chosen empirical therapy and to define antibiotic treatment after isolation of the microorganism and determination of its antibiotic susceptibility. We all agree that blood culture is the gold standard for aetiological diagnosis. However, it has limitations: the time required for bacteria to multiply to a detectable number of cells, the inadequate sensitivity of blood culture for fastidious pathogens and in patients who have previously received antibiotics, or when there is a catheter-related bloodstream infection. We must, however, remember that the current blood culture data constitute an important epidemiological tool on which clinicians can base empirical therapy. Over the past few years many new molecular tests have been developed that are now entering mainstream practice. These tests are more rapid, specific and sensitive; however, there are still some problems: antibiotic susceptibility testing is still lacking, and sometimes they are so sensitive that a skilled operator may be necessary for an accurate interpretation of the results. These new methods are promising, and their performance can only get better as they are increasingly used in clinical microbiological laboratories.

Transition of Enterococcus faecium from commensal organism to nosocomial pathogen

The Gram-positive species Enterococcus faecium has long been thought of as a harmless commensal of the mammalian GI tract. In the last two decades, however, E. faecium has become an important cause of nosocomial bacteremias. These infections are often difficult to treat owing to the resistance of E. faecium to a large number of antibiotics. In this article, we review the recent transition of E. faecium from commensal to nosocomial pathogen. We focus on population biology-based studies, which suggest that several clonal populations of E. faecium are mostly responsible for causing infections. We also discuss the role of the accessory genome of E. faecium in contributing to the infectious phenotype and examine the role that surface proteins of E. faecium may have in colonization and infection.

SgrA, a nidogen-binding LPXTG surface adhesin implicated in biofilm formation, and EcbA, a collagen binding MSCRAMM, are two novel adhesins of hospital-acquired Enterococcus faecium

Hospital-acquired Enterococcus faecium isolates responsible for nosocomial outbreaks and invasive infections are enriched in the orf2351 and orf2430 genes, encoding the SgrA and EcbA LPXTG-like cell wall-anchored proteins, respectively. These two surface proteins were characterized to gain insight into their function, since they may have favored the rapid emergence of this nosocomial pathogen. We are the first to identify a surface adhesin among bacteria (SgrA) that binds to the extracellular matrix molecules nidogen 1 and nidogen 2, which are constituents of the basal lamina. EcbA is a novel E. faecium MSCRAMM (microbial surface component recognizing adhesive matrix molecules) that binds to collagen type V. In addition, both SgrA and EcbA bound to fibrinogen; however, SgrA targeted the alpha and beta chains, whereas EcbA bound to the gamma chain of fibrinogen. An E. faecium sgrA insertion mutant displayed reduced binding to both nidogens and fibrinogen. SgrA did not mediate binding of E. faecium cells to biotic materials, such as human intestinal epithelial cells, human bladder cells, and kidney cells, while this LPXTG surface adhesin is implicated in E. faecium biofilm formation. The acm and scm genes, encoding two other E. faecium MSCRAMMs, were expressed at the mRNA level together with sgrA during all phases of growth, whereas ecbA was expressed only in exponential and late exponential phase, suggesting orchestrated expression of these adhesins. Expression of these surface proteins, which bind to extracellular matrix proteins and are involved in biofilm formation (SgrA), may contribute to the pathogenesis of hospital-acquired E. faecium infections.