Dynamics of Hemodialysis Catheter Colonization by Coagulase-Negative Staphylococci

Formation of Single-Species and Multispecies Biofilm by Isolates from Septic Transfusion Reactions in Platelet Bag Model

During 2018-2021, eight septic transfusion reactions occurred from transfusion of platelet units contaminated with Acinetobacter spp., Staphylococcus saprophyticus, Leclercia adecarboxylata, or a combination of those environmental organisms. Whether biofilm formation contributed to evasion of bacterial risk mitigations, including bacterial culture, point-of-care testing, or pathogen-reduction technology, is unclear. We designed a 12-well plate-based method to evaluate environmental determinants of single-species and multispecies biofilm formation in platelets. We evaluated bacteria isolated from septic transfusion reactions for biofilm formation by using crystal violet staining and enumeration of adherent bacteria. Most combinations of bacteria had enhanced biofilm production compared with single bacteria. Combinations involving L. adecarboxylata had increased crystal violet biofilm production and adherent bacteria. This study demonstrates that transfusion-relevant bacteria can produce biofilms well together. More work is needed to clarify the effect of biofilms on platelet bacterial risk control strategies, but US Food and Drug Administration-recommended strategies remain acceptable.

Central Venous Disease Increases the Risk of Microbial Colonization in Hemodialysis Catheters

Objectives: Tunneled-cuffed catheters (TCCs) are widely used in maintenance hemodialysis patients. However, microbial colonization in catheters increases the likelihood of developing various complications, such as catheter-related infection (CRI), catheter failure, hospitalization, and death. Identification of the risk factors related to microorganism colonization may help us reduce the incidence of these adverse events. Therefore, a retrospective analysis of patients who underwent TCC removal was conducted.

Methods: From a pool of 389 adult patients, 145 were selected for inclusion in the study. None of the patients met the diagnostic criteria for CRI within 30 days before recruitment. The right internal jugular vein was the unique route evaluated. The catheter removal procedure was guided by digital subtraction angiography. Catheter tips were collected for culture. Biochemical and clinical parameters were collected at the time of catheter removal.

Results: The average age of this cohort was 55.46 ± 17.25 years. A total of 45/145 (31.03%) patients were verified to have a positive catheter culture. The proportions of gram-positive bacteria, gram-negative bacteria, and fungi were 57.8, 28.9, and 13.3%, respectively. History of CRI [odds ratio (OR) = 2.44, 95% confidence interval (CI) 1.09 to 5.49], fibrin sheath (OR = 2.93, 95% CI 1.39–6.19), white blood cell (WBC) count ≥5.9 × 10⁹/l (OR = 2.31, 95% CI 1.12–4.77), moderate (OR = 4.87, 95% CI 1.61–14.78) or severe central venous stenosis (CVS) (OR = 4.74, 95% CI 1.16–19.38), and central venous thrombosis (CVT) (OR = 3.41, 95% CI 1.51–7.69) were associated with a significantly increased incidence of microbial colonization in a univariate analysis. Central venous disease (CVD) elevated the risk of microbial colonization, with an OR of 3.37 (1.47–7.71, P = 0.004). A multivariate analysis showed that both CVS and CVT were strongly associated with catheter microbial colonization, with ORs of 3.06 (1.20–7.78, P = 0.019) and 4.13 (1.21–14.05, P = 0.023), respectively. As the extent of stenosis increased, the relative risk of catheter microbial colonization also increased. In patients with moderate and severe stenosis, a sustained and significant increase in OR from 5.13 to 5.77 was observed.

Conclusions: An elevated WBC count and CVD can put hemodialysis patients with TCCs at a higher risk of microbial colonization, even if these patients do not have the relevant symptoms of infection. Avoiding indwelling catheters is still the primary method for preventing CRI.

Extensive Horizontal Gene Transfer within and between Species of Coagulase-Negative Staphylococcus

Members of the gram-positive bacterial genus Staphylococcus have historically been classified into coagulase-positive Staphylococcus (CoPS) and coagulase-negative Staphylococcus (CoNS) based on the diagnostic presentation of the coagulase protein. Previous studies have noted the importance of horizontal gene transfer (HGT) and recombination in the more well-known CoPS species Staphylococcus aureus, yet little is known of the contributions of these processes in CoNS evolution. In this study, we aimed to elucidate the phylogenetic relationships, genomic characteristics, and frequencies of HGT in CoNS, which are now being recognized as major opportunistic pathogens of humans. We compiled a data set of 1,876 publicly available named CoNS genomes. These can be delineated into 55 species based on allele differences in 462 core genes and variation in accessory gene content. CoNS species are a reservoir of transferrable genes associated with resistance to diverse classes of antimicrobials. We also identified nine types of the mobile genetic element SCCmec, which carries the methicillin resistance determinant mecA. Other frequently transferred genes included those associated with resistance to heavy metals, surface-associated proteins related to virulence and biofilm formation, type VII secretion system, iron capture, recombination, and metabolic enzymes. The highest frequencies of receipt and donation of recombined DNA fragments were observed in Staphylococcus capitis, Staphylococcus caprae, Staphylococcus hominis, Staphylococcus haemolyticus, and members of the Saprophyticus species group. The variable rates of recombination and biases in transfer partners imply that certain CoNS species function as hubs of gene flow and major reservoir of genetic diversity for the entire genus.

Influence of Tunneled Hemodialysis-Catheters on Inflammation and Mortality in Dialyzed Patients

Older age and comorbidities in hemodialysis patients determines the use of tunneled catheters as vascular access despite their reported clinical and mortality disadvantages. This prospective matched study analyzes the impact of permanent catheters on inflammation and mortality in hemodialysis patients; We studied 108 patients, 54 with AV-fistula (AVF) and 54 with indwelling hemodialysis catheters (HDC) matched by sex, age, diabetes and time under renal-replacement therapy comparing dialysis efficacy, inflammation and micro-inflammation parameters as well as mortality. Cox-regression analysis was applied to determine predictors of mortality, HDC patients presented higher C-reactive-protein (CRP) blood levels and percentage of pro-inflammatory lymphocytes CD14+/CD16+ with worse dialysis-efficacy parameters. Thirty-six-months mortality appeared higher in the HDC group although statistical significance was not reached. Age with a Hazard Ratio (HR) = 1.06, hypoalbuminemia (HR = 0.43), hypophosphatemia (HR = 0.75) and the increase in CD14+/CD16+ monocyte count (HR = 1.02) were predictors of mortality; elder patients dialyzing through HDC show increased inflammation parameters as compared with nAVF bearing patients, although they do not present a significant increase in mortality when matched by covariates. Increasing age and percentage of pro-inflammatory monocytes as well as decreased phosphate and serum-albumin were predictors of mortality and indicate the main conclusions or interpretations.

Intra-Catheter Leukocyte Culture to Monitor Hemodialysis Catheter Colonization. a Prospective Study to Prevent Catheter-Related Bloodstream Infections

The most serious problem related to the use of tunneled catheters in hemodialysis is bacteremia. The aim of this study was to detect hemodialysis catheter colonization and, establish a preemptive therapy based on a catheter antibiotic lock in order to prevent development of catheter-related bloodstream infections. During a 24-month period, all patients with tunneled catheters in our hemodialysis unit were evaluated by extracting a through-catheter leukocyte culture every 15 days. There were 28 episodes of catheter colonization occurring in 13 patients (2.2 colonization episodes per 1000 catheter patient-days). At the time of colonization, catheters had been in place for a mean of 562 days (range: 16 to 1475 days). Coagulase negative staphylococci (CNS) were the most common microorganisms to be isolated. A preemptive therapy consisting in teicoplanin locks (10 mg/mL) for 21 days was able to eradicate catheter colonization in 89% of the cases when CNS were isolated. However, relapse of colonization occurred in 61.2% of these cases. The mean duration of catheter use was 239 days (range: 9 to 483 days) after treatment of a colonization episode. The incidence of catheter-related bloodstream infection in our population was 0.78 episodes per 1000 catheter patient-days (IC 95%: 0.374–1.434). This study shows the utility of intra-catheter leukocyte culture for early detection of hemodialysis catheter colonization. Moreover, it establishes that the eradication of biofilm-related CNS is possible without the removal of the catheter, thus enabling a longer catheter lifespan. (Int J Artif Organs 2008; 31: 820–6)

Protein resistance efficacy of PEO-silane amphiphiles: Dependence on PEO-segment length and concentration

In contrast to modification with conventional PEO-silanes (i.e. no siloxane tether), silicones with dramatically enhanced protein resistance have been previously achieved via bulk-modification with poly(ethylene oxide) (PEO)-silane amphiphiles α-(EtO)3Si(CH2)2-oligodimethylsiloxane13-block-PEOn-OCH3 when n=8 and 16 but not when n=3. In this work, their efficacy was evaluated in terms of optimal PEO-segment length and minimum concentration required in silicone. For each PEO-silane amphiphile (n=3, 8, and 16), five concentrations (5, 10, 25, 50, and 100μmol per 1g silicone) were evaluated. Efficacy was quantified in terms of the modified silicones' abilities to undergo rapid, water-driven surface restructuring to form hydrophilic surfaces as well as resistance to fibrinogen adsorption. Only n=8 and 16 were effective, with a lower minimum concentration in silicone required for n=8 (10μmol per 1g silicone) versus n=16 (25μmol per 1g silicone).

STATEMENT OF SIGNIFICANCE

Silicone is commonly used for implantable medical devices, but its hydrophobic surface promotes protein adsorption which leads to thrombosis and infection. Typical methods to incorporate poly(ethylene oxide) (PEO) into silicones have not been effective due to the poor migration of PEO to the surface-biological interface. In this work, PEO-silane amphiphiles - comprised of a siloxane tether (m=13) and variable PEO segment lengths (n=3, 8, 16) - were blended into silicone to improve its protein resistance. The efficacy of the amphiphiles was determined to be dependent on PEO length. With the intermediate PEO length (n=8), water-driven surface restructuring and resulting protein resistance was achieved with a concentration of only 1.7wt%.

The bacterial colonization in tunneled cuffed dialysis catheter and its effects on residual renal function in incident hemodialysis patients

BACKGROUND

The bacterial colonization of hemodialysis catheter occurs frequently and reaches to the catheter-related bloodstream infections (CRBSIs). We hypothesized bacterial colonization promotes inflammation and that might be associated with renal outcome. The aim of this study was to investigate the colonization status for tunneled cuffed dialysis catheter (TCC) and the factors for contributing to the catheter colonization and explore whether bacterial colonization would be related with declining of residual renal function (RRF).

METHODS

115 patients who received TCC removal operation and underwent catheter tip culture from January 2005 to June 2014 were enrolled. The follow-up data such as urine output (UO), time to anuria and patients' survival were collected from the patients or their family members by telephone in June, 2014.

RESULTS

There were nineteen patients (16.5 %, 19/115) with positive tip culture (colonization group). In the analysis of demographic and biochemical parameters, there were no significant differences between both groups. Fifty of all the subjects responded to the telephone survey and ten patients (20.0 %, 10/50) belonged to colonization group. The monthly decreasing rate of UO was significantly more rapid in colonization group (p = 0.001). The survival analysis showed that colonization group had worse estimated anuria-free survival than non-colonization group (p < 0.001). In multivariate cox regression, bacterial colonization of TCC was an independent factor influencing the loss of RRF (HR 4.29, 95 % CI: 1.905-9.683, p ≤ 0.001).

CONCLUSIONS

Bacterial colonization of TCC was associated with rapid loss of RRF.

Screening for Carriage of Methicillin-Resistant Staphylococcus aureus Shortly After Exposure May Lead to False-Negative Results

We evaluated a double screening strategy for carriage of methicillin-resistant Staphylococcus aureus (MRSA) in patients exposed to a newly detected MRSA carrier. If the first screening of the exposed patient yielded negative results, screening was repeated 4 days later. This strategy detected 12 (28%) of the 43 new MRSA carriers identified during the study period. The results suggest that there is an incubation period before MRSA carriage is detectable.

Quasi-experimental study of sodium citrate locks and the risk of acute hemodialysis catheter infection among critically ill patients

Critically ill patients who require renal replacement therapy (RRT) are vulnerable to catheter-related bloodstream infections (CRBSI). This study compared the risks of dialysis catheter infection according to the choice of locking solution in the intensive care unit (ICU). A prospective quasi-experimental study with marginal structural models (MSM) and 2:1 greedy propensity-score matching (PSM) was conducted at nine university-affiliated hospitals and three general hospitals. A total of 596 critically ill patients received either saline solution or heparin lock solution (the standard of care [SOC]) from 2004 to 2007 in the Cathedia cohort (n = 464 for MSM; n = 124 for PSM) or 46.7% citrate lock from 2011 to 2012 in the citrate (CLock) cohort (n = 132 for MSM; n = 62 for PSM) to perform RRT using intermittent hemodialysis. Catheter-tip colonization and CRBSI were analyzed. The mean duration (standard deviation [SD]) of catheterization was 7.1 days (6.1) in the SOC group and 7.0 days (5.9) in the CLock group (P = 0.84). The risk of dialysis catheter-tip colonization was lower in the CLock group (20.5 versus 38.7 per 1,000 catheter-days in the SOC group; hazard ratio [HR] from MSM, 0.73; 95% confidence interval [CI], 0.57 to 0.93; P < 0.02). Consistent findings were found from PSM (HR, 0.46; 95% CI, 0.22 to 0.95; P < 0.04). The risk of CRBSI was nonsignificantly different in the CLock group (1.1 versus 1.8 per 1,000 catheter-days in the SOC group; HR from MSM, 0.48; 95% CI, 0.12 to 1.87; P = 0.29). By reducing the risk of catheter-tip colonization, citrate lock has the potential to improve hemodialysis safety in the ICU. Additional studies are warranted before the routine use of citrate locks can be recommended in the ICU.

Predictors of Failure of Catheter Salvage in Incident Hemodialysis Patients

Purpose

Catheter-related bloodstream infection is a frequent complication for patients who use catheter as dialysis access. This study was performed to identify the risk factors for failed catheter salvage.

Methods

We enrolled patients who received non-tunneled catheters as initial vascular access during a two-year period. Catheter salvage was attempted in all symptomatically mild patients. Patients were prospectively followed for 8 weeks starting from the day of infection. Risk factors for salvage failure were explored.

Results

A total of 77 bacteremia episodes occurred in 69 patient, with an infection rate of 1.61 per 1,000 catheter days. Salvage was successful in 73.4% of all episodes. We found that higher ferritin levels (greater vs. lower than 500 mg/l, (odds ratio (OR) 6.388, 95% confidence interval (CI) 2.073, 19.686), higher phosphate levels (greater vs. lower than 5.5 mg/dl, OR 4.084, 95% CI 1.391, 11.978) and shorter time intervals between catheterization and infection (within vs. beyond 3 weeks, OR 4.190, 95% CI 1.279, 13.725) predicted salvage failure.

Conclusions

Catheter salvage can be a reasonable initial strategy for symptomatically mild patients. We propose salvaging aggressively and waiting watchfully; however, clinical judgment is prior to any specific management protocol.

Changes in inflammatory markers during a hemodialysis session and their relation to vascular access type

PURPOSE

In an attempt to better understand the relationship between vascular access and inflammation we assessed the effect of vascular access on inflammatory markers changes during hemodialysis (HD) session.

METHODS

Fifty HD patients were included: 23 patients with central venous catheters (CVC) and 27 patients with arteriovenous fistulas (AVF). Blood samples for high sensitivity C-reactive protein (hsCRP), Interleukin 6 (IL-6), and Tumor Necrosis Factor α (TNF α) were collected before and after HD session. The outcome was the change in the inflammatory markers during the dialysis.

RESULTS

Predialysis hsCRP levels were high in 70% of patients, without differences between the groups. Predialysis values were also similar in the two groups for IL-6 and TNF α. There was no increase in hsCRP values following HD and no difference between the change from baseline values in the CVC and AVF groups (-0.01±0.09 mg/dL and -0.01±0.13 mg/dL, respectively [P=.95]). IL-6 values increased during the HD session in the AVF group and non-significantly decreased in the CVC group. The change from baseline values was statistically significantly greater in the AVF group compared to the CVC group (0.76±1.44 ng/mL and -0.52±1.66 ng/mL, respectively, P=.006). TNF α values were significantly decreased in the CVC group and were not changed in the AVF group. The decrease from baseline values was not different between the groups.

CONCLUSIONS

Chronic inflammation is present in most HD patients. No increase in pro-inflammatory parameters was seen after a HD session in patients treated via CVC or AVF.

[Colonization management of methicillin resistant Staphylococcus aureus in patients and health professional in the haemodialysis unit in a situation of high risk of endemic disease: looking for zero nasal carriers?]

AIMS

To describe the dynamics of colonization by methicillin resistant Staphylococcus aureus (MRSA) detected in the Haemodialysis Unit (UHD) of the Hospital San Pedro de Alcantara of Caceres due to the detection of catheter-associated infections. Additionally, we attempt to evaluate the effectiveness of preventive strategies introduced.

METHODS

Nasal swab tests were performed in order to detect MRSA colonization in patients and health professionals from August 2008 to January 2009, according to the Consensus GEIH-SEIMC Y SEMPSPH Consensus. An active surveillance was performed with treatment and control of the carriers until negative results were achieved. A consensus document was drawn up in the UHD with registered preventive measures and work systems were reviewed. Prevalence, cumulative incidence, colonization pressure (carrier ratio per day/total patients or experts per day) were calculated. A chi-square test was performed, as well as a Z test for the comparison ratio.

RESULTS

The nasal swabs of 54 acute and chronic patients on haemodialysis showed an initial carrier prevalence of 29.6%; cumulative incidence in patients of 42.6%. Nasal swabs of 48 professionals had a cumulative incidence of 39.5%. There was a parallel decrease in colonization pressure in patients and specialists. After five months A smear was performed 5 months later on 40 patients and 26 specialists, which showed no carriers among the patients, and one among the health professionals.

CONCLUSION

We detected a high number of MRSA carriers among patients and Health professionals from the Haemodialysis Unit. Screening and treatment measures were effective for the decolonization of this population. It is important to adopt long-term strategies for active surveillance for the rapid detection of alert situations.

Impact of switch of vascular access type on key clinical and laboratory parameters in chronic haemodialysis patients

BACKGROUND

Observational studies demonstrate poor clinical outcomes in chronic haemodialysis patients with venous catheters as vascular access. This longitudinal study examines the impact of vascular access change on key clinical and laboratory parameters.

METHODS

We studied 2616 haemodialysis patients who had no or one vascular access change between January 2002 and June 2003. Two hundred and seventy-one patients switched from a catheter to an arteriovenous (AV) access (AV fistula or graft) and 69 patients from an AV access to a catheter. Accesses remained unchanged in 430 patients with catheters, and in 1846 patients with an AV access, who served as controls. Levels of serum albumin, white blood cell count (WBC), enPCR, eKdrt/V, blood haemoglobin and erythropoietin dosage were obtained monthly. Data were averaged over 6 months preceding (pre) and 6 months following the access change (post). Differences between post- and pre-access change were compared to changes in respective parameters between the last and first 6 months of the study period in controls.

RESULTS

The change from a catheter to an AV access was associated with a rise of serum albumin (+0.12 g/dL; P < 0.001), enPCR (+0.05 g/kg body weight/day; P = 0.001) and haemoglobin (+0.41 g/dL; P < 0.001) and a decrease in WBC (-370/microL; P = 0.048). Conversely, switching from an AV access to a catheter was followed by a significant fall in albumin (-0.11 g/dL; P = 0.035), enPCR (-0.07 g/ kg body weight/day; P = 0.001) and eKdrt/V (-0.09; P < 0.001) and a rise in erythropoietin dosage (+89 IU/kg body weight/week; P = 0.002), as compared to controls.

CONCLUSION

Change from a catheter to an AV access seems to alleviate malnutrition, inflammation and anaemia. Efforts to replace catheters with fistulae or grafts should be intensified.

Identification of Staphylococcus species directly from positive blood culture broth by use of molecular and conventional methods

We compared two real-time PCR assays (both by the use of melting curve analysis) for their ability to identify Staphylococcus species directly from 200 positive blood culture bottles. The PCR assays correctly identified 83% to 94% of the Staphylococcus isolates to species clusters. Molecular testing significantly outperformed commercially available latex tests (sensitivity for both latex tests, <15%) when it was used directly with broth from signal-positive blood cultures.

Clonal dissemination of Staphylococcus epidermidis in an oncology ward

Coagulase-negative staphylococci (CoNS) are the main cause of catheter-related infections, especially among immunosuppressed and neutropenic patients, as well as a source of bacterial contamination in blood cultures. Using biochemical identification and pulsed-field gel electrophoresis (PFGE), we sought to identify possible clonal isolates of bacteremia in patients with central lines in an oncology ward (OW), with comparison to isolates that were recovered by venipuncture from an adult emergency room (ER). A total of 243 CoNS isolates were identified to species level from the OW (126) and ER (117), with Staphylococcus epidermidis isolates being the most common (OW, 79.4%; ER, 45.3%). PFGE demonstrated a predominant clone of S. epidermidis (major subtype A) which was 35.5 times more likely (odds ratio [OR] = 35.5; 95% confidence interval [CI] = 4.7 to 267.0; P < 0.00001) to be present in the OW versus the ER. These (CoNS or major subtype A) isolates were more frequently resistant to gentamicin (OR = 2.83; 95% CI = 1.23 to 6.53; P = 0.016) and less frequently resistant to trimethoprim-sulfamethoxazole (OR = 0.38; 95% CI = 0.18 to 0.80; P = 0.013). Subset analysis of S. epidermidis isolates 2 years after the study period showed the persistence of the clone of major subtype A within the OW. This study demonstrates the presence of a predominant clone among central line isolates from an OW that is not present in CoNS venipuncture isolates from an ER.

Clonal relatedness of methicillin-resistant coagulase-negative staphylococci in the haemodialysis unit of a single university centre in Greece

BACKGROUND

Coagulase-negative staphylococci (CoNS) are frequently encountered pathogens in hospital environment. Dialysis patients, often carrying central venous catheters, are prone to CoNS infections. Methicillin-resistant (MR) staphylococci in hospitals are resistant to multiple antibiotics and may cause an overall increase in the incidence of staphylococcal infections rather than simply replacing the more susceptible strains. The aim of this study was to evaluate the antimicrobial resistance and the clonal relatedness of all clinically significant CoNS isolates recovered from haemodialysis patient infections treated in a tertiary care centre, the University Hospital of Larissa, in central Greece. In addition, the CoNS isolates from carriers among health-care workers of the local haemodialysis unit were tested.

METHODS

All staphylococci recovered from chronic haemodialysis patients who developed CoNS infections according to Herwaldt criteria in the University Hospital of Larissa, from October 2002 to October 2005, were included. In addition, isolates from the palms and the nasal mucosa of the nursing and medical personnel in the haemodialysis unit were also collected. Isolates were identified and tested for antimicrobial resistance by conventional microbiological methods. The clonal relationship of both patients' and carriers' isolates was tested by pulsed-field gel electrophoresis (PFGE) analysis.

RESULTS

Forty-two CoNS isolates were recovered from clinical culture specimens of patients hospitalized for various reasons. In 37 out of 42 CoNS isolates, methicillin resistance was determined. The majority of the MR Staphylococcus epidermidis isolates from patients belonged to one main clone (27 out of 32), arbitrarily named clone z. Clone z was also found to colonize 40% of the haemodialysis unit personnel.

CONCLUSIONS

The high prevalence of clone z emphasizes the great capacity of CoNS to colonize patients with central venous catheters such as haemodialysis patients and personnel. This emphasizes the need for the establishment of control and prevention measures.

Slime production and antibiotic susceptibility in staphylococci isolated from clinical samples

A total of 187 isolates from several clinical specimens were identified to species level as 129 Staphylococcus aureus strains and 58 coagulase-negative staphylococci (CNS) strains by the API Staph System (Biomerieux). Slime production was detected both by the conventional Christensen's method as well as by the Congo red agar method. Seventy-two strains of staphylococci isolates (38.5%) were found to be slime producers by Christensen's test tube method whereas 58 strains (31%) were slime positive with Congo red agar method. There was no statistically significant difference between the two methods for the detection of slime production (P > 0.05). Susceptibility of isolates against antimicrobial agents was tested by the disk diffusion method. Staphylococcal species had resistance to one or more antibiotics. Among the various antimicrobial agents, oxacillin (71.1%) and erythromycin (47.1%) showed higher resistance than most of the agents used against all isolates. Oxacillin resistant S. aureus (ORSA) and oxacillin resistant coagulase-negative staphylococci (ORCNS), 97 (75.2%) and 36 (62.1%) respectively were frequently observed in strains isolated from clinical materials. Among the ORSA strains, two strains were resistant to vancomycin. Moreover, 96 (74.4%) of 129 S. aureus strains were positive for beta-lactamase enzyme. However, 78 (81.25%) of 96 beta-lactamase positive S. aureus strains were beta-lactamase positive ORSA isolates, but none of them had vancomycin resistance.

Duration of methicillin-resistant Staphylococcus aureus carriage, according to risk factors for acquisition

OBJECTIVE

To examine the duration of methicillin-resistant Staphylococcus aureus (MRSA) carriage and its determinants and the influence of eradication regimens.

DESIGN

Retrospective cohort study.

SETTING

A 1,033-bed tertiary care university hospital in Bern, Switzerland, in which the prevalence of methicillin resistance among S. aureus isolates is less than 5%.

PATIENTS

A total of 116 patients with first-time MRSA detection identified at University Hospital Bern between January 1, 2000, and December 31, 2003, were followed up for a mean duration of 16.2 months.

RESULTS

Sixty-eight patients (58.6%) cleared colonization, with a median time to clearance of 7.4 months. Independent determinants for shorter carriage duration were the absence of any modifiable risk factor (receipt of antibiotics, use of an indwelling device, or presence of a skin lesion) (hazard ratio [HR], 0.20 [95% confidence interval {CI}, 0.09-0.42]), absence of immunosuppressive therapy (HR, 0.49 [95% CI, 0.23-1.02]), and hemodialysis (HR, 0.08 [95% CI, 0.01-0.66]) at the time MRSA was first MRSA detected and the administration of decolonization regimen in the absence of a modifiable risk factor (HR, 2.22 [95% CI, 1.36-3.64]). Failure of decolonization treatment was associated with the presence of risk factors at the time of treatment (P=.01). Intermittent screenings that were negative for MRSA were frequent (26% of patients), occurred early after first detection of MRSA (median, 31.5 days), and were associated with a lower probability of clearing colonization (HR, 0.34 [95% CI, 0.17-0.67]) and an increased risk of MRSA infection during follow-up.

CONCLUSIONS

Risk factors for MRSA acquisition should be carefully assessed in all MRSA carriers and should be included in infection control policies, such as the timing of decolonization treatment, the definition of MRSA clearance, and the decision of when to suspend isolation measures.

Optimizing antimicrobial therapy for gram-positive bloodstream infections in patients on hemodialysis

Infections with gram-positive organisms are highly prevalent in hemodialysis patients and are a major cause of morbidity and mortality in this population. Antimicrobial therapy is widely used to treat these infections, and prolonged therapy with these agents is often necessary. Extensive use of antimicrobials in hemodialysis patients has resulted in a growing threat of resistance, especially among gram-positive bacteria such as Enterococcus spp and Staphylococcus aureus. Vancomycin-resistant enterococci and S. aureus isolates with reduced susceptibility to vancomycin are increasingly being reported in hemodialysis patients. Additionally, resistance of these organisms to newer agents, such as linezolid and daptomycin, has been documented. Appropriate utilization of antimicrobial therapy to treat these organisms requires an understanding of the pharmacokinetic and pharmacodynamic principles to optimize therapy and avoid adverse drug events. The pharmacokinetic and pharmacodynamic profile of antimicrobial agents can be significantly altered in patients with chronic kidney disease. This review will describe mechanisms of antimicrobial resistance among common gram-positive organisms. The pharmacokinetic and pharmacodynamic principles of cephalosporins, vancomycin, aminoglycosides, linezolid, and daptomycin and applications for use of these agents in the treatment of patients with bloodstream infections on hemodialysis are discussed.

Avoiding trouble down the line: the management and prevention of hemodialysis catheter-related infections

Over the last 2 decades, hemodialysis catheter use has increased. Annually, approximately 30% of patients using a central venous catheter (CVC) experience a septic or bacteremic episode and are subsequently at risk of its associated long-term complications and mortality. Because of the serious clinical and financial impact of hemodialysis catheter-related bacteremias (HCRIs), standardized, validated definitions based on the hemodialysis patient population are necessary in order to better diagnose, monitor, and report HCRI for patient quality assurance and research purposes. The pathophysiology of HCRI involves a complex interaction between a triad that consists of the host patient, the infecting microorganism, and the vehicle catheter. Although the microorganism contribution in the pathogenesis of HCRI is likely most important, certain patient and catheter-related characteristics may be more amenable to manipulation. The key to managing HCRI is on prophylaxis against the initial microorganism catheter adherence and subsequent biofilm development. General and specific prophylactic maneuvers directed at both an intravascular and extraluminal route of microorganism entry are discussed including antibiotic- and silver-impregnated catheters and dressings, subcutaneous access devices, and topical prophylaxis at the exit site. In addition to systemic antibiotic use, the 3 methods of HRCI treatment using catheter salvage, guidewire exchange, and concurrent antibiotic lock are compared. The outcome and complications of HCRI may be serious and highlight the importance of careful, continual infection surveillance. Although the use of a multidisciplinary hemodialysis infection control team is desirable, staffing education and physician feedback have been shown to improve adherence to infection control guidelines and reduce HCRI.