A multilayered infection control intervention on carbapenem-resistant Acinetobacter baumannii acquisition: An interrupted time series.

BACKGROUND: Carbapenem-resistant Acinetobacter baumannii (CRAB) causes life-threating hospital-acquired. Due to a limited number of Intensive-Care-Unit (ICU) beds, these patients are often treated in high-dependency (HD) non-ICUs within internal-medicine wards (IMW) in Israel. We aimed to assess the effectiveness of a multilayered infection-control intervention on CRAB infection rate in IMWs, especially in its HD non-ICUs with ongoing CRAB transmission. METHODS: A quasi-experimental, before-and-after, interrupted time-series study with control outcomes. We conducted a multilayered intervention over 3.5years, which included 4 phases: (1) Pre intervention; (2) Intervention introduction: introduced enhanced environment cleaning; (3) Intervention phase 1: introduced active surveillance; (4) Intervention phase 2: introduced CRAB-positive patient cohorting, in addition to previous ongoing measures taken. RESULTS: CRAB was isolated from 204 patients aged 69.8y/o ± 15.86y, 59.8% male, 34.3% had CRAB-positive clinical samples. Mean hospital length-of-stay was 30.5days, with a 30-day postdischarge mortality rate of 55.9%. Mean CRAB clinical cases decreased from 0.89 in preintervention to 0.11 at the end of phase 2, with a change in slope and level after the intervention of P = .02 (CI: -0.204 to -0.040) and P = .004 (CI: -0.013 to -0.003), respectively. CONCLUSIONS: This intervention, including enhanced environment cleaning, active surveillance, and patient cohorting, successfully reduced CRAB acquisition in IMWs and their HD non-ICUs.

Risk Factors and Outcomes of Patients Colonized with KPC and NDM Carbapenemase-Producing Enterobacterales.

Carbapenemase-producing enterobacterales (CPE) poses an increasing threat in hospitals worldwide. Recently, the prevalence of different carbapenemases conferring carbapenem resistance in enterobacterales changed in our country, including an increase in New Delhi Metallo-beta-lactamase (NDM)-CPE. We conducted a comparative historical study of adult patients colonized with Klebsiella pneumoniae carbapenemase (KPC)-CPE (July 2016 to June 2018, a historical cohort) vs. NDM-CPE (July 2016 to January 2023). We identified patients retrospectively through the microbiology laboratory and reviewed their files, extracting demographics, underlying diseases, Charlson Comorbidity Index (CCI) scores, treatments, and outcomes. This study included 228 consecutive patients from whom a CPE rectal swab screening was obtained: 136 NDM-CPE positive and 92 KPC-CPE positive. NDM-CPE-colonized patients had a shorter hospitalization length and a significantly lower 30-day post-discharge mortality rate (p = 0.002) than KPC-CPE-colonized patients. Based on multivariate regression, independent risk factors predicting CPE-NDM colonization included admission from home and CCI < 4 (p < 0.001, p = 0.037, respectively). The increase in NDM-CPE prevalence necessitates a modified CPE screening strategy upon hospital admission tailored to the changing local CPE epidemiology. In our region, the screening of younger patients residing at home with fewer comorbidities should be considered, regardless of a prior community healthcare contact or hospital admission.

Nursing students led simulations to improve healthcare workers' hand hygiene compliance.

BACKGROUND: Hand hygiene compliance (HHC) is recognised as a major factor in the prevention of healthcare-associated infections. Healthcare workers (HCWs) compliance is still suboptimal. Simulation as an educational strategy may contribute to improved performance. OBJECTIVE: This study aimed to assess the effect of simulation interventions led by nursing students on HCWs' HHC. METHOD: A prospective quasi-experimental design with before and after intervention measurements was implemented in an 1150-bed tertiary hospital. Four consecutive periods, measuring before and after HHC, were examined in four hospital divisions. For each division, unique simulation activities were developed and led by nursing students, educators, and hospital leaders. Sixty seven students and 286 healthcare workers, along with two nurse educators, participated in the simulation sessions. HHC of all HCWs in the divisions was assessed by hospital infection control personnel. RESULTS: Hospital HHC rose across the four periods in all four divisions during this study. In three out of four periods and divisions, HHC increased significantly more in the simulation intervention groups compared to the overall hospital improvement. CONCLUSION: Student-led simulation for HCWs is an additional effective method to improve HHC. Nursing managers should consider joining forces with nursing educators to enable students to become agents of change in healthcare settings and encourage further collaboration.

Getting the drop on Staphylococcus aureus: Semiquantitative Staphylococcus aureus nasal colony reduction in orthopedic surgery reduces surgical site infection.

BACKGROUND: Surgical site infection (SSI) is a frequent health care-associated infection. We aimed to reduce SSI risk after joint arthroplasty and spine surgery by reducing Staphylococcus aureus colonization burden with presurgery intranasal povidone-iodine (PVP-I) application in conjunction with skin antisepsis ("the intervention"). METHODS: Retrospective case-control study; postintervention cohort versus a historical cohort. Adults who underwent joint arthroplasty or spine surgery during February 2018 through October 2021 ("post-intervention cohort") included. In the analysis cases any patient who underwent surgery and developed SSI within 90 days postsurgery, controls had no SSI. Postintervention cohort data were compared with a similar retrospective 2016 to 2017 patient cohort that did not use intranasal PVP-I. RESULTS: The postintervention cohort comprised 688 consecutive patients aged 65y/o, 48.8% male, 28 cases, and 660 controls. Relatively more cases than controls had diabetes mellitus (P = .019). There was a 39.6% eradication rate of S aureus nasal colonization post intranasal PVP-I (P < .0001). SSI rate was higher in patients positive versus those negative for S aureus on a 24-hour postsurgery nasal culture (P < .0001). The deep SSI rate per 100 operations postintervention versus the historical cohort decreased for all surgical procedures. CONCLUSIONS: Semiquantitative S aureus nasal colony reduction using intranasal PVP-I is effective for decreasing SSI rate in joint arthroplasty and spine surgery. In patients with presurgery S aureus nasal colonization additional intranasal PVP-I postsurgery application should be considered.

The appropriateness of the decision to quarantine healthcare workers exposed to a severe acute respiratory coronavirus virus 2 (SARS-CoV-2)-positive coworker based on national guidelines.

OBJECTIVE: To examine the appropriateness of the decision to quarantine healthcare workers (HCWs) exposed to coronavirus disease 2019 (COVID-19). DESIGN: Retrospective cohort study. SETTING: A tertiary-care medical center in Israel. PARTICIPANTS: HCWs exposed to a coworker infected with severe acute respiratory coronavirus virus 2 (SARS-CoV-2). METHODS: Quarantined and nonquarantined HCWs were followed for up to 1 month following exposure and their COVID-19 status was determined. The validity of the decision to quarantine was assessed. RESULTS: In total, 2,595 HCWs exposed to 419 confirmed index cases were studied. Of the contact cases, 752 HCWs were quarantined and 1,843 HCWs were not. Of those quarantined, 36 became SARS-CoV-2 positive (4.7%). Among those who were not quarantined, only 13 (0.7%) became SARS-CoV-2 positive, which translated to a sensitivity of 73.5% and a specificity of 71.9% for the decision to quarantine (positive and negative predictive values: 4.7% and 99.3%, respectively). Controlling for confounders, the decision to quarantine the HCW by the Israeli Ministry of Health guidelines was associated with a significant risk of becoming SARS-CoV-2 positive (RR, 3.83; 95% CI, 1.98-7.36; P = .001). If a nonselective policy was used, 11,700 working days would have been lost (902 working days lost per positive case). CONCLUSIONS: An efficient and tight system of HCW contact investigations served its purpose in our hospital during the COVID-19 pandemic. This study was based on HCW reports and reported adherence to safety regulations, and these findings are relevant to the massive pandemic waves due to the SARS-CoV-2 α (alpha) variant. These Methods demonstrate an effective way of handling risk without causing damage due to arbitrary risk-control measures.

The long-term impact of immediate verbal feedback of hand hygiene compliance after overt observation sessions, as assessed by continuous closed-circuit television monitoring in an intensive care setting.

BACKGROUND: Hand hygiene compliance by health care workers (HCWs) is pivotal in controlling and preventing health care associated infections. The aim of this interventional study is to assess the long-term impact of personal verbal feedback on hand hygiene compliance of HCWs in an intensive care unit (ICU) immediately after overt observation by an infection control nurse. METHODS: An infection control nurse overtly observed HCWs' hand hygiene compliance and immediately gave personal verbal feedback with emphasis on aseptic technique. Overt non-interventional sessions were also performed. We measured compliance rates using covert continuous closed-circuit television (CCTV) monitoring. We compared these rates to previously-published hand hygiene compliance data. RESULTS: Overall compliance rates in the first (41.5%) and third phases (42%) of the study, before and after the intervention were similar. The two moments that were lowest in the first phase, "before aseptic contact" and "after exposure to body fluids", showed significant improvement, but two moments showed a significant decline in compliance: "before patient contact" and "after contact with patient surrounding". The compliance rates during the intervention phase were 64.8% and 63.8% during the sessions with and without immediate verbal personal feedback, respectively. CONCLUSION: The overall hand hygiene compliance rate of HCWs did not show an improvement after immediate verbal personal feedback. Covert CCTV observational sessions yielded much lower hand hygiene compliance rates then overt interventional and non-interventional observations. We suggest that a single intervention of personal feedback immediately after an observational session is an ineffective strategy to change habitual practices.

The impact of a multimodel approach to designing a new orthopedic department.

OBJECTIVE: To determine whether a multifaceted approach effectively influenced antibiotic use in an orthopedics department. DESIGN: Retrospective cohort study comparing the readmission rate and antibiotic use before and after an intervention. SETTING: A 1,000-bed, tertiary-care, university hospital. PATIENTS: Adult patients admitted to the orthopedics department between January 2015 and December 2018. METHODS: During the preintervention period (2015-2016), 1 general orthopedic department was in operation. In the postintervention period (2017-2018), 2 separate departments were created: one designated for elective "clean" surgeries and another that included a "complicated wound" unit. A multifaceted strategy including infection prevention measures and introducing antibiotic stewardship practices was implemented. Admission rates, hand hygiene practice compliance, surgical site infections, and antibiotic treatment before versus after the intervention were analyzed. RESULTS: The number of admissions and hospitalization days in the 2 periods did not change. Seven-day readmissions per annual quarter decreased significantly from the preintervention period (median, 7 days; interquartile range [IQR], 6-9) to the postintervention period (median, 4 days; IQR, 2-7; P = .038). Hand hygiene compliance increased and surgical site infections decreased in the postintervention period. Although total antibiotic use was not reduced, there was a significant change in the breakdown of the different antibiotic classes used before and after the intervention: increased use of narrow-spectrum ß-lactams (P < .001) and decreased use of ß-lactamase inhibitors (P < .001), third-generation cephalosporins (P = .044), and clindamycin (P < .001). CONCLUSIONS: Restructuring the orthopedics department facilitated better infection prevention measures accompanied by antibiotic stewardship implementation, resulting in a decreased use of broad-spectrum antibiotics and a significant reduction in readmission rates.

Efficacy of covert closed-circuit television monitoring of the hand hygiene compliance of health care workers caring for patients infected with multidrug-resistant organisms in an intensive care unit.

BACKGROUND: To compare covert closed-circuit television (CCTV) monitoring to standard overt observation in assessing the hand hygiene (HH) conduct of health care workers (HCWs) caring for patients infected with multidrug-resistant organisms (MDROs). This was a cross-sectional study in a general intensive care unit of a 1,000-bed university hospital. METHODS: Forty-six general intensive care unit HCWs (staff physicians, registered nurses, and auxiliary workers) caring for contact isolation MDRO-infected patients. The study incorporated the following 3 phases: phase 1, establishment of interrater reliability between 2 simultaneous observers using the overt observation method; phase 2, establishment of interrater reliability between 2 simultaneous observers using the CCTV method; and phase 3, simultaneous monitoring of HH by both methods to evaluate the suitability of CCTV as an alternative to direct observation of the HH conduct of HCWs caring for MDRO-infected patients. RESULTS: Overall, 1,104 opportunities to perform HH were documented during 49 observation sessions. The compliance rate observed by the overt method (37.3%) was significantly higher than that observed when only the covert method was used (26.5%). However, simultaneous overt-covert observations were found to have intraclass correlation coefficients of >0.85. CONCLUSIONS: Covert CCTV observation of HCW HH compliance appears to provide a truer and more realistic picture than overt observation, probably because of its ability to neutralize the Hawthorne effect of overt observation. The high intraclass correlation coefficients between covert observation and overt observation supports this conclusion.

Relationship between shared patient care items and healthcare-associated infections: a systematic review.

BACKGROUND: Environmental surfaces may contribute to transmission of nosocomial pathogens. Noninvasive portable clinical items potentially shared among patients (NPIs) are part of the patient's immediate surroundings and may pose a threat of pathogen transmission. OBJECTIVE: To assess the body of literature describing the range of microorganisms found on NPIs and evaluate the evidence regarding the potential for cross-transmission of microorganisms between NPIs and hospitalized patients in non-outbreak conditions. DESIGN: A comprehensive list of NPIs was developed, and a systematic review of these items combined with healthcare-associated infection related keywords was performed. DATA SOURCES: PubMed, Scopus, and Cochrane Library. REVIEW METHODS: A systematic review was performed using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) checklist to identify and synthesize research reports published between January 1990 and July 2013 on studies regarding contamination of NPIs and association to infections in non-outbreak circumstances. RESULTS: 1498 records were scanned for eligibility. Thirteen studies met inclusion criteria. Overall, rates of NPI contamination ranged from 23% to 100%. Normal skin or environmental flora were found on almost all positive cultures. Potential pathogens, e.g., Staphylococcus aureus, were present on up to 86%, and Pseudomonas spp. and/or Enterobacteriaceae in 38% of positive cultures. Multi-drug resistant organisms were isolated from up to 25% of items. Three studies explored association between NPIs contamination and patient colonization and infection. One study reported 5 patients with healthcare-associated infections with pathogens found concurrently on NPIs, one found cross-transmission between patient skin bacteria and NPI contamination, and a third did not find any cross-transmission. CONCLUSIONS: Potential pathogens and multiply resistant organisms present on NPIs in routine, non-outbreak conditions and in a variety of settings confirms the need to improve NPIs decontamination practices.

Nursing students' intentions to comply with standard precautions: an exploratory prospective cohort study.

BACKGROUND: Partial compliance of health care workers with standard precaution (SP) guidelines has been extensively documented. The aim of this study was to describe the development of nursing students' intentions to comply with SPs. METHODS: Prospective cohort study. Two consecutive classes of a 4-year bachelor of nursing program completed questionnaires 3 times. The transtheoretical model of change was used to describe the change in intentions to comply with SPs. Factor analysis displayed 2 behavioral categories: commonly used standard precautions (CUSPs) and less commonly used standard precautions (LUSPs). Knowledge, risk perception, sense of coherence (SOC), safety climate (SC), and emphasis given by educators were evaluated as associated factors. RESULTS: Of the 91 students, 85 (93%) completed the questionnaire during their second year, 57 of 88 students (65%) completed it during the third year, and 70 of 82 students (85%) completed it at the end of the fourth year. Of the 82 students, 45 (55%) completed 3 measurements. CUSPs exhibited a rise from the second to the third year, with a moderate decline from the third to the fourth year, whereas LUSPs continued ascending. CUSPs were positively associated with SC and SOC; LUSPs were commonly associated with risk perception. CONCLUSION: The different evolution of CUSPs and LUSPs and dissimilar associations may suggest that different strategies might encourage diverse SP behaviors. Improving the SC might be appropriate when aiming to encourage CUSPs, and highlighting risks may be appropriate to encourage LUSPs.

Risk factors for developing clinical infection with carbapenem-resistant Klebsiella pneumoniae in hospital patients initially only colonized with carbapenem-resistant K pneumoniae.

BACKGROUND: This study examined predictors of carbapenem-resistant Klebsiella pneumoniae (CRKP) colonization and risk factors for the development of CRKP infection in patients initially only colonized with CRKP. METHODS: A total of 464 patients with CRKP rectal colonization (CRKP-RC) were identified. Two case-control studies were performed, one comparing risk factors for CRKP-RC in patients who did not develop CRKP infection (CRKP-IN) versus patients without CRKP-RC and CRKP-IN, and the other comparing CRKP-RC patients who did not develop CRKP-IN with those who did. RESULTS: Forty-two of the 464 colonized patients developed CRKP-IN. Multivariate analysis identified the following predictors for CRKP-RC: antibiotic therapy (odds ratio [OR], 5.76; P ≤ .0001), aminopenicillin therapy (OR, 7.753; P = .004), bedridden (OR, 3.09; P = .021), and nursing home residency (OR, 3.09; P = .013). Risk factors for CRKP-IN in initially CRKP-RC-positive patients were previous invasive procedure (OR, 5.737; P = .021), diabetes mellitus (OR, 4.362; P = .017), solid tumor (OR, 3.422; P = .025), tracheostomy (OR, 4.978; P = .042), urinary catheter insertion (OR, 4.696; P = .037), and antipseudomonal penicillin (OR, 23.09; P ≤ .0001). CONCLUSIONS: We suggest that in patients with CRKP-RC, a strategy for preventing CRKP-IN might include limiting antipseudomonal penicillin and carbapenem use and preventing infections by closely following compliance with infection control bundles.

A multifaceted intervention strategy for eradication of a hospital-wide outbreak caused by carbapenem-resistant Klebsiella pneumoniae in Southern Israel.

OBJECTIVE: To devise a local strategy for eradication of a hospital-wide outbreak caused by carbapenem-resistant Klebsiella pneumoniae (CRKP). DESIGN: Quasi-experimental, before-and-after, interrupted time-series study. SETTING: A 1,000-bed tertiary-care university teaching hospital. METHODS: Retrospectively, all relevant data were collected from the medical records of patients with CRKP infections from May 2006 through April 2007, the preintervention period. From May 1, 2007, through May 1, 2010, the postintervention period, the intervention was applied and prospectively followed. The 5 key elements of this strategy were an emergency department flagging system, the building of a cohort ward, the eradication of clusters, environmental and personnel hand cultures, and a carbapenem-restriction policy. The demographic and clinical parameters of patients colonized by and/or infected with CRKP were collected from medical records. RESULTS: A total of 10,680 rectal cultures were performed for 8,376 patients; 433 (5.16%) and 370 (4.4%) were CRKP-colonized and CRKP-infected patients, respectively, and 789 (98%) of 803 patients were admitted to the CRKP cohort ward. The CRKP infection density was reduced from 5.26 to 0.18 per 10,000 patient-days (P ≤ .001), and no nosocomial CRKP infections were diagnosed. Twenty-three percent of environmental cultures were found to be positive. Meropenem use was reduced from 283 ± 70.92 to 118 ± 74.32 defined daily doses per 1,000 patient-days (P ≤ .001). CONCLUSION: This intervention produced an enormous impact on patient location, surveillance cultures, and antibiotic policies and a massive investment in infection control resources.

Risk factors for community-acquired pneumonia with influenza A/H1N1 in southern Israel.

OBJECTIVES: To determine the risk factors for community-acquired pneumonia (CAP) with influenza A/H1N1 flu in our region. METHODS: Adult patients with CAP from July 2009 to February 2010 who were screened for influenza A/H1N1 were identified retrospectively. This was a retrospective case-control study. Cases had CAP with influenza A/H1N1 and controls had CAP without influenza A/H1N1. Patient files were reviewed for demographics, clinical characteristics, treatment, and outcome. RESULTS: Three hundred and eight patients with CAP were identified: 107 cases and 201 controls. For cases vs. controls there were significant differences in the following: median age (40 (range 18-82) vs. 56 (range 18-89) years; p<0.001), female gender (63.6% vs. 44.3%; p<0.05), Bedouin Arab origin (41.1% vs. 26.4%; p<0.05), pyrexia (97.6% vs. 88.5%; p<0.01), cough (96.3% vs. 75%; p<0.05), admission to the intensive care unit (18.7% vs. 10.6%; p<0.05), and CURB-65 score ≥ 3 (2.8% vs. 11.4%; p<0.05). Laboratory values including white blood cell (WBC) and platelet counts were lower in cases than in controls, whereas creatine phosphokinase and lactate dehydrogenase levels were higher (p<0.01). By logistic regression models, young age, Bedouin origin, and lower WBC and platelet counts were independent risk factors for the acquisition of CAP with influenza A/H1N1. CONCLUSIONS: In our region CAP with influenza A/H1N1 occurred in younger females of Bedouin Arab origin with less co-morbidity. No difference in mortality was found. We believe that inequalities in socioeconomic conditions could explain our findings.

Epidemiologic, clinical, laboratory, and therapeutic characteristics of influenza A/H1N1 in Moslem Bedouin and Jewish children hospitalized in southern Israel during 2009.

A total of 739 (225 H1N1(+)) children with a diagnosis of acute respiratory infection were hospitalized during July to December 2009. The H1N1(+) children were compared with 225 randomly enrolled H1N1(-) children with an influenza-like illness. As compared with influenza-like illness patients, patients with 2009 influenza A/H1N1 were characterized by older age, more vomiting, less hypoxemia and wheezing, lower white blood cell counts, less neutrophilia, and severe lymphopenia.

Attributable mortality rate for carbapenem-resistant Klebsiella pneumoniae bacteremia.

OBJECTIVE: To determine the attributable (direct) mortality and morbidity caused by carbapenem-resistant Klebsiella pneumoniae bacteremia. DESIGN: A matched retrospective, historical cohort design, using a stepwise procedure to stringently match the best control subjects to the best case subjects. SETTING: A 1,000-bed tertiary-care university teaching hospital. PATIENTS: Case subjects were defined as adult patients with carbapenem-resistant K. pneumoniae bacteremia during the period from October 2005 through October 2008. Control subjects were defined as patients who were very similar to case subjects except that they did not have bacteremia. METHODS: Matching potential control subjects to case subjects was performed at a 1:1 ratio using a computerized record system. The criteria used included same hospitalization period, similar Charlson comorbidity index, same underlying disease, same age within 10 years, and same sex. Demographic and clinical characteristics were collected from medical records. RESULTS: During the study period, 319 patients developed an infection due to carbapenem-resistant K. pneumoniae. Of these 319 patients, 39 (12.2%) developed a bloodstream infection, for an overall rate of 0.59 episodes of carbapenem-resistant K. pneumoniae bacteremia per 10,000 patient-days. We excluded 7 patients from our study, leaving a total of 32 case subjects in our cohort. Case subjects were significantly more likely than control subjects (n = 32) to require care in an intensive care unit (12 case subjects [37.5%] vs 3 control subjects [9.4%]), ventilator support (17 case subjects [53.1%] vs 8 control subjects [25%]), and use of a central venous catheter (19 case subjects [59.4%] vs 9 control subjects [28.1%]). For case subjects, the crude mortality rate was 71.9% (ie, 23 of the 32 case subjects died); for control subjects, the crude mortality rate was 21.9% (ie, 7 of the 32 control subjects died) (P < .001. For case subjects, the attributable mortality was 50% (95% confidence interval [CI], 15.3%-98.6%). A mortality risk ratio of 3.3 (95% CI, 2.9-28.5) was found for case subjects with carbapenem-resistant K. pneumoniae bacteremia. CONCLUSIONS: Patients with carbapenem-resistant K. pneumoniae require more intensive and invasive care. We have shown that the crude and attributable mortality rates associated with carbapenem-resistant K. pneumoniae bacteremia were striking.

Compound-specific isotope analysis of RDX and stable isotope fractionation during aerobic and anaerobic biodegradation.

Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) is a common contaminant at explosives production sites. Here, we report on the use of compound-specific isotope analysis of RDX to obtain delta(15)N and delta(18)O enrichment factors during biodegradation in batch cultures. A new preparation method has been developed based on RDX purification using thin-layer chromatography. RDX is then subjected to an elemental analyzer coupled with an isotope-ratio mass spectrometer (EA-IRMS). The precision of the method shows standard deviations of 0.13% per hundred and 1.18% per hundred for delta(15)N and delta(18)O, respectively, whereas the accuracy of the method has been checked routinely, adhering to external standards. The method was applied to RDX samples subjected to biodegradation under aerobic or anaerobic conditions. Enrichment factors under aerobic conditions were -2.1% per hundred and -1.7% per hundred for delta(15)N and delta(18)O, respectively, and under anaerobic conditions, -5.0% per hundred and -5.3% per hundred for delta(15)N and delta(18)O, respectively. The results of this study provide a tool for monitoring natural attenuation of RDX in a contaminated environment.

Dilution tests in a low-permeability fractured aquifer: matrix diffusion effect.

A point dilution test is commonly used in single-borehole tracer experiments designed to determine the Darcy velocity of a formation. This method is based on the concept that, in a borehole, a tracer's concentration declines as a consequence of the water flux. Based on theoretical simulations and field observations, this study indicates that for low-permeability, yet highly porous fractured formations, the common practice of excluding the effect of diffusive mass flux between the dissolved tracer within the borehole and the surrounding matrix may lead to significant errors in the assessment of the Darcy velocity. This conclusion was confirmed by a model adapted to simulate experimental data collected from a tracer test performed in a vertical, large-diameter (25-cm) borehole drilled along a subvertical fracture intersecting a chalk formation.

Two-dimensional distribution of microbial activity and flow patterns within naturally fractured chalk.

The two-dimensional distribution of flow patterns and their dynamic change due to microbial activity were investigated in naturally fractured chalk cores. Long-term biodegradation experiments were conducted in two cores ( approximately 20 cm diameter, 31 and 44 cm long), intersected by a natural fracture. 2,4,6-tribromophenol (TBP) was used as a model contaminant and as the sole carbon source for aerobic microbial activity. The transmissivity of the fractures was continuously reduced due to biomass accumulation in the fracture concurrent with TBP biodegradation. From multi-tracer experiments conducted prior to and following the microbial activity, it was found that biomass accumulation causes redistribution of the preferential flow channels. Zones of slow flow near the fracture inlet were clogged, thus further diverting the flow through zones of fast flow, which were also partially clogged. Quantitative evaluation of biodegradation and bacterial counts supported the results of the multi-tracer tests, indicating that most of the bacterial activity occurs close to the inlet. The changing flow patterns, which control the nutrient supply, resulted in variations in the concentrations of the chemical constituents (TBP, bromide and oxygen), used as indicators of biodegradation.

Correlating fracture trends and hydraulic head using semivariogram cloud analysis.

Fracture trends (defined as kilometer-scale linear features interpolated between field observations of fractures along their strikes) often have a dominant orientation. Finding a correlation between this orientation and hydraulic data could shed light on their hydraulic influence. A significant correlation between head residuals from first-order regional drift and the orientation of 2- to 4-km-long fracture trends was found in a study site in the Negev, Israel, using the semivariogram cloud analysis. Correlation of head residuals rather than the head itself implies that the orientation of the fracture trends controls the anisotropy and heterogeneity at this scale, mainly because the fracture trends define the orientation of blocks, which differ in their hydraulic properties. Preferential transmissive pathways are probably shorter than the full extent of the fracture trends, causing a relatively high head difference along the trends on the 2- to 4-km scale. Fracture trend density and additional data from short-range hydraulic tests helped characterize two blocks separated by a fault zone. The identification of hydraulic features on a kilometer scale is necessary for better modeling of regional ground water flow and transport. Hydraulic tests at this scale are not feasible, thereby rendering combined analyses of head and structural data, such as the one presented here, essential.