Sampling designs for rare time-dependent exposures: a comparison of the nested exposure case-control design and exposure density sampling.

In extensive cohort studies, the ascertainment of covariate information on all individuals can be challenging. In hospital epidemiology, an additional issue is often the time-dependency of the exposure of interest. We revisit and compare two sampling designs constructed for rare time-dependent exposures and possibly common outcomes - the nested exposure case-control design and exposure density sampling. Both designs enable efficient hazard ratio estimation by sampling all exposed individuals but only a small fraction of the unexposed ones. Moreover, they account for time-dependent exposure to avoid immortal time bias. We evaluate and compare their performance using data of patients hospitalised in the neuro-intensive care unit at the Burdenko Neurosurgery Institute in Moscow, Russia. Three different types of hospital-acquired infections with different prevalence are considered. Additionally, inflation factors, a primary performance measure, are discussed. We enhance both designs to allow for a competitive analysis of combined and competing endpoints compared to the full cohort approach while substantially reducing the amount of necessary information. Nonetheless, exposure density sampling outperforms the nested exposure case-control design concerning efficiency and accuracy in most considered settings.

Microscope-based imaging platform for large-scale analysis of oral biofilms.

A microscopic method for noninvasively monitoring oral biofilms at the macroscale was developed to describe the spatial distribution of biofilms of different bacterial composition on bovine enamel surfaces (BES). For this purpose, oral biofilm was grown in situ on BES that were fixed at approximal sites of individual upper jaw acrylic devices worn by a volunteer for 3 or 5 days. Eubacteria, Streptococcus spp., and Fusobacterium nucleatum were stained using specific fluorescence in situ hybridization (FISH) probes. The resulting fluorescence signals were subsequently tested by confocal laser scanning microscopy (CLSM) and monitored by an automated wide-field microscope-based imaging platform (Scan∧R). Automated image processing and data analysis were conducted by microscope-associated software and followed by statistical evaluation of the results. The full segmentation of biofilm images revealed a random distribution of bacteria across the entire area of the enamel surfaces examined. Significant differences in the composition of the microflora were recorded across individual as well as between different enamel surfaces varying from sparsely colonized (47.26%) after 3 days to almost full surface coverage (84.45%) after 5 days. The enamel plates that were positioned at the back or in the middle of the oral cavity were found to be more suitable for the examination of biofilms up to 3 days old. In conclusion, automated microscopy combined with the use of FISH can enable the efficient visualization and meaningful quantification of bacterial composition over the entire sample surface. Due to the possibility of automation, Scan∧R overcomes the technical limitations of conventional CLSM.

Implementing strategic bundles for infection prevention and management.

Healthcare-associated infections (HAI) are considered to be the most frequent adverse event in healthcare delivery. Active efforts to curb HAI have increased across Europe thanks to the growing emphasis on patient safety and quality of care. Recently, there has been dramatic success in improving the quality of patient care by focusing on the implementation of a group or "bundle" of evidenced-based preventive practices to achieve a better outcome than when implemented individually. The project entitled IMPLEMENT is designed to spread and test knowledge on how to implement strategic bundles for infection prevention and management in a diverse sample of European hospitals. The general goal of this project is to provide evidence on how to decrease the incidence of HAI and to improve antibiotic use under routine conditions.

Burden of antimicrobial resistance in European hospitals: excess mortality and length of hospital stay associated with bloodstream infections due to Escherichia coli resistant to third-generation cephalosporins.

OBJECTIVES: This study determined excess mortality and length of hospital stay (LOS) attributable to bloodstream infection (BSI) caused by third-generation-cephalosporin-resistant Escherichia coli in Europe. METHODS: A prospective parallel matched cohort design was used. Cohort I consisted of patients with third-generation-cephalosporin-resistant E. coli BSI (REC) and cohort II consisted of patients with third-generation-cephalosporin-susceptible E. coli BSI (SEC). Patients in both cohorts were matched for LOS before infection with patients free of the respective BSI. Thirteen European tertiary care centres participated between July 2007 and June 2008. RESULTS: Cohort I consisted of 111 REC patients and 204 controls and cohort II consisted of 1110 SEC patients and 2084 controls. REC patients had a higher mortality at 30 days (adjusted odds ratio = 4.6) and a higher hospital mortality (adjusted hazard ratio = 5.7) than their controls. LOS was increased by 8 days. For SEC patients, these figures were adjusted odds ratio = 1.9, adjusted hazard ratio = 2.0 and excess LOS = 3 days. A 2.5 times [95% confidence interval (95% CI) 0.9-6.8] increase in all-cause mortality at 30 days and a 2.9 times (95% CI 1.2-6.9) increase in mortality during entire hospital stay as well as an excess LOS of 5 days (95% CI 0.4-10.2) could be attributed to resistance to third-generation cephalosporins in E. coli BSI. CONCLUSIONS: Morbidity and mortality attributable to third-generation-cephalosporin-resistant E. coli BSI is significant. If prevailing resistance trends continue, high societal and economic costs can be expected. Better management of infections caused by resistant E. coli is becoming essential.

Microhardness of composite materials with different organic phases in deep class II cavities: an in vitro study.

OBJECTIVE: This study compared the microhardness of three composite resins with different organic matrices in deep class II cavities. MATERIALS AND METHOD: A total of 36 extracted molars were randomly assigned to six groups and standardized class II cavities were prepared. The cavity design comprised three steps in a mesiodistal direction with an increasing depth (2, 4, and 6 mm). Twelve cavities each were restored using Filtek Supreme (FS), Quixfil (QF), and Filtek Silorane (SI). The materials were applied in incremental layers of 2 mm and cured either with Halogen Translux Energy (HTE) (n=18) or LED Bluephase C8 (LED) (n=18). Subsequently, the specimens were cross-sectioned, and microhardness was determined in various depths and at two different distances from the matrix. RESULTS: QF yielded the highest KHN microhardness values (92.67 ± 12.77), followed by FS (65.53 ± 19.52) and SI (57.67 ± 8.33). Composites cured with LED achieved higher KHN values. All materials showed the highest microhardness values within the superficial increments and at a distance of 1000 µm from the matrix.

Optimizing design of research to evaluate antibiotic stewardship interventions: consensus recommendations of a multinational working group.

BACKGROUND: Antimicrobial stewardship interventions and programmes aim to ensure effective treatment while minimizing antimicrobial-associated harms including resistance. Practice in this vital area is undermined by the poor quality of research addressing both what specific antimicrobial use interventions are effective and how antimicrobial use improvement strategies can be implemented into practice. In 2016 we established a working party to identify the key design features that limit translation of existing research into practice and then to make recommendations for how future studies in this field should be optimally designed. The first part of this work has been published as a systematic review. Here we present the working group's final recommendations. METHODS: An international working group for design of antimicrobial stewardship intervention evaluations was convened in response to the fourth call for leading expert network proposals by the Joint Programming Initiative on Antimicrobial Resistance (JPIAMR). The group comprised clinical and academic specialists in antimicrobial stewardship and clinical trial design from six European countries. Group members completed a structured questionnaire to establish the scope of work and key issues to develop ahead of a first face-to-face meeting that (a) identified the need for a comprehensive systematic review of study designs in the literature and (b) prioritized key areas where research design considerations restrict translation of findings into practice. The working group's initial outputs were reviewed by independent advisors and additional expertise was sought in specific clinical areas. At a second face-to-face meeting the working group developed a theoretical framework and specific recommendations to support optimal study design. These were finalized by the working group co-ordinators and agreed by all working group members. RESULTS: We propose a theoretical framework in which consideration of the intervention rationale the intervention setting, intervention features and the intervention aims inform selection and prioritization of outcome measures, whether the research sets out to determine superiority or non-inferiority of the intervention measured by its primary outcome(s), the most appropriate study design (e.g. experimental or quasi- experimental) and the detailed design features. We make 18 specific recommendation in three domains: outcomes, objectives and study design. CONCLUSIONS: Researchers, funders and practitioners will be able to draw on our recommendations to most efficiently evaluate antimicrobial stewardship interventions.

Cleanliness of dentinal tubules following gutta-percha removal with and without solvents: a scanning electron microscopic study.

AIM: To determine the influence of solvents on gutta-percha and sealer remaining on root canal walls and in dentinal tubules. METHODOLOGY: The root canals of 70 teeth were prepared chemomechanically to apical size 40. In group 1 (n = 10; control group), the canals remained unfilled. In groups 2-4 (n = 20 each), the canals were filled using lateral compaction with gutta-percha and sealer. Removal of root fillings was undertaken after 2 weeks using Gates Glidden burs and hand files without solvent (group 2), with eucalyptol (60 microL; group 3) and with chloroform (60 microL; group 4) to size 50. After further irrigation using sodium hypochlorite and ethylenediaminetetraacetic acid, the roots were split, photographed and scanning electron microscopy (SEM) was performed. The number of filled dentinal tubules (SEM) and the surface covered by root filling remnants (photographs) were evaluated for the coronal, middle and apical third of each root half. Statistical analysis was performed via mixed model for clustered data followed by Tukey's test. RESULTS: After pooling the results of all thirds of the canal, open tubules were more prevalent in the control group, followed by the nonsolvent group, the eucalyptol group and the chloroform group (P < 0.05 between all groups). Less surface was covered by root filling remnants in the nonsolvent group than in the eucalyptol group and the chloroform group (P < 0.05); again, fewer remnants were found in the control group than in all other groups (P < 0.05). CONCLUSIONS: Solvents led to more gutta-percha and sealer remnants on root canal walls and inside dentinal tubules.

Results of a prospective randomized controlled trial of posterior ZrSiO(4)-ceramic crowns.

The aim of this randomized controlled clinical trial was to evaluate over a 5-year period, the clinical outcome of shrinkage-free ZrSiO(4)-ceramic (KaVo Everest HPC) full coverage crowns on posterior teeth in comparison with conventional gold crowns that served as the control. This study reports results of a 5-year study protocol up to 24 months. Patients totalling 224 were randomly divided into two treatment groups. Of these, 123 patients were restored with 123 Everest HPC crowns, fabricated by the Kavo Everest computer-aided manufacturing (CAM) procedure and 101 patients received 101 gold crowns, but two were excluded from analysis. All crowns were conventionally cemented with glass-ionomer cement. After an observation period of 6, 12 and 24 months, the prospective survival rates (Kaplan-Meier) for the KaVo Everest HPC crowns were 97.9%, 95.1% and 89.8% and for the gold crowns 100%, 94.8% and 92.7%, respectively. There were no significant differences between the two groups (P = 0.2). The 1-year failure rates were 4.9% for the KaVo Everest HPC crowns and 5.2% for the gold crowns. The 1-year cumulative risks for loss of vitality, secondary caries, fractures, loss of crown and extraction of abutment of the analyzed abutments (88) were 8.9%, 0%, 0%, 1.1% and 1.1%, respectively, for the gold crowns and 2.8%, 0%, 4.7%, 0% and 0.9%, respectively, for the ceramic crowns (107 analyzed abutments). No perfect marginal fit was shown by 49.5% of the evaluated ceramic crowns and 26.1% of the gold crowns. Only 1.9% of the KaVo Everest HPC crowns had a marginal crevice. In conclusion, Everest HPC crowns with an adequate occlusal tooth reduction of >1.5 mm are suitable for posterior restorations, but the marginal fit shows a potential for improvement.

Effectiveness of a hospital-wide infection control programme on the incidence of healthcare-associated infections and associated severe sepsis and septic shock: a prospective interventional study.

OBJECTIVES: To evaluate whether a hospital-wide infection control programme (ICP) is effective at reducing the burden of healthcare-associated infections (HAIs) and associated severe sepsis/septic shock or death (severe HAIs). METHODS: Prospective, quasi-experimental study with two surveillance periods (September 2011 to August 2012; May 2013 to August 2014). Starting October 2012, the ICP included hand hygiene promotion and bundle implementation for common HAIs. We applied segmented mixed-effects Poisson regression and multi-state models. We reported adjusted incidence rate ratios (aIRR) and adjusted hazard ratios (aHR) with 95% confidence intervals (CI). RESULTS: Overall, 62 154 patients were under surveillance, with 1568 HAIs identified in 1170 patients (4.3 per 100 admissions) in the first and 2336 HAIs identified in 1711 patients (4.9 per 100 admissions) in the second surveillance period. No differences were found in the overall HAI incidence rates between the periods in the general wards (aIRR 1.29, 95% CI 0.78-2.15) and intensive care units (ICUs) (aIRR 0.59, 95% CI 0.27-1.31). However, the HAI incidence rate was declining in the ICUs after starting the ICP (aIRR 0.98, 95% CI 0.97-1.00 per 1-week increment), in contrast to general wards (aIRR 1.01, 95% CI 1.00-1.02). A reduction in severe HAIs (aIRR 0.13, 95% CI 0.05-0.32) and a lower probability of HAI-associated in-hospital deaths (aHR 0.56, 95% CI 0.31-0.99) were observed in the second period in the ICUs. CONCLUSIONS: There was no overall reduction in HAIs after implementation of the ICP. However, there was a significant reduction in severe HAIs in ICUs. Whether this difference was a consequence of the ICP or improvement in HAI case management is not clear.

Accurate variance estimation for prevalence ratios.

OBJECTIVES: The log-binomial model is recommended for calculating the prevalence ratio in cross-sectional studies with binary outcomes. However, convergence problems may occur as this model is numerically unstable. If this happens, the Poisson model should be used, but the Poisson model variance needs to be adjusted. Here, we compare different adjustments. METHODS: Using simulation we evaluated the performance of Poisson models with i) a robust variance, ii) the scale parameter adjusted by Pearson's chi-square, and iii) the scale parameter adjusted by the deviance. These models were compared with the log-binomial model with respect to hypothesis testing. Confounding and effect modification are considered. RESULTS: All adjustment models improved the variance estimation. The Poisson model with a robust variance performed best. When the log-binomial model is numerically stable as well as unstable, this model yields reasonable power and type I error values. But the Poisson model with the scale parameter adjusted by Pearson's chi-square also showed good results. CONCLUSIONS: When estimating prevalence ratios, if the log-binomial fails to converge, we recommend the Poisson model with a robust estimate of variance.

Attributable mortality due to nosocomial infections. A simple and useful application of multistate models.

OBJECTIVES: Nosocomial infections constitute a major medical problem leading to increased morbidity and mortality of patients. Besides prolongation of length of hospital stay, hospital mortality attributable to those infections is often the quantity of interest when describing their impact and consequences. Since occurrence of nosocomial infections is a time-dynamic process, estimation of this quantity might be hampered by that fact. A general framework shall be developed for defining and estimating attributable mortality that in addition is taking discharge of patients as competing risk and potential censoring of observation time into account. METHODS: Since the term "attributable mortality" is used in a variety of meanings we first review basic definitions; the quantities of interest are then derived in terms of transition probabilities arising in a suitably defined multistate model that allows straightforward estimation and interpretation. Bootstrap resampling is used to calculate corresponding standard errors and confidence intervals. RESULTS: The methodology is applied to the data of the SIR-3 study, a prospective cohort study on the incidence of nosocomial infections in intensive care unit patients. Occurrence of nosocomial pneumonia is shown to be associated with increased mortality; the population-attributable fraction is estimated as 7.7% (95% confidence interval: 2.6-12.8%) for an observation period of 120 days. CONCLUSION: Attributable mortality is an important risk measure in epidemiology. If risk exposure is time dependent, multistate models provide an easily understandable framework to define and estimate attributable mortality. The approach is capable of handling competing events, which are omnipresent in clinical research and censoring.

Landmark prediction of nosocomial infection risk to disentangle short- and long-stay patients.

Length of stay is one of the key determinants for the risk of nosocomial infections. The distribution of this at-risk time is heavily skewed and depends on discharge or death. This study applied landmark competing risk prediction models to account for a large proportion of short-stay patients and a small proportion of long-stay patients.

Staphylococcus aureus colonization at ICU admission as a risk factor for developing S. aureus ICU pneumonia.

OBJECTIVE: To quantify the incidence of intensive care unit (ICU)-acquired pneumonia caused by Staphylococcus aureus (S. aureus) and its association with S. aureus colonization at ICU admission. METHODS: This was a post-hoc analysis of two cohort studies in critically ill patients. The primary outcome was the incidence of microbiologically confirmed S. aureus ICU-acquired pneumonia. Incidences of S. aureus ICU pneumonia and associations with S. aureus colonization at ICU admission were determined using competing risks analyses. In all ICUs, patients were screened for respiratory tract S. aureus carriage on admission as part of infection control policies. Pooling of data was not deemed possible because of heterogeneity in baseline differences in patient population. RESULTS: The two cohort studies contained data of 9156 ICU patients. The average carriage rate of S. aureus among screened patients was 12.7%. In total, 1185 (12.9%) patients developed ICU pneumonia. Incidences of S. aureus ICU pneumonia were 1.33% and 1.08% in cohorts 1 and 2, respectively. After accounting for competing events, the adjusted subdistribution hazard ratio (SHR) of S. aureus colonization at admission for developing S. aureus ICU pneumonia was 9.55 (95% CI 5.31-17.18) in cohort 1 and 14.54 (95% CI 7.24-29.21) in cohort 2. CONCLUSION: The overall cumulative incidence of S. aureus ICU pneumonia in these ICUs was low. Patients colonized with S. aureus at ICU admission had an up to 15 times increased risk for developing this outcome compared with non-colonized patients.

Quantifying the Burden of Hospital-Acquired Bloodstream Infection in Children in England by Estimating Excess Length of Hospital Stay and Mortality Using a Multistate Analysis of Linked, Routinely Collected Data.

BACKGROUND: Hospital-acquired bloodstream infection (HA-BSI) is associated with substantial morbidity, mortality, and healthcare costs in all patient populations. Young children have been shown to have a high rate of healthcare-associated infections compared with the adult population. We aimed to quantify the excess mortality and length of stay in pediatric patients from HA-BSI. METHODS: We analyzed data collected retrospectively from a probabilistically linked national database of pediatric (aged 1 month-18 years) in-patients with a microbiologically confirmed HA-BSI in England between January and March 2009. A time-dependent Cox regression model was fit to determine the presence of any effect. Furthermore, a multistate model, adjusted for the time to onset of HA-BSI, was used to compare outcomes in patients with HA-BSI to those without HA-BSI. We further adjusted for patients' characteristics as recorded in hospital admission data. RESULTS: The dataset comprised 333 605 patients, with 214 cases of HA-BSI. After adjustment for time to HA-BSI and comorbidities, the hazard for discharge (dead or alive) from hospital for patients with HA-BSI was 0.9 times (95% confidence interval [CI], .8-1.1) that of noninfected patients. Excess length of stay associated with all-cause HA-BSI was 1.6 days (95% CI, .2-3.0), although this duration varied by pathogen. Patients with HA-BSI had a 3.6 (95% CI, 1.3-10.4) times higher hazard for in-hospital death than noninfected patients. CONCLUSIONS: Hospital-acquired bloodstream infection increased the length of stay and mortality of pediatric inpatients. The results of this study provide an evidence base to judge the health and economic impact of programs to prevent and control HA-BSI in children.

Analysis of Clinical Cohort Data Using Nested Case-control and Case-cohort Sampling Designs. A Powerful and Economical Tool.

BACKGROUND: Sampling from a large cohort in order to derive a subsample that would be sufficient for statistical analysis is a frequently used method for handling large data sets in epidemiological studies with limited resources for exposure measurement. For clinical studies however, when interest is in the influence of a potential risk factor, cohort studies are often the first choice with all individuals entering the analysis. OBJECTIVES: Our aim is to close the gap between epidemiological and clinical studies with respect to design and power considerations. Schoenfeld's formula for the number of events required for a Cox' proportional hazards model is fundamental. Our objective is to compare the power of analyzing the full cohort and the power of a nested case-control and a case-cohort design. METHODS: We compare formulas for power for sampling designs and cohort studies. In our data example we simultaneously apply a nested case-control design with a varying number of controls matched to each case, a case cohort design with varying subcohort size, a random subsample and a full cohort analysis. For each design we calculate the standard error for estimated regression coefficients and the mean number of distinct persons, for whom covariate information is required. RESULTS: The formula for the power of a nested case-control design and the power of a case-cohort design is directly connected to the power of a cohort study using the well known Schoenfeld formula. The loss in precision of parameter estimates is relatively small compared to the saving in resources. CONCLUSIONS: Nested case-control and case-cohort studies, but not random subsamples yield an attractive alternative for analyzing clinical studies in the situation of a low event rate. Power calculations can be conducted straightforwardly to quantify the loss of power compared to the savings in the num-ber of patients using a sampling design instead of analyzing the full cohort.

Interventions to control nosocomial infections: study designs and statistical issues.

There is a wide range of potential study designs for intervention studies to decrease nosocomial infections in hospitals. The analysis is complex due to competing events, clustering, multiple timescales and time-dependent period and intervention variables. This review considers the popular pre-post quasi-experimental design and compares it with randomized designs. Randomization can be done in several ways: randomization of the cluster [intensive care unit (ICU) or hospital] in a parallel design; randomization of the sequence in a cross-over design; and randomization of the time of intervention in a stepped-wedge design. We introduce each design in the context of nosocomial infections and discuss the designs with respect to the following key points: bias, control for non-intervention factors, and generalizability. Statistical issues are discussed. A pre-post-intervention design is often the only choice that will be informative for a retrospective analysis of an outbreak setting. It can be seen as a pilot study with further, more rigorous designs needed to establish causality. To yield internally valid results, randomization is needed. Generally, the first choice in terms of the internal validity should be a parallel cluster randomized trial. However, generalizability might be stronger in a stepped-wedge design because a wider range of ICU clinicians may be convinced to participate, especially if there are pilot studies with promising results. For analysis, the use of extended competing risk models is recommended.

In vivo study of the initial bacterial adhesion on different implant materials.

OBJECTIVE: Biofilm formation on implant materials plays a major role in the aetiology of periimplantitis. The aim of this study was to examine in vivo the initial bacterial adhesion on six different implant materials. METHODS: The implant materials Ti-m, TiUnite®, ZiUnite®, ATZ-m, ATZ-s, TZP-A-m were tested using bovine enamel slabs as controls. All materials, fixed on splint systems, were examined after 30 min and 120 min of oral exposure. DAPI staining was used for quantitative analysis of the initially adherent microorganisms. Initial adherent microorganisms were visualised by fluorescence In situ-hybridisation (FISH) and quantified by confocal laser scanning microscopy (CLSM). The targets of the oligonucleotide probes were Eubacteria, Veillonella spp., Fusobacterium nucleatum, Actinomyces naeslundii and Streptococcus spp. RESULTS: DAPI analysis showed that increasing the time of oral exposure resulted in an increasing amount of initial adherent bacteria. The highest level of colonisation was on ZiUnite®, with the lowest occurring on the bovine enamel, followed by Ti-m. This early colonisation correlated significantly with the surface roughnesses of the materials. FISH and CLSM showed no significant differences relating to total bacterial composition. However, Streptococcus spp. was shown to be the main colonisers on each of the investigated materials. CONCLUSION: it could be shown that within an oral exposure time of 30 min and 120 min, despite the salivary acquired pellicle initial biofilm formation is mainly influenced directly or indirect by the material surface topography. Highly polished surfaces should minimise the risk of biofilm formation, plaque accumulation and possibly periimplantitis.

Multistate modelling to estimate the excess length of stay associated with meticillin-resistant Staphylococcus aureus colonisation and infection in surgical patients.

Currently available evidence on the excess length of stay (LOS) associated with nosocomial infections is limited by methodology, including time-dependent bias. To determine the excess LOS associated with nosocomial meticillin-resistant Staphylococcus aureus (MRSA) infection and colonisation, 797 MRSA-colonised, 167 MRSA-infected and 13,640 MRSA-negative surgical patients were included in a multistate model. The occurrence of MRSA infection or colonisation was the time-dependent exposure, and discharge or death was the study endpoint. The excess LOS was extracted by computing the Aalen-Johansen estimator of the matrix of transition probabilities. Multivariate Cox regression analysis was used to assess the independent effect of MRSA on excess LOS. MRSA infection prolonged LOS by 14.5 [95% confidence interval (CI): 7.8, 21.3] days compared to uninfected patients, and by 5.9 (95% CI: 0.1, 11.7) days compared to patients only colonised by MRSA. The hazard of discharge was reduced by nosocomial MRSA infection both with respect to MRSA-free patients and MRSA carriers [adjusted hazard ratio (HR): 0.69; 95% CI: 0.59, 0.81; and HR: 0.79; 95% CI: 0.65, 0.95, respectively]. MRSA carriage alone did not decrease the hazard of discharge after adjustment for confounding (HR: 1.00; 95% CI: 0.93, 1.07). Multistate modelling is a promising statistical method to evaluate the health-economic impact of nosocomial antibiotic-resistant infections.