Derivation and validation of a simple clinical bedside score (ATLAS) for Clostridium difficile infection which predicts response to therapy

BACKGROUND

Clostridium difficile infection (CDI) continues to be a frequent and potentially severe infection. There is currently no validated clinical tool for use at the time of CDI diagnosis to categorize patients in order to predict response to therapy.

METHODS

Six clinical and laboratory variables, measured at the time of CDI diagnosis, were combined in order to assess their correlation with treatment response in a large CDI clinical trial database (derivation cohort). The final categorization scheme was chosen in order to maximize the number of categories (discrimination) while maintaining a high correlation with clinical cure assessed two days after the end of therapy. Validation of the derived scoring scheme was done on a second large CDI clinical trial database (validation cohort). A third comparison was done on the two pooled databases (pooled cohort).

RESULTS

In the derivation cohort, the best discrimination and correlation with cure was seen with a five-component ATLAS score (age, treatment with systemic antibiotics, leukocyte count, albumin and serum creatinine as a measure of renal function), which divided CDI patients into 11 groups (scores of 0 to 10 inclusive) and was highly correlated with treatment outcome (R(2) = 0.95; P<0.001). This scheme showed excellent prediction of cure in the validation cohort (overall Kappa = 95.2%; P<0.0001), as well as in the pooled cohort, regardless of treatment (fidaxomicin or vancomycin).

CONCLUSIONS

A combination of five simple and commonly available clinical and laboratory variables measured at the time of CDI diagnosis, combined into a scoring system (ATLAS), are able to accurately predict treatment response to CDI therapy. The ATLAS scoring system may be useful in stratifying CDI patients so that appropriate therapies can be chosen to maximize cure rates, as well as for categorization of patients in CDI therapeutic studies in order allow comparisons of patient groups.

Fluid-structure interactions in micro-interlocked regions of the cement-bone interface

Experimental tests and computational modelling were used to explore the fluid dynamics at the trabeculae-cement interlock regions found in the tibial component of total knee replacements. A cement-bone construct of the proximal tibia was created to simulate the immediate post-operative condition. Gap distributions along nine trabeculae-cement regions ranged from 0 to 50.4 μm (mean = 12 μm). Micro-motions ranged from 0.56 to 4.7 μm with a 1 MPa compressive load to the cement. Fluid-structure analysis between the trabeculae and the cement used idealised models with parametric evaluation of loading direction, gap closing fraction (GCF), gap thickness, loading frequency and fluid viscosity. The highest fluid shear stresses (926 Pa) along the trabecular surface were found for conditions with very thin and large GCFs, much larger than reported physiological levels (~1-5 Pa). A second fluid-structure model was created with a provision for bone resorption using a constitutive model with resorption velocity proportional to fluid shear rate. A lower cut-off was used, below which bone resorption would not occur (50 s(-1)). Results showed that there was initially high shear rates (>1000 s(-1)) that diminished after initial trabecular resorption. Resorption continued in high shear rate regions, resulting in a final shape with bone left deep in the cement layer, and is consistent with morphology found in post-mortem retrievals. Small gaps between the trabecular surface and the cement in the immediate post-operative state produce fluid flow conditions that appear to be supra-physiologic; these may cause fluid-induced lysis of trabeculae in the micro-interlock regions.

Immunohistochemical evaluation of the effects of paraffin section storage on biomarker stability

Environmental stresses can alter immunoreactivity of biomarkers in stored tissue sections. The effect of temperature and lighting on 49 cellular or microbial antigens was evaluated in 4 serial paraffin sections, cut 12 months, 10 months, 8 months, 5 months, 3 months, 1 month, 3 days, and 1 day before immunohistochemistry. Slides were stored at room temperature (RT) in the dark, at 4°C in the dark, at RT under fluorescent light, or at RT with windowpane exposure to sunlight. Immunohistochemistry was performed simultaneously in an automated immunostainer. Immunoreactivity was compared with that in the corresponding 1-day-old section and scored as 4 (<10% reduction), 3 (10%-25% reduction), 2 (26%-60% reduction), 1(>60% reduction), or 0 (no reactivity). Any loss of immunoreactivity was proportional to the tissue section age and was least in sections stored in the dark. Immunoreactivity was only completely lost in light-exposed sections and as early as 1 month for CD45. Other markers with complete loss of immunoreactivity were bovine viral diarrhea virus, CD18 (only with fluorescent light), CD31, CD68, canine parvovirus, chromogranins, and thyroid transcription factor-1. Markers with complete loss after light exposure also had reduced immunoreactivity when stored in the dark, as early as day 3. Eight markers (Bartonella spp, CD11d, high molecular weight cytokeratins, feline coronavirus, GATA-4, insulin, p63, progesterone receptor) had minimal decrease in immunoreactivity, regardless of treatment. In conclusion, light-induced antigen decay (tissue section aging) is antigen dependent and could explain unexpectedly weak or negative immunohistochemical reactions in stored paraffin sections.

Latitudinal variations in seasonal activity of influenza and respiratory syncytial virus (RSV): a global comparative review

BACKGROUND

There is limited information on influenza and respiratory syncytial virus (RSV) seasonal patterns in tropical areas, although there is renewed interest in understanding the seasonal drivers of respiratory viruses.

METHODS

We review geographic variations in seasonality of laboratory-confirmed influenza and RSV epidemics in 137 global locations based on literature review and electronic sources. We assessed peak timing and epidemic duration and explored their association with geography and study settings. We fitted time series model to weekly national data available from the WHO influenza surveillance system (FluNet) to further characterize seasonal parameters.

RESULTS

Influenza and RSV activity consistently peaked during winter months in temperate locales, while there was greater diversity in the tropics. Several temperate locations experienced semi-annual influenza activity with peaks occurring in winter and summer. Semi-annual activity was relatively common in tropical areas of Southeast Asia for both viruses. Biennial cycles of RSV activity were identified in Northern Europe. Both viruses exhibited weak latitudinal gradients in the timing of epidemics by hemisphere, with peak timing occurring later in the calendar year with increasing latitude (P<0.03). Time series model applied to influenza data from 85 countries confirmed the presence of latitudinal gradients in timing, duration, seasonal amplitude, and between-year variability of epidemics. Overall, 80% of tropical locations experienced distinct RSV seasons lasting 6 months or less, while the percentage was 50% for influenza.

CONCLUSION

Our review combining literature and electronic data sources suggests that a large fraction of tropical locations experience focused seasons of respiratory virus activity in individual years. Information on seasonal patterns remains limited in large undersampled regions, included Africa and Central America. Future studies should attempt to link the observed latitudinal gradients in seasonality of viral epidemics with climatic and population factors, and explore regional differences in disease transmission dynamics and attack rates.

Effect of age on treatment outcomes in Clostridium difficile infection

OBJECTIVES

To determine the effect of advancing age on the clinical outcomes of Clostridium difficile (CDI) treatment.

DESIGN

Regression modeling of results from two double-blind randomized multicenter studies on the treatment of primary and first recurrent cases of CDI to examine for effects of age and study drug on outcomes of cure (resolution of diarrhea), recurrence within 4 weeks of completing successful therapy, and cure without recurrence.

SETTING

Participants were randomized into studies in the United States, Canada, and Europe.

PARTICIPANTS

Nine hundred ninety-nine individuals with toxin-positive CDI were randomized to receive vancomycin (125 mg 4 times daily) or fidaxomicin (200 mg twice daily) for 10 days.

MEASUREMENTS

The effect of advancing age in those aged 18 to 40 years and in 10-year increments thereafter was examined.

RESULTS

The model predicts a 17% lower clinical cure, 17% greater recurrence, and 13% lower sustained clinical response by advancing decade than in those younger than 40 (P < .01 each). Clinical cure was similar in the fidaxomicin and vancomycin treatment groups, although fidaxomicin was associated with a more than 50% lower relative risk for recurrence than vancomycin (P < .001). Multivariate regression modeling showed that risk factors accounting for poorer outcomes with advancing age include infection with the BI strain type, inpatient status, renal insufficiency, leukocytosis, hypoalbuminemia, and concomitant medication exposure.

CONCLUSION

Measurable and progressive deterioration in CDI treatment outcomes occurred with advancing age in those aged 40 and older, highlighting the need for prevention and treatment strategies. Fidaxomicin treatment was associated with a 60% lower risk of recurrence than vancomycin after adjusting for age, concomitant antibiotics, and C. difficile strain.

Correlation of inflammation with adrenocortical atrophy in canine adrenalitis

Hypoadrenocorticism or Addison's disease (AD) is a functional disorder in which insufficient mineralocorticoid and glucocorticoid hormones are produced by the adrenal cortex. Human AD is usually attributed to lymphoplasmacytic adrenalitis with autoimmune destruction of the adrenal cortex. Lymphoplasmacytic adrenalitis is also reported in some descriptions of canine AD; however, the histological aspects of adrenalitis or adrenocortical atrophy have not been well characterized because microscopical examination is not required for diagnosis of AD. In this study, sections of adrenal glands from 33 dogs with adrenalitis were compared with those of 37 dogs without adrenal lesions. The affected dogs were classified clinically as having AD (n = 3), being suspected of having AD (n = 17), not having AD (n = 11) or were unclassified (n = 2). The adrenal inflammation was lymphoplasmacytic in 17 dogs, lymphocytic in four, lymphohistiocytic in one, granulomatous in three and neutrophilic in eight cases. Adrenal glands from control dogs lacked leucocyte infiltration and had a cortical to medullary area ratio of 1.1-7.2. All three dogs with AD, 8/17 dogs with suspected AD and 1/11 dogs without AD had a cortical to medullary area ratio <1.1. Because the area ratio was correlated (r = 0.94) with a linear cortical to medullary thickness ratio, a thickness ratio <1.1 could also indicate severe adrenocortical atrophy. Severe adrenocortical atrophy was associated typically with lymphoplasmacytic infiltration and nearly complete loss of cortical cells; however, the zona glomerulosa was partially spared in three dogs with lymphoplasmacytic adrenalitis and severe cortical atrophy. In contrast, non-lymphoid inflammation was generally part of systemic disease, multifocal and was unaccompanied by severe adrenocortical atrophy.

The influence of climatic conditions on the transmission dynamics of the 2009 A/H1N1 influenza pandemic in Chile

Background

The role of demographic factors, climatic conditions, school cycles, and connectivity patterns in shaping the spatio-temporal dynamics of pandemic influenza is not clearly understood. Here we analyzed the spatial, age and temporal evolution of the 2009 A/H1N1 influenza pandemic in Chile, a southern hemisphere country covering a long and narrow strip comprising latitudes 17°S to 56°S.

Methods

We analyzed the dissemination patterns of the 2009 A/H1N1 pandemic across 15 regions of Chile based on daily hospitalizations for severe acute respiratory disease and laboratory confirmed A/H1N1 influenza infection from 01-May to 31-December, 2009. We explored the association between timing of pandemic onset and peak pandemic activity and several geographical and demographic indicators, school vacations, climatic factors, and international passengers. We also estimated the reproduction number (R) based on the growth rate of the exponential pandemic phase by date of symptoms onset, estimated using maximum likelihood methods.

Results

While earlier pandemic onset was associated with larger population size, there was no association with connectivity, demographic, school or climatic factors. In contrast, there was a latitudinal gradient in peak pandemic timing, representing a 16-39-day lag in disease activity from the southern regions relative to the northernmost region (P < 0.001). Geographical differences in latitude of Chilean regions, maximum temperature and specific humidity explained 68.5% of the variability in peak timing (P = 0.01). In addition, there was a decreasing gradient in reproduction number from south to north Chile (P < 0.0001). The regional mean R estimates were 1.6-2.0, 1.3-1.5, and 1.2-1.3 for southern, central and northern regions, respectively, which were not affected by the winter vacation period.

Conclusions

There was a lag in the period of most intense 2009 pandemic influenza activity following a South to North traveling pattern across regions of Chile, significantly associated with geographical differences in minimum temperature and specific humidity. The latitudinal gradient in timing of pandemic activity was accompanied by a gradient in reproduction number (P < 0.0001). Intensified surveillance strategies in colder and drier southern regions could lead to earlier detection of pandemic influenza viruses and improved control outcomes.

Reduced acquisition and overgrowth of vancomycin-resistant enterococci and Candida species in patients treated with fidaxomicin versus vancomycin for Clostridium difficile infection

Fidaxomicin causes less disruption of anaerobic microbiota during treatment of Clostridium difficile infection (CDI) than vancomycin and has activity against many vancomycin-resistant enterococci (VRE). In conjunction with a multicenter randomized trial of fidaxomicin versus vancomycin for CDI treatment, we tested the hypothesis that fidaxomicin promotes VRE and Candida species colonization less than vancomycin. Stool was cultured for VRE and Candida species before and after therapy. For patients with negative pretreatment cultures, the incidence of VRE and Candida species acquisition was compared. For those with preexisting VRE, the change in concentration during treatment was compared. The susceptibility of VRE isolates to fidaxomicin was assessed. Of 301 patients, 247 (82%) had negative VRE cultures and 252 (84%) had negative Candida species cultures before treatment. In comparison with vancomycin-treated patients, fidaxomicin-treated patients had reduced acquisition of VRE (7% vs 31%, respectively; P < .001) and Candida species (19% vs 29%, respectively; P = .03). For patients with preexisting VRE, the mean concentration decreased significantly in the fidaxomicin group (5.9 vs 3.8 log₁₀ VRE/g stool; P = .01) but not the vancomycin group (5.3 vs 4.2 log₁₀ VRE/g stool; P = .20). Most VRE isolates recovered after fidaxomicin treatment had elevated fidaxomicin minimum inhibitory concentrations (MICs; MIC₉₀, 256 µg/mL), and subpopulations of VRE with elevated fidaxomicin MICs were common before therapy. Fidaxomicin was less likely than vancomycin to promote acquisition of VRE and Candida species during CDI treatment. However, selection of preexisting subpopulations of VRE with elevated fidaxomicin MICs was common during fidaxomicin therapy.

Clinical Trials Registration. NCT00314951.

Fidaxomicin versus vancomycin for Clostridium difficile infection: meta-analysis of pivotal randomized controlled trials

Two recently completed phase 3 trials (003 and 004) showed fidaxomicin to be noninferior to vancomycin for curing Clostridium difficile infection (CDI) and superior for reducing CDI recurrences. In both studies, adults with active CDI were randomized to receive blinded fidaxomicin 200 mg twice daily or vancomycin 125 mg 4 times a day for 10 days. Post hoc exploratory intent-to-treat (ITT) time-to-event analyses were undertaken on the combined study 003 and 004 data, using fixed-effects meta-analysis and Cox regression models. ITT analysis of the combined 003/004 data for 1164 patients showed that fidaxomicin reduced persistent diarrhea, recurrence, or death by 40% (95% confidence interval [CI], 26%–51%; P < .0001) compared with vancomycin through day 40. A 37% (95% CI, 2%–60%; P = .037) reduction in persistent diarrhea or death was evident through day 12 (heterogeneity P = .50 vs 13–40 days), driven by 7 (1.2%) fidaxomicin versus 17 (2.9%) vancomycin deaths at <12 days. Low albumin level, low eosinophil count, and CDI treatment preenrollment were risk factors for persistent diarrhea or death at 12 days, and CDI in the previous 3 months was a risk factor for recurrence (all P < .01). Fidaxomicin has the potential to substantially improve outcomes from CDI.

Renal failure and leukocytosis are predictors of a complicated course of Clostridium difficile infection if measured on day of diagnosis

Nonsevere Clostridium difficile infection (CDI) and severe CDI, which carries a higher risk than nonsevere CDI for treatment failure and CDI recurrence, are difficult to distinguish at the time of diagnosis. To investigate the prognostic value of 3 markers of severe CDI suggested by recent guidelines (fever, leukocytosis, and renal failure), we used the database of 2 randomized controlled trials, which contained information for 1105 patients with CDI. Leukocytosis (risk ratio [RR], 2.29; 95% confidence interval [CI], 1.63–3.21) and renal failure (RR, 2.52; 95% CI, 1.82–3.50) were associated with treatment failure. Fever, although associated with treatment failure (RR, 2.45; 95% CI, 1.07–5.61), was rare. Renal failure was the only significant predictor of recurrence (RR, 1.45; 95% CI, 1.05–2.02). Different timing of measurements of leukocyte count and serum creatinine level around the CDI diagnosis led to a different severity classification in many cases. In conclusion, both leukocytosis and renal failure are useful predictors, although timing of measurement is important.

Fidaxomicin attains high fecal concentrations with minimal plasma concentrations following oral administration in patients with Clostridium difficile infection

Fidaxomicin has recently been approved for the treatment of Clostridium difficile infection (CDI). As part of phase III studies, plasma and fecal samples were analyzed for concentrations of fidaxomicin and its metabolite, OP-1118. Plasma samples were collected before and after dose receipt on the first and last days of therapy, and fecal samples were collected on the last day of therapy. Samples were analyzed for fidaxomicin and OP-1118 (metabolite), using validated liquid chromatography/tandem mass spectrometric methods. Plasma concentrations were low for both fidaxomicin (mean [± standard deviation {SD}], 22.8 ± 26.7 ng/mL and 28.5 ± 33.4 ng/mL on the first and last days of therapy, respectively) and OP-1118 (mean [±SD], 44.5 ± 50.4 ng/mL and 85.6 ± 131 ng/mL, respectively). In contrast, fecal levels were >1000 µg/g for fidaxomicin and >800 µg/g for OP-1118. Fidaxomicin mean fecal levels were >5000 times the minimum inhibitory concentration for C. difficile of 0.25 µg/mL.

Treatment of first recurrence of Clostridium difficile infection: fidaxomicin versus vancomycin

Recurrence of Clostridium difficile infection (CDI) occurs in approximately 25% of successfully treated patients. Two phase 3 randomized, double-blind trials were conducted at 154 sites in the United States, Canada, and Europe to compare fidaxomicin vs vancomycin in treating CDI. Patients with CDI received fidaxomicin 200 mg twice daily or vancomycin 125 mg 4 times daily for 10 days. The primary end point was clinical cure of CDI at end of treatment, and a secondary end point was recurrence during the 28 days following clinical cure. In all, 1164 subjects were enrolled, of which a subgroup of 128 in the per-protocol population had another recent episode of CDI prior to the CDI diagnosis at study enrollment. In the analysis of this subgroup, initial response to therapy was similar for both drugs (>90% cure). However, recurrence within 28 days occurred in 35.5% of patients treated with vancomycin and 19.7% of patients treated with fidaxomicin (−15.8% difference; 95% confidence interval, −30.4% to −0.3%; P = .045). Early recurrence (within 14 days) was reported in 27% of patients treated with vancomycin and 8% of patients treated with fidaxomicin (P = .003). In patients with a first recurrence of CDI, fidaxomicin was similar to vancomycin in achieving a clinical response at end of therapy but superior in preventing a second recurrence within 28 days.

Clinical Trials Registration. NCT00314951 and NCT00468728.

Cutaneous metastasis of transitional cell carcinoma in 12 dogs

In humans, cutaneous metastasis of transitional cell carcinoma (TCC) has been attributed to direct extension, lymphatic or hematogenous dissemination, or surgical implantation. The purpose of this study was to characterize the clinical and histologic features of cutaneous TCC metastasis, confirmed by uroplakin-III immunohistochemistry, in dogs. The 12 cases were 9 spayed female and 3 neutered male dogs, 6 to 14 years old (mean, 11 years). Four dogs had a history of urinary incontinence. Three had undergone abdominal surgery for TCC diagnosis or treatment. The primary neoplasms were 7 papillary infiltrating and 5 nonpapillary infiltrating TCC. Cutaneous lesions were detected at a mean of 123 days (median, 38 days) after diagnosis of the primary TCC and appeared as plaques, papules, or nodules in, with 1 exception, perineal, inguinal, or ventral abdominal dermis or subcutis. Of 8 dogs with dermal TCC, 5 had epidermal erosion or ulceration. In 10 dogs, TCC was detected in cutaneous lymphatic vessels, identified by endothelial immunoreactivity for Prox1. Metastases were also detected in lymph nodes in all dogs and at distant noncutaneous sites, usually the lungs, in 10 dogs. Mean survival after diagnosis was 162 days (median, 90 days). Despite medical treatment of 10 dogs after the development of cutaneous metastasis, remission was not achieved; 4 dogs had stable disease. Although TCC could have spread to skin by direct extension or lymphatic or vascular dissemination, the proximity of most cutaneous metastases to the vulva or prepuce raises the additional possibility of transepidermal spread through urine-scalded skin.

Epidemiological characterization of a fourth wave of pandemic A/H1N1 influenza in Mexico, winter 2011-2012: age shift and severity

BACKGROUND AND AIMS

A substantial recrudescent wave of pandemic influenza A/H1N1 affected the Mexican population from December 1, 2011-March 20, 2012 following a 2-year period of sporadic transmission.

METHODS

We analyzed demographic and geographic data on all hospitalizations with severe acute respiratory infection (SARI) and laboratory-confirmed A/H1N1 influenza, and inpatient deaths, from a large prospective surveillance system maintained by a Mexican social security medical system during April 1, 2009-March 20, 2012. We also estimated the reproduction number (R) based on the growth rate of the daily case incidence by date of symptoms onset.

RESULTS

A total of 7569 SARI hospitalizations and 443 in-patient deaths (5.9%) were reported between December 1, 2011, and March 20, 2012 (1115 A/H1N1-positive inpatients and 154 A/H1N1-positive deaths). The proportion of laboratory-confirmed A/H1N1 hospitalizations and deaths was higher among subjects ≥60 years of age (χ(2) test, p <0.0001) and lower among younger age groups (χ(2) test, p <0.04) for the 2011-2012 pandemic wave compared to the earlier waves in 2009. The reproduction number of the winter 2011-2012 wave in central Mexico was estimated at 1.2-1.3, similar to that reported for the fall 2009 wave, but lower than that of spring 2009.

CONCLUSIONS

We documented a substantial increase in the number of SARI hospitalizations during the period December 2011-March 2012 and an older age distribution of laboratory-confirmed A/H1N1 influenza hospitalizations and deaths relative to 2009 A/H1N1 pandemic patterns. The gradual change in the age distribution of A/H1N1 infections in the post-pandemic period is consistent with a build-up of immunity among younger populations.

Androgen receptor gene expression in the rat central nervous system: Evidence for two mRNA transcripts

Androgen receptor (AR) gene expression in the central nervous system (CNS) and peripheral tissues of male rats was examined using cDNA probes to measure AR mRNA by RNA (Northern) blot analysis and by in situ hybridization. Using a probe from the 5' untranslated region of the rat cDNA (AR-1), a single mRNA species of approximately 11 kb was seen in Northern blots of poly(A)(+) RNA from reproductive tissues, kidney, liver, and muscle. Using a probe from the 5' end of the coding region (AR-2), in addition to the 11-kb band, a novel transcript was seen in whole brain at about 9.3 kb. In poly(A)(+) RNA from dissected brain regions, the 9.3-kb transcript was predominant in the cortex, cerebellum, and brain stem, while in the hippocampus, both transcripts were expressed to a similar degree. AR mRNA levels increased two- to threefold in the prostate on Days 1 and 3 following castration but no significant change was seen in either CNS transcript in whole brain or cortex. Specific in situ hybridization of an (35)S-labeled AR-2 riboprobe was observed in brain regions known to bind radiolabeled androgens. We conclude that two AR RNA species exist in the adult male rat which differ in their 5' untranslated region and that the relative proportion of the two species varies between brain regions. In contrast to observations in the prostate, AR gene expression in the cerebral cortex is not regulated in the short term by androgen withdrawal.

NaxD is a deacetylase required for lipid A modification and Francisella pathogenesis

Modification of specific Gram-negative bacterial cell envelope components, such as capsule, O-antigen and lipid A, are often essential for the successful establishment of infection. Francisella species express lipid A molecules with unique characteristics involved in circumventing host defences, which significantly contribute to their virulence. In this study, we show that NaxD, a member of the highly conserved YdjC superfamily, is a deacetylase required for an important modification of the outer membrane component lipid A in Francisella. Mass spectrometry analysis revealed that NaxD is essential for the modification of a lipid A phosphate with galactosamine in Francisella novicida, a model organism for the study of highly virulent Francisella tularensis. Significantly, enzymatic assays confirmed that this protein is necessary for deacetylation of its substrate. In addition, NaxD was involved in resistance to the antimicrobial peptide polymyxin B and critical for replication in macrophages and in vivo virulence. Importantly, this protein is also required for lipid A modification in F. tularensis as well as Bordetella bronchiseptica. Since NaxD homologues are conserved among many Gram-negative pathogens, this work has broad implications for our understanding of host subversion mechanisms of other virulent bacteria.

Interface micromechanics of transverse sections from retrieved cemented hip reconstructions: an experimental and finite element comparison

In finite element analysis (FEA) models of cemented hip reconstructions, it is crucial to include the cement-bone interface mechanics. Recently, a micromechanical cohesive model was generated which reproduces the behavior of the cement-bone interface. The goal was to investigate whether this cohesive model was directly applicable on a macro level. From transverse sections of retrieved cemented hip reconstructions, two FEA-models were generated. The cement-bone interface was modeled with cohesive elements. A torque was applied and the cement-bone interface micromotions, global stiffness and stem translation were monitored. A sensitivity analysis was performed to investigate whether the cohesive model could be improved. All results were compared with experimental findings. That the original cohesive model resulted in a too compliant macromechanical response; the motions were too large and the global stiffness too small. When the cohesive model was modified, the match with the experimental response improved considerably.

Were equatorial regions less affected by the 2009 influenza pandemic? The Brazilian experience

Although it is in the Tropics where nearly half of the world population lives and infectious disease burden is highest, little is known about the impact of influenza pandemics in this area. We investigated the mortality impact of the 2009 influenza pandemic relative to mortality rates from various outcomes in pre-pandemic years throughout a wide range of latitudes encompassing the entire tropical, and part of the subtropical, zone of the Southern Hemisphere (+5^°N to −35^°S) by focusing on a country with relatively uniform health care, disease surveillance, immunization and mitigation policies: Brazil. To this end, we analyzed laboratory-confirmed deaths and vital statistics mortality beyond pre-pandemic levels for each Brazilian state. Pneumonia, influenza and respiratory mortality were significantly higher during the pandemic, affecting predominantly adults aged 25 to 65 years. Overall, there were 2,273 and 2,787 additional P&I- and respiratory deaths during the pandemic, corresponding to a 5.2% and 2.7% increase, respectively, over average pre-pandemic annual mortality. However, there was a marked spatial structure in mortality that was independent of socio-demographic indicators and inversely related with income: mortality was progressively lower towards equatorial regions, where low or no difference from pre-pandemic mortality levels was identified. Additionally, the onset of pandemic-associated mortality was progressively delayed in equatorial states. Unexpectedly, there was no additional mortality from circulatory causes. Comparing disease burden reliably across regions is critical in those areas marked by competing health priorities and limited resources. Our results suggest, however, that tropical regions of the Southern Hemisphere may have been disproportionally less affected by the pandemic, and that climate may have played a key role in this regard. These findings have a direct bearing on global estimates of pandemic burden and the assessment of the role of immunological, socioeconomic and environmental drivers of the transmissibility and severity of this pandemic.

Structure and stability of charged clusters

When a cluster or nanodroplet bears charge, its structure and thermodynamics are altered and, if the charge exceeds a certain limit, the system becomes unstable with respect to fragmentation. Some of the key results in this area were derived by Rayleigh in the nineteenth century using a continuum model of liquid droplets. Here we revisit the topic using a simple particle-based description, presenting a systematic case study of how charge affects the physical properties of a Lennard-Jones cluster composed of 309 particles. We find that the ability of the cluster to sustain charge depends on the number of particles over which the charge is distributed-a parameter not included in Rayleigh's analysis. Furthermore, the cluster may fragment before the charge is strong enough to drive all charged particles to the surface. The charged particles in stable clusters are therefore likely to reside in the cluster's interior even without considering solvation effects.

Epidemiological characteristics and underlying risk factors for mortality during the autumn 2009 pandemic wave in Mexico

Background

Elucidating the role of the underlying risk factors for severe outcomes of the 2009 A/H1N1 influenza pandemic could be crucial to define priority risk groups in resource-limited settings in future pandemics.

Methods

We use individual-level clinical data on a large series of ARI (acute respiratory infection) hospitalizations from a prospective surveillance system of the Mexican Social Security medical system to analyze clinical features at presentation, admission delays, selected comorbidities and receipt of seasonal vaccine on the risk of A/H1N1-related death. We considered ARI hospitalizations and inpatient-deaths, and recorded demographic, geographic, and medical information on individual patients during August-December, 2009.

Results

Seasonal influenza vaccination was associated with a reduced risk of death among A/H1N1 inpatients (OR = 0.43 (95% CI: 0.25, 0.74)) after adjustment for age, gender, geography, antiviral treatment, admission delays, comorbidities and medical conditions. However, this result should be interpreted with caution as it could have been affected by factors not directly measured in our study. Moreover, the effect of antiviral treatment against A/H1N1 inpatient death did not reach statistical significance (OR = 0.56 (95% CI: 0.29, 1.10)) probably because only 8.9% of A/H1N1 inpatients received antiviral treatment. Moreover, diabetes (OR = 1.6) and immune suppression (OR = 2.3) were statistically significant risk factors for death whereas asthmatic persons (OR = 0.3) or pregnant women (OR = 0.4) experienced a reduced fatality rate among A/H1N1 inpatients. We also observed an increased risk of death among A/H1N1 inpatients with admission delays >2 days after symptom onset (OR = 2.7). Similar associations were also observed for A/H1N1-negative inpatients.

Conclusions

Geographical variation in identified medical risk factors including prevalence of diabetes and immune suppression may in part explain between-country differences in pandemic mortality burden. Furthermore, access to care including hospitalization without delay and antiviral treatment and are also important factors, as well as vaccination coverage with the 2008–09 trivalent inactivated influenza vaccine.

An all-atom model of the structure of human copper transporter 1

Human copper transporter 1 (hCTR1) is the major high affinity copper influx transporter in mammalian cells that also mediates uptake of the cancer chemotherapeutic agent cisplatin. A low resolution structure of hCTR1 determined by cryoelectron microscopy was recently published. Several protein structure simulation techniques were used to create an all-atom model of this important transporter using the low resolution structure as a starting point. The all-atom model provides new insights into the roles of specific residues of the N-terminal extracellular domain, the intracellular loop, and C-terminal region in metal ion transport. In particular, the model demonstrates that the central region of the pore contains four sets of methionine triads in the intramembranous region. The structure confirms that two triads of methionine residues delineate the intramembranous region of the transporter, and further identifies two additional methionine triads that are located in the extracellular N-terminal part of the transporter. Together, the four triads create a structure that promotes stepwise transport of metal ions into and then through the intramembranous channel of the transporter via transient thioether bonds to methionine residues. Putative copper-binding sites in the hCTR1 trimer were identified by a program developed by us for prediction of metal-binding sites. These sites correspond well with the known effects of mutations on the ability of the protein to transport copper and cisplatin.

How much do PPIs contribute to C. difficile infections?

Two separate systematic reviews and meta-analyses published in this edition of the American Journal of Gastroenterology conclude that proton pump inhibitor (PPI) use is associated with an ~70% increase in the risk of Clostridium difficile infection (CDI). The two reviews employed different methodology but reached very similar conclusions. However, since the quality of evidence from the individual studies that were included in these analyses is relatively weak, their conclusions must be interpreted cautiously. Observational studies--and even well-conducted systematic reviews of observational studies--rarely provide adequate evidence to prove causality rather than mere association. However, given both the widespread use of PPIs and the increasing incidence and importance of CDI, it is important that this association is adequately explored.

Controlling the folding and substrate-binding of proteins using polymer brushes

The extent of coupling between the folding of a protein and its binding to a substrate varies from protein to protein. Some proteins have highly structured native states in solution, while others are natively disordered and only fold fully upon binding. In this Letter, we use Monte Carlo simulations to investigate how disordered polymer chains grafted around a binding site affect the folding and binding of three model proteins. The protein that approaches the substrate fully folded is more hindered during the binding process than those whose folding and binding are cooperative. The polymer chains act as localized crowding agents and can select correctly folded and bound configurations in favor of nonspecifically adsorbed states. The free energy change for forming all intraprotein and protein-substrate contacts can depend nonmonotonically on the polymer length.