Kinetic limitations in gas-particle reactions arising from slow diffusion in secondary organic aerosol

The potential for aerosol physical properties, such as phase, morphology and viscosity/diffusivity, to affect particle reactivity remains highly uncertain. We report here a study of the effect of bulk diffusivity of polycyclic aromatic hydrocarbons (PAHs) in secondary organic aerosol (SOA) on the kinetics of the heterogeneous reaction of particle-borne benzo[a]pyrene (BaP) with ozone. The experiments were performed by coating BaP-ammonium sulfate particles with multilayers of SOA formed from ozonolysis of α-pinene, and by subsequently investigating the kinetics of BaP loss via reaction with excess ozone using an aerosol flow tube coupled to an Aerodyne Aerosol Mass Spectrometer (AMS). All reactions exhibit pseudo-first order kinetics and are empirically well described by a Langmuir–Hinshelwood (L-H) mechanism. The results show that under dry conditions (RH 1 × 10^(−12) for dry (RH < 5%), 50% RH and 70% RH conditions, respectively. These results clearly indicate that slow diffusion of reactants through SOA coats under specific conditions can provide shielding from gas-phase oxidants, enabling the long-range atmospheric transport of toxic trace species, such as PAHs and persistent organic pollutants

Perspectives on key principles of generalist medical practice in public service in sub-saharan africa: a qualitative study

The original publication is available at http://www.biomedcentral.comAbstract Background: The principles and practice of Family Medicine that arose in developed Western countries have been imported and adopted in African countries without adequate consideration of their relevance and appropriateness to the African context. In this study we attempted to elicit a priori principles of generalist medical practice from the experience of long-serving medical officers in a variety of African counties, through which we explored emergent principles of Family Medicine in our own context. Methods A descriptive study design was utilized, using qualitative methods. 16 respondents who were clinically active medical practitioners, working as generalists in the public services or non-profit sector for at least 5 years, and who had had no previous formal training or involvement in academic Family Medicine, were purposively selected in 8 different countries in southern, western and east Africa, and interviewed. Results The respondents highlighted a number of key issues with respect to the external environment within which they work, their collective roles, activities and behaviours, as well as the personal values and beliefs that motivate their behaviour. The context is characterized by resource constraints, high workload, traditional health beliefs, and the difficulty of referring patients to the next level of care. Generalist clinicians in sub-Saharan Africa need to be competent across a wide range of clinical disciplines and procedural skills at the level of the district hospital and clinic, in both chronic and emergency care. They need to understand the patient's perspective and context, empowering the patient and building an effective doctor-patient relationship. They are also managers, focused on coordinating and improving the quality of clinical care through teamwork, training and mentoring other health workers in the generalist setting, while being life-long learners themselves. However, their role in the community, was found to be more aspirational than real. Conclusions The study derived a set of principles for the practice of generalist doctors in sub-Saharan Africa based on the reported activities and approaches of the respondents. Patient-centred care using a biopsychosocial approach remains as a common core principle despite wide variations in context. Procedural and hospital care demands a higher level of skills particularly in rural areas, and a community orientation is desirable, but not widely practiced. The results have implications for the postgraduate training of family physicians in sub-Saharan Africa, and highlight questions regarding the realization of community-orientated primary care.Publishers' Versio

Adjunctive rifampicin to reduce early mortality from Staphylococcus aureus bacteraemia: the ARREST RCT.

BACKGROUND: Staphylococcus aureus bacteraemia is a common and frequently fatal infection. Adjunctive rifampicin may enhance early S. aureus killing, sterilise infected foci and blood faster, and thereby reduce the risk of dissemination, metastatic infection and death. OBJECTIVES: To determine whether or not adjunctive rifampicin reduces bacteriological (microbiologically confirmed) failure/recurrence or death through 12 weeks from randomisation. Secondary objectives included evaluating the impact of rifampicin on all-cause mortality, clinically defined failure/recurrence or death, toxicity, resistance emergence, and duration of bacteraemia; and assessing the cost-effectiveness of rifampicin. DESIGN: Parallel-group, randomised (1 : 1), blinded, placebo-controlled multicentre trial. SETTING: UK NHS trust hospitals. PARTICIPANTS: Adult inpatients (≥ 18 years) with meticillin-resistant or susceptible S. aureus grown from one or more blood cultures, who had received < 96 hours of antibiotic therapy for the current infection, and without contraindications to rifampicin. INTERVENTIONS: Adjunctive rifampicin (600-900 mg/day, oral or intravenous) or placebo for 14 days in addition to standard antibiotic therapy. Investigators and patients were blinded to trial treatment. Follow-up was for 12 weeks (assessments at 3, 7, 10 and 14 days, weekly until discharge and final assessment at 12 weeks post randomisation). MAIN OUTCOME MEASURES: The primary outcome was all-cause bacteriological (microbiologically confirmed) failure/recurrence or death through 12 weeks from randomisation. RESULTS: Between December 2012 and October 2016, 758 eligible participants from 29 UK hospitals were randomised: 370 to rifampicin and 388 to placebo. The median age was 65 years [interquartile range (IQR) 50-76 years]. A total of 485 (64.0%) infections were community acquired and 132 (17.4%) were nosocomial; 47 (6.2%) were caused by meticillin-resistant S. aureus. A total of 301 (39.7%) participants had an initial deep infection focus. Standard antibiotics were given for a median of 29 days (IQR 18-45 days) and 619 (81.7%) participants received flucloxacillin. By 12 weeks, 62 out of 370 (16.8%) patients taking rifampicin versus 71 out of 388 (18.3%) participants taking the placebo experienced bacteriological (microbiologically confirmed) failure/recurrence or died [absolute risk difference -1.4%, 95% confidence interval (CI) -7.0% to 4.3%; hazard ratio 0.96, 95% CI 0.68 to 1.35; p = 0.81]. There were 4 (1.1%) and 5 (1.3%) bacteriological failures (p = 0.82) in the rifampicin and placebo groups, respectively. There were 3 (0.8%) versus 16 (4.1%) bacteriological recurrences (p = 0.01), and 55 (14.9%) versus 50 (12.9%) deaths without bacteriological failure/recurrence (p = 0.30) in the rifampicin and placebo groups, respectively. Over 12 weeks, there was no evidence of differences in clinically defined failure/recurrence/death (p = 0.84), all-cause mortality (p = 0.60), serious (p = 0.17) or grade 3/4 (p = 0.36) adverse events (AEs). However, 63 (17.0%) participants in the rifampicin group versus 39 (10.1%) participants in the placebo group experienced antibiotic or trial drug-modifying AEs (p = 0.004), and 24 (6.5%) participants in the rifampicin group versus 6 (1.5%) participants in the placebo group experienced drug-interactions (p = 0.0005). Evaluation of the costs and health-related quality-of-life impacts revealed that an episode of S. aureus bacteraemia costs an average of £12,197 over 12 weeks. Rifampicin was estimated to save 10% of episode costs (p = 0.14). After adjustment, the effect of rifampicin on total quality-adjusted life-years (QALYs) was positive (0.004 QALYs), but not statistically significant (standard error 0.004 QALYs). CONCLUSIONS: Adjunctive rifampicin provided no overall benefit over standard antibiotic therapy in adults with S. aureus bacteraemia. FUTURE WORK: Given the substantial mortality, other antibiotic combinations or improved source management should be investigated. TRIAL REGISTRATIONS: Current Controlled Trials ISRCTN37666216, EudraCT 2012-000344-10 and Clinical Trials Authorisation 00316/0243/001. FUNDING: This project was funded by the National Institute for Health Research (NIHR) Health Technology Assessment programme and will be published in full in Health Technology Assessment; Vol. 22, No. 59. See the NIHR Journals Library website for further project information.NIHR HTA Programm

Adjunctive rifampicin for Staphylococcus aureus bacteraemia (ARREST): a multicentre, randomised, double-blind, placebo-controlled trial.

BACKGROUND: Staphylococcus aureus bacteraemia is a common cause of severe community-acquired and hospital-acquired infection worldwide. We tested the hypothesis that adjunctive rifampicin would reduce bacteriologically confirmed treatment failure or disease recurrence, or death, by enhancing early S aureus killing, sterilising infected foci and blood faster, and reducing risks of dissemination and metastatic infection. METHODS: In this multicentre, randomised, double-blind, placebo-controlled trial, adults (≥18 years) with S aureus bacteraemia who had received ≤96 h of active antibiotic therapy were recruited from 29 UK hospitals. Patients were randomly assigned (1:1) via a computer-generated sequential randomisation list to receive 2 weeks of adjunctive rifampicin (600 mg or 900 mg per day according to weight, oral or intravenous) versus identical placebo, together with standard antibiotic therapy. Randomisation was stratified by centre. Patients, investigators, and those caring for the patients were masked to group allocation. The primary outcome was time to bacteriologically confirmed treatment failure or disease recurrence, or death (all-cause), from randomisation to 12 weeks, adjudicated by an independent review committee masked to the treatment. Analysis was intention to treat. This trial was registered, number ISRCTN37666216, and is closed to new participants. FINDINGS: Between Dec 10, 2012, and Oct 25, 2016, 758 eligible participants were randomly assigned: 370 to rifampicin and 388 to placebo. 485 (64%) participants had community-acquired S aureus infections, and 132 (17%) had nosocomial S aureus infections. 47 (6%) had meticillin-resistant infections. 301 (40%) participants had an initial deep infection focus. Standard antibiotics were given for 29 (IQR 18-45) days; 619 (82%) participants received flucloxacillin. By week 12, 62 (17%) of participants who received rifampicin versus 71 (18%) who received placebo experienced treatment failure or disease recurrence, or died (absolute risk difference -1·4%, 95% CI -7·0 to 4·3; hazard ratio 0·96, 0·68-1·35, p=0·81). From randomisation to 12 weeks, no evidence of differences in serious (p=0·17) or grade 3-4 (p=0·36) adverse events were observed; however, 63 (17%) participants in the rifampicin group versus 39 (10%) in the placebo group had antibiotic or trial drug-modifying adverse events (p=0·004), and 24 (6%) versus six (2%) had drug interactions (p=0·0005). INTERPRETATION: Adjunctive rifampicin provided no overall benefit over standard antibiotic therapy in adults with S aureus bacteraemia. FUNDING: UK National Institute for Health Research Health Technology Assessment

The combined effects of physicochemical properties of size-fractionated ambient particulate matter on in vitro toxicity in human A549 lung epithelial cells

Epidemiological and toxicological studies have suggested that the health effects associated with exposure to particulate matter (PM) are related to the different physicochemical properties of PM. These effects occur through the initiation of differential cellular responses including: the induction of antioxidant defenses, proinflammatory responses, and ultimately cell death. The main objective of this study was to investigate the effects of size-fractionated ambient PM on epithelial cells in relation to their physicochemical properties. Concentrated ambient PM was collected on filters for three size fractions: coarse (aerodynamic diameter [AD] 2.5–10 μm), fine (0.15–2.5 μm), and quasi-ultrafine (<0.2 μm), near a busy street in Toronto, Ontario, Canada. Filters were extracted and analyzed for chemical composition and redox activity. Chemical analyses showed that the coarse, fine, and quasi-ultrafine particles were comprised primarily of metals, water-soluble species, and organic compounds, respectively. The highest redox activity was observed for fine PM. After exposure of A549 cells to PM (10–100 μg/ml) for 4 h, activation of antioxidant, proinflammatory and cytotoxic responses were assessed by determining the expression of heme oxygenase (HMOX-1, mRNA), interleukin-8 (IL-8, mRNA), and metabolic activity of the cells, respectively. All three size fractions induced mass-dependent antioxidant, proinflammatory, and cytotoxic responses to different degrees. Quasi-ultrafine PM caused significant induction of HMOX-1 at the lowest exposure dose. Correlation analyses with chemical components suggested that the biological responses correlated mainly with transition metals and organic compounds for coarse and fine PM and with organic compounds for quasi-ultrafine PM. Overall, the observed biological responses appeared to be related to the combined effects of size and chemical composition and thus both of these physicochemical properties should be considered when explaining PM toxicity

Filterable Redox Cycling Activity: A Comparison between Diesel Exhaust Particles and Secondary Organic Aerosol Constituents

The redox activity of diesel exhaust particles (DEP) collected from a light-duty diesel passenger car engine was examined using the dithiothreitol (DTT) assay. DEP was highly redox-active, causing DTT to decay at a rate of 23–61 pmol min^–1 μg^–1 of particle used in the assay, which was an order of magnitude higher than ambient coarse and fine particulate matter (PM) collected from downtown Toronto. Only 2–11% of the redox activity was in the water-soluble portion, while the remainder occurred at the black carbon surface. This is in contrast to redox-active secondary organic aerosol constituents, in which upward of 90% of the activity occurs in the water-soluble fraction. The redox activity of DEP is not extractable by moderately polar (methanol) and nonpolar (dichloromethane) organic solvents, and is hypothesized to arise from redox-active moieties contiguous with the black carbon portion of the particles. These measurements illustrate that “Filterable Redox Cycling Activity” may therefore be useful to distinguish black carbon-based oxidative capacity from water-soluble organic-based activity. The difference in chemical environment leading to redox activity highlights the need to further examine the relationship between activity in the DTT assay and toxicology measurements across particles of different origins and composition