Observation of Sommerfeld precursors on a fluid surface

We report the observation of two types of Sommerfeld precursors (or forerunners) on the surface of a layer of mercury. When the fluid depth increases, we observe a transition between these two precursor surface waves in good agreement with the predictions of asymptotic analysis. At depths thin enough compared to the capillary length, high frequency precursors propagate ahead of the ''main signal'' and their period and amplitude, measured at a fixed point, increase in time. For larger depths, low frequency ''precursors'' follow the main signal with decreasing period and amplitude. These behaviors are understood in the framework of the analysis first introduced for linear transient electromagnetic waves in a dielectric medium by Sommerfeld and Brillouin [1].Comment: to be published in Physical Review Letter

A diamond detector based dosimetric system for instantaneous dose rate measurements in FLASH electron beams

Objective. A reliable determination of the instantaneous dose rate (I-DR) delivered in FLASH radiotherapy treatments is believed to be crucial to assess the so-called FLASH effect in preclinical and biological studies. At present, no detectors nor real-time procedures are available to do that in ultra high dose rate (UH-DR) electron beams, typically consisting of μs pulses characterized by I-DRs of the order of MGy/s. A dosimetric system is proposed possibly overcoming the above reported limitation, based on the recently developed flashDiamond (fD) detector (model 60025, PTW-Freiburg, Germany). Approach. A dosimetric system is proposed, based on a flashDiamond detector prototype, properly modified and adapted for very fast signal transmission. It was used in combination with a fast transimpedance amplifier and a digital oscilloscope to record the temporal traces of the pulses delivered by an ElectronFlash linac (SIT S.p.A., Italy). The proposed dosimetric systems was investigated in terms of the temporal characteristics of its response and the capability to measure the absolute delivered dose and instantaneous dose rate (I-DR). A ‘standard’ flashDiamond was also investigated and its response compared with the one of the specifically designed prototype. Main results. Temporal traces recorded in several UH-DR irradiation conditions showed very good signal to noise ratios and rise and decay times of the order of a few tens ns, faster than the ones obtained by the current transformer embedded in the linac head. By analyzing such signals, a calibration coefficient was derived for the fD prototype and found to be in agreement within 1% with the one obtained under reference 60Co irradiation. I-DRs as high as about 2 MGy s−1 were detected without any undesired saturation effect. Absolute dose per pulse values extracted by integrating the I-DR signals were found to be linear up to at least 7.13 Gy and in very good agreement with the ones obtained by connecting the fD to a UNIDOS electrometer (PTW-Freiburg, Germany). A good short term reproducibility of the linac output was observed, characterized by a pulse-to-pulse variation coefficient of 0.9%. Negligible differences were observed when replacing the fD prototype with a standard one, with the only exception of a somewhat slower response time for the latter detector type. Significance. The proposed fD-based system was demonstrated to be a suitable tool for a thorough characterization of UH-DR beams, providing accurate and reliable time resolved I-DR measurements from which absolute dose values can be straightforwardly derived

Treatment Interruption and Variation in Tablet Taking Behaviour Result in Viral Failure: A Case-Control Study from Cape Town, South Africa

BACKGROUND: Understanding of the impact of non-structured treatment interruption (TI) and variation in tablet-taking on failure of first-line antiretroviral therapy (ART) is limited in a resource-poor setting. METHODS: A retrospective matched case-control analysis. Individuals failing ART were matched by time on ART with 4 controls. Viral load (VL) and CD4 count were completed 4-monthly. Adherence percentages, from tablet returns, were calculated 4-monthly (interval) and from ART start (cumulative). Variation between intervals and TI (>27 days off ART) were recorded. Conditional multivariate logistic regression analysis was performed to estimate the effect of cumulative adherence 10% and TI on virological failure. Age, gender, baseline log VL and CD4 were included as possible confounders in the multivariate model. RESULTS: 244 patients (44 cases, 200 controls) were included. Median age was 32 years (IQR28-37), baseline CD4 108 cells/mm3 (IQR56-151), VL 4.82 log (IQR4.48-5.23). 94% (96% controls, 86% failures) had cumulative adherence >90%. The odds of failure increased 3 times (aOR 3.01, 95%CI 0.81-11.21) in individuals with cumulative adherence 10% and 4.01 times (aOR 4.01, 95%CI 1.45-11.10) in individuals with TIs. For individuals with TI and cumulative adherence >95%, the odds of failing were 5.65 (CI 1.40-22.85). CONCLUSION: It is well known that poor cumulative adherence increases risk of virological failure, but less well understood that TI and variations in tablet-taking also play a key role, despite otherwise excellent adherence

What are the most efficacious treatment regimens for isoniazid-resistant tuberculosis?:A systematic review and network meta-analysis

INTRODUCTION: Consensus on the best treatment regimens for patients with isoniazid-resistant TB is limited; global treatment guidelines differ. We undertook a systematic review and meta-analysis using mixed-treatment comparisons methodology to provide an up-to-date summary of randomised controlled trials (RCTs) and relative regimen efficacy. METHODS: Ovid MEDLINE, the Web of Science and EMBASE were mined using search terms for TB, drug therapy and RCTs. Extracted data were inputted into fixed-effects and random-effects models. ORs for all possible network comparisons and hierarchical rankings for different regimens were obtained. RESULTS: 12 604 records were retrieved and 118 remained postextraction, representing 59 studies-27 standalone and 32 with multiple papers. In comparison to a baseline category that included the WHO-recommended regimen for countries with high levels of isoniazid resistance (rifampicin-containing regimens using fewer than three effective drugs at 4 months, in which rifampicin was protected by another effective drug at 6 months, and rifampicin was taken for 6 months), extending the duration of rifampicin and increasing the number of effective drugs at 4 months lowered the odds of unfavourable outcomes (treatment failure or the lack of microbiological cure; relapse post-treatment; death due to TB) in a fixed-effects model (OR 0.31 (95% credible interval 0.12-0.81)). In a random-effects model all estimates crossed the null. CONCLUSIONS: Our systematic review and network meta-analysis highlight a regimen category that may be more efficacious than the WHO population level recommendation, and identify knowledge gaps where data are sparse. SYSTEMATIC REVIEW REGISTRATION NUMBER: PROSPERO CRD42014015025

Uptake of home-based voluntary HIV testing in sub-Saharan Africa: a systematic review and meta-analysis

Improving access to HIV testing is a key priority in scaling up HIV treatment and prevention services. Home-based voluntary counselling and testing (HBT) as an approach to delivering wide-scale HIV testing is explored here

Predictors of linkage to care following community-based HIV counseling and testing in rural Kenya

Despite innovations in HIV counseling and testing (HCT), important gaps remain in understanding linkage to care. We followed a cohort diagnosed with HIV through a community-based HCT campaign that trained persons living with HIV/AIDS (PLHA) as navigators. Individual, interpersonal, and institutional predictors of linkage were assessed using survival analysis of self-reported time to enrollment. Of 483 persons consenting to follow-up, 305 (63.2%) enrolled in HIV care within 3 months. Proportions linking to care were similar across sexes, barring a sub-sample of men aged 18–25 years who were highly unlikely to enroll. Men were more likely to enroll if they had disclosed to their spouse, and women if they had disclosed to family. Women who anticipated violence or relationship breakup were less likely to link to care. Enrolment rates were significantly higher among participants receiving a PLHA visit, suggesting that a navigator approach may improve linkage from community-based HCT campaigns.Vestergaard Frandse

Periodic Active Case Finding for TB: When to Look?

OBJECTIVE: To investigate the factors influencing the performance and cost-efficacy of periodic rounds of active case finding (ACF) for TB. METHODS: A mathematical model of TB dynamics and periodic ACF (PACF) in the HIV era, simplified by assuming constant prevalence of latent TB infection, is analyzed for features that control intervention outcome, measured as cases averted and cases found. Explanatory variables include baseline TB incidence, interval between PACF rounds, and different routine and PACF case-detection rates among HIV-infected and uninfected TB cases. FINDINGS: PACF can be cost-saving over a 10 year time frame if the cost-per-round is lower than a threshold proportional to initial incidence and cost-per-case-treated. More cases are averted at higher baseline incidence rates, when more potent PACF strategies are used, intervals between PACF rounds are shorter, and when the ratio of HIV-negative to positive TB cases detected is higher. More costly approaches, e.g. radiographic screening, can be as cost-effective as less costly alternatives if PACF case-detection is higher and/or implementation less frequent. CONCLUSION: Periodic ACF can both improve control and save medium-term health care costs in high TB burden settings. Greater costs of highly effective PACF at frequent (e.g. yearly) intervals may be offset by higher numbers of cases averted in populations with high baseline TB incidence, higher prevalence of HIV-uninfected cases, higher costs per-case-treated, and more effective routine case-detection. Less intensive approaches may still be cost-neutral or cost-saving in populations lacking one or more of these key determinants

What happens to ART-eligible patients who do not start ART? Dropout between screening and ART initiation: a cohort study in Karonga, Malawi

BACKGROUND: Routine ART programme statistics generally only provide information about individuals who start treatment. We aimed to investigate the outcome of those who are eligible but do not start ART in the Malawi programme, factors associated with this dropout, and reasons for not starting treatment, in a prospective cohort study. METHODS: Individuals having a first screening visit at the ART clinic at Karonga District Hospital, northern Malawi, between September 2005 and July 2006 were interviewed. Study follow-up to identify treatment outcomes was conducted at the clinic and in the community. Logistic regression models were used to identify factors associated with dropout before ART initiation among participants identified as clinically eligible for ART. RESULTS: 88 participants eligible for ART at their first screening visit (out of 633, 13.9%) defaulted before starting ART. Participants with less education, difficulties in dressing, a more delayed ART initiation appointment, and mid-upper arm circumference (MUAC) < 22 cm were significantly less likely to have visited the clinic subsequently. Thirty-five (58%) of the 60 participants who defaulted and were tracked at home had died, 21 before their ART initiation appointment. CONCLUSIONS: MUAC and reported difficulties in dressing may provide useful screening indicators to identify sicker ART-eligible individuals at high risk of dropping out of the programme who might benefit from being brought back quickly or admitted to hospital for observation. Individuals with less education may need adapted health information at screening. Deaths of ART-eligible individuals occurring prior to ART initiation are not included in routine programme statistics. Considering all those who are eligible for ART as a denominator for programme indicators would help to highlight this vulnerable group, in order to identify new opportunities for further improving ART programmes

Development of a Standardized Screening Rule for Tuberculosis in People Living with HIV in Resource-Constrained Settings: Individual Participant Data Meta-analysis of Observational Studies

Haileyesus Getahun and colleagues report the development of a simple, standardized tuberculosis (TB) screening rule for resource-constrained settings, to identify people living with HIV who need further investigation for TB disease