Search

Contains fulltext : 108066.pdf (publisher's version ) (Open Access), BACKGROUND: Many mathematical models have investigated the impact of expanding access to antiretroviral therapy (ART) on new HIV infections. Comparing results and conclusions across models is challenging because models have addressed slightly different questions and have reported different outcome metrics. This study compares the predictions of several mathematical models simulating the same ART intervention programmes to determine the extent to which models agree about the epidemiological impact of expanded ART. METHODS AND FINDINGS: Twelve independent mathematical models evaluated a set of standardised ART intervention scenarios in South Africa and reported a common set of outputs. Intervention scenarios systematically varied the CD4 count threshold for treatment eligibility, access to treatment, and programme retention. For a scenario in which 80% of HIV-infected individuals start treatment on average 1 y after their CD4 count drops below 350 cells/microl and 85% remain on treatment after 3 y, the models projected that HIV incidence would be 35% to 54% lower 8 y after the introduction of ART, compared to a counterfactual scenario in which there is no ART. More variation existed in the estimated long-term (38 y) reductions in incidence. The impact of optimistic interventions including immediate ART initiation varied widely across models, maintaining substantial uncertainty about the theoretical prospect for elimination of HIV from the population using ART alone over the next four decades. The number of person-years of ART per infection averted over 8 y ranged between 5.8 and 18.7. Considering the actual scale-up of ART in South Africa, seven models estimated that current HIV incidence is 17% to 32% lower than it would have been in the absence of ART. Differences between model assumptions about CD4 decline and HIV transmissibility over the course of infection explained only a modest amount of the variation in model results. CONCLUSIONS: Mathematical models evaluati

Antiretroviral therapy (ART) for those infected with HIV can prevent onward transmission of infection, but biological efficacy alone is not enough to guide policy decisions about the role of ART in reducing HIV incidence. Epidemiology, economics, demography, statistics, biology, and mathematical modelling will be central in framing key decisions in the optimal use of ART. PLoS Medicine, with the HIV Modelling Consortium, has commissioned a set of articles that examine different aspects of HIV treatment as prevention with a forward-looking research agenda. Interlocking themes across these articles are discussed in this introduction. We hope that this article, and others in the collection, will provide a foundation upon which greater collaborations between disciplines will be formed, and will afford deeper insights into the key factors involved, to help strengthen the support for evidence-based decision-making in HIV prevention.

Background: Many mathematical models have investigated the impact of expanding access to antiretroviral therapy (ART) on new HIV infections. Comparing results and conclusions across models is challenging because models have addressed slightly different questions and have reported different outcome metrics. This study compares the predictions of several mathematical models simulating the same ART intervention programmes to determine the extent to which models agree about the epidemiological impact of expanded ART. Methods and Findings: Twelve independent mathematical models evaluated a set of standardised ART intervention scenarios in South Africa and reported a common set of outputs. Intervention scenarios systematically varied the CD4 count threshold for treatment eligibility, access to treatment, and programme retention. For a scenario in which 80% of HIV-infected individuals start treatment on average 1 y after their CD4 count drops below 350 cells/ml and 85% remain on treatment after 3 y, the models Conclusions: Mathematical models evaluating the impact of ART vary substantially in structure, complexity, and parameter choices, but all suggest that ART, at high levels of access and with high adherence, has the potential to substantially reduce new HIV infections. There was broad agreement regarding the short-term epidemiologic impact of ambitious treatment scale-up, but more variation in longer term projections and in the efficiency with which treatment can reduce new infections. Differences

Background: Trials in Africa indicate that medical adult male circumcision (MAMC) reduces the risk of HIV by 60%. MAMC may avert 2 to 8 million HIV infections over 20 years in sub-Saharan Africa and cost less than treating those who would have been infected. This paper estimates the financial and human resources required to roll out MAMC and the net savings due to reduced infections. Methods: We developed a model which included costing, demography and HIV epidemiology. We used it to investigate 14 countries in sub-Saharan Africa where the prevalence of male circumcision was lower than 80% and HIV prevalence among adults was higher than 5%, in addition to Uganda and the Nyanza province in Kenya. We assumed that the roll-out would take 5 years and lead to an MC prevalence among adult males of 85%. We also assumed that surgery would be done as it was in the trials. We calculated public program cost, number of full-time circumcisers and net costs or savings when adjusting for averted HIV treatments. Costs were in USD, discounted to 2007. 95% percentile intervals (95% PI) were estimated by Monte Carlo simulations. Results: In the first 5 years the number of circumcisers needed was 2 282 (95% PI: 2 018 to 2 959), or 0.24 (95% PI: 0.21 to 0.31) per 10 000 adults. In years 6-10, the number of circumcisers needed fell to 513 (95% PI: 452 to 664). The estimated 5-year cost of rolling out MAMC in the public sector was $919 million (95% PI: 726 to 1 245).The cumulative net cost over the first 10 years was $672 million (95% PI: 437 to 1 021) and over 20 years there were net savings of $2.3 billion (95% PI: 1.4 to 3.4). Conclusion: A rapid roll-out of MAMC in sub-Saharan Africa requires substantial funding and a high number of circumcisers for the first five years. These investments are justified by MAMC's substantial health benefits and the savings accrued by averting future HIV infections. Lower ongoing costs and continued care savings suggest long-term sustainability.

Problems are discussed with pit wall stability in certain areas of the Navachab, Namibia, Au mine, mainly due to the fact that the geology comprises many joints and faults. The mine has installed an advanced seismic monitoring system with sensors positioned at various locations and depths. Information recorded by the system showed that the energy release into the high-wall is predominantly influenced by the mining rate, water content and mining tempo, and to a lesser extent by the blasting operations. In order to limit the negative effects of blast vibrations, the use of electronic delay detonators (EDDs) was introduced. The optimal delays were determined through signature trace analysis. The vibrations obtained during blasts initiated by means of EDDs were monitored and compared to those obtained using standard pyrotechnic delay detonators. The results indicated an improvement of 25-100% in relation to reduced vibration amplitude., Problems are discussed with pit wall stability in certain areas of the Navachab, Namibia, Au mine, mainly due to the fact that the geology comprises many joints and faults. The mine has installed an advanced seismic monitoring system with sensors positioned at various locations and depths. Information recorded by the system showed that the energy release into the high-wall is predominantly influenced by the mining rate, water content and mining tempo, and to a lesser extent by the blasting operations. In order to limit the negative effects of blast vibrations, the use of electronic delay detonators (EDDs) was introduced. The optimal delays were determined through signature trace analysis. The vibrations obtained during blasts initiated by means of EDDs were monitored and compared to those obtained using standard pyrotechnic delay detonators. The results indicated an improvement of 25-100% in relation to reduced vibration amplitude.

The use is discussed of electronic delay detonators (EDDs) to add value in quarrying and mining operations. The differences between EDDs and conventional detonators are described in relation to accuracy and programming and the benefits of their use are considered in relation to improved safety, environmental impact, fragmentation and slope stability. EDDs combined with the correct supporting blast-design software can be used to carry out complicated blasts and to control movement of the blasted material in selective mining. Two case studies are presented, a mobile crusher operation in Mpumalanga, South Africa, and the world's largest EDD blast which was carried out in an open-pit strip mine to create a new box cut for a dragline operation., The use is discussed of electronic delay detonators (EDDs) to add value in quarrying and mining operations. The differences between EDDs and conventional detonators are described in relation to accuracy and programming and the benefits of their use are considered in relation to improved safety, environmental impact, fragmentation and slope stability. EDDs combined with the correct supporting blast-design software can be used to carry out complicated blasts and to control movement of the blasted material in selective mining. Two case studies are presented, a mobile crusher operation in Mpumalanga, South Africa, and the world's largest EDD blast which was carried out in an open-pit strip mine to create a new box cut for a dragline operation.

The basic structure of a control system should address five levels, from the basic tripping, interlocking and safety control of furnace, charging, demand, gas handling and cooling systems to the collating of metallurgical and electrical data for use with online optimisation models and online financial and management models. A commercial control system comprising Minstral and an intelligent supervisory system has been designed by Mintek to address concern over electrode management issues such as online measurement of electrode length and prediction of electrode breaks, general logging and distributed control systems, and intelligent control. Minstral's model-based system for control of submerged arc furnaces ensures that if supervisory control fails (as when the rules in an expert system do not sufficiently describe a process) the furnace is still controlled. Several modules are available which could form part of an intelligent control system., The basic structure of a control system should address five levels, from the basic tripping, interlocking and safety control of furnace, charging, demand, gas handling and cooling systems to the collating of metallurgical and electrical data for use with online optimisation models and online financial and management models. A commercial control system comprising Minstral and an intelligent supervisory system has been designed by Mintek to address concern over electrode management issues such as online measurement of electrode length and prediction of electrode breaks, general logging and distributed control systems, and intelligent control. Minstral's model-based system for control of submerged arc furnaces ensures that if supervisory control fails (as when the rules in an expert system do not sufficiently describe a process) the furnace is still controlled. Several modules are available which could form part of an intelligent control system.

The safety aspects involved in the use of cyanide, including the toxic effects of cyanide, cyanide handling and storage, hazardous properties, and cyanide poisoning - symptoms and prevention, are discussed., The safety aspects involved in the use of cyanide, including the toxic effects of cyanide, cyanide handling and storage, hazardous properties, and cyanide poisoning - symptoms and prevention, are discussed.