Vancomycin Heteroresistance and Clinical Outcomes in Bloodstream Infections Caused by Coagulase-Negative Staphylococci.

Coagulase-negative staphylococci (CoNS) are a common etiology of serious and recurrent infections in immunocompromised patients. Although most isolates appear susceptible to vancomycin, a single strain might have a subpopulation of resistant bacteria. This phenomenon is termed heteroresistance and may adversely affect the response to treatment. A retrospective cohort study was performed of pediatric patients with leukemia treated at St. Jude Children's Research Hospital who developed CoNS central line-associated bloodstream infection (CLABSI). Available isolates were sequenced and tested for vancomycin heteroresistance by population analysis profiling. Risk factors for heteroresistance and the association of heteroresistance with treatment failure (death or relapse of infection) or poor clinical response to vancomycin therapy (treatment failure or persistent bacteremia after vancomycin initiation) were evaluated. For 65 participants with CoNS CLABSI, 62 initial isolates were evaluable, of which 24 (39%) were vancomycin heteroresistant. All heteroresistant isolates were of Staphylococcus epidermidis and comprised multiple sequence types. Participants with heteroresistant bacteria had more exposure to vancomycin prophylaxis (P = 0.026) during the 60 days prior to infection. Of the 40 participants evaluable for clinical outcomes, heteroresistance increased the risk of treatment failure (P = 0.012) and poor clinical response (P = 0.001). This effect persisted after controlling for identified confounders. These data indicate that vancomycin heteroresistance is common in CoNS isolates from CLABSIs in pediatric patients with leukemia and is associated with poor clinical outcomes. Validation of these findings in an independent cohort and evaluation of alternative antibiotic therapy in patients with heteroresistant infections have the potential to improve care for serious CoNS infections.

Application of Schistosomiasis Consortium for Operational Research and Evaluation Study Findings to Refine Predictive Modeling of Schistosoma mansoni and Schistosoma haematobium Control in Sub-Saharan Africa.

An essential mission of the Schistosomiasis Consortium for Operational Research and Evaluation (SCORE) was to help inform global health practices related to the control and elimination of schistosomiasis. To provide more accurate, evidence-based projections of the most likely impact of different control interventions, whether implemented alone or in combination, SCORE supported mathematical modeling teams to provide simulations of community-level Schistosoma infection outcomes in the setting of real or hypothetical programs implementing multiyear mass drug administration (MDA) for parasite control. These models were calibrated using SCORE experience with Schistosoma mansoni and Schistosoma haematobium gaining and sustaining control studies, and with data from comparable programs that used community-based or school-based praziquantel MDA in other parts of sub-Saharan Africa. From 2010 to 2019, models were developed and refined, first to project the likely SCORE control outcomes, and later to more accurately reflect impact of MDA across different transmission settings, including the role of snail ecology and the impact of seasonal rainfall on snail abundance. Starting in 2014, SCORE modeling projections were also compared with the models of colleagues in the Neglected Tropical Diseases Modelling Consortium. To explore further possible improvement to program-based control, later simulations examined the cost-effectiveness of combining MDA with environmental snail control, and the utility of early impact assessment to more quickly identify persistent hot spots of transmission. This article provides a nontechnical summary of the 11 SCORE-related modeling projects and provides links to the original open-access articles describing model development and projections relevant to schistosomiasis control policy.

Astrovirus infects actively secreting goblet cells and alters the gut mucus barrier.

Astroviruses are a global cause of pediatric diarrhea, but they are largely understudied, and it is unclear how and where they replicate in the gut. Using an in vivo model, here we report that murine astrovirus preferentially infects actively secreting small intestinal goblet cells, specialized epithelial cells that maintain the mucus barrier. Consequently, virus infection alters mucus production, leading to an increase in mucus-associated bacteria and resistance to enteropathogenic E. coli colonization. These studies establish the main target cell type and region of the gut for productive murine astrovirus infection. They further define a mechanism by which an enteric virus can regulate the mucus barrier, induce functional changes to commensal microbial communities, and alter host susceptibility to pathogenic bacteria.

Improved yield and accuracy for DNA extraction in microbiome studies with variation in microbial biomass.

A major challenge for microbiome studies is maintaining an even and accurate DNA extraction in the presence of samples with a wide range of bacterial content. Here we compare five DNA extraction methods using replicate stool samples that were diluted to create high and low biomass samples. Our results indicate greater variation in microbiome composition between high and low biomass samples than variation between methods. Many of the extraction methods had reduced yield from low biomass samples; however, our adapted plate column-based extraction method was evenly efficient and captured the largest number of high-quality reads. Based on these results, we have identified a DNA extraction method that ensures adequate yield in metagenomic microbiome studies that have samples with a broad range of bacterial content.

The design of schistosomiasis monitoring and evaluation programmes: The importance of collecting adult data to inform treatment strategies for Schistosoma mansoni.

Monitoring and evaluation (M&E) programmes are used to collect data which are required to assess the impact of current interventions on their progress towards achieving the World Health Organization (WHO) goals of morbidity control and elimination as a public health problem for schistosomiasis. Prevalence and intensity of infection data are typically collected from school-aged children (SAC) as they are relatively easy to sample and are thought to be most likely to be infected by schistosome parasites. However, adults are also likely to be infected. We use three different age-intensity profiles of infection for Schistosoma mansoni with low, moderate and high burdens of infection in adults to investigate how the age distribution of infection impacts the mathematical model generated recommendations of the preventive chemotherapy coverage levels required to achieve the WHO goals. We find that for moderate prevalence regions, regardless of the burden of infection in adults, treating SAC only may achieve the WHO goals. However, for high prevalence regions with a high burden of infection in adults, adult treatment is required to meet the WHO goals. Hence, we show that the optimal treatment strategy for a defined region requires consideration of the burden of infection in adults as it cannot be based solely on the prevalence of infection in SAC. Although past epidemiological data have informed mathematical models for the transmission and control of schistosome infections, more accurate and detailed data are required from M&E programmes to accurately determine the optimal treatment strategy for a defined region. We highlight the importance of collecting prevalence and intensity of infection data from a broader age-range, specifically the inclusion of adult data at baseline (prior to treatment) and throughout the treatment programme if possible, rather than SAC only, to accurately determine the treatment strategy for a defined region. Furthermore, we discuss additional epidemiological data, such as individual longitudinal adherence to treatment, that should ideally be collected in M&E programmes.

Are We on Our Way to Achieving the 2020 Goals for Schistosomiasis Morbidity Control Using Current World Health Organization Guidelines?

Background: Schistosomiasis remains an endemic parasitic disease affecting millions of people around the world. The World Health Organization (WHO) has set goals of controlling morbidity to be reached by 2020, along with elimination as a public health problem in certain regions by 2025. Mathematical models of parasite transmission and treatment impact have been developed to assist in controlling the morbidity caused by schistosomiasis. These models can inform and guide implementation policy for mass drug administration programs, and help design monitoring and evaluation activities. Methods: We use these models to predict whether the guidelines set by the WHO are on track for achieving their 2020 goal for the control of morbidity, specifically for Schistosoma mansoni. We examine whether programmatic adaptations; namely increases in treatment coverage and/or expansion to adult inclusion in treatment, will improve the likelihood of reaching the WHO goals. Results: We find that in low-prevalence settings, the goals are likely to be attainable under current WHO guidelines, but in moderate to high-prevalence settings, the goals are less likely to be achieved unless treatment coverage is increased and expanded to at least 85% for school-aged children and 40% for adults. Conclusions: To improve the likelihood of reaching the WHO goals, programmatic adaptations are required, particularly for moderate- to high-prevalence settings. Furthermore, improvements in adherence to treatment, potential development of candidate vaccines, and enhanced snail control and WASH (water, sanitation, and hygiene) measures will all assist in achieving the goals.

Quantitative assessment of the impact of partially protective anti-schistosomiasis vaccines.

BACKGROUND: Mass drug administration (MDA) of praziquantel has been the intervention of choice against schistosomiasis but with limited success in interrupting the transmission. The development of anti-Schistosoma vaccines is underway. Our objective is to quantify the population-level impact of anti-Schistosoma vaccines when administered alone and in combination with mass drug administration (MDA) and determine factors in vaccine design and public health implementation that optimize vaccination role in schistosomiasis control and elimination. METHODS AND FINDINGS: We developed a deterministic compartmental model simulation of schistosomiasis transmission in a high-risk Kenyan community, including stratification by age, parasite burden, and vaccination status. The modeled schistosomiasis vaccines differed in terms of vaccine duration of protection (durability) and three biological efficacies. These are vaccine susceptibility effect (SE) of reducing person's susceptibility to Schistosoma acquisition, vaccine mortality effect (ME) of reducing established worm burden and vaccine fecundity effect (FE) of reducing egg release by mature worms. We quantified the population-level impact of vaccination over two decades under diverse vaccination schemes (childhood vs. mass campaigns), with different age-targeting scenarios, different risk settings, and with combined intervention with MDA. We also assessed the sensitivity of our predictions to uncertainties in model parameters. Over two decades, our base case vaccine with 80% SE, FE, and ME efficacies, 10 years' durability, provided by mass vaccination every 10 years, reduced host prevalence, mean intensity, incidence, and patent snail prevalence to 31%, 20 eggs/10-ml sample/person, 0.87 worm/person-year, and 0.74%, from endemic-state values of 71%, 152, 3.3, and 0.98%, respectively. Lower impact was found when coverage did not encompass all potential contaminators, and childhood-only vaccination schemes showed delayed and lower impact. In lower prevalence settings, the base case vaccine generated a proportionately smaller impact. A substantially larger vaccine program effect was generated when MDA + mass vaccination was provided every 5 years, which could be achieved by an MDA-only program only if drug was offered annually. Vaccine impact on schistosomiasis transmission was sensitive to a number of parameters including vaccine efficacies, human contact rates with water, human density, patent snails' rate of patency and lifespan, and force of infection to snails. CONCLUSIONS: To be successful a vaccine-based control strategy will need a moderately to highly effective formulation combined with early vaccination of potential contaminators and aggressive coverage in repeated rounds of mass vaccination. Compared to MDA-only program, vaccination combined with MDA accelerates and prolongs the impact by reducing the acquisition of new worms and reducing egg release from residual worms.

The potential impact and cost of focusing HIV prevention on young women and men: A modeling analysis in western Kenya.

OBJECTIVE: We compared the impact and costs of HIV prevention strategies focusing on youth (15-24 year-old persons) versus on adults (15+ year-old persons), in a high-HIV burden context of a large generalized epidemic. DESIGN: Compartmental age-structured mathematical model of HIV transmission in Nyanza, Kenya. INTERVENTIONS: The interventions focused on youth were high coverage HIV testing (80% of youth), treatment at diagnosis (TasP, i.e., immediate start of antiretroviral therapy [ART]) and 10% increased condom usage for HIV-positive diagnosed youth, male circumcision for HIV-negative young men, pre-exposure prophylaxis (PrEP) for high-risk HIV-negative females (ages 20-24 years), and cash transfer for in-school HIV-negative girls (ages 15-19 years). Permutations of these were compared to adult-focused HIV testing coverage with condoms and TasP. RESULTS: The youth-focused strategy with ART treatment at diagnosis and condom use without adding interventions for HIV-negative youth performed better than the adult-focused strategy with adult testing reaching 50-60% coverage and TasP/condoms. Over the long term, the youth-focused strategy approached the performance of 70% adult testing and TasP/condoms. When high coverage male circumcision also is added to the youth-focused strategy, the combined intervention outperformed the adult-focused strategy with 70% testing, for at least 35 years by averting 94,000 more infections, averting 5.0 million more disability-adjusted life years (DALYs), and saving US$46.0 million over this period. The addition of prevention interventions beyond circumcision to the youth-focused strategy would be more beneficial if HIV care costs are high, or when program delivery costs are relatively high for programs encompassing HIV testing coverage exceeding 70%, TasP and condoms to HIV-infected adults compared to combination prevention programs among youth. CONCLUSION: For at least the next three decades, focusing in high burden settings on high coverage HIV testing, ART treatment upon diagnosis, condoms and male circumcision among youth may outperform adult-focused ART treatment upon diagnosis programs, unless the adult testing coverage in these programs reaches very high levels (>70% of all adults reached) at similar program costs. Our results indicate the potential importance of age-targeting for HIV prevention in the current era of 'test and start, ending AIDS' goals to ameliorate the HIV epidemic globally.

Gender-Specific Combination HIV Prevention for Youth in High-Burden Settings: The MP3 Youth Observational Pilot Study Protocol.

BACKGROUND: Nearly three decades into the epidemic, sub-Saharan Africa (SSA) remains the region most heavily affected by human immunodeficiency virus (HIV), with nearly 70% of the 34 million people living with HIV globally residing in the region. In SSA, female and male youth (15 to 24 years) are at a disproportionately high risk of HIV infection compared to adults. As such, there is a need to target HIV prevention strategies to youth and to tailor them to a gender-specific context. This protocol describes the process for the multi-staged approach in the design of the MP3 Youth pilot study, a gender-specific, combination, HIV prevention intervention for youth in Kenya. OBJECTIVE: The objective of this multi-method protocol is to outline a rigorous and replicable methodology for a gender-specific combination HIV prevention pilot study for youth in high-burden settings, illustrating the triangulated methods undertaken to ensure that age, sex, and context are integral in the design of the intervention. METHODS: The mixed-methods, cross-sectional, longitudinal cohort pilot study protocol was developed by first conducting a systematic review of the literature, which shaped focus group discussions around prevention package and delivery options, and that also informed age- and sex- stratified mathematical modeling. The review, qualitative data, and mathematical modeling created a triangulated evidence base of interventions to be included in the pilot study protocol. To design the pilot study protocol, we convened an expert panel to select HIV prevention interventions effective for youth in SSA, which will be offered in a mobile health setting. The goal of the pilot study implementation and evaluation is to apply lessons learned to more effective HIV prevention evidence and programming. RESULTS: The combination HIV prevention package in this protocol includes (1) offering HIV testing and counseling for all youth; (2) voluntary medical circumcision and condoms for males; (3) pre-exposure prophylaxis (PrEP), conditional cash transfer (CCT), and contraceptives for females; and (4) referrals for HIV care among those identified as HIV-positive. The combination package platform selected is mobile health teams in an integrated services delivery model. A cross-sectional analysis will be conducted to determine the uptake of the interventions. To determine long-term impact, the protocol outlines enrolling selected participants in mutually exclusive longitudinal cohorts (HIV-positive, PrEP, CCT, and HIV-negative) followed by using mobile phone text messages (short message service, SMS) and in-person surveys to prospectively assess prevention method uptake, adherence, and risk compensation behaviors. Cross-sectional and sub-cohort analyses will be conducted to determine intervention packages uptake. CONCLUSIONS: The literature review, focus groups, and modeling indicate that offering age- and gender- specific combination HIV prevention interventions that include biomedical, behavioral, and structural interventions can have an impact on HIV risk reduction. Implementing this protocol will show the feasibility of delivering these services at scale. The MP3 Youth study is one of the few combination HIV prevention intervention protocols incorporating youth- and gender-specific interventions in one delivery setting. Lessons learned from the design of the protocol can be incorporated into the national guidance for combination HIV prevention for youth in Kenya and other high-burden SSA settings. TRIAL REGISTRATION: ClinicalTrials.gov NCT01571128; http://clinicaltrials.gov/ct2/show/NCT01571128?term=MP3+youth&rank=1 (Archived by WebCite at http://www.webcitation.org/6nmioPd54).

Understanding the potential impact of a combination HIV prevention intervention in a hyper-endemic community.

OBJECTIVES: Despite demonstrating only partial efficacy in preventing new infections, available HIV prevention interventions could offer a powerful strategy when combined. In anticipation of combination HIV prevention programs and research studies we estimated the population-level impact of combining effective scalable interventions at high population coverage, determined the factors that influence this impact, and estimated the synergy between the components. METHODS: We used a mathematical model to investigate the effect on HIV incidence of a combination HIV prevention intervention comprised of high coverage of HIV testing and counselling, risk reduction following HIV diagnosis, male circumcision for HIV-uninfected men, and antiretroviral therapy (ART) for HIV-infected persons. The model was calibrated to data for KwaZulu-Natal, South Africa, where adult HIV prevalence is approximately 23%. RESULTS: Compared to current levels of HIV testing, circumcision, and ART, the combined intervention with ART initiation according to current guidelines could reduce HIV incidence by 47%, from 2.3 new infections per 100 person-years (pyar) to 1.2 per 100 pyar within 4 years and by almost 60%, to 1 per 100 pyar, after 25 years. Short-term impact is driven primarily by uptake of testing and reductions in risk behaviour following testing while long-term effects are driven by periodic HIV testing and retention in ART programs. If the combination prevention program incorporated HIV treatment upon diagnosis, incidence could be reduced by 63% after 4 years and by 76% (to about 0.5 per 100 pyar) after 15 years. The full impact of the combination interventions accrues over 10-15 years. Synergy is demonstrated between the intervention components. CONCLUSION: High coverage combination of evidence-based strategies could generate substantial reductions in population HIV incidence in an African generalized HIV epidemic setting. The full impact could be underestimated by the short assessment duration of typical evaluations.

The new role of antiretrovirals in combination HIV prevention: a mathematical modelling analysis.

BACKGROUND AND OBJECTIVES: Antiretroviral drugs can reduce HIV acquisition among uninfected individuals (as pre-exposure prophylaxis: PrEP) and reduce onward transmission among infected individuals (as antiretroviral treatment: ART). We estimate the potential impact and cost-effectiveness of antiretroviral-based HIV prevention strategies. DESIGN AND METHODS: We developed and analysed a mathematical model of a hyperendemic setting with relatively low levels of condom use. We estimated the prevention impact and cost of various PrEP interventions, assuming a fixed amount of spending on PrEP; investigated the optimal role of PrEP and earlier ART in terms of epidemiological impact and cost; and systematically explored the impact of earlier ART and PrEP, in combination with medical male circumcision services; on HIV transmission. RESULTS: A PrEP intervention is unlikely to generate a large reduction in HIV incidence, unless the cost is substantially reduced. In terms of infections averted and quality adjusted life years gained, at a population-level maximal cost-effectiveness is achieved by providing ART to more infected individuals earlier rather than providing PrEP to uninfected individuals. However, early ART alone cannot reduce HIV incidence to very low levels and PrEP can be used cost-effectively in addition to earlier ART to reduce incidence further. If implemented in combination and at ambitious coverage levels, medical male circumcision, earlier ART and PrEP could produce dramatic declines in HIV incidence, but not stop transmission completely. CONCLUSION: A combination prevention approach based on proven-efficacy interventions provides the best opportunity for achieving the much hoped for prevention advance and curbing the spread of HIV.

HIV treatment as prevention: considerations in the design, conduct, and analysis of cluster randomized controlled trials of combination HIV prevention.

The rigorous evaluation of the impact of combination HIV prevention packages at the population level will be critical for the future of HIV prevention. In this review, we discuss important considerations for the design and interpretation of cluster randomized controlled trials (C-RCTs) of combination prevention interventions. We focus on three large C-RCTs that will start soon and are designed to test the hypothesis that combination prevention packages, including expanded access to antiretroviral therapy, can substantially reduce HIV incidence. Using a general framework to integrate mathematical modelling analysis into the design, conduct, and analysis of C-RCTs will complement traditional statistical analyses and strengthen the evaluation of the interventions. Importantly, even with combination interventions, it may be challenging to substantially reduce HIV incidence over the 2- to 3-y duration of a C-RCT, unless interventions are scaled up rapidly and key populations are reached. Thus, we propose the innovative use of mathematical modelling to conduct interim analyses, when interim HIV incidence data are not available, to allow the ongoing trials to be modified or adapted to reduce the likelihood of inconclusive outcomes. The preplanned, interactive use of mathematical models during C-RCTs will also provide a valuable opportunity to validate and refine model projections.

Towards an improved investment approach for an effective response to HIV/AIDS.

Substantial changes are needed to achieve a more targeted and strategic approach to investment in the response to the HIV/AIDS epidemic that will yield long-term dividends. Until now, advocacy for resources has been done on the basis of a commodity approach that encouraged scaling up of numerous strategies in parallel, irrespective of their relative effects. We propose a strategic investment framework that is intended to support better management of national and international HIV/AIDS responses than exists with the present system. Our framework incorporates major efficiency gains through community mobilisation, synergies between programme elements, and benefits of the extension of antiretroviral therapy for prevention of HIV transmission. It proposes three categories of investment, consisting of six basic programmatic activities, interventions that create an enabling environment to achieve maximum effectiveness, and programmatic efforts in other health and development sectors related to HIV/AIDS. The yearly cost of achievement of universal access to HIV prevention, treatment, care, and support by 2015 is estimated at no less than US$22 billion. Implementation of the new investment framework would avert 12·2 million new HIV infections and 7·4 million deaths from AIDS between 2011 and 2020 compared with continuation of present approaches, and result in 29·4 million life-years gained. The framework is cost effective at $1060 per life-year gained, and the additional investment proposed would be largely offset from savings in treatment costs alone.

Will circumcision provide even more protection from HIV to women and men? New estimates of the population impact of circumcision interventions.

BACKGROUND: Mathematical modelling has indicated that expansion of male circumcision services in high HIV prevalence settings can substantially reduce population-level HIV transmission. However, these projections need revision to incorporate new data on the effect of male circumcision on the risk of acquiring and transmitting HIV. METHODS: Recent data on the effect of male circumcision during wound healing and the risk of HIV transmission to women were synthesised based on four trials of circumcision among adults and new observational data of HIV transmission rates in stable partnerships from men circumcised at younger ages. New estimates were generated for the impact of circumcision interventions in two mathematical models, representing the HIV epidemics in Zimbabwe and Kisumu, Kenya. The models did not capture the interaction between circumcision, HIV and other sexually transmitted infections. RESULTS: An increase in the risk of HIV acquisition and transmission during wound healing is unlikely to have a major impact of circumcision interventions. However, it was estimated that circumcision confers a 46% reduction in the rate of male-to-female HIV transmission. If this reduction begins 2 years after the procedure, the impact of circumcision is substantially enhanced and accelerated compared with previous projections with no such effect-increasing by 40% the infections averted by the intervention overall and doubling the number of infections averted among women. CONCLUSIONS: Communities, and especially women, may benefit much more from circumcision interventions than had previously been predicted, and these results provide an even greater imperative to increase scale-up of safe male circumcision services.

Population level impact of an imperfect prophylactic vaccine for herpes simplex virus-2.

BACKGROUND: The continuation of developing Herpes simplex virus type-2 (HSV-2) prophylactic vaccines requires parallel mathematical modeling to quantify the effect on the population of these vaccines. METHODS: Using mathematical modeling we derived 3 summary measures for the population effect of imperfect HSV-2 vaccines as a function of their efficacies in reducing susceptibility (VES), genital shedding (VEP), and infectivity during shedding (VEI). In addition, we studied the population level effect of vaccine intervention using representative vaccine efficacies. RESULTS: A vaccine with limited efficacy of reducing shedding frequency (VEP = 10%) and infectivity (VEI = 0%) would need to reduce susceptibility by 75% (VES = 75%) to substantially reduce the sustainability of HSV-2 infection in a population. No reduction in susceptibility would be required to reach this target in a vaccine that decreased shedding by 75% (VES = 0%, VEP = 75%, VEI = 0%). Mass vaccination using a vaccine with imperfect efficacies (VES = 30%, VEP = 75%, and VEI = 0%) in Kisumu, Kenya, in 2010 would decrease prevalence and incidence in 2020 by 7% and 30%, respectively. For lower prevalence settings, vaccination is predicted to have a lower effect on prevalence. CONCLUSION: A vaccine with substantially high efficacy of reducing HSV-2 shedding frequency would have a desirable effect at the population level. The vaccine's short-term impact in a high prevalence setting in Africa would be a substantial decrease in incidence, whereas its immediate impact on prevalence would be small and would increase slowly over time.

HSV-2 serology can be predictive of HIV epidemic potential and hidden sexual risk behavior in the Middle East and North Africa.

BACKGROUND: HIV prevalence is low in the Middle East and North Africa (MENA) region, though the risk or potential for further spread in the future is not well understood. Behavioral surveys are limited in this region and when available have serious limitations in assessing the risk of HIV acquisition. We demonstrate the potential use of herpes simplex virus-2 (HSV-2) seroprevalence as a marker for HIV risk within MENA. METHODS: We designed a mathematical model to assess whether HSV-2 prevalence can be predictive of future HIV spread. We also conducted a systematic literature review of HSV-2 seroprevalence studies within MENA. RESULTS: We found that HSV-2 prevalence data are rather limited in this region. Prevalence is typically low among the general population but high in established core groups prone to sexually transmitted infections such as men who have sex with men and female sex workers. Our model predicts that if HSV-2 prevalence is low and stable, then the risk of future HIV epidemics is low. However, expanding or high HSV-2 prevalence (greater than about 20%), implies a risk for a considerable HIV epidemic. Based on available HSV-2 prevalence data, it is not likely that the general population in MENA is experiencing or will experience such a considerable HIV epidemic. Nevertheless, the risk for concentrated HIV epidemics among several high-risk core groups is present. CONCLUSIONS: HSV-2 prevalence surveys provide a useful mechanism for identifying and corroborating populations at risk for HIV within MENA. HSV-2 serology offers an effective tool for probing hidden sexual risk behaviors in a region where quality behavioral data are limited.

Quantitative assessment of the role of male circumcision in HIV epidemiology at the population level.

OBJECTIVE: Three recent randomized trials have shown that male circumcision (circumcision) reduces HIV incidence in heterosexual men by about 60%. Mathematical models are needed to assess the historical role of circumcision in the observed disparate levels of prevalence in sub-Saharan Africa and to translate these findings into estimates of the population-level impact of circumcision on HIV prevalence. METHODS AND FINDINGS: A deterministic compartmental model of HIV dynamics with circumcision was parameterized by empirical data from the Rakai, Masaka, and Four-City studies. Circumcision was found to account for about two-thirds of the differential HIV prevalence between West Africa and East and Southern Africa. We found that in Kisumu, Kenya, and in Rakai, Uganda, universal circumcision implemented in 2008 would reduce HIV prevalence by 19% and 14%, respectively, by 2020. In Kisumu, a setting with high HIV prevalence, about 6 circumcisions would be needed for each infection averted while in Rakai, 11 circumcisions would be needed. Females will also benefit from circumcision with a substantial reduction in prevalence of about 8% in Kisumu and 4% in Rakai within a few years of universal circumcision. The beneficial impact of circumcision for both males and females will not be undermined by risk behavior compensation unless the increase in risk behavior is in excess of 30%. The effectiveness of circumcision as an intervention is maximized by universal circumcision within 2-3 years. CONCLUSIONS: In West Africa, circumcision may have "quarantined" the spread of HIV by limiting sustainable transmission to within high risk groups and bridge populations. Our findings indicate that circumcision is an effective intervention in both high and intermediate HIV prevalence settings. Circumcision coverage should be expanded as soon as possible to optimize the epidemiological impact.

Protein association with circular DNA: rate enhancement by nonspecific binding.

An analytical solution for the nonspecific-binding-facilitated diffusion-controlled rate of association of a protein with a specific site on a circular DNA is derived. Nonspecific binding is modeled by a short-range attractive surface potential. The protein undergoes diffusion in the bulk solution and in the surface layer. The association rate for a circular DNA is compared to the counterpart for a linear DNA, in which the ends of the surface layer are treated as reflecting. As expected, when the DNA length is long, the shape of the DNA does not affect the association rate. For a shorter length, the association rate for the linear DNA is modestly higher than the circular counterpart. The higher rate of the linear DNA is possibly due to its more open shape, which affords it a higher ability to draw the protein from the bulk to its surface. The analytical solution is verified by Brownian dynamics simulations.

Electrostatic rate enhancement and transient complex of protein-protein association.

The association of two proteins is bounded by the rate at which they, via diffusion, find each other while in appropriate relative orientations. Orientational constraints restrict this rate to approximately 10(5)-10(6) M(-1) s(-1). Proteins with higher association rates generally have complementary electrostatic surfaces; proteins with lower association rates generally are slowed down by conformational changes upon complex formation. Previous studies (Zhou, Biophys J 1997;73:2441-2445) have shown that electrostatic enhancement of the diffusion-limited association rate can be accurately modeled by $k_{\bf D}$ = $k_{D}0\ {exp} ( - \langle U_{el} \rangle;{\star}/k_{B} T),$ where k(D) and k(D0) are the rates in the presence and absence of electrostatic interactions, respectively, U(el) is the average electrostatic interaction energy in a "transient-complex" ensemble, and k(B)T is the thermal energy. The transient-complex ensemble separates the bound state from the unbound state. Predictions of the transient-complex theory on four protein complexes were found to agree well with the experiment when the electrostatic interaction energy was calculated with the linearized Poisson-Boltzmann (PB) equation (Alsallaq and Zhou, Structure 2007;15:215-224). Here we show that the agreement is further improved when the nonlinear PB equation is used. These predictions are obtained with the dielectric boundary defined as the protein van der Waals surface. When the dielectric boundary is instead specified as the molecular surface, electrostatic interactions in the transient complex become repulsive and are thus predicted to retard association. Together these results demonstrate that the transient-complex theory is predictive of electrostatic rate enhancement and can help parameterize PB calculations.

Prediction of protein-protein association rates from a transition-state theory.

We recently developed a theory for the rates of protein-protein association. The theory is based on the concept of a transition state, which separates the bound state, with numerous short-range interactions but restricted translational and rotational freedom, and the unbound state, with, at most, a small number of interactions but expanded configurational freedom. When not accompanied by large-scale conformational changes, protein-protein association becomes diffusion limited. The association rate is then predicted as k(a)=k(a)(0)exp(-DeltaG(el)(double dagger)/k(B)T), where DeltaG(el)(double dagger) is the electrostatic interaction free energy in the transition state, k(a)(0) is the rate in the absence of electrostatic interactions, and k(B)T is thermal energy. Here, this transition-state theory is used to predict the association rates of four protein complexes. The predictions for the wild-type complexes and 23 mutants are found to agree closely with experimental data over wide ranges of ionic strength.