The spread of HIV-1 in Africa: sexual contact patterns and the predicted demographic impact of AIDS

The impact of COVID-19 on sexual risk behaviour for HIV acquisition in east Zimbabwe: An observational study

The Covid-19 pandemic and associated restrictions have the potential to alter sexual risk behaviours for HIV acquisition with important implications for HIV prevention programmes in sub-Saharan Africa. To date, no large-scale data have been published to substantiate hypothesised changes in sexual risk behaviours. We used longitudinal survey data to assess the impact of Covid-19 on sexual risk behaviours in east Zimbabwe. Data on sexual behaviours in HIV-negative adults aged 15-54 years were collected in two rounds of a general population open-cohort survey conducted in Manicaland, Zimbabwe shortly before (July 2018 to December 2019; N = 7316) and several months into the Covid-19 epidemic (February to July 2021; N = 6356). Descriptive statistics and logistic regression models of serial cross-sectional and prospective cohort data were used to assess changes in sexual risk behaviours. The proportion of females aged 15-19 years reporting sexual debut declined from 29.7% before Covid-19 to 20.3% during Covid-19 (adjusted odds ratio (AOR) = 0.49, 95% confidence interval (95% CI), 0.38-0.63). Fewer sexually-active females reported multiple sexual partners during Covid-19 (3.35% versus 6.07%; AOR = 0.55, 95% CI, 0.43-0.72). No population-level changes in male behaviour between survey rounds were recorded but the cohort analysis revealed a complex pattern of behaviour change with HIV risk behaviours increasing for some individuals and decreasing for others. Overall HIV risk behaviours remained high in a sub-Saharan African population with a generalised HIV epidemic over a period of Covid-19 lockdowns when movements and social contacts were restricted.

Does the resumption of international tourism heighten COVID-19 transmission?

Reopening countries also carries the risk of another wave of infections in many parts of the world, raising the question of whether we are ready to reopen our countries. This study examines the impact of reopening countries to receive foreign tourists on the spread of COVID-19 in 2022, encompassing 83 countries worldwide. We employ spatial quantile models capable of analyzing the spatial impact of tourism on the spread of the virus at different quantile levels. The research categorizes countries into three groups: low infection rate (10th-30th quantiles), moderate infection rate (40th-60th quantiles), and high infection rate (70th-90th quantiles). This allows for a more comprehensive and detailed comparison of the impacts. Additionally, considering the spatial dimension enables the explanation of both the direct and indirect effects of tourists on the country itself and neighboring countries. The findings reveal that the number of international tourists has a significant effect on the COVID-19 infection rate, particularly in countries with high initial infection rates. However, countries that effectively controlled their infection rates at a low level could maintain a low infection rate even after reopening to foreign tourists. It is also observed that reopening a country's borders negatively impacts the infection rate of neighboring countries. These important findings imply that governments of highly infected countries should shift their focus towards bolstering their economy by promoting domestic tourism and should delay reopening until the number of infections decreases.

Risk heterogeneity in compartmental HIV transmission models of ART as prevention in Sub-Saharan Africa: A scoping review

BACKGROUND

Transmission models provide complementary evidence to clinical trials about the potential population-level incidence reduction attributable to ART (ART prevention impact). Different modelling assumptions about risk heterogeneity may influence projected ART prevention impacts. We sought to review representations of risk heterogeneity in compartmental HIV transmission models applied to project ART prevention impacts in Sub-Saharan Africa.

METHODS

We systematically reviewed studies published before January 2020 that used non-linear compartmental models of sexual HIV transmission to simulate ART prevention impacts in Sub-Saharan Africa. We summarized data on model structure/assumptions (factors) related to risk and intervention heterogeneity, and explored multivariate ecological associations of ART prevention impacts with modelled factors.

RESULTS

Of 1384 search hits, 94 studies were included. 64 studies considered sexual activity stratification and 39 modelled at least one key population. 21 studies modelled faster/slower ART cascade transitions (HIV diagnosis, ART initiation, or cessation) by risk group, including 8 with faster and 4 with slower cascade transitions among key populations versus the wider population. In ecological analysis of 125 scenarios from 40 studies (subset without combination intervention), scenarios with risk heterogeneity that included turnover of higher risk groups were associated with smaller ART prevention benefits. Modelled differences in ART cascade across risk groups also influenced the projected ART benefits, including: ART prioritized to key populations was associated with larger ART prevention benefits. Of note, zero of these 125 scenarios considered lower ART coverage among key populations.

CONCLUSION

Among compartmental transmission models applied to project ART prevention impacts in Sub-Saharan Africa, representations of risk heterogeneity and projected impacts varied considerably. Inclusion/exclusion of risk heterogeneity with turnover, and intervention heterogeneity across risk groups could influence the projected impacts of ART scale-up. These findings highlight a need to capture risk heterogeneity with turnover and cascade heterogeneity when projecting ART prevention impacts.

Understanding the epidemiological HIV risk factors and underlying risk context for youth residing in or originating from the Middle East and North Africa (MENA) region: A scoping review of the literature

Introduction

HIV is the second leading cause of death among young people globally, and adolescents are the only group where HIV mortality is not declining. Middle East and North Africa (MENA) is one of few regions seeing rapid increase of HIV infections (31.0%) since 2001. MENA youth are at particular risk of HIV due to dearth of research and challenges in accessing services.

Objective

The purpose of this scoping review is to establish the epidemiological HIV risk factors and underlying risk context for youth residing in or originating from the MENA region.

Methods

Online database searches were conducted using combination of search terms. Screening 5,853 citations, published between 1990–2019 with age groups 16 to 29, resulted in 57 studies included across 18 MENA countries.

Results

‘Key populations’ engage in risky behaviors, including: overlapping risky behaviors among youth who inject drugs (PWID); lack of access to HIV testing, condomless sex, and multiple sex partners among young men who have sex with men (MSM); and high and overlapping risk behaviors among young sex workers. Challenges facing other youth groups and bridging populations include: peer pressure, inhibition about discussing sexual health, lack of credible sex education sources, low condom use, and lack of access to HIV protection/prevention services, especially testing.

Conclusion

Poor surveillance coupled with scarcity of rigorous studies limit what is known about epidemiology of HIV among youth in MENA. Homophobia, stigma around PWID, and illegal status of sex work promote non-disclosure of risk behaviors among youth and curtail serving this population.

Optimizing COVID-19 control with asymptomatic surveillance testing in a university environment

The high proportion of transmission events derived from asymptomatic or presymptomatic infections make SARS-CoV-2, the causative agent in COVID-19, difficult to control through the traditional non-pharmaceutical interventions (NPIs) of symptom-based isolation and contact tracing. As a consequence, many US universities developed asymptomatic surveillance testing labs, to augment NPIs and control outbreaks on campus throughout the 2020-2021 academic year (AY); several of those labs continue to support asymptomatic surveillance efforts on campus in AY2021-2022. At the height of the pandemic, we built a stochastic branching process model of COVID-19 dynamics at UC Berkeley to advise optimal control strategies in a university environment. Our model combines behavioral interventions in the form of group size limits to deter superspreading, symptom-based isolation, and contact tracing, with asymptomatic surveillance testing. We found that behavioral interventions offer a cost-effective means of epidemic control: group size limits of six or fewer greatly reduce superspreading, and rapid isolation of symptomatic infections can halt rising epidemics, depending on the frequency of asymptomatic transmission in the population. Surveillance testing can overcome uncertainty surrounding asymptomatic infections, with the most effective approaches prioritizing frequent testing with rapid turnaround time to isolation over test sensitivity. Importantly, contact tracing amplifies population-level impacts of all infection isolations, making even delayed interventions effective. Combination of behavior-based NPIs and asymptomatic surveillance also reduces variation in daily case counts to produce more predictable epidemics. Furthermore, targeted, intensive testing of a minority of high transmission risk individuals can effectively control the COVID-19 epidemic for the surrounding population. Even in some highly vaccinated university settings in AY2021-2022, asymptomatic surveillance testing offers an effective means of identifying breakthrough infections, halting onward transmission, and reducing total caseload. We offer this blueprint and easy-to-implement modeling tool to other academic or professional communities navigating optimal return-to-work strategies.

Optimizing COVID-19 control with asymptomatic surveillance testing in a university environment

The high proportion of transmission events derived from asymptomatic or presymptomatic infections make SARS-CoV-2, the causative agent in COVID-19, difficult to control through the traditional non-pharmaceutical interventions (NPIs) of symptom-based isolation and contact tracing. As a consequence, many US universities developed asymptomatic surveillance testing labs, to augment NPIs and control outbreaks on campus throughout the 2020-2021 academic year (AY); several of those labs continue to support asymptomatic surveillance efforts on campus in AY2021-2022. At the height of the pandemic, we built a stochastic branching process model of COVID-19 dynamics at UC Berkeley to advise optimal control strategies in a university environment. Our model combines behavioral interventions in the form of group size limits to deter superspreading, symptom-based isolation, and contact tracing, with asymptomatic surveillance testing. We found that behavioral interventions offer a cost-effective means of epidemic control: group size limits of six or fewer greatly reduce superspreading, and rapid isolation of symptomatic infections can halt rising epidemics, depending on the frequency of asymptomatic transmission in the population. Surveillance testing can overcome uncertainty surrounding asymptomatic infections, with the most effective approaches prioritizing frequent testing with rapid turnaround time to isolation over test sensitivity. Importantly, contact tracing amplifies population-level impacts of all infection isolations, making even delayed interventions effective. Combination of behavior-based NPIs and asymptomatic surveillance also reduces variation in daily case counts to produce more predictable epidemics. Furthermore, targeted, intensive testing of a minority of high transmission risk individuals can effectively control the COVID-19 epidemic for the surrounding population. Even in some highly vaccinated university settings in AY2021-2022, asymptomatic surveillance testing offers an effective means of identifying breakthrough infections, halting onward transmission, and reducing total caseload. We offer this blueprint and easy-to-implement modeling tool to other academic or professional communities navigating optimal return-to-work strategies.

How do biases in sex ratio and disease characteristics affect the spread of sexually transmitted infections?

The epidemiology of sexually transmitted infections (STIs) is inherently linked to host mating dynamics. Studies across many taxa show that adult sex ratio, a major determinant of host mating dynamics, is often skewed - sometimes strongly - toward males or females. However, few predictions exist for the effects of skewed sex ratio on STI epidemiology, and none when coupled with sex biased disease characteristics. Here we use mathematical modelling to examine how interactions between sex ratio and disease characteristics affect STI prevalence in males and females. Notably, we find that while overall disease prevalence peaks at equal sex ratios, prevalence per sex peaks at skewed sex ratios. Furthermore, disease characteristics, sex-biased or not, drive predictable differences in male and female STI prevalence as sex ratio varies, with higher transmission and lower virulence generally increasing differences between the sexes for a given sex ratio. Our work reveals new insights into how STI prevalence in males and females depends on a complex interaction between host population sex ratio and disease characteristics.

Reductions in HIV incidence are likely to increase the importance of key population programmes for HIV control in sub-Saharan Africa

INTRODUCTION

An efficient HIV response requires that resources be focussed on effective interventions for those most at risk of acquiring and transmitting infection. As HIV epidemics evolve the distribution of HIV across key and other populations will change. Here, the epidemiological concepts underpinning these changes are described and the importance of appropriate allocation of effective interventions is discussed.

DISCUSSION

In many sub-Saharan African countries HIV epidemics have been categorized as "generalized," and HIV testing, treatment and prevention interventions have focussed on the "general" population. As HIV epidemics are better controlled the relative importance of "key" populations will increase, dominating the ongoing burden of disease and providing the potential for repeated outbreaks of HIV if interventions are relaxed. The basic reproductive number (R0 ) describes the potential for an infectious disease to spread at the boundary of invasion or elimination, whereas the effective reproduction number (Rt ) describes the current potential for spread. Heterogeneity in risk means that while Rt is temporarily below one and prevalence declining, the R0 can remain above one, preventing eventual elimination. Patterns of HIV acquisition are often used to guide interventions but inadequately capture the transmission dynamics of the virus and the most efficient approach to controlling HIV. Risks for HIV acquisition are not identical to risks for HIV transmission and will change depending on the epidemiological context. In addition to the challenges in measuring HIV transmission dynamics, there is a tension between using epidemiology to drive the HIV response and the social and political realities constraining how programmes and providers can practically and appropriately focus on key populations and maintain political support. In addition to being well focussed, interventions need to be effective and cost-effective, which requires a better understanding of packages of interventions rather than specific tools.

CONCLUSIONS

Continued control of HIV will increasingly rely on resources, programmes and interventions supporting key populations. Current epidemiological and programmatic approaches for key populations in sub-Saharan Africa are insufficient with a need for an improved understanding of local epidemiology and the effectiveness of interventions.

Condom use, symptoms of suggestive sexually transmitted infections, and health care seeking among female sex workers in Bangladesh

This article presents a mixed-method cross-sectional study reporting condom use, sexually transmitted infection (STI) symptoms, and care seeking of female sex workers (FSWs) in Dhaka, Bangladesh. A survey of 1228 FSWs, in-depth interviews (n = 24), and key informants' interviews (n = 26) were used for data collection. Among the 1228 FSWs included in this study, 50% of them were illiterate and 39.3% were married, and their mean age was 27.1 years. The consistent use of condoms was reported by 75.6% of the FSWs, 88.7% reported having STI symptoms in the last 6 months, while 91.8% visited one of the drop-in centers for services. FSWs without formal education had lower odds of using condoms consistently (AOR: 0.72; 95% CI: 0.55-0.95), and those working elsewhere than in the streets showed higher odds (AOR: 1.63; 95% CI: 1.23-2.15) to use condoms. Stigma to access health care services, poor knowledge about STI/HIV, and low perceived risk were mentioned as causes of having STI symptoms in the survey as well as in qualitative in-depth interviews. Self-reported condom use, STI symptoms, and care-seeking practices were found to be high among the FSWs. Inconsistent condom use and a high number of sex partners could be the reasons for high levels of STI symptoms. Innovative objectively verifiable approaches should be tested to collect condom use data.

Simulating the progression of the COVID-19 disease in Cameroon using SIR models

This paper analyses the evolution of COVID-19 in Cameroon over the period March 6-April 2020 using SIR models. Specifically, we 1) evaluate the basic reproduction number of the virus, 2) determine the peak of the infection and the spread-out period of the disease, and 3) simulate the interventions of public health authorities. Data used in this study is obtained from the Cameroonian Public Health Ministry. The results suggest that over the identified period, the reproduction number of COVID-19 in Cameroon is about 1.5, and the peak of the infection should have occurred at the end of May 2020 with about 7.7% of the population infected. Furthermore, the implementation of efficient public health policies could help flatten the epidemic curve.

Identification of key interactions between SARS-CoV-2 main protease and inhibitor drug candidates

The number of cases of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection (COVID-19) has reached over 114,000. SARS-CoV-2 caused a pandemic in Wuhan, China, in December 2019 and is rapidly spreading globally. It has been reported that peptide-like anti-HIV-1 drugs are effective against SARS-CoV Main protease (Mpro). Due to the close phylogenetic relationship between SARS-CoV and SARS-CoV-2, their main proteases share many structural and functional features. Thus, these drugs are also regarded as potential drug candidates targeting SARS-CoV-2 Mpro. However, the mechanism of action of SARS-CoV-2 Mpro at the atomic-level is unknown. In the present study, we revealed key interactions between SARS-CoV-2 Mpro and three drug candidates by performing pharmacophore modeling and 1 μs molecular dynamics (MD) simulations. His41, Gly143, and Glu166 formed interactions with the functional groups that were common among peptide-like inhibitors in all MD simulations. These interactions are important targets for potential drugs against SARS-CoV-2 Mpro.

High Hepatitis B Seroprevalence, Low Knowledge, and Poor Attitude towards Hepatitis B Virus Infection among Market Women in Bolgatanga Metropolis in the Upper East Region of Ghana

The Bolgatanga Municipal Health Directorate has reported liver cirrhosis among the first three diseases causing mortality from 2013 to 2015. This implicates hepatitis B virus (HBV) infection considering its high prevalence among blood donors in the Upper East Region of Ghana. However, for a vulnerable group such as market women, there is not much information with regard to the prevalence, knowledge, and attitude towards HBV infection. Thus, this study sought to bridge this gap by determining the seroprevalence, knowledge, and attitude of market women in the Bolgatanga Municipality of Ghana, towards HBV infection. A cross-sectional descriptive study was conducted (from October 2017 to March 2018) among 404 market women using a pretested questionnaire to ascertain the knowledge and attitudes of market women towards HBV infection, while hepatitis B surface Antigen Rapid Diagnostic Test strips were used to screen for the infection. The study revealed that the seroprevalence of hepatitis B among the market women was 15.6%, and majority of the study subjects (>60%) were unaware of HBV infection. Overall, knowledge on and attitude towards HBV infection were low and poor, respectively, with a significantly high number of the market women not wanting infected individuals to be isolated (p=0.049). A high seroprevalence, together with poor attitude and low knowledge levels, as seen in this study is of great public health concern. The study recommends regular HBV screening for market women for prompt treatment and vaccination as well as continuous health education to increase knowledge level and improve the poor attitudes of market women towards HBV infection.

Lipid-drug conjugates and associated carrier strategies for enhanced antiretroviral drug delivery

Mortality rate of patients infected with HIV-1 has been significantly reduced by using HAART. However, the virus to date has not been eradicated. Transmission of HIV-1 infection through sexual intercourse remains an ongoing challenge, with increased risk of infection occurring in women. Interestingly, ARV drugs can be chemically linked with lipids to produce lipid-drug conjugates (LDCs). This alters pharmacokinetic properties of ARV drugs and thereby resulting in improved effectiveness. Although LDCs can be administered without a delivery carrier, they are usually incorporated into suitable delivery systems such as lipid nanoparticles, polymeric nanoparticles, micelles, liposomes, emulsions, and carbon nanotubes. Given that LDCs have the potential to improve oral bioavailability, lipophilicity, toxicity, and drug targeting, it is of our great interest to review strategies of lipid-drug conjugation together with their delivery systems for enhanced antiretroviral efficacy.

Molecular Dynamics Simulation reveals the mechanism by which the Influenza Cap-dependent Endonuclease acquires resistance against Baloxavir marboxil

Baloxavir marboxil (BXM), an antiviral drug for influenza virus, inhibits RNA replication by binding to RNA replication cap-dependent endonuclease (CEN) of influenza A and B viruses. Although this drug was only approved by the FDA in October 2018, drug resistant viruses have already been detected from clinical trials owing to an I38 mutation of CEN. To investigate the reduction of drug sensitivity by the I38 mutant variants, we performed a molecular dynamics (MD) simulation on the CEN-BXM complex structure to analyze variations in the mode of interaction. Our simulation results suggest that the side chain methyl group of I38 in CEN engages in a CH-pi interaction with the aromatic ring of BXM. This interaction is abolished in various I38 mutant variants. Moreover, MD simulation on various mutation models and binding free energy prediction by MM/GBSA method suggest that the I38 mutation precludes any interaction with the aromatic ring of BXA and thereby reduces BXA sensitivity.

Ensemble-Based Modeling of Chemical Compounds with Antimalarial Activity

Background:

Malaria or Paludism is a tropical disease caused by parasites of the Plasmodium genre and transmitted to humans through the bite of infected mosquitos of the Anopheles genre. This pathology is considered one of the first causes of death in tropical countries and, despite several existing therapies, they have a high toxicity. Computational methods based on Quantitative Structure- Activity Relationship studies have been widely used in drug design work flows.

Objective:

The main goal of the current research is to develop computational models for the identification of antimalarial hit compounds.

Materials and Methods:

For this, a data set suitable for the modeling of the antimalarial activity of chemical compounds was compiled from the literature and subjected to a thorough curation process. In addition, the performance of a diverse set of ensemble-based classification methodologies was evaluated and one of these ensembles was selected as the most suitable for the identification of antimalarial hits based on its virtual screening performance. Data curation was conducted to minimize noise. Among the explored ensemble-based methods, the one combining Genetic Algorithms for the selection of the base classifiers and Majority Vote for their aggregation showed the best performance.

Results:

Our results also show that ensemble modeling is an effective strategy for the QSAR modeling of highly heterogeneous datasets in the discovery of potential antimalarial compounds.

Conclusion:

It was determined that the best performing ensembles were those that use Genetic Algorithms as a method of selection of base models and Majority Vote as the aggregation method.

Summary results of the 2014-2015 DARPA Chikungunya challenge

Background: Emerging pathogens such as Zika, chikungunya, Ebola, and dengue viruses are serious threats to national and global health security. Accurate forecasts of emerging epidemics and their severity are critical to minimizing subsequent mortality, morbidity, and economic loss. The recent introduction of chikungunya and Zika virus to the Americas underscores the need for better methods for disease surveillance and forecasting.

Methods: To explore the suitability of current approaches to forecasting emerging diseases, the Defense Advanced Research Projects Agency (DARPA) launched the 2014–2015 DARPA Chikungunya Challenge to forecast the number of cases and spread of chikungunya disease in the Americas. Challenge participants (n=38 during final evaluation) provided predictions of chikungunya epidemics across the Americas for a six-month period, from September 1, 2014 to February 16, 2015, to be evaluated by comparison with incidence data reported to the Pan American Health Organization (PAHO). This manuscript presents an overview of the challenge and a summary of the approaches used by the winners.

Results: Participant submissions were evaluated by a team of non-competing government subject matter experts based on numerical accuracy and methodology. Although this manuscript does not include in-depth analyses of the results, cursory analyses suggest that simpler models appear to outperform more complex approaches that included, for example, demographic information and transportation dynamics, due to the reporting biases, which can be implicitly captured in statistical models. Mosquito-dynamics, population specific information, and dengue-specific information correlated best with prediction accuracy.

Conclusion: We conclude that with careful consideration and understanding of the relative advantages and disadvantages of particular methods, implementation of an effective prediction system is feasible. However, there is a need to improve the quality of the data in order to more accurately predict the course of epidemics.

Modeling the Intervention of HIV Transmission across Intertwined Key Populations

The HIV transmissions between multiple key populations make interventions difficult, particularly with multiple transmission behaviors. It remains unclear how significant the role of bridge individuals (who connect multiple communities) is in HIV transmission, and how to develop more effective intervention strategies targeting different transmission modes across key populations. In this research, we proposed a 2-layer social network framework to simulate the HIV transmissions across female sex workers (FSWs) and persons who inject drugs (PWID) through two behaviors: unprotected sex and needle-sharing. We proposed a set of intervention strategies based on the topological properties of individuals in the social network and estimated the efficacy of these strategies. Simulation studies demonstrated that bridge individuals played a significant role in HIV transmissions across the two networks. Prevention on such bridge individuals could help reduce both the scale and speed of HIV transmissions.

The effects of HIV on fertility by infection duration: evidence from African population cohorts before antiretroviral treatment availability

OBJECTIVES

To estimate the relationship between HIV natural history and fertility by duration of infection in east and southern Africa before the availability of antiretroviral therapy and assess potential biases in estimates of age-specific subfertility when using retrospective birth histories in cross-sectional studies.

DESIGN

Pooled analysis of prospective population-based HIV cohort studies in Masaka (Uganda), Kisesa (Tanzania) and Manicaland (Zimbabwe).

METHODS

Women aged 15-49 years who had ever tested for HIV were included. Analyses were censored at antiretroviral treatment roll-out. Fertility rate ratios were calculated to see the relationship of duration of HIV infection on fertility, adjusting for background characteristics. Survivorship and misclassification biases on age-specific subfertility estimates from cross-sectional surveys were estimated by reclassifying person-time from the cohort data to simulate cross-sectional surveys and comparing fertility rate ratios with true cohort results.

RESULTS

HIV-negative and HIV-positive women contributed 15 440 births and 86 320 person-years; and 1236 births and 11 240 000 person-years, respectively, to the final dataset. Adjusting for age, study site and calendar year, each additional year since HIV seroconversion was associated with a 0.02 (95% confidence interval 0.01-0.03) relative decrease in fertility for HIV-positive women. Survivorship and misclassification biases in simulated retrospective birth histories resulted in modest underestimates of subfertility by 2-5% for age groups 20-39 years.

CONCLUSION

Longer duration of infection is associated with greater relative fertility reduction for HIV-positive women. This should be considered when creating estimates for HIV prevalence among pregnant women and prevention of mother-to-child transmission need over the course of the HIV epidemic and antiretroviral treatment scale up.

Transmission networks and risk of HIV infection in KwaZulu-Natal, South Africa: a community-wide phylogenetic study

BACKGROUND

The incidence of HIV infection in young women in Africa is very high. We did a large-scale community-wide phylogenetic study to examine the underlying HIV transmission dynamics and the source and consequences of high rates of HIV infection in young women in South Africa.

METHODS

We did a cross-sectional household survey of randomly selected individuals aged 15-49 years in two neighbouring subdistricts (one urban and one rural) with a high burden of HIV infection in KwaZulu-Natal, South Africa. Participants completed structured questionnaires that captured general demographic, socioeconomic, psychosocial, and behavioural data. Peripheral blood samples were obtained for HIV antibody testing. Samples with HIV RNA viral load greater than 1000 copies per mL were selected for genotyping. We constructed a phylogenetic tree to identify clusters of linked infections (defined as two or more sequences with bootstrap or posterior support ≥90% and genetic distance ≤4·5%).

FINDINGS

From June 11, 2014, to June 22, 2015, we enrolled 9812 participants, 3969 of whom tested HIV positive. HIV prevalence (weighted) was 59·8% in 2835 women aged 25-40 years, 40·3% in 1548 men aged 25-40 years, 22·3% in 2224 women younger than 25 years, and 7·6% in 1472 men younger than 25 years. HIV genotyping was done in 1589 individuals with a viral load of more than 1000 copies per mL. In 90 transmission clusters, 123 women were linked to 103 men. Of 60 possible phylogenetically linked pairings with the 43 women younger than 25 years, 18 (30·0%) probable male partners were younger than 25 years, 37 (61·7%) were aged 25-40 years, and five (8·3%) were aged 41-49 years: mean age difference 8·7 years (95% CI 6·8-10·6; p<0·0001). For the 92 possible phylogenetically linked pairings with the 56 women aged 25-40 years, the age difference dropped to 1·1 years (95% CI -0·6 to 2·8; p=0·111). 16 (39·0%) of 41 probable male partners linked to women younger than 25 years were also linked to women aged 25-40 years. Of 79 men (mean age 31·5 years) linked to women younger than 40 years, 62 (78·5%) were unaware of their HIV-positive status, 76 (96·2%) were not on antiretroviral therapy, and 29 (36·7%) had viral loads of more than 50 000 copies per mL.

INTERPRETATION

Sexual partnering between young women and older men, who might have acquired HIV from women of similar age, is a key feature of the sexual networks driving transmission. Expansion of treatment and combination prevention strategies that include interventions to address age-disparate sexual partnering is crucial to reducing HIV incidence and enabling Africa to reach the goal of ending AIDS as a public health threat.

FUNDING

President's Emergency Program for AIDS Relief, US Centers for Disease Control and Prevention, South African Medical Research Council, and MAC AIDS Fund.

Factors Related to Condom Use among Young People in Kenya

Survey questionnaires were provided to a convenience sample of 197 students in four educational settings. When regressing the knowledge score on the independent variables, it was found that the knowledge score increased with years of education, the practice of Islam, getting HIV/AIDS information from a radio, worrying about contracting HIV/AIDS, and receiving AIDS education or family life education in school. The knowledge score was negatively related with age. When regressing condom use on the independent variables, including the knowledge score, the likelihood that a respondent would use a condom significantly increased when the respondent was willing to use a condom, when a sexual partner requested it, when the respondent knew where to purchase condoms, and when the respondent had received education in school on family planning and AIDS education. The likelihood of using condoms was negatively related with age and the statement “real men do not wear condoms.”

Data and methods to characterize the role of sex work and to inform sex work programs in generalized HIV epidemics: evidence to challenge assumptions

In the context of generalized human immunodeficiency virus (HIV) epidemics, there has been limited recent investment in HIV surveillance and prevention programming for key populations including female sex workers. Often implicit in the decision to limit investment in these epidemic settings are assumptions including that commercial sex is not significant to the sustained transmission of HIV, and HIV interventions designed to reach "all segments of society" will reach female sex workers and clients. Emerging empiric and model-based evidence is challenging these assumptions. This article highlights the frameworks and estimates used to characterize the role of sex work in HIV epidemics as well as the relevant empiric data landscape on sex work in generalized HIV epidemics and their strengths and limitations. Traditional approaches to estimate the contribution of sex work to HIV epidemics do not capture the potential for upstream and downstream sexual and vertical HIV transmission. Emerging approaches such as the transmission population attributable fraction from dynamic mathematical models can address this gap. To move forward, the HIV scientific community must begin by replacing assumptions about the epidemiology of generalized HIV epidemics with data and more appropriate methods of estimating the contribution of unprotected sex in the context of sex work.

Intravaginal practices and lactobacilli colonization among women in Accra, Ghana

Background

Intravaginal practices may affect the colonization of vaginal flora and lead to vaginal infections due to the potential effects on the vaginal environment. This study investigated the vaginal practices and their possible effects on vaginal lactobacilli flora colonization in women in Accra.

Methods

A cross-sectional, descriptive single-site study was carried out on 141 women assessing medical care at the Obstetrics and Gynaecology Department of the Korle-Bu Teaching Hospital (KBTH) in Accra. Study-relevant information on participants was obtained by means of questionnaire. Vaginal swab samples were collected and processed for laboratory analyses.

Results

All the participants (141/141, 100.0 %) indicated they performed intravaginal practices using various methods. Almost half (46.1 %) of these women were between the ages of 25–34 years and 65.0 % were married. Internal douching (82.3 %; p > 0.05) was the commonest practice reported. Other practices such as insertion and wiping with hands and objects, as well as use of locally prepared concoctions and certain commercial products were also reported. The reason most commonly given was for hygienic purpose (83.0 %); a few (10.6 %) did it for sexual satisfaction, while others indicated vaginal tightness (5.7 %) and wound healing (0.7 %) as reasons for their practice. No Lactobacillus sp. was detected in as many as 78.7 % of the sample. Association tests by the Pearson correlation analysis showed strong significant negative correlation (r = −0.954, p < 0.05) between use of traditional herbs/concoction and vaginal lactobacilli colonization; and douching being the least negatively (r = −0.601, p > 0.05) correlated practice.

Conclusions

Vaginal practices were common among the women studied. A more elaborate prospective, case–control study into intravaginal practices and their impact on the health of women in Ghana should be explored.

Electronic supplementary material

The online version of this article (doi:10.1186/s12905-015-0205-2) contains supplementary material, which is available to authorized users.

Estimating the range of potential epidemiological impact of pre-exposure prophylaxis: run-away success or run-away failure?

OBJECTIVE

To investigate the influence of potential interactions between key aspects of a pre-exposure prophylaxis (PrEP) intervention on projections of epidemiological impact and cost-effectiveness.

METHODS

A mathematical model representing the HIV epidemic and intervention context in Nyanza province in Kenya was developed. We consider a scenario whereby a fixed annual budget is allocated to a PrEP intervention. A standard projection of impact is generated, assuming that the unit cost of PrEP, adherence to PrEP and the ability of the programme to direct PrEP to those at high risk, all stay constant. The influence of dynamic assumptions and possible interactions between PrEP intervention assumptions is then assessed in comparison.

RESULTS

The cumulative impact of a PrEP intervention could be increased approximately two-fold, relative to the standard projection, if positive interactions (between coverage and cost, coverage and adherence, prioritization and time) are assumed, whereas negative interactions between these factors could almost entirely negate the preventive benefit of the PrEP intervention. The corresponding estimates of cost per infection averted span a wide range from $2060 to $36360.

CONCLUSIONS

Multiple potentially interacting factors will determine the impact of PrEP. Model forecasts should reflect that uncertainty and programmes should focus on these factors and measure them, to maximize the impact of programmes.

Predicting epidemic risk from past temporal contact data

Understanding how epidemics spread in a system is a crucial step to prevent and control outbreaks, with broad implications on the system’s functioning, health, and associated costs. This can be achieved by identifying the elements at higher risk of infection and implementing targeted surveillance and control measures. One important ingredient to consider is the pattern of disease-transmission contacts among the elements, however lack of data or delays in providing updated records may hinder its use, especially for time-varying patterns. Here we explore to what extent it is possible to use past temporal data of a system’s pattern of contacts to predict the risk of infection of its elements during an emerging outbreak, in absence of updated data. We focus on two real-world temporal systems; a livestock displacements trade network among animal holdings, and a network of sexual encounters in high-end prostitution. We define the node’s loyalty as a local measure of its tendency to maintain contacts with the same elements over time, and uncover important non-trivial correlations with the node’s epidemic risk. We show that a risk assessment analysis incorporating this knowledge and based on past structural and temporal pattern properties provides accurate predictions for both systems. Its generalizability is tested by introducing a theoretical model for generating synthetic temporal networks. High accuracy of our predictions is recovered across different settings, while the amount of possible predictions is system-specific. The proposed method can provide crucial information for the setup of targeted intervention strategies.

Following the emergence of a transmissible disease epidemic, interventions and resources need to be prioritized to efficiently control its spread. While the knowledge of the pattern of disease-transmission contacts among hosts would be ideal for this task, the continuously changing nature of such pattern makes its use less practical in real public health emergencies (or otherwise highly resource-demanding when possible). We show that in such situations critical knowledge to assess the real-time risk of infection can be extracted from past temporal contact data. An index expressing the conservation of contacts over time is proposed as an effective tool to prioritize interventions, and its efficiency is tested considering real data on livestock movements and on human sexual encounters.

The end of AIDS: possibility or pipe dream? A tale of transitions

Globally, in the last 20 years health has improved. In this generally optimistic setting HIV and AIDS accounts for the fastest growing burden of disease. The data show the bulk of this is experienced in Southern Africa. In this region, HIV and AIDS (and tuberculosis [TB]) peaks among young adults. Women carry the greater proportion of infections and provided most of the care. South Africa has the dubious distinction of having the largest number of people living with HIV in the world, 6.4 million. HIV began spreading from about 1990 and today the prevalence among antenatal clinic attendees is 29.5%. A similar situation exists in other nations of the region. It is an expensive disease, requiring more resources than are available, and it is slipping off the global agenda, both in terms of attention and international funding. Those halcyon days of the decade from 2000 to 2010 are over. This paper explores the concept of three transition points: economic, epidemiological and programmatic. The first two have been developed and written about by others. We add a third transition point, namely programmatic, argue this is an important concept, and show how it can become a powerful tool in the response to the epidemic. The economic transition point assesses HIV incidence and mortality of people infected with HIV. Until the number of newly infected people falls below the number of deaths of people living with HIV, the demand for treatment and costs will increase. This is a concern for the health sector, finance ministry and all working in the field of HIV. Once an economic transition occurs the treatment future is predictable and the number of people living with HIV and AIDS decreases. This paper plots two more lines. These are the number of new people from the HIV infected pool initiated on treatment and the number of people from the HIV infected pool requiring treatment. This introduces new transition points on the graph. The first when the number of people initiated on treatment exceeds the number of people needing treatment. The second when the number initiated on treatment exceeds the new infections. That is the theory. When we applied South African data from the ASSA2008 model, we were able to plot transition points marking progress in the national response. We argue these concepts can and should be applied to any country or HIV epidemic.

Molecular epidemiology of HIV-1 in Jilin province, northeastern China: emergence of a new CRF07_BC transmission cluster and intersubtype recombinants

Objective

To investigate the HIV-1 molecular epidemiology among newly diagnosed HIV-1 infected persons living in the Jilin province of northeastern China.

Methods

Plasma samples from 189 newly diagnosed HIV-1 infected patients were collected between June 2010 and August 2011 from all nine cities of Jilin province. HIV-1 nucleotide sequences of gag P17–P24 and env C2–C4 gene regions were amplified using a multiplex RT-PCR method and sequenced. Phylogenetic and recombination analyses were used to determine the HIV-1 genotypes.

Results

Based on all sequences generated, the subtype/CFR distribution was as follows: CRF01_AE (58.1%), CRF07_BC (13.2%), subtype B’ (13.2%), recombinant viruses (8.1%), subtype B (3.7%), CRF02_AG (2.9%), subtype C (0.7%). In addition to finding CRF01_AE strains from previously reported transmission clusters 1, 4 and 5, a new transmission cluster was described within the CRF07_BC radiation. Among 11 different recombinants identified, 10 contained portions of gene regions from the CRF01_AE lineage. CRF02_AG was found to form a transmission cluster of 4 in local Jilin residents.

Conclusions

Our study presents a molecular epidemiologic investigation describing the complex structure of HIV-1 strains co-circulating in Jilin province. The results highlight the critical importance of continuous monitoring of HIV-infections, along with detailed socio-demographic data, in order to design appropriate prevention measures to limit the spread of new HIV infections.

Marriage, like income and education, fails to provide shelter for women against HIV infection in sub-Saharan Africa: widowhood and divorce increase the risk

Since HIV infection and its consequence, AIDS, were first described, many initial assumptions have proven to be wrong. In Africa, it is women who bear the greater burden of the disease. In many ways they are less visible than men, although at least as much at risk, often even more so. Marriage is no protection against infection, and widowhood and divorce leave them still more vulnerable. This is reflected in higher proportions of infection for bereaved and separated wives. Programmes of control, which depend on education, testing and access to treatment should be visible and accessible to all women in sub-Saharan Africa.

The role of viral introductions in sustaining community-based HIV epidemics in rural Uganda: evidence from spatial clustering, phylogenetics, and egocentric transmission models

BACKGROUND

It is often assumed that local sexual networks play a dominant role in HIV spread in sub-Saharan Africa. The aim of this study was to determine the extent to which continued HIV transmission in rural communities--home to two-thirds of the African population--is driven by intra-community sexual networks versus viral introductions from outside of communities.

METHODS AND FINDINGS

We analyzed the spatial dynamics of HIV transmission in rural Rakai District, Uganda, using data from a cohort of 14,594 individuals within 46 communities. We applied spatial clustering statistics, viral phylogenetics, and probabilistic transmission models to quantify the relative contribution of viral introductions into communities versus community- and household-based transmission to HIV incidence. Individuals living in households with HIV-incident (n = 189) or HIV-prevalent (n = 1,597) persons were 3.2 (95% CI: 2.7-3.7) times more likely to be HIV infected themselves compared to the population in general, but spatial clustering outside of households was relatively weak and was confined to distances <500 m. Phylogenetic analyses of gag and env genes suggest that chains of transmission frequently cross community boundaries. A total of 95 phylogenetic clusters were identified, of which 44% (42/95) were two individuals sharing a household. Among the remaining clusters, 72% (38/53) crossed community boundaries. Using the locations of self-reported sexual partners, we estimate that 39% (95% CI: 34%-42%) of new viral transmissions occur within stable household partnerships, and that among those infected by extra-household sexual partners, 62% (95% CI: 55%-70%) are infected by sexual partners from outside their community. These results rely on the representativeness of the sample and the quality of self-reported partnership data and may not reflect HIV transmission patterns outside of Rakai.

CONCLUSIONS

Our findings suggest that HIV introductions into communities are common and account for a significant proportion of new HIV infections acquired outside of households in rural Uganda, though the extent to which this is true elsewhere in Africa remains unknown. Our results also suggest that HIV prevention efforts should be implemented at spatial scales broader than the community and should target key populations likely responsible for introductions into communities.

Dynamics of infectious diseases

Modern infectious disease epidemiology has a strong history of using mathematics both for prediction and to gain a deeper understanding. However the study of infectious diseases is a highly interdisciplinary subject requiring insights from multiple disciplines, in particular a biological knowledge of the pathogen, a statistical description of the available data and a mathematical framework for prediction. Here we begin with the basic building blocks of infectious disease epidemiology--the SIS and SIR type models--before considering the progress that has been made over the recent decades and the challenges that lie ahead. Throughout we focus on the understanding that can be developed from relatively simple models, although accurate prediction will inevitably require far greater complexity beyond the scope of this review. In particular, we focus on three critical aspects of infectious disease models that we feel fundamentally shape their dynamics: heterogeneously structured populations, stochasticity and spatial structure. Throughout we relate the mathematical models and their results to a variety of real-world problems.

A stochastic multi-scale model of HIV-1 transmission for decision-making: application to a MSM population

BACKGROUND

In the absence of an effective vaccine against HIV-1, the scientific community is presented with the challenge of developing alternative methods to curb its spread. Due to the complexity of the disease, however, our ability to predict the impact of various prevention and treatment strategies is limited. While ART has been widely accepted as the gold standard of modern care, its timing is debated.

OBJECTIVES

To evaluate the impact of medical interventions at the level of individuals on the spread of infection across the whole population. Specifically, we investigate the impact of ART initiation timing on HIV-1 spread in an MSM (Men who have Sex with Men) population.

DESIGN AND METHODS

A stochastic multi-scale model of HIV-1 transmission that integrates within a single framework the in-host cellular dynamics and their outcomes, patient health states, and sexual contact networks. The model captures disease state and progression within individuals, and allows for simulation of therapeutic strategies.

RESULTS

Early ART initiation may substantially affect disease spread through a population.

CONCLUSIONS

Our model provides a multi-scale, systems-based approach to evaluate the broader implications of therapeutic strategies.

Modelling HIV/AIDS epidemic among men who have sex with men in China

A compartmental model with antiviral therapy was proposed to identify the important factors that influence HIV infection among gay men in China and suggest some effective control strategies. We proved that the disease will be eradicated if the reproduction number is less than one. Based on the number of annual reported HIV/AIDS among MSM we used the Markov-Chain Monte-Carlo (MCMC) simulation to estimate the unknown parameters. We estimated a mean reproduction number of 3.88 (95% CI: 3.69-4.07). The estimation results showed that there were a higher transmission rate and a lower diagnose rate among MSM than those for another high-risk population. We compared the current treatment policy and immediate therapy once people are diagnosed with HIV, and numerical studies indicated that immediate antiviral therapy would lead to few HIV new infections conditional upon relatively low infectiousness; otherwise the current treatment policy would result in low HIV new infection. Further, increasing treatment coverage rate may lead to decline in HIV new infections and be beneficial to disease control, depending on the infectiousness of the infected individuals with antiviral therapy. The finding suggested that treatment efficacy (directly affecting infectiousness), behavior changes, and interventions greatly affect HIV new infection; strengthening intensity will contribute to the disease control.

Spatiotemporal infectious disease modeling: a BME-SIR approach

This paper is concerned with the modeling of infectious disease spread in a composite space-time domain under conditions of uncertainty. We focus on stochastic modeling that accounts for basic mechanisms of disease distribution and multi-sourced in situ uncertainties. Starting from the general formulation of population migration dynamics and the specification of transmission and recovery rates, the model studies the functional formulation of the evolution of the fractions of susceptible-infected-recovered individuals. The suggested approach is capable of: a) modeling population dynamics within and across localities, b) integrating the disease representation (i.e. susceptible-infected-recovered individuals) with observation time series at different geographical locations and other sources of information (e.g. hard and soft data, empirical relationships, secondary information), and c) generating predictions of disease spread and associated parameters in real time, while considering model and observation uncertainties. Key aspects of the proposed approach are illustrated by means of simulations (i.e. synthetic studies), and a real-world application using hand-foot-mouth disease (HFMD) data from China.

Sexually transmitted infections in polygamous mating systems

Sexually transmitted infections (STIs) are often associated with chronic diseases and can have severe impacts on host reproductive success. For airborne or socially transmitted pathogens, patterns of contact by which the infection spreads tend to be dispersed and each contact may be of very short duration. By contrast, the transmission pathways for STIs are usually characterized by repeated contacts with a small subset of the population. Here we review how heterogeneity in sexual contact patterns can influence epidemiological dynamics, and present a simple model of polygyny/polyandry to illustrate the impact of biased mating systems on disease incidence and pathogen virulence.

Improving questions on sexual partnerships: lessons learned from cognitive interviews for Britain's third National Survey of Sexual Attitudes and Lifestyles ("Natsal-3")

Patterns of sexual partnership formation and dissolution are key drivers of sexually transmitted infection transmission. Sexual behavior survey participants may be unable or unwilling to report accurate details about their sexual partners, limiting the potential to capture information on sexual mixing and timing of partnerships. We examined how questions were interpreted, including recall strategies and judgments made in selecting responses, to inform development of a module on recent sexual partnerships in Britain's third National Survey of Sexual Attitudes and Lifestyles ("Natsal-3"). Face-to-face cognitive interviews were conducted with 14 men and 18 women aged 18-74 years, during development work for Natsal-3. People with multiple recent partners were purposively sampled and questions were presented as a computer-assisted self-interview. Participants were generally agreeable to answering questions about their sexual partners and practices. Interpretation of questions designed to measure concurrent (overlapping) partnerships was broadly consistent with the epidemiological concept of concurrency. Partners' ages, genders, ethnicity, and participants' perceptions of whether partner(s) had had concurrent partnerships were reported without offense. Recall problems and lack of knowledge were reported by some participants (of all ages), especially about former, casual, and/or new partnerships, and some reported guessing partners' ages and dates of sex. Generally, participants were able to answer questions about their sexual partners accurately, even when repeated for multiple partners. Cognitive interviews provided insight into the participants' understanding of, ability to answer, and willingness to answer questions. This enabled us to improve questions used in previous surveys, refine new questions, and ensure the questionnaire order was logical for participants.

Linking predator-prey interactions with exposure to a trophically transmitted parasite using PCR-based analyses

Parasite transmission is determined by the rate of contact between a susceptible host and an infective stage and susceptibility to infection given an exposure event. Attempts to measure levels of variation in exposure in natural populations can be especially challenging. The level of exposure to a major class of parasites, trophically transmitted parasites, can be estimated by investigating the host's feeding behaviour. Since the parasites rely on the ingestion of infective intermediate hosts for transmission, the potential for exposure to infection is inherently linked to the definitive host's feeding ecology. Here, we combined epidemiological data and molecular analyses (polymerase chain reaction) of the diet of the definitive host, the white-footed mouse (Peromyscus leucopus), to investigate temporal and individual heterogeneities in exposure to infection. Our results show that the consumption of cricket intermediate hosts accounted for much of the variation in infection; mice that had consumed crickets were four times more likely to become infected than animals that tested negative for cricket DNA. In particular, pregnant female hosts were three times more likely to consume crickets, which corresponded to a threefold increase in infection compared with nonpregnant females. Interestingly, males in breeding condition had a higher rate of infection even though breeding males were just as likely to test positive for cricket consumption as nonbreeding males. These results suggest that while heterogeneity in host diet served as a strong predictor of exposure risk, differential susceptibility to infection may also play a key role, particularly among male hosts. By combining PCR analyses with epidemiological data, we revealed temporal variation in exposure through prey consumption and identified potentially important individual heterogeneities in parasite transmission.

Identifying the HIV transmission bridge: which men are having unsafe sex with female sex workers and with their own wives or steady partners?

OBJECTIVE

To gain insights into bridging behaviors and their correlates among male clients of female sex workers (FSWs).

METHODS

Men aged ≥18 years who recently paid or traded for sex with FSWs were recruited in Tijuana in 2008-2009. Participants underwent interviews and testing for HIV, chlamydia, syphilis, and gonorrhea. Logistic regression compared "bridgers" (clients who had unprotected sex with FSWs and with a wife or steady partner) with men who did not.

RESULTS

Of 383 men, 134 (35%) had a steady partner. Half (n = 70) of those had unprotected sex with both FSWs and the steady partner. Prevalence of any sexually transmitted infection or HIV was 16.5% among bridgers and 2.3% among nonbridgers. Compared with other clients, bridgers were more likely to use drugs during sex with FSWs (81.4% versus 46.9%, P < 0.0001), had higher sensation-seeking (P < 0.0001) and misogyny scores (P = 0.05) and were more likely to offer FSWs extra money for unprotected sex (34.4% versus 1.6%, P < 0.0001). Factors independently associated with bridging were as follows: using drugs during sex with FSWs [adjusted odds ratio (AOR): 3.4, P = 0.007], sensation seeking (AOR: 4.3 per unit increase, P = 0.05), and offering FSWs more money for unprotected sex (AOR: 24.5, P = 0.003).

CONCLUSION

Sensation-seeking clients who use drugs during sex and coerce FSWs into unprotected sex may be less responsive to standard risk reduction interventions. Interventions are needed that target clients rather than rely on FSWs to change behaviors that may not be under their control.

A systematic review and meta-analysis of risk factors for sexual transmission of HIV in India

Background

Approximately 2.4 million people are living with HIV in India. This large disease burden, and potential for epidemic spread in some areas, demands a full understanding of transmission in that country. We wished to quantify the effects of key sexual risk factors for HIV infection for each gender and among high- and low-HIV risk populations in India.

Methodology

We conducted a systematic review of sexual risk factors for HIV infection from 35 published studies. Risk factors analyzed were: male circumcision/religion, Herpes Simplex Virus 2, syphilis, gonorrhoea, genital ulcer, multiple sexual partners and commercial sex. Studies were included if they met predetermined criteria. Data were extracted and checked by two researchers and random-effects meta analysis of effects was conducted. Heterogeneity in effect estimates was examined by I² statistic. Publication bias was tested by Begg's test and funnel plots. Meta regression was used to assess effect modification by various study attributes.

Results

All risk factors were significantly associated with HIV status. The factor most strongly associated with HIV for both sexes was HSV-2 infection (OR_men: 5.87; 95%CI: 2.46–14.03; OR_women: 6.44; 95%CI: 3.22–12.86). The effect of multiple sexual partners was similar among men (OR = 2.46; 95%CI: 1.91–3.17,) and women (OR = 2.02; 95%CI: 1.43–2.87) and when further stratified by HIV-risk group. The association between HSV-2 and HIV prevalence was consistently stronger than other STIs or self-reported genital ulcer. If the strong associations between HSV-2 and HIV were interpreted causally, these results implied that approximately half of the HIV infections observed in our study population were attributable to HSV-2 infection.

Conclusions

The risk factors examined in our analysis should remain targets of HIV prevention programs. Our results confirm that sexual risk factors for HIV infection continue to be an important part of Indian HIV epidemic 26 years after it began.

Marital shopping and epidemic AIDS

HIV risks decline sharply at age 30 for women in South Africa, long before coital frequencies or pregnancies decrease. I evaluate several prominent behavioral models of HIV, and find that these do not suggest sharply decreasing risks with age. I formulate a model of spousal search and find that "marital shopping" can generate epidemic HIV prevalence despite low transmission rates because search behavior interacts with dynamics of HIV infectiousness. The implied age-infection profile closely mimics that in South Africa, and the suggested behavior matches that reported by South Africans. Condom use in new relationships and transmission rate reductions are both found to be effective policies and, when used together, eliminate the potential of spousal search to spread HIV. In contrast, antiretroviral treatment is found to have only a minimal effect on the epidemic.

Large-scale spatial population databases in infectious disease research

Modelling studies on the spatial distribution and spread of infectious diseases are becoming increasingly detailed and sophisticated, with global risk mapping and epidemic modelling studies now popular. Yet, in deriving populations at risk of disease estimates, these spatial models must rely on existing global and regional datasets on population distribution, which are often based on outdated and coarse resolution data. Moreover, a variety of different methods have been used to model population distribution at large spatial scales. In this review we describe the main global gridded population datasets that are freely available for health researchers and compare their construction methods, and highlight the uncertainties inherent in these population datasets. We review their application in past studies on disease risk and dynamics, and discuss how the choice of dataset can affect results. Moreover, we highlight how the lack of contemporary, detailed and reliable data on human population distribution in low income countries is proving a barrier to obtaining accurate large-scale estimates of population at risk and constructing reliable models of disease spread, and suggest research directions required to further reduce these barriers.

A MODEL-INDEPENDENT ANALYSIS OF THE DEMOGRAPHIC IMPACT OF HIV/AIDS IN THE STATE OF SÃO PAULO, BRAZIL

The devastating figures that recently emerged from a demographic study of the impact of HIV/AIDS in some African countries mark the return to the conditions of the XIXth century, when high birth rates were neutralized by equally high death rates. In the State of São Paulo, Brazil, AIDS is the second cause of death among men aged twenty to forty nine years and the first cause of death of women in the same age class. In this work we propose a mathematical treatment to evaluate the impact of AIDS mortality on the age structure of an affected population, namely, that of the state of São Paulo, Brazil. We propose four indicators for the estimation of the impact of AIDS mortality. The first is the age-dependent differences in ten years survival probabilities attributable to AIDS. The second is the difference in the average age of survivors after 10 years of AIDS. The next is the conventional life expectancy at birth for children born in 1996 and with AIDS prevalence assumed at its maximum value and remaining in steady-state afterwards. Finally, we calculate the differences in the life expectancy of individuals considering the effect of AIDS for only ten years. We found that, in the period between 1987 and 1996 the effects were small but very interesting. However, projecting to the future the conditions of 1996, we calculate that the population of the state of São Paulo would lose 3 years in the average life expectancy at birth.

A tale of two countries: rethinking sexual risk for HIV among young people in South Africa and the United States

PURPOSE

To compare the sexual behaviors of young people in South Africa (SA) and the United States (US) with the aim to better understand the potential role of sexual behavior in HIV transmission in these two countries that have strikingly different HIV epidemics.

METHODS

Nationally representative, population-based surveys of young people aged 18-24 years from SA (n = 7,548) and the US (n = 13,451) were used for the present study.

RESULTS

The prevalence of HIV was 10.2% in SA and <1% in the US. Young women and men in the US reported an earlier age of first sex than those in SA (mean age of coital debut for women: US [16.5], SA [17.4]; for men: US [16.4], SA [16.7]). The median number of lifetime partners is higher in the US than in SA: women: US (4), SA (2); men: US (4), SA (3). The use of condom at last sex is reported to be lower in the US than in SA: women: US (36.1%), SA (45.4%); men: US (48%), SA (58%). On average, young women in SA report greater age differences with their sex partners than young women in the US.

CONCLUSION

Young people in the US report riskier sexual behaviors than young people in SA, despite the much higher prevalence of HIV infection in SA. Factors above and beyond sexual behavior likely play a key role in the ongoing transmission of HIV in South African youth, and thus should be urgently uncovered to develop maximally effective prevention strategies.

Modeling the gender-specific impact of vaginal microbicides on HIV transmission

Vaginal microbicides (VMB) are currently among the few women-initiated biomedical interventions for preventing heterosexual transmission of HIV. In this paper we use a deterministic model of HIV transmission to assess the public-health benefits of a VMB intervention and evaluate its gender-specific impact over short (initial) and extended periods of time. We define two distinct quantitative benefit ratios (QBRs) based on infections prevented in men and women to create and study regions of male advantage in different parameter spaces. Our analysis exposes complicated temporal correlations between the QBRs and series of pre-intervention (e.g., HIV acquisition risks per act) and intervention parameters (e.g., VMB efficacy mechanisms, rates of resistance development and reversion) and indicates that different QBRs may often disagree on the gender distribution of the benefits from a VMB intervention. We also outline the strong influence of some modeling assumptions on the reported results and conclude that the assessment of VMB and other biomedical interventions must be based on more comprehensive analyses than calculations of infections prevented over a fixed period of time.

Interaction of mathematical modeling and social and behavioral HIV/AIDS research

PURPOSE OF REVIEW

HIV is transmitted within complex biobehavioral systems. Mathematical modeling can provide insight to complex population-level outcomes of various behaviors measured at an individual level.

RECENT FINDINGS

HIV models in the social and behavioral sciences can be categorized in a number of ways; here, we consider two classes of applications common in the field generally, and in the past year in particular: those models that explore significant behavioral determinants of HIV disparities within and between populations; and those models that seek to evaluate the potential impact of specific social and behavioral interventions.

SUMMARY

We discuss two overarching issues we see in the field: the need to further systematize effectiveness models of behavioral interventions, and the need for increasing investigation of the use of behavioral data in epidemic models. We believe that a recent initiative by the National Institutes of Health will qualitatively change the relationships between epidemic modeling and sociobehavioral prevention research in the coming years.

Pre-exposure prophylaxis and the promise of combination prevention approaches

Pre-exposure prophylaxis (PrEP) for HIV prevention is a promising experimental approach currently being tested globally. A number of PrEP trials are evaluating the safety and effectiveness of PrEP in men who have sex with men (MSM) and other populations at risk for HIV, and results will be available from this first generation of efficacy trials over the next few years. Here we review the rationale for orally-administered antiretrovirals for prevention, and outline issues the first generation trials will address as well as questions that may be addressed in future studies. We also describe the rationale for combination prevention approaches that may combine PrEP with other prevention modalities as part of a larger prevention package.

Investigation of a large community-based outbreak of hepatitis B infection in the United Kingdom

We describe the largest outbreak of hepatitis B virus infection reported to date in the UK. Between July 2001 and December 2005, 237 cases were identified in Avon, South West England. The likely route of transmission was injecting drug use in 44% (104/237) and heterosexual intercourse in 30% (71/237) of cases. A case-control study in injectors showed that injecting crack cocaine [adjusted odds ratio (aOR) 23·8, 95% confidence interval (CI) 3·04-186, P<0·001] and sharing injecting paraphernalia in the year before diagnosis (aOR 16·67, 95% CI 1·78-100, P=0·010) were strongly associated with acute hepatitis B. In non-IDUs number of sexual partners and lack of consistent condom use were high compared to a national sample. We describe the control measures implemented in response to the outbreak. This outbreak has highlighted the problems associated with the low uptake from the national hepatitis B vaccination policy which targets high-risk groups, the difficulties of identifying those at risk of acquiring hepatitis B infection through heterosexual sex, and injecting crack cocaine as a risk factor for hepatitis B.

Mapping the architecture of the HIV-1 Tat circuit: A decision-making circuit that lacks bistability and exploits stochastic noise

Upon infection of a CD4(+) T cell, HIV-1 appears to 'choose' between two alternate fates: active replication or a long-lived dormant state termed proviral latency. A transcriptional positive-feedback loop generated by the HIV-1 Tat protein appears sufficient to mediate this decision. Here, we describe a coupled wet-lab and computational approach that uses mathematical modeling and live-cell time-lapse microscopy to map the architecture of the HIV-1 Tat transcriptional regulatory circuit and generate predictive models of HIV-1 latency. This approach provided the first characterization of a 'decision-making' circuit that lacks bistability and instead exploits stochastic fluctuations in cellular molecules (i.e. noise) to generate a decision between an on or off transcriptional state.

Treating cofactors can reverse the expansion of a primary disease epidemic

BACKGROUND

Cofactors, "nuisance" conditions or pathogens that affect the spread of a primary disease, are likely to be the norm rather than the exception in disease dynamics. Here we present a "simplest possible" demographic model that incorporates two distinct effects of cofactors: that on the transmission of the primary disease from an infected host bearing the cofactor, and that on the acquisition of the primary disease by an individual that is not infected with the primary disease but carries the cofactor.

METHODS

We constructed and analyzed a four-patch compartment model that accommodates a cofactor. We applied the model to HIV spread in the presence of the causal agent of genital schistosomiasis, Schistosoma hematobium, a pathogen commonly co-occurring with HIV in sub-Saharan Africa.

RESULTS

We found that cofactors can have a range of effects on primary disease dynamics, including shifting the primary disease from non-endemic to endemic, increasing the prevalence of the primary disease, and reversing demographic growth when the host population bears only the primary disease to demographic decline. We show that under parameter values based on the biology of the HIV/S. haematobium system, reduction of the schistosome-bearing subpopulations (e.g. through periodic use of antihelminths) can slow and even reverse the spread of HIV through the host population.

CONCLUSIONS

Typical single-disease models provide estimates of future conditions and guidance for direct intervention efforts relating only to the modeled primary disease. Our results suggest that, in circumstances under which a cofactor affects the disease dynamics, the most effective intervention effort might not be one focused on direct treatment of the primary disease alone. The cofactor model presented here can be used to estimate the impact of the cofactor in a particular disease/cofactor system without requiring the development of a more complicated model which incorporates many other specific aspects of the chosen disease/cofactor pair. Simulation results for the HIV/S. haematobium system have profound implications for disease management in developing areas, in that they provide evidence that in some cases treating cofactors may be the most successful and cost-effective way to slow the spread of primary diseases.