Concurrent sexual partnerships and primary HIV infection: a critical interaction

A potential transition from a concentrated to a generalized HIV epidemic: the case of Madagascar

BACKGROUND

HIV expansion is controlled by a range of interrelated factors, including the natural history of HIV infection and socio-economical and structural factors. However, how they dynamically interact in particular contexts to drive a transition from concentrated HIV epidemics in vulnerable groups to generalized epidemics is poorly understood. We aim to explore these mechanisms, using Madagascar as a case-study.

METHODS

We developed a compartmental dynamic model using available data from Madagascar, a country with a contrasting concentrated epidemic, to explore the interaction between these factors with special consideration of commercial and transactional sex as HIV-infection drivers.

RESULTS

The model predicts sigmoidal-like prevalence curves with turning points within years 2020-2022, and prevalence reaching stabilization by 2033 within 9 to 24% in the studied (10 out of 11) cities, similar to high-prevalence regions in Southern Africa. The late/slow introduction of HIV and  circumcision, a widespread traditional practice in Madagascar, could have slowed down HIV propagation, but, given the key interplay between risky behaviors associated to young women and acute infections prevalence, mediated by transactional sex, the protective effect of circumcision is currently insufficient to contain the expansion of the disease in Madagascar.

CONCLUSIONS

These results suggest that Madagascar may be experiencing a silent transition from a concentrated to a generalized HIV epidemic. This case-study model could help to understand how this HIV epidemic transition occurs.

Polygamy and safe sex negotiation among married women: evidence from Cameroon

BACKGROUND

Research indicates that women in polygamous relationships may be exposed to unique sexual and reproductive health challenges. However, there are very few studies that examine whether polygamy is associated with safe sex negotiation among married women in sub-Saharan Africa, including Cameroon.

METHODS

Using the 2018 Cameroon Demographic and Health Survey, we apply logistic regression analysis to compare two indicators of safe sex negotiation (i.e., the ability to ask for condom use and refuse sex against their partner) between polygamous (n = 1,628) and monogamous (n = 5,686) women aged 15-49 years old.

RESULTS

We find that 67% and 50% of married women can ask for condom use and refuse sex against their partner, respectively. Multivariate analysis further reveals that women in polygamous relationships are less likely to report they can ask for condom use (OR = 0.71, p < 0.001) and refuse sex (OR = 0.64, p < 0.001) in comparison to their monogamous counterparts.

CONCLUSIONS

Our analysis found that in Cameroon, women in polygamous relationships, Muslim women, married women with inadequate HIV knowledge, those who had never been tested for HIV and women with lower socioeconomic status are less likely to negotiate for safe sex. Based on these findings, we discuss several implications for policymakers, including the establishment of a comprehensive family planning educational program and the deployment of community health workers to disseminate educational initiatives pertaining to safe sex negotiation to community members.

An agent-based model of binge drinking, inequitable gender norms and their contribution to HIV transmission, with application to South Africa

BACKGROUND

Binge drinking, inequitable gender norms and sexual risk behaviour are closely interlinked. This study aims to model the potential effect of alcohol counselling interventions (in men and women) and gender-transformative interventions (in men) as strategies to reduce HIV transmission.

METHODS

We developed an agent-based model of HIV and other sexually transmitted infections, allowing for effects of binge drinking on sexual risk behaviour, and effects of inequitable gender norms (in men) on sexual risk behaviour and binge drinking. The model was applied to South Africa and was calibrated using data from randomized controlled trials of alcohol counselling interventions (n = 9) and gender-transformative interventions (n = 4) in sub-Saharan Africa. The model was also calibrated to South African data on alcohol consumption and acceptance of inequitable gender norms. Binge drinking was defined as five or more drinks on a single day, in the last month.

RESULTS

Binge drinking is estimated to be highly prevalent in South Africa (54% in men and 35% in women, in 2021), and over the 2000-2021 period 54% (95% CI: 34-74%) of new HIV infections occurred in binge drinkers. Binge drinking accounted for 6.8% of new HIV infections (0.0-32.1%) over the same period, which was mediated mainly by an effect of binge drinking in women on engaging in casual sex. Inequitable gender norms accounted for 17.5% of incident HIV infections (0.0-68.3%), which was mediated mainly by an effect of inequitable gender norms on male partner concurrency. A multi-session alcohol counselling intervention that reaches all binge drinkers would reduce HIV incidence by 1.2% (0.0-2.5%) over a 5-year period, while a community-based gender-transformative intervention would reduce incidence by 3.2% (0.8-7.2%) or by 7.3% (0.6-21.2%) if there was no waning of intervention impact.

CONCLUSIONS

Although binge drinking and inequitable gender norms contribute substantially to HIV transmission in South Africa, recently-trialled alcohol counselling and gender-transformative interventions are likely to have only modest effects on HIV incidence. Further innovation in developing locally-relevant interventions to address binge drinking and inequitable gender norms is needed.

Comparing Sexual Network Mean Active Degree Measurement Metrics Among Men Who Have Sex With Men

BACKGROUND

Mean active degree is an important proxy measure of cross-sectional network connectivity commonly used in HIV/sexually transmitted infection epidemiology research. No current studies have compared measurement methods of mean degree using a cross-sectional study design for men who have sex with men (MSM) in the United States. We compared mean degree estimates based on reported ongoing main and casual sexual partnerships (current method) against dates of first and last sex (retrospective method).

METHODS

We used data from ARTnet, a cross-sectional survey of MSM in the United States (2017-2019). ARTnet collected data on the number and types of sexual partners in the past year, limited to the 5 most recent partners (data truncation). We quantified partnerships for months 0 to 12 before the survey date (retrospective method) and compared that with ongoing partnerships on the day of survey (current method). We used linear regression to understand the impact of truncated partnership data on mean degree estimation.

RESULTS

The retrospective method yielded similar degree estimates to the current for months proximate to the day of survey. The retrospective method mean degree systematically decreased as the month increased from 0 to 12 months before survey date. This was driven by data truncation: among participants with >5 partners in the past year compared with those with ≤5, the average change in main partnership degree between 12 and 0 months before survey date was -0.05 (95% confidence interval, -0.08 to -0.03) after adjusting for race/ethnicity, age, and education. The adjusted average change in casual partnership degree was -0.40 (95% confidence interval, -0.45 to -0.35).

CONCLUSIONS

The retrospective method underestimates mean degree for MSM in surveys with truncated partnership data, especially for casual partnerships. The current method is less prone to bias from partner truncation when the target population has high rate of partners per year.

Multilevel analysis of determinants of polygyny among married men in Ethiopia

BACKGROUND

Polygyny occurs when a man has more than one wife at the same time. It often contributes to poor health among family members, particularly young children. It encourages the spread of sexually transmitted infections (STIs) including HIV/AIDS. The determinants of polygyny have not yet been adequately explored in Ethiopia. This study adds to the body of knowledge concerning the prevalence and distribution of polygyny in the country.

METHODS

This study is a secondary analysis of the 2016 Ethiopian Demographic and Health Survey (EDHS) data. Using a two-stage stratified cluster sampling, 7470 married men were selected. After verifying the assumptions of multilevel logistic regression analysis, Stata version 14.0 was used to analyse the data. A multilevel mixed-effects logistic regression model was used to identify predictors of polygyny. An adjusted odds ratio with a 95% confidence interval was used to measure the association. A p-value of < 0.05 was considered to indicate statistical significance.

RESULTS

Age from 30 to 44 years [AOR = 5.78, 95% CI = (3.13, 10.7)], age from 45 to 59 years [AOR = 16.5, 95% CI = (8.59, 31.8)], men with primary education or no formal education [AOR = 3.40, 95% CI = (1.50, 7.69)], being Muslim [AOR = 2.47, 95% CI = (1.28, 4.77)], sexual initiation at or above the age of 18 years [AOR = 0.46, 95% CI = (0.30, 0.68)] and being from a less developed region of Ethiopia [AOR = 3.67, 95% CI = (2.30, 5.83)] were factors associated with polygyny.

CONCLUSION

Both individual and community level factors were identified as predictors of polygyny. Improving educational attainment and delaying men's sexual debut could encourage the reduction of polygyny in Ethiopia.

HIV and Sexually Transmitted Infection Epidemic Potential of Networks of Men Who Have Sex With Men in Two Cities

BACKGROUND

The speed with which a pathogen circulates in a sexual network is a function of network connectivity. Cross-sectional connectivity is a function of network features like momentary degree and assortative mixing. Temporal connectivity is driven by partner acquisition rates. The forward-reachable path (FRP) has been proposed as a summary measure of these two aspects of transmission potential. We use empirical data from San Francisco and Atlanta to estimate the generative parameters of the FRP and compare results to the HIV/sexually transmitted infection epidemics in each city.

METHODS

We used temporal exponential random graph models to estimate the generative parameters for each city's dynamic sexual network from survey data. We then simulated stochastic dynamic networks from the fitted models and calculated the FRP for each realization, overall, and stratified by partnership type and demographics.

RESULTS

The overall mean and median paths were higher in San Francisco than in Atlanta. The overall paths for each city were greater than the sum of the paths in each individual partnership network. In the casual partnership network, the mean path was highest in the youngest age group and lowest in the oldest age group, despite the fact that the youngest group had the lowest mean momentary degree and past-year partner counts.

CONCLUSIONS

The FRP by age group revealed the additional utility of the measure beyond the temporal and cross-sectional network connectivity measures. Other nonnetwork factors are still necessary to infer total epidemic potential for any specific pathogen.

Concurrency measures in the era of temporal network epidemiology: a review

Diseases spread over temporal networks of interaction events between individuals. Structures of these temporal networks hold the keys to understanding epidemic propagation. One early concept of the literature to aid in discussing these structures is concurrency-quantifying individuals' tendency to form time-overlapping 'partnerships'. Although conflicting evaluations and an overabundance of operational definitions have marred the history of concurrency, it remains important, especially in the area of sexually transmitted infections. Today, much of theoretical epidemiology uses more direct models of contact patterns, and there is an emerging body of literature trying to connect methods to the concurrency literature. In this review, we will cover the development of the concept of concurrency and these new approaches.

Partnership dynamics in mathematical models and implications for representation of sexually transmitted infections: a review

Mathematical models of sexually transmitted disease (STI) are increasingly relied on to inform policy, practice, and resource allocation. Because STI transmission requires sexual contact between two or more people, a model's ability to represent the dynamics of sexual partnerships can influence the validity of findings. This ability is to a large extent constrained by the model type, as different modeling frameworks vary in their capability to capture patterns of sexual contact at individual, partnership, and network levels. In this paper, we classify models into three groups: compartmental, individual-based, and statistical network models. For each framework, we describe the basic model structure and discuss key aspects of sexual partnership dynamics: how and with whom partnerships are formed, partnership duration and dissolution, and temporal overlap in partnerships (concurrency). We illustrate the potential implications of accurately accounting for partnership dynamics, but these effects depend on characteristics of both the population and pathogen; the combined impact of these partnership and epidemiologic dynamics can be difficult to predict. While each of the reviewed model frameworks may be appropriate to inform certain research or policy questions, modelers and consumers of models should carefully consider the implications of sexual partnership dynamics for the questions under study.

Assessment of Bias in Estimates of Sexual Network Degree using Prospective Cohort Data

BACKGROUND

Sexual network degree, a count of ongoing partnerships, plays a critical role in the transmission dynamics of human immunodeficiency virus and other sexually transmitted infections. Researchers often quantify degree using self-reported cross-sectional data on the day of survey, which may result in bias because of uncertainty about future sexual activity.

METHODS

We evaluated the bias of a cross-sectional degree measure with a prospective cohort study of men who have sex with men (MSM). At baseline, we asked men about whether recent sexual partnerships were ongoing. We confirmed the true, ongoing status of those partnerships at baseline at follow-up. With logistic regression, we estimated the partnership-level predictors of baseline measure accuracy. With Poisson regression, we estimated the longitudinally confirmed degree as a function of baseline predicted degree.

RESULTS

Across partnership types, the baseline ongoing status measure was 70% accurate, with higher negative predictive value (91%) than positive predictive value (39%). Partnership exclusivity and racial pairing were associated with higher accuracy. Baseline degree generally overestimated confirmed degree. Bias, or number of ongoing partners different than predicted at baseline, was -0.28 overall, ranging from -1.91 to -0.41 for MSM with any ongoing partnerships at baseline. Comparing MSM of the same baseline degree, the level of bias was stronger for black compared with white MSM, and for younger compared with older MSM.

CONCLUSIONS

Research studies may overestimate degree when it is quantified cross-sectionally. Adjustment and structured sensitivity analyses may account for bias in studies of human immunodeficiency virus or sexually transmitted infection prevention interventions.

Current Computational Approaches for the Development of Anti-HIV Inhibitors: An Overview

BACKGROUND

Today, HIV-1 infection has become an extensive problem to public health and a greater challenge to all working researchers throughout the world. Since the beginning of HIV-1 virus, several antiviral therapeutic agents have been developed at various stages to combat HIV-1 infection. But, many of antiviral drugs are on the platform of drug resistance and toxicology issues, needs an urgent constructive investigation for the development of productive and protective therapeutics to make an improvement of individual life suffering with viral infection. As developing a novel agent is very costly, challenging and time taking route in the recent times.

METHODS

The review summarized about the modern approaches of computational aided drug discovery to developing a novel inhibitor within a short period of time and less cost.

RESULTS

The outcome suggests on the premise of reported information that the computational drug discovery is a powerful technology to design a defensive and fruitful therapeutic agents to combat HIV-1 infection and recover the lifespan of suffering one.

CONCLUSION

Based on survey of the reported information, we concluded that the current computational approaches is highly supportive in the progress of drug discovery and controlling the viral infection.

Willingness to use PrEP among female university students in Lesotho

Oral pre-exposure prophylaxis (PrEP) for HIV-negative individuals at high risk was introduced in Lesotho in April 2016. To assess the feasibility and acceptability of PrEP in Lesotho and to study the attitudes and beliefs around HIV risk and prevention measures among young women, between September and December 2016 we asked 302 female university students at fourteen higher education institutions in Lesotho about their sexual behavior, experiences of sexual coercion and abuse, HIV risk perception, willingness to use PrEP, as well as their attitudes toward condom use and self-administration of daily medications. Overall, 57.3% of the sample reported perceiving themselves at risk of acquiring HIV and 32.1% reported being strongly willing to use PrEP if it were available in their community. In a multivariate mediation analysis, perceived HIV risk was associated with 11.5 percentage points increase in likelihood of using PrEP (p = 0.041). Multiple concurrent sexual partnership was associated with 16.1 percentage points increase in likelihood of self-perceived HIV risk (p = 0.007), while having sexual partners in polygamous relationships was associated with 17.8 percentage points increase in likelihood of self-perceived HIV risk (p = 0.002) and the mediated indirect effect accounted for 18.2% of its total effect. Those who reported strong adherence to antibiotics were 23.1 percentage points more likely to express willingness to use PrEP than those who did not (p = 0.004), and those who reported to dislike condoms were 19.1 percentage points more likely to be willing to use PrEP than those who did not report aversion to condom use: these effect were direct and not mediated by HIV risk perception. Intimate partner violence (IPV) in the network of peers was also directly associated with willingness to use PrEP and its effect was not significantly mediated by HIV risk perception: those who had friends who experienced intimate partner violence were 14.9 percentage points more likely to be willing to use PrEP than those who did not report IPV in their network of peers (p = 0.009). These findings support the inclusion of individuals with multiple concurrent sexual partners among the key populations for PrEP provision and confirm that willingness to use PrEP is not solely driven by HIV risk perception. They also indicate that the presence of IPV in peer networks is related to one’s willingness to use PrEP. PrEP service provision may generate synergies with IPV prevention programs when offered within this framework.

Characterizing Men Who Have Sex with Transgender Women in Lima, Peru: Sexual Behavior and Partnership Profiles

HIV prevalence is high among transgender women (TW), but how HIV is transmitted to this population is not well understood. This analysis aims to characterize sexual partners of TW (PTW) to understand how their behavior contributes to HIV risk among TW. We examined baseline data from TW, PTW, and men who have sex with men (MSM) from a treatment-as-prevention study in Lima, Peru. Individual and partnership characteristics were compared across groups, and Poisson regression was used to calculate prevalence ratios for associations between sexual concurrency and potential correlates. We found that 81% of PTW had no cisgender male partners. Prevalence of alcohol dependency, concurrency, and condomless anal intercourse was high and HIV testing was low compared to the other groups. Our results suggest that PTW are a distinct population from MSM and TW, engage in behavior associated with HIV transmission, and are likely not well reached by HIV prevention interventions.

Trends in Number and Composition of Sex Partners Among Men Who Have Sex With Men in the United States, National HIV Behavioral Surveillance, 2008-2014

BACKGROUND

Social and legal acceptance of long-term same-sex partnerships in the United States has increased over the past decade which may impact sexual partnering among men who have sex with men (MSM). Identifying whether and how partnering trends have evolved at a national level could improve understanding of HIV transmission and prevention among MSM partnerships.

METHODS

We used Centers for Disease Control and Prevention's National HIV Behavioral Surveillance data (2008, 2011, and 2014) to study trends in the number and partner type composition (main/casual) of male sex partners among US MSM. Changes over time were assessed in Poisson regression models with the link function tailored to the count and binary outcomes.

RESULTS

The mean total number of partners in the past year increased, while the mean number of main partners remained stable. The percentage of MSM with both main and casual partners increased, and we observed a shift from having ≥1 main and 0 casual partners to having ≥1 main and ≥2 casual partners. Condomless anal sex in the past year increased regardless of partner composition.

DISCUSSION

Findings suggest casual partnering among MSM has increased in recent years, including among those with ≥1 main partners. Both partner-based and individual prevention programs remain critical to reaching MSM.

Correlates of concurrent partnerships and patterns of condom use among men who have sex with men and transgender women in Peru

Background

In Peru, there is an ongoing high-incidence HIV epidemic among men who have sex with men (MSM) and transgender women (TW). Sexual concurrency, or having sex with a partner in between two acts of sex with another partner, may be a key factor in onward HIV transmission. In this study, we quantify concurrency, evaluate factors associated with concurrency, and assess condom use with concurrent partners among MSM and TW in Peru.

Methods

We conducted a secondary analysis of data from the 2011 Peruvian Biobehavioral Survey. Pearson’s Chi-squared test was used to identify individual-level characteristics associated with concurrency. We estimated the association between participant characteristics, concurrent partnerships, partnership type (stable vs. non-stable), and CLAI within the context of concurrent partnerships using multivariate and repeated-measure Poisson regression.

Results

3-month cumulative prevalence of concurrency was higher among TW compared to MSM (30.7% vs 25.2%, p = 0.014). Among those with concurrent stable and non-stable partners, 45% used condoms with both partners (95% CI: 40%-50%) and 30% preferentially had CLAI with the stable partner only (95%CI: 26%-35%). Factors associated with CLAI within the context of concurrent partnerships varied between MSM and TW.

Conclusions

Although concurrency is common among TW and MSM in Peru, patterns of concurrency and differential condom use may vary between TW and MSM. Future research may explore differential condom use with stable and non-stable partners to better understand behavioral factors that may alter vulnerability to HIV in TW compared to MSM.

Coital Frequency and Male Concurrent Partnerships During Pregnancy and Postpartum in Agbogbloshie, Ghana

During pregnancy and postpartum, women in high HIV prevalence regions continue to be at high risk for acquiring HIV, due to both behavioral and biological mechanisms, despite declines in coital frequency as a pregnancy advances. We estimated differences in rates of partnership concurrency for men with and without pregnant or postpartum sexual partners. We used monthly retrospective panel data from Ghana from three perspectives: couple-level data, female reports of pregnancy and male partner concurrency, and male reports of concurrent partnerships and female partner pregnancy. Coital frequency increased during the first trimester and then declined with advancing pregnancy. However, in all three analyses, there was no compelling evidence that men with pregnant or postpartum partners had additional concurrent partnerships. Our findings suggest that even though women's sexual activity likely declines during pregnancy and postpartum, they may not be at increased risk of HIV/STI due to their partners seeking additional partnerships.

Projected effectiveness of HIV detection during early infection and rapid ART initiation among MSM and transgender women in Peru: A modeling study

Background

The Sabes study, a treatment as prevention intervention in Peru, tested the hypothesis that initiating antiretroviral therapy (ART) early in HIV infection when viral load is high, would markedly reduce onward HIV transmission among high-risk men who have sex with men (MSM) and transgender women (TW). We investigated the potential population-level benefits of detection of HIV early after acquisition and rapid initiation of ART.

Methods

We designed a transmission dynamic model to simulate the HIV epidemic among MSM and TW in Peru, calibrated to data on HIV prevalence and ART coverage from 2004 to 2011. We assessed the impact of an intervention starting in 2018 in which up to 50% of the new infections were diagnosed within three months of acquisition and initiated on ART within 1 month of diagnosis. We estimated the impact of the intervention over 20 years using the cumulative prevented fraction of new HIV infections compared to scenarios without intervention.

Findings

Our model suggests that only 19% of the infected MSM and TW are virally suppressed in 2018 and 35%-40% of the new HIV infections are transmitted from contacts with acutely-infected partners. An intervention reaching 10% of all acutely infected MSM and TW is projected to prevent 13.3% [Uncertainty interval: 11.9%-14.3%] of the new infections over 20 years and reduce HIV incidence in 2038 by 24%. Reaching 50% of all acutely infected MSM and TW will increase the prevalence of viral suppression in 2038 to 59% and prevent 41% of expected infections over 20 years. Reaching 50% of the high-risk MSM and TW in acute phase would reduce HIV incidence in 2038 by 60% and prevent 36% of new infections between 2018 and 2038.

Conclusions

Early detection of HIV infections and rapid initiation of ART among MSM is desirable as it would increase the effectiveness of the HIV prevention program in Peru. Targeting high-risk MSM and TW will be highly efficient.

Sexual Concurrency and Contraceptive Use Among Young Adult Women

Leveraging 2.5 years of weekly data from the Relationship Dynamics and Social Life Study, we investigate the relationship between young women's sexual concurrency and their contraceptive behavior. Specifically, we (1) examine whether young women changed their contraceptive use when switching from one to multiple concurrent sexual partners in the same week; (2) explore the uniformity of contraceptive responses to concurrency across relationship context; and (3) compare the contraceptive behaviors of never-concurrent women with those of ever-concurrent women in weeks when they were not concurrent. Nearly one in five sexually active young women had sex with two or more people in the same week. When they were concurrent, these women's odds of using any contraception increased threefold, and their odds of using condoms increased fourfold. This pattern of contraceptive adjustments was the same across relationship characteristics, such as duration and exclusivity. Yet when they were not concurrent, ever-concurrent women were less likely to use any contraception and used condoms less consistently than women who were never concurrent. We discuss these findings in the context of ongoing debates about the role of sexual concurrency in STI transmission dynamics.

Relational concurrency, stages of infection, and the evolution of HIV set point viral load

HIV viral load (VL) predicts both transmission potential and rate of disease progression. For reasons that are still not fully understood, the set point viral load (SPVL) established after acute infection varies across individuals and populations. Previous studies have suggested that population mean SPVL (MSPVL) has evolved near an optimum that reflects a trade-off between transmissibility and host survival. Sexual network structures affect rates of potential exposure during different within-host phases of infection marked by different transmission probabilities, and thus affect the number and timing of transmission events. These structures include relational concurrency, which has been argued to explain key differences in HIV burden across populations. We hypothesize that concurrency will alter the fitness landscape for SPVL in ways that differ from other network features whose impacts accrue at other times during infection. To quantitatively test this hypothesis, we developed a dynamic, stochastic, data-driven network model of HIV transmission, and evolution to assess the impact of key sexual network phenomena on MSPVL evolution. Experiments were repeated in sensitivity runs that made different assumptions about transmissibility during acute infection, SPVL heritability, and the functional form of the relationship between VL and transmissibility. For our main transmission model, scenarios yielded MSPVLs ranging from 4.4 to 4.75 log10 copies/ml, covering much of the observed empirical range. MSPVL evolved to be higher in populations with high concurrency and shorter relational durations, with values varying over a clinically significant range. In linear regression analyses on these and other predictors, main effects were significant (P < 0.05), as were interaction terms, indicating that effects are interdependent. We also noted a strong correlation between two key emergent properties measured at the end of the simulations-MSPVL and HIV prevalence-most clearly for phenomena that affect transmission networks early in infection. Controlling for prevalence, high concurrency yielded higher MSPVL than other network phenomena. Interestingly, we observed lower prevalence in runs in which SPVL heritability was zero, indicating the potential for viral evolution to exacerbate disease burden over time. Future efforts to understand empirical variation in MSPVL should consider local HIV burden and basic sexual behavioral and network structure.

Inter-partner and Temporal Variations in the Perception of Sexual Risk for HIV

This study uses longitudinal qualitative methods to examine how gay and bisexual men perceive sexual risk across both a variety of partners and across time. Over ten weeks, participants completed three quantitative personal relationship diaries (PRD) describing sexual encounters during that time period. Participants then completed a timeline-based individual in-depth interview to unpack the PRD data. Participants used multiple factors to determine their own sexual risk (e.g., type of sex, partner concurrency, emotional connections), which often resulted in inconsistencies in defining sexual risk and determining the level of risk both within and across partners and across time. These findings can inform HIV prevention messages and programming.

Couple serostatus patterns in sub-Saharan Africa illuminate the relative roles of transmission rates and sexual network characteristics in HIV epidemiology

HIV prevalence has surpassed 30% in some African countries while peaking at less than 1% in others. The extent to which this variation is driven by biological factors influencing the HIV transmission rate or by variation in sexual network characteristics remains widely debated. Here, we leverage couple serostatus patterns to address this question. HIV prevalence is strongly correlated with couple serostatus patterns across the continent; in particular, high prevalence countries tend to have a lower ratio of serodiscordancy to concordant positivity. To investigate the drivers of this continental pattern, we fit an HIV transmission model to Demographic and Health Survey data from 45,041 cohabiting couples in 25 countries. In doing so, we estimated country-specific HIV transmission rates and sexual network characteristics reflective of pre-couple and extra-couple sexual contact patterns. We found that variation in the transmission rate could parsimoniously explain between-country variation in both couple serostatus patterns and prevalence. In contrast, between-country variation in pre-couple or extra-couple sexual contact rates could not explain the observed patterns. Sensitivity analyses suggest that future work should examine the robustness of this result to between-country variation in how heterogeneous infection risk is within a country, or to assortativity, i.e. the extent to which individuals at higher risk are likely to partner with each other.

Saturation effects and the concurrency hypothesis: Insights from an analytic model

Sexual partnerships that overlap in time (concurrent relationships) may play a significant role in the HIV epidemic, but the precise effect is unclear. We derive edge-based compartmental models of disease spread in idealized dynamic populations with and without concurrency to allow for an investigation of its effects. Our models assume that partnerships change in time and individuals enter and leave the at-risk population. Infected individuals transmit at a constant per-partnership rate to their susceptible partners. In our idealized populations we find regions of parameter space where the existence of concurrent partnerships leads to substantially faster growth and higher equilibrium levels, but also regions in which the existence of concurrent partnerships has very little impact on the growth or the equilibrium. Additionally we find mixed regimes in which concurrency significantly increases the early growth, but has little effect on the ultimate equilibrium level. Guided by model predictions, we discuss general conditions under which concurrent relationships would be expected to have large or small effects in real-world settings. Our observation that the impact of concurrency saturates suggests that concurrency-reducing interventions may be most effective in populations with low to moderate concurrency.

Sexual Partner Concurrency Among Partners Reported by MSM with Recent HIV Infection

We examined concurrency among sexual partners reported by men who have sex with men (MSM) with recent (acute or early) HIV infection in San Diego, California (2002-2015). Partners overlapping in time in the past 3 months were considered concurrent. Logistic generalized linear mixed models were used to identify factors associated with concurrency at the partner-level. 56% (388/699) of partners were concurrent to ≥1 other partner. The odds of concurrency were higher among partners >10 years younger than the participant (vs. within 10 years of age) [adjusted odds ratio (AOR) = 2.22, 95% confidence interval (CI) 1.09-4.52], longer term partners (AOR per month = 1.02, 95% CI 1.01-1.03), and partners met online (AOR = 1.56, 95% CI 0.98-2.48). Concurrency is common among partners of recently HIV-infected MSM. Tailored HIV prevention strategies for MSM with older partners, longer term partners, and partners met online may help minimize the potential impact of concurrency on HIV transmission.

Concurrency-Induced Transitions in Epidemic Dynamics on Temporal Networks

Social contact networks underlying epidemic processes in humans and animals are highly dynamic. The spreading of infections on such temporal networks can differ dramatically from spreading on static networks. We theoretically investigate the effects of concurrency, the number of neighbors that a node has at a given time point, on the epidemic threshold in the stochastic susceptible-infected-susceptible dynamics on temporal network models. We show that network dynamics can suppress epidemics (i.e., yield a higher epidemic threshold) when the node's concurrency is low, but can also enhance epidemics when the concurrency is high. We analytically determine different phases of this concurrency-induced transition, and confirm our results with numerical simulations.

Partnership duration, concurrency, and HIV in sub-Saharan Africa

A widely accepted explanation for the exceptionally high HIV prevalence in sub-Saharan Africa is the practice of long-term overlapping heterosexual partnering. This article shows that long-duration concurrent partnering can be protective against HIV transmission rather than promoting it. Monogamous partnering prevents sexual transmission to anyone outside the partnership and, in an initially concordant-seronegative partnership, prevents sexual acquisition of HIV by either partner. Those protections against transmission and acquisition last as long as the partnership persists without new outside partnerships. Correspondingly, these two protective effects characterise polygynous partnerships, whether or not the polygyny is formal or informal, until a partner initiates a new partnership. Stable and exclusive unions of any size protect against HIV transmission, and more durable unions provide a longer protective effect. Survey research provides little information on partnership duration in sub-Saharan Africa and sheds no light on the interaction of duration, concurrency, and HIV. This article shows how assumptions about partnership duration in individual-based sexual-network models affect the contours of simulated HIV epidemics. Longer mean partnership duration slows the pace at which simulated epidemics grow. With plausible assumptions about partnership duration and at levels of concurrency found in the region, simulated HIV epidemics grow slowly or not at all. Those results are consistent with the hypothesis that long-duration partnering is protective against HIV and inconsistent with the hypothesis that long-term concurrency drives the HIV epidemics in sub-Saharan Africa.

Geographic mobility and potential bridging for sexually transmitted infections in Agbogbloshie, Ghana

Short-term mobility can significantly influence the spread of infectious disease. In order for mobile individuals to geographically spread sexually transmitted infections (STIs), individuals must engage in sexual acts with different partners in two places within a short time. In this study, we considered the potential of mobile individuals as bridge populations - individuals who link otherwise disconnected sexual networks and contributed to ongoing STI transmission. Using monthly retrospective panel data, we examined associations between short-term mobility and sexual partner concurrency in Agbogbloshie, Ghana. We also examined bridging by the location of sex acts and the location of sexual partners in concurrent triads, and whether mobile individuals from our sample were more likely to be members of geographic bridging triads. Although reported rates of sexual partnership concurrency were much higher for men compared to women, mobility was only associated with increased concurrency for women. Additionally, this association held for middle-distance mobility and short-duration trips for women. Taking into account the location of sex acts and the location of sexual partners, about 22% of men (21.7% and 22.4% for mobile and non-mobile men, respectively) and only 3% of women (1.4% and 3.3% for mobile and non-mobile women, respectively) were potential bridges for STIs over the last year. Our results highlight the gendered nature of mobility and sexual risk behavior, reflecting the normative social context that encourages women to conceal certain types of sexual behavior.

Forward reachable sets: Analytically derived properties of connected components for dynamic networks

Formal analysis of the emergent structural properties of dynamic networks is largely uncharted territory. We focus here on the properties of forward reachable sets (FRS) as a function of the underlying degree distribution and edge duration. FRS are defined as the set of nodes that can be reached from an initial seed via a path of temporally ordered edges; a natural extension of connected component measures to dynamic networks. Working in a stochastic framework, we derive closed-form expressions for the mean and variance of the exponential growth rate of the FRS for temporal networks with both edge and node dynamics. For networks with node dynamics, we calculate thresholds for the growth of the FRS. The effects of finite population size are explored via simulation and approximation. We examine how these properties vary by edge duration and different cross-sectional degree distributions that characterize a range of scientifically interesting normative outcomes (Poisson and Bernoulli). The size of the forward reachable set gives an upper bound for the epidemic size in disease transmission network models, relating this work to epidemic modeling (Ferguson, 2000; Eames, 2004).

Ecological correlates of multiple sexual partnerships among adolescents and young adults in urban Cape Town: a cumulative risk factor approach

Studies in South Africa have reported unsafe levels of risky sexual behvaiours among adolescents and young adults, with the country reporting the highest burden of HIV/AIDS globally, as well as a high rate of teenage pregnancy. While determinants of risky sexual behaviours have been investigated for factors occurring at the individual and household levels, not fully explored in the literature is the effect of community level factors. Furthermore, it is unclear whether risk factors occurring within the ecology of adolescents and young adults act cumulatively to influence their sexual practices. This article aims to address this knowledge gap using a case study of the Cape Area Panel Study of adolescents and young adults in urban Cape Town, South Africa. The ecological framework was adopted to guide the selection of risk factors at the individual, household, and community levels. Multivariate linear discriminant function analyses were used to select significant risk factors for multiple sexual partnerships and used to produce risk indices for the respondents. The cumulative risk approach was applied to test whether significant risk factors acted cumulatively. Findings point to the importance of ecological factors in influencing outcomes of multiple sexual partnerships among respondents and further demonstrate that ecological risk factors may act cumulatively. These findings are important for South Africa that is grappling with teenage pregnancy and disproportionate HIV epidemic among the youth.

Branching process approach for epidemics in dynamic partnership network

We study the spread of sexually transmitted infections (STIs) and other infectious diseases on a dynamic network by using a branching process approach. The nodes in the network represent the sexually active individuals, while connections represent sexual partnerships. This network is dynamic as partnerships are formed and broken over time and individuals enter and leave the sexually active population due to demography. We assume that individuals enter the sexually active network with a random number of partners, chosen according to a suitable distribution and that the maximal number of partners that an individual can have at a time is finite. We discuss two different branching process approximations for the initial stages of an outbreak of the STI. In the first approximation we ignore some dependencies between infected individuals. We compute the offspring mean of this approximating branching process and discuss its relation to the basic reproduction number \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$R_0$$\end{document}R0. The second branching process approximation is asymptotically exact, but only defined if individuals can have at most one partner at a time. For this model we compute the probability of a minor outbreak of the epidemic starting with one or few initial cases. We illustrate complications caused by dependencies in the epidemic model by showing that if individuals have at most one partner at a time, the probabilities of extinction of the two approximating branching processes are different. This implies that ignoring dependencies in the epidemic model leads to a wrong prediction of the probability of a large outbreak. Finally, we analyse the first branching process approximation if the number of partners an individual can have at a given time is unbounded. In this model we show that the branching process approximation is asymptomatically exact as the population size goes to infinity.

Differences in Risk Behavior and Demographic Factors Between Men Who Have Sex With Men With Acute and Nonacute Human Immunodeficiency Virus Infection in a Community-Based Testing Program in Los Angeles

INTRODUCTION

High viremia combined with HIV-infection status unawareness and increased sexual risk behavior contributes to a disproportionate amount of new HIV infections.

METHODS

From August 2011 to July 2015, the Los Angeles Lesbian, Gay, Bisexual, and Transgender Center conducted 66,546 HIV tests. We compared factors, including the presence of concomitant sexually transmitted infections, number of recent sex partners and reported condomless anal intercourse between men who have sex with men (MSM) diagnosed with an acute HIV infection and a nonacute HIV infection using multivariable logistic regression.

RESULTS

Of 1082 unique MSM who tested HIV-infected for the first time, 165 (15%) had an acute infection and 917 had a nonacute infection. HIV rapid antibody testing was 84.8% sensitive for detecting HIV infection (95% confidence interval (CI): 82.9% to 87.1%). Median HIV viral load among acutely infected MSM was 842,000 copies per milliliter (interquartile range = 98,200-4,897,318). MSM with acute infection had twice the number of sex partners in the prior 30 days (median = 2) and prior 3 months (median = 4) before diagnosis compared with those diagnosed with nonacute infection (P ≤ 0.0001). The odds of acute HIV infection were increased with the numbers of recent sex partners after controlling for age and race/ethnicity (adjusted odds ratio (aOR) >5 partners in past 30 days = 2.74; 95% CI: 1.46 to 5.14; aOR >10 partners in past 3 months = 2.41; 95% CI: 1.36 to 4.25). Non-African American MSM had almost double the odds of being diagnosed with an acute HIV infection compared with African American MSM (aOR = 1.97; 95% CI: 1.10 to 3.52).

CONCLUSIONS

MSM with acute HIV infection had nearly twice as many sex partners in the past 30 days and 3 months compared with MSM with newly diagnosed nonacute HIV infection. Those diagnosed with acute HIV infection had decreased odds of being African American MSM.

Gender asymmetry in concurrent partnerships and HIV prevalence

The structure of the sexual network of a population plays an essential role in the transmission of HIV. Concurrent partnerships, i.e. partnerships that overlap in time, are important in determining this network structure. Men and women may differ in their concurrent behavior, e.g. in the case of polygyny where women are monogamous while men may have concurrent partnerships. Polygyny has been shown empirically to be negatively associated with HIV prevalence, but the epidemiological impacts of other forms of gender-asymmetric concurrency have not been formally explored. Here we investigate how gender asymmetry in concurrency, including polygyny, can affect the disease dynamics. We use a model for a dynamic network where individuals may have concurrent partners. The maximum possible number of simultaneous partnerships can differ for men and women, e.g. in the case of polygyny. We control for mean partnership duration, mean lifetime number of partners, mean degree, and sexually active lifespan. We assess the effects of gender asymmetry in concurrency on two epidemic phase quantities (R₀ and the contribution of the acute HIV stage to R₀) and on the endemic HIV prevalence. We find that gender asymmetry in concurrent partnerships is associated with lower levels of all three epidemiological quantities, especially in the polygynous case. This effect on disease transmission can be attributed to changes in network structure, where increasing asymmetry leads to decreasing network connectivity.

Concurrency and HIV transmission network characteristics among MSM with recent HIV infection

OBJECTIVE

Sexual partner concurrency is common among MSM and may increase the probability of HIV transmission during recent (acute or early) infection. We examined the relationship between concurrency and HIV transmission network characteristics (proxies for HIV transmission) among MSM with recent HIV infection.

DESIGN

Observational study integrating behavioral, clinical, and molecular epidemiology.

METHODS

We inferred a partial HIV transmission network using 986 HIV-1 pol sequences obtained from HIV-infected individuals in San Diego, California (1996-2015). We further analyzed data from 285 recently HIV-infected MSM in the network who provided information on up to three sexual partners in the past 3 months, including the timing of intercourse with each partner. Concurrency was defined as sexual partners overlapping in time. Logistic and negative binomial regressions were used to investigate the link between concurrency and HIV transmission network characteristics (i.e. clustering and degree or number of connections to others in the network) among these MSM.

RESULTS

Of recently HIV-infected MSM (n = 285), 54% reported concurrent partnerships and 54% were connected by at least one putative transmission link to others (i.e. clustered) in the network (median degree = 1.0; interquartile range: 0.0-3.0). Concurrency was positively associated with HIV transmission network clustering (adjusted odds ratio = 1.83, 95% confidence interval: 1.08, 3.10) and degree (adjusted incidence rate ratio = 1.48, 95% confidence interval: 1.02, 2.15).

CONCLUSION

Our findings provide empirical evidence consistent with the hypothesis that concurrency facilitates HIV transmission during recent infection. Interventions to mitigate the impact of concurrency on HIV transmission may help curb the HIV epidemic among MSM.

Impact of Heterogeneity in Sexual Behavior on Effectiveness in Reducing HIV Transmission with Test-and-Treat Strategy

The WHO’s early-release guideline for antiretroviral treatment (ART) of HIV infection based on a recent trial conducted in 34 countries recommends starting treatment immediately upon an HIV diagnosis. Therefore, the test-and-treat strategy may become more widely used in an effort to scale up HIV treatment and curb further transmission. Here we examine behavioural determinants of HIV transmission and how heterogeneity in sexual behaviour influences the outcomes of this strategy. Using a deterministic model, we perform a systematic investigation into the effects of various mixing patterns in a population of men who have sex with men (MSM), stratified by partner change rates, on the elimination threshold and endemic HIV prevalence. We find that both the level of overdispersion in the distribution of the number of sexual partners and mixing between population subgroups have a large influence on endemic prevalence before introduction of ART and on possible long term effectiveness of ART. Increasing heterogeneity in risk behavior may lead to lower endemic prevalence levels, but requires higher coverage levels of ART for elimination. Elimination is only feasible for populations with a rather low degree of assortativeness of mixing and requires treatment coverage of almost 80% if rates of testing and treatment uptake by all population subgroups are equal. In this case, for fully assortative mixing and 80% coverage endemic prevalence is reduced by 57%. In the presence of heterogeneity in ART uptake, elimination is easier to achieve when the subpopulation with highest risk behavior is tested and treated more often than the rest of the population, and vice versa when it is less. The developed framework can be used to extract information on behavioral heterogeneity from existing data which is otherwise hard to determine from population surveys.

HIV is endemic in populations of MSM in Western countries. As ART reduces transmission risk, increased testing and treatment rates are expected to lower HIV incidence. However, concerns are that in MSM populations changing risk behavior may counteract the impact of ART on transmission. Using a mathematical model, we investigated how heterogeneity in sexual behavior influences the possible effects of a test-and-treat strategy on HIV prevalence and in particular the prospects of eliminating HIV from these populations. We demonstrated that behavioral heterogeneity plays an important role in determining the impact of ART on reducing HIV transmission. Knowledge of behavioral heterogeneity is key in setting intervention goals in populations of MSM.

Effectiveness of combination packages for HIV-1 prevention in sub-Saharan Africa depends on partnership network structure: a mathematical modelling study

OBJECTIVES

Combination packages for HIV prevention can leverage the effectiveness of biomedical and behavioural elements to lower disease incidence with realistic targets for individual and population risk reduction. We investigated how sexual network structures can maximise the effectiveness of a package targeting sexually active adults in sub-Saharan Africa (SSA) with intervention components for medical male circumcision (MMC) and sexual partnership concurrency (having >1 ongoing partner).

METHODS

Network-based mathematical models of HIV type 1 (HIV-1) transmission dynamics among heterosexual couples were used to explore how changes to MMC alone and in combination with changes to concurrency impacted endemic HIV-1 prevalence and incidence. Starting from a base model parameterised from empirical data from West Africa, we simulated the prevalence of circumcision from 10% to 90% and concurrency was modelled at four discrete levels corresponding to values observed across SSA.

RESULTS

MMC and concurrency could contribute to the empirical variation in HIV-1 disease prevalence across SSA. Small reductions in concurrency resulted in large declines in HIV-1 prevalence. Scaling up circumcision in low-concurrency settings yields a greater relative benefit, but the absolute number of infections averted depends on both the circumcision coverage and baseline incidence. Epidemic extinction with this package will require substantial scale-up of MMC in low-concurrency settings.

CONCLUSIONS

Dynamic sexual network structure should be considered in the design and targeting of MMC within combination HIV-1 prevention packages. Realistic levels of coverage for these packages within southern Africa could lead to a reduction of incidence to the low levels observed in western Africa, and possibly, epidemic extinction.

Predictors of perceived male partner concurrency among women at risk for HIV and STI acquisition in Durban, South Africa

BACKGROUND

Women in sub-Saharan Africa continue to be at greater risk for HIV acquisition than men. Concurrency, viz. multiple sexual partnerships that overlap over time, has been studied as a possible risk factor for HIV transmission. The aim of this study was to identify predictors of perceived male partner concurrency among sexually active, HIV negative women.

METHODS

Socio-demographic and behavioural data from women enrolled in a biomedical HIV prevention clinical trial were assessed in relation to perceived male partner concurrency using the Chi squared test. Univariate and multivariate logistic regression was performed to assess the independent predictors of perceived male partner concurrency. Kaplan-Meier survival estimates were obtained for HIV and STI incidence in relation to male partner concurrency. A Cox Proportional Hazards model was used to assess the association between perceived male partner concurrency and HIV and STI incidence.

RESULTS

The results revealed that 29 % of women reported their male partners to be in concurrent sexual relationships, 22 % reported partners that were not engaging in concurrency, whilst 49 % reported not knowing their partners concurrency status. Older women, having never married, experiencing economic abuse, and women reporting individual concurrency, were found to be significant predictors of perceived male partner concurrency in the studied population. Perceived male partner concurrency was not found to be a significantly associated with incident HIV and STI infections in this analysis.

CONCLUSIONS

The study provides insight into predictors of perceived male partner concurrency among women at high risk for STI and HIV acquisition. These results may inform the design of behavioural and biomedical interventions, to address the role of multiple sexual partnerships in HIV prevention.

Current Scenario of HIV/AIDS, Treatment Options, and Major Challenges with Compliance to Antiretroviral Therapy

The discovery of the human immunodeficiency virus (HIV) as the causative organism of acquired immunodeficiency syndrome (AIDS) and the inability of modern medicine to find a cure for it has placed HIV as one of the most dreaded pathogens of the 21(st) century. With millions of people infected with HIV, it was once thought to result in "medical apocalypse". However, with the advent of antiretroviral therapy (ART), it is now possible to control HIV. Adherence to ART helps to keep the viral load under control and prolong the time of progression to AIDS, resulting in near normal life expectancy. Even with the introduction of ART, a substantial number of patients fail to adhere due to a variety of reasons, including adverse side effects, drug abuse, mental disorders, socioeconomic status, literacy, and social stigma. With the availability of so many options for HIV treatment at each stage of the disease progression, physicians can switch between the treatment regimens to avoid and/or minimize the adverse effects of drugs. Close monitoring, major social reforms, and adequate counselling should also be implemented to circumvent other challenges.

On the road again: concurrency and condom use among Uganda truck drivers

Long-distance truck drivers have been shown to be a critical population in the spread of HIV in Africa. In 2009, surveys with 385 Ugandan long-distance truck drivers measured concurrency point prevalence with two methods; it ranged from 37.4% (calendar-method) to 50.1% (direct question). The majority (84%) of relationships reported were long-term resulting in a long duration of overlap (average of 58 months) across concurrent partnerships. Only 7% of these men reported using any condoms with their spouses during the past month. Among all non-spousal relationships, duration of relationship was the factor most strongly associated with engaging in unprotected sex in the past month in a multivariable analyses controlling for partner and relationship characteristics. Innovative intervention programs for these men and their partners are needed that address the realities of truck drivers' lifestyles.

A comparison of sexual risk behaviours and HIV seroprevalence among circumcised and uncircumcised men before and after implementation of the safe male circumcision programme in Uganda

BACKGROUND

Although male circumcision reduces the heterosexual HIV transmission risk, its effect may be attenuated if circumcised men increase sexual risk behaviours (SRB) due to perceived low risk. In Uganda information about the protective effects of circumcision has been publicly disseminated since 2007. If increased awareness of the protection increases SRB among circumcised men, it is likely that differences in prevalence of SRB among circumcised versus uncircumcised men will change over time. This study aimed at comparing SRBs and HIV sero-status of circumcised and uncircumcised men before and after the launch of the safe male circumcision programme.

METHODS

Data from the 2004 and 2011 Uganda AIDS Indicator Surveys (UAIS) were used. The analyses were based on generalized linear models, obtaining prevalence ratios (PR) as measures of association between circumcision status and multiple sexual partners, transactional sex, sex with non-marital partners, condom use at last non-marital sex, and HIV infection. In addition we conducted multivariate analyses adjusted for sociodemographic characteristics, and the multivariate models for HIV status were also adjusted for SRB.

RESULTS

Twenty six percent of men were circumcised in 2004 and 28% in 2011. Prevalence of SRB was higher among circumcised men in both surveys. In the unadjusted analysis, circumcision was associated with having multiple sexual partners and non-marital partners. Condom use was not associated with circumcision in 2004, but in 2011 circumcised men were less likely to report condom use with the last non-marital partner. The associations between the other sexual risk behaviours and circumcision status were stable across the two surveys." In both surveys, circumcised men were less likely to be HIV positive (Adj PR 0.55; CI: 0.41-0.73 in 2004 and Adj PR 0.64; CI: 0.49-0.83 in 2011).

CONCLUSIONS

There was higher prevalence of SRBs among circumcised men in both surveys, but the only significant change from 2004 to 2011 was a lower prevalence of condom use among the circumcised. Nevertheless, HIV prevalence was lower among circumcised men. Targeted messages for circumcised men and their sexual partners to continue using condoms even after circumcision should be enhanced to avoid risk compensation.

Sexual Partnership Patterns Among South African Adolescent Girls Enrolled in HPTN [corrected] 068: Measurement Challenges and Implications for HIV/STI Transmission

BACKGROUND

Estimates of sexual partnership durations, gaps between partnerships, and overlaps across partnerships are important for understanding sexual partnership patterns and developing interventions to prevent transmission of HIV/sexually transmitted infections (STIs). However, a validated, optimal approach for estimating these parameters, particularly when partnerships are ongoing, has not been established.

METHODS

We assessed 4 approaches for estimating partnership parameters using cross-sectional reports on dates of first and most recent sex and partnership status (ongoing or not) from 654 adolescent girls in rural South Africa. The first, commonly used, approach assumes all partnerships have ended, resulting in underestimated durations for ongoing partnerships. The second approach treats reportedly ongoing partnerships as right-censored, resulting in bias if partnership status is reported with error. We propose 2 "hybrid" approaches, which assign partnership status to reportedly ongoing partnerships based on how recently girls last had sex with their partner. We estimate partnership duration, gap length, and overlap length under each approach using Kaplan-Meier methods with a robust variance estimator.

RESULTS

Median partnership duration and overlap length varied considerably across approaches (from 368 to 1024 days and 168 to 409 days, respectively), but gap length was stable. Lifetime prevalence of concurrency ranged from 28% to 33%, and at least half of gap lengths were shorter than 6 months, suggesting considerable potential for HIV/STI transmission.

CONCLUSIONS

Estimates of partnership duration and overlap lengths are highly dependent on measurement approach. Understanding the effect of different approaches on estimates is critical for interpreting partnership data and using estimates to predict HIV/STI transmission rates.

Measuring the Potential Impact of Combination HIV Prevention in Sub-Saharan Africa

A public health approach to combination HIV prevention is advocated to contain the epidemic in sub-Saharan Africa. We explore the implications of universal access to treatment along with HIV education scale-up in the region. We develop an HIV transmission model to investigate the impacts of universal access to treatment, as well as an analytical framework to estimate the effects of HIV education scale-up on the epidemic. We calibrate the model with data from South Africa and simulate the impacts of universal access to treatment along with HIV education scale-up on prevalence, incidence, and HIV-related deaths over a course of 15 years. Our results show that the impact of combined interventions is significantly larger than the summation of individual intervention impacts (super-additive property). The combined strategy of universal access to treatment and HIV education scale-up decreases the incidence rate by 74% over the course of 15 years, whereas universal access to treatment and HIV education scale up will separately decrease that by 43% and 8%, respectively. Combination HIV prevention could be notably effective in transforming HIV epidemic to a low-level endemicity. Our results suggest that in designing effective combination prevention in sub-Saharan Africa, priorities should be given to achieving universal access to treatment as quickly as possible and improving compliance to condom use.

Programmatic Implications of Acute and Early HIV Infection

Human immunodeficiency virus (HIV) infection includes acute, early, chronic, and late stages. Acute HIV infection lasts approximately 3 weeks and early HIV infection, which includes acute HIV infection, lasts approximately 7 weeks. Many testing and blood screening algorithms detect HIV antibodies about 3 weeks after HIV infection. Incidence estimates are based on results of modeling, cohort studies, surveillance, and/or assays. Viral load is the key modifiable risk factor for HIV transmission and peaks during acute and early HIV infection. Empirical evidence characterizing the impact of acute and early HIV infection on the spread of the HIV epidemic are limited. Time trends of HIV prevalence collected from concentrated and generalized epidemics suggest that acute and early HIV infection may have a limited role in population HIV transmission. Collectively, these data suggest that acute and early HIV infection is relatively short and does not currently require fundamentally different programmatic approaches to manage the HIV/AIDS epidemic in most settings. Research and surveillance will inform which epidemic contexts and phases may require tailored strategies for these stages of HIV infection.

How can we better identify early HIV infections?

PURPOSE OF REVIEW

Detection of early HIV infections (EHIs), including acute HIV infection (AHI), is important for individual health, prevention of HIV transmission, and measurement of HIV incidence. We describe markers of EHI, diagnostic strategies for detecting these markers, and ways to incorporate these strategies into diagnostic and HIV incidence algorithms.

RECENT FINDINGS

For individual diagnosis in the USA and Europe, laboratory-based diagnostic algorithms increasingly incorporate fourth-generation HIV antigen tests, allowing for earlier detection. In some sub-Saharan African settings, symptom-based screening is being explored to identify subsets of persons at high risk for AHI. Point-of-care diagnostics designed for AHI detection are in the pipeline and, if validated, represent an opportunity for real-time AHI diagnosis. At the population level, multiassay algorithms are promising new strategies for estimating HIV incidence on the basis of several assays applied to cross-sectional samples. These algorithms can be developed to optimize performance, in addition to cost and logistical considerations.

SUMMARY

There are important recent advances in detection of EHIs at the individual and population levels. Applying optimal combinations of tests in diagnostic and HIV incidence algorithms is urgently needed to support the multiple goals derived from enhanced detection and discrimination of EHIs.

A longitudinal population-based analysis of relationship status and mortality in KwaZulu-Natal, South Africa 2001-2011

Background

Mortality risk is lower in married than in unmarried men and women. However, little is known about the association between mortality and relationship status in South Africa where marriage rates are low, migration is common, many couples are not co-resident and HIV prevalence is high.

Method

Using demographic surveillance data collected from 2001 to 2011, relationship status was categorised as conjugal (partners belong to the same household), non-conjugal (partners do not belong to the same household) or not partnered. Rates of relationship formation and dissolution were calculated by age and sex. Controlling for antiretroviral treatment (ART) introduction in 2005 as well as education, sex-specific and age-specific Cox proportional hazards models were used to investigate the association between relationship status and (1) all-cause mortality and (2) non-AIDS mortality.

Results

Before 2005, individuals in conjugal relationships had a lower hazard of all-cause mortality in all age groups than not partnered men and women. Non-conjugal relationships lowered the risk of dying compared with not partnered men and women in fewer age groups. After ART introduction, the protective association of conjugal relationships was weaker but remained generally significant for men and women but not in non-conjugal relationships. In the later period, the association is reversed in young men (20–29 years) with mortality higher in conjugal and non-conjugal relationships compared with men not partnered. The analysis of non-AIDS deaths provided similar results.

Conclusions

The higher degree of social connections within a shared household environment that characterises conjugal relationships affords men and women greater protection against mortality.

Sampling dynamic networks with application to investigation of HIV epidemic drivers

We propose a method for randomly sampling dynamic networks that permits isolation of the impact of different network features on processes that propagate on networks. The new methods permit uniform sampling of dynamic networks in ways that ensure that they are consistent with both a given cumulative network and with specified values for constraints on the dynamic network properties. Development of such methods is challenging because modifying one network property will generally tend to modify others as well. Methods to sample constrained dynamic networks are particularly useful in the investigation of network-based interventions that target and modify specific dynamic network properties, especially in settings where the whole network is unobservable and therefore many network properties are unmeasurable. We illustrate this method by investigating the incremental impact of changes in networks properties that are relevant for the spread of infectious diseases, such as concurrency in sexual relationships. Development of the method is motivated by the challenges that arise in investigating the role of HIV epidemic drivers due to the often limited information available about contact networks. The proposed methods for randomly sampling dynamic networks facilitate investigation of the type of network data that can best contribute to an understanding of the HIV epidemic dynamics as well as of the limitations of conclusions drawn in the absence of such information. Hence, the methods are intended to aid in the design and interpretation of studies of network-based interventions.

Concurrency can drive an HIV epidemic by moving R0 across the epidemic threshold

OBJECTIVE

The objective of this study is to investigate whether concurrency can drive an HIV epidemic by moving R0 across the epidemic threshold.

DESIGN AND METHODS

We use a mathematical framework for a dynamic partnership network and the spread of a one-stage infection to study how concurrency is related to the basic reproduction number R0. Two concurrency indices were used to measure the level of concurrency. The model allows varying the level of concurrency in the population, while other key network properties such as partnership duration and lifetime number of partners are kept fixed. In this way, the effect of concurrency on R0 is investigated as an isolated phenomenon.

RESULTS

We find that an increase in concurrency is associated with an increase of R0. For plausible parameter sets for MSM populations, R0 is always above the epidemic threshold of 1. For scenarios that are plausible for sub-Saharan African populations, we show that increasing the level of concurrency can lead to R0 crossing the epidemic threshold. This occurs already at low levels of concurrency. Only a slight shift of the network structure from a purely monogamous population to one wherein individuals are allowed to have at most two partners is enough for this to happen.

CONCLUSION

Concurrency can be a driver of an HIV epidemic in sub-Saharan Africa for low levels of concurrency, although it is not decisive in MSM populations. A small increase in the level of concurrency can lead to R0 crossing the epidemic threshold in a sub-Saharan African setting.

Reassessment of HIV-1 acute phase infectivity: accounting for heterogeneity and study design with simulated cohorts

BACKGROUND

The infectivity of the HIV-1 acute phase has been directly measured only once, from a retrospectively identified cohort of serodiscordant heterosexual couples in Rakai, Uganda. Analyses of this cohort underlie the widespread view that the acute phase is highly infectious, even more so than would be predicted from its elevated viral load, and that transmission occurring shortly after infection may therefore compromise interventions that rely on diagnosis and treatment, such as antiretroviral treatment as prevention (TasP). Here, we re-estimate the duration and relative infectivity of the acute phase, while accounting for several possible sources of bias in published estimates, including the retrospective cohort exclusion criteria and unmeasured heterogeneity in risk.

METHODS AND FINDINGS

We estimated acute phase infectivity using two approaches. First, we combined viral load trajectories and viral load-infectivity relationships to estimate infectivity trajectories over the course of infection, under the assumption that elevated acute phase infectivity is caused by elevated viral load alone. Second, we estimated the relative hazard of transmission during the acute phase versus the chronic phase (RHacute) and the acute phase duration (dacute) by fitting a couples transmission model to the Rakai retrospective cohort using approximate Bayesian computation. Our model fit the data well and accounted for characteristics overlooked by previous analyses, including individual heterogeneity in infectiousness and susceptibility and the retrospective cohort's exclusion of couples that were recorded as serodiscordant only once before being censored by loss to follow-up, couple dissolution, or study termination. Finally, we replicated two highly cited analyses of the Rakai data on simulated data to identify biases underlying the discrepancies between previous estimates and our own. From the Rakai data, we estimated RHacute = 5.3 (95% credibility interval [95% CrI]: 0.79-57) and dacute = 1.7 mo (95% CrI: 0.55-6.8). The wide credibility intervals reflect an inability to distinguish a long, mildly infectious acute phase from a short, highly infectious acute phase, given the 10-mo Rakai observation intervals. The total additional risk, measured as excess hazard-months attributable to the acute phase (EHMacute) can be estimated more precisely: EHMacute = (RHacute - 1) × dacute, and should be interpreted with respect to the 120 hazard-months generated by a constant untreated chronic phase infectivity over 10 y of infection. From the Rakai data, we estimated that EHMacute = 8.4 (95% CrI: -0.27 to 64). This estimate is considerably lower than previously published estimates, and consistent with our independent estimate from viral load trajectories, 5.6 (95% confidence interval: 3.3-9.1). We found that previous overestimates likely stemmed from failure to account for risk heterogeneity and bias resulting from the retrospective cohort study design. Our results reflect the interaction between the retrospective cohort exclusion criteria and high (47%) rates of censorship amongst incident serodiscordant couples in the Rakai study due to loss to follow-up, couple dissolution, or study termination. We estimated excess physiological infectivity during the acute phase from couples data, but not the proportion of transmission attributable to the acute phase, which would require data on the broader population's sexual network structure.

CONCLUSIONS

Previous EHMacute estimates relying on the Rakai retrospective cohort data range from 31 to 141. Our results indicate that these are substantial overestimates of HIV-1 acute phase infectivity, biased by unmodeled heterogeneity in transmission rates between couples and by inconsistent censoring. Elevated acute phase infectivity is therefore less likely to undermine TasP interventions than previously thought. Heterogeneity in infectiousness and susceptibility may still play an important role in intervention success and deserves attention in future analyses.

Modelling challenges in context: lessons from malaria, HIV, and tuberculosis

Malaria, HIV, and tuberculosis (TB) collectively account for several million deaths each year, with all three ranking among the top ten killers in low-income countries. Despite being caused by very different organisms, malaria, HIV, and TB present a suite of challenges for mathematical modellers that are particularly pronounced in these infections, but represent general problems in infectious disease modelling, and highlight many of the challenges described throughout this issue. Here, we describe some of the unifying challenges that arise in modelling malaria, HIV, and TB, including variation in dynamics within the host, diversity in the pathogen, and heterogeneity in human contact networks and behaviour. Through the lens of these three pathogens, we provide specific examples of the other challenges in this issue and discuss their implications for informing public health efforts.

The racial disparities in STI in the U.S.: Concurrency, STI prevalence, and heterogeneity in partner selection

Background

There is a large and persistent racial disparity in STI in the U.S. which has placed non-Hispanic-Blacks at disproportionately high risk. We tested a hypothesis that both individual-level risk factors (partner number, anal sex, condom use) and local-network features (concurrency and assortative mixing by race) combine to account for the association between race and chlamydia status.

Methods

Data from the Longitudinal Survey of Adolescent Health Wave III were used. Chlamydia status was determined using biomarkers. Individual-level risk behaviors were self-reported. Network location variables for concurrency and assortative mixing were imputed using egocentrically sample data on sexual partnerships.

Results

After controlling for demographic attributes including age, sex, marital status, education and health care access there remained a strong association between race and chlamydia status (OR = 5.23, 95% CI] 3.83–7.15], p < .001 for Non-Hispanic Blacks with Non-Hispanic Whites as the reference category). The inclusion of individual-level risk factors did not alter the association between race and chlamydia(OR = 5.23 for Non-Hispanic Blacks). The inclusion of concurrency and assortative mixing by race substantially reduced the association between race and chlamydia status (OR = 1.87, 95% CI [0.89–3.91] p > .05 for Non-Hispanic Blacks).

Concurrent partnerships in Cape Town, South Africa: race and sex differences in prevalence and duration of overlap

Introduction

Concurrent partnerships (CPs) have been suggested as a risk factor for transmitting HIV, but their impact on the epidemic depends upon how prevalent they are in populations, the average number of CPs an individual has and the length of time they overlap. However, estimates of prevalence of CPs in Southern Africa vary widely, and the duration of overlap in these relationships is poorly documented. We aim to characterize concurrency in a more accurate and complete manner, using data from three disadvantaged communities of Cape Town, South Africa.

Methods

We conducted a sexual behaviour survey (n=878) from June 2011 to February 2012 in Cape Town, using Audio Computer-Assisted Self-Interviewing to collect sexual relationship histories on partners in the past year. Using the beginning and end dates for the partnerships, we calculated the point prevalence, the cumulative prevalence and the incidence rate of CPs, as well as the duration of overlap for relationships begun in the previous year. Linear and binomial regression models were used to quantify race (black vs. coloured) and sex differences in the duration of overlap and relative risk of having CPs in the past year.

Results

The overall point prevalence of CPs six months before the survey was 8.4%: 13.4% for black men, 1.9% for coloured men, 7.8% black women and 5.6% for coloured women. The median duration of overlap in CPs was 7.5 weeks. Women had less risk of CPs in the previous year than men (RR 0.43; 95% CI: 0.32–0.57) and black participants were more at risk than coloured participants (RR 1.86; 95% CI: 1.17–2.97).

Conclusions

Our results indicate that in this population the prevalence of CPs is relatively high and is characterized by overlaps of long duration, implying there may be opportunities for HIV to be transmitted to concurrent partners.