The mathematics of concurrent partnerships and HIV: a commentary on Lurie and Rosenthal, 2009

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.

Characteristics and Risk Behaviors of Men Who Have Sex With Men and Women Compared With Men Who Have Sex With Men-20 US Cities, 2011 and 2014

BACKGROUND

Men who have sex with men (MSM) are heterogeneous with respect to sexual behavior. We examined differences in sex behaviors between men who have sex with men and women (MSMW) and men who have sex with men only (MSMO).

METHODS

Data for this analysis were from MSM who participated in National HIV Behavioral Surveillance in 2011 and 2014. We used the combined years to evaluate demographic and behavioral differences between MSMW and MSMO. Using log-linked Poisson regression models, adjusted prevalence ratios (aPR) were calculated for behavioral outcomes.

RESULTS

Overall, 2042 (11.9%) participants were classified as MSMW. MSMW were less likely than MSMO to have condomless sex with male partners [aPR 0.77; 95% confidence interval (CI): 0.74 to 0.81] and to have been diagnosed with another sexually transmitted disease (aPR 0.83; 95% CI: 0.72 to 0.95). MSMW were more likely than MSMO to have given money or drugs for sex (aPR 2.85; 95% CI: 2.52 to 3.24) or received money or drugs for sex (aPR 2.64; 95% CI: 2.37 to 2.93) and to ever have injected drugs (aPR 2.05; 95% CI: 1.80 to 2.34). MSMW had more total sex partners (median 6, interquartile range: 4-11 vs. 3, 2-8), casual sex partners (5, 2-10 vs. 3, 1-7), and condomless sex partners (2, 1-4 vs. 1, 0-2) in the last 12 months (P < 0.01 for all comparisons).

CONCLUSIONS

MSMW have distinct sexual risk behaviors from MSMO and may contribute to HIV transmission among women. MSMW could benefit from tailored interventions to reduce HIV risk behaviors.

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.

Measuring concurrency using a joint multistate and point process model for retrospective sexual history data

Understanding the impact of concurrency, defined as overlapping sexual partnerships, on the spread of HIV within various communities has been complicated by difficulties in measuring concurrency. Retrospective sexual history data consisting of first and last dates of sexual intercourse for each previous and ongoing partnership is often obtained through use of cross-sectional surveys. Previous attempts to empirically estimate the magnitude and extent of concurrency among these surveyed populations have inadequately accounted for the dependence between partnerships and used only a snapshot of the available data. We introduce a joint multistate and point process model in which states are defined as the number of ongoing partnerships an individual is engaged in at a given time. Sexual partnerships starting and ending on the same date are referred to as one-offs and modeled as discrete events. The proposed method treats each individual's continuation in and transition through various numbers of ongoing partnerships as a separate stochastic process and allows the occurrence of one-offs to impact subsequent rates of partnership formation and dissolution. Estimators for the concurrent partnership distribution and mean sojourn times during which a person has k ongoing partnerships are presented. We demonstrate this modeling approach using epidemiological data collected from a sample of men having sex with men and seeking HIV testing at a Los Angeles clinic. Among this sample, the estimated point prevalence of concurrency was higher among men later diagnosed HIV positive. One-offs were associated with increased rates of subsequent partnership dissolution. Copyright © 2016 John Wiley & Sons, Ltd.

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.

Migration, Multiple Sexual Partnerships, and Sexual Concurrency in the Garífuna Population of Honduras

The Garífuna, an ethnic minority group in Honduras, have been disproportionately affected by HIV. Previous research suggests that migration and high rates of multiple sexual partnerships are major drivers of the epidemic. Using data from a 2012 population-based survey, we assessed whether temporary migration was associated with (1) multiple sexual partnerships and (2) sexual concurrency among Garífuna men and women in Honduras. Among both men and women, temporary migration in the last year was associated with an increased likelihood of multiple sexual partnerships and with concurrency, though only the association between migration and multiple sexual partnerships among men was statistically significant (Adjusted Prevalence Ratio 1.7, 95 % CI 1.2-2.4). Migration may contribute to HIV/STI vulnerability among Garífuna men and women via increases in these sexual risk behaviors. Research conducted among men and women at elevated risk of HIV should continue to incorporate measures of mobility, including history of internal migration.

A new approach to measuring partnership concurrency and its association with HIV risk in couples

Empirical estimates of the association between concurrent partnerships (CP) and HIV risk are affected by non-sampling errors in survey data on CPs, e.g., because respondents misreport the extent of their CPs. We propose a new approach to measuring CPs in couples, which permits assessing how respondent errors affect estimates of the association between CPs and HIV risk. Each couple member is asked (1) to report whether s/he has engaged in CPs and (2) to assess whether his/her partner has engaged in CPs, since their couple started. Cross-tabulating these data yields multiple classifications (with varying combinations of sensitivity/specificity) of the CPs of each couple member. We then measure the association between CPs and HIV outcomes according to each classification. The resulting range of estimates is an indicator of the uncertainty associated with respondent errors. We tested this approach using data on 520 matched couples drawn from the Likoma Network Study. Results suggest that existing tests of the concurrency hypothesis are affected by significant uncertainty.

An association between neighbourhood wealth inequality and HIV prevalence in sub-Saharan Africa

This paper investigates whether community-level wealth inequality predicts HIV serostatus using DHS household survey and HIV biomarker data for men and women ages 15-59 pooled from six sub-Saharan African countries with HIV prevalence rates exceeding 5%. The analysis relates the binary dependent variable HIV-positive serostatus and two weighted aggregate predictors generated from the DHS Wealth Index: the Gini coefficient, and the ratio of the wealth of households in the top 20% wealth quintile to that of those in the bottom 20%. In separate multilevel logistic regression models, wealth inequality is used to predict HIV prevalence within each statistical enumeration area, controlling for known individual-level demographic predictors of HIV serostatus. Potential individual-level sexual behaviour mediating variables are added to assess attenuation, and ordered logit models investigate whether the effect is mediated through extramarital sexual partnerships. Both the cluster-level wealth Gini coefficient and wealth ratio significantly predict positive HIV serostatus: a 1 point increase in the cluster-level Gini coefficient and in the cluster-level wealth ratio is associated with a 2.35 and 1.3 times increased likelihood of being HIV positive, respectively, controlling for individual-level demographic predictors, and associations are stronger in models including only males. Adding sexual behaviour variables attenuates the effects of both inequality measures. Reporting eleven plus lifetime sexual partners increases the odds of being HIV positive over five-fold. The likelihood of having more extramarital partners is significantly higher in clusters with greater wealth inequality measured by the wealth ratio. Disaggregating logit models by sex indicates important risk behaviour differences. Household wealth inequality within DHS clusters predicts HIV serostatus, and the relationship is partially mediated by more extramarital partners. These results emphasize the importance of incorporating higher-level contextual factors, investigating behavioural mediators, and disaggregating by sex in assessing HIV risk in order to uncover potential mechanisms of action and points of preventive intervention.

Measuring prevalence and correlates of concurrent sexual partnerships among young sexually active men in Kisumu, Kenya

Our objectives were to: (1) compare multiple measures of partnership concurrency, including the UNAIDS-recommended definition and (2) describe the prevalence and correlates of concurrent sexual partnerships among young Kenyan men. We analyzed 10,907 lifetime partnerships of 1,368 men ages 18-24 years enrolled in a randomized trial of male circumcision to reduce HIV-1 incidence in Kisumu. Partnership concurrency was determined by overlapping dates and examined over varying recall periods and assumptions. The lifetime prevalence of concurrency was 77 %. Sixty-one percent of all partnerships were concurrent and factors associated with concurrency differed by partner type. Point prevalence of concurrency at the time of the interview was consistently the highest and UNAIDS-recommended definition was the most conservative (25 vs. 18 % at baseline, respectively). Estimates of concurrency were influenced by methods for definition and measurement. Regardless of definition, concurrent partnerships are frequent in this population of young, sexually active men in high HIV prevalence Kisumu, Kenya.

Reciprocal sex partner concurrency and STDs among heterosexuals at high-risk of HIV infection

Inconsistent findings on the relationship of sex partner concurrency to infection with HIV and other sexually transmitted diseases (STDs) may result from differences in how sex partner concurrency is conceptualized. We examine the relationship of reciprocal sex partner concurrency (RSPC) to diagnosed STDs among heterosexuals. Heterosexually active adults (N = 717) were recruited for a cross-sectional study using respondent-driven sampling (RDS) from high-HIV-risk areas in New York City (NYC, 2006-2007) and interviewed about their sexual risk behaviors, number of sex partners, last sex partners, and STD diagnoses (prior 12 months). RSPC was when both the participant and her/his last sex partner had sex with other people during their sexual relationship. Odds ratios (OR), adjusted odds ratios (aOR), and 95 % confidence intervals (95%CI) were estimated by logistic regression. The sample was 52.4 % female, 74.3 % Black; median age was 40 years. RSPC was reported by 40.7 % and any STD diagnoses by 23.4 %. Any STDs was reported by 31.5 % of those reporting RSPC vs. 17.9 % of those who did not (OR = 2.11, 95%CI = 1.49-3.0). Any STDs was independently associated with RSPC (aOR = 1.54, 95%CI = 1.02-2.32), female gender (aOR = 2.15, 95%CI = 1.43-3.23), having more than three sex partners (aOR = 1.72, 95%CI = 1.13-2.63), and unprotected anal sex (aOR = 1.65, 95%CI = 1.12-2.42). Heterosexuals in high-HIV-risk neighborhoods in sexual partnerships that involve RSPC are at greater risk of STDs and, potentially, HIV. RSPC, in addition to sexual risk behaviors and the number of sex partners, may facilitate the heterosexual spread of HIV through STD cofactors and linkage into larger STD/HIV sexual transmission networks.

Sexual partnership patterns in malawi: implications for HIV/STI transmission

BACKGROUND

Concurrent sexual partnerships are believed to play an important role in HIV transmission in sub-Saharan Africa, but the contributions of concurrency to HIV and sexually transmitted infection (STI) spread depend on the details of infectious periods and relationship patterns. To contribute to the understanding of sexual partnership patterns in this region, we estimated partnership lengths, temporal gaps between partners, and periods of overlap across partners at an STI clinic in Lilongwe, Malawi.

METHODS

Participants underwent physical examinations and HIV tests, and responded to questionnaires about demographics and risk behaviors, including detailed questions about a maximum of 3 sexual partners in the previous 2 months. We calculated partnership length as the time between the first and most recent sexual contact with a partner, and gap length as the time between the most recent contact with 1 partner and the first contact with the next. We defined concurrent and consecutive partnerships as gap length ≤0 days and gap length >0 days, respectively.

RESULTS

In the study population (n = 183), 86% reported 0 or 1 partner, 5% reported multiple consecutive partnerships, and 9% reported concurrency. The mean partnership length was 858 days (median = 176 days). Gaps between consecutive partnerships were short (mean = 21 days), and overlaps across concurrent partners tended to be long (mean = 246 days).

CONCLUSIONS

Multiple sexual partnerships were uncommon, and partnerships were long on average. Among those reporting multiple recent partners, both long-term concurrency and narrowly spaced consecutive partnerships could present substantial risk for efficient transmission of HIV and classical STIs.

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.

Sexual partner concurrency of urban male and female STD clinic patients: a qualitative study

Partner concurrency (i.e., overlapping sexual partnerships) facilitates the spread of STDs, including HIV. The present study explored the context of and motivations for partner concurrency among patients recruited from an urban STD clinic. Eight focus groups were conducted with 59 patients (47% women; 77% African American). Qualitative analyses revealed five motivational themes related to the occurrence of concurrent partnerships for men and women. Participants reported these partnerships tend to occur: when people believe that sexual partners are unfaithful or cannot be trusted; when sexual satisfaction is low; when patients report the need for different partners to fulfill multiple needs; in retaliation for a partner's concurrency; and when people wish to maintain a sexual relationship with an ex-partner who is the parent of a shared child. Four additional themes unique to men were identified. Men reported that they had multiple partners because this practice supports their sense of masculinity and is consistent with familial modeling and community norms, and because having multiple partners is "in a man's nature." Men also mentioned that the imbalance in the number of women-to-men in their sexual network facilitates partner concurrency. These findings can help prevention practitioners and researchers to develop interventions to reduce risk associated with partner concurrency.

The role of acute and early HIV infection in the spread of HIV and implications for transmission prevention strategies in Lilongwe, Malawi: a modelling study

BACKGROUND

HIV transmission risk is higher during acute and early HIV infection than it is during chronic infection, but the contribution of early infection to the spread of HIV is controversial. We estimated the contribution of early infection to HIV incidence in Lilongwe, Malawi, and predict the future effect of hypothetical prevention interventions targeted at early infection only, chronic infection only, or both stages.

METHODS

We developed a deterministic mathematical model describing heterosexual HIV transmission, informed by detailed behavioural and viral-load data collected in Lilongwe. We included sexual contact within and outside of steady pairs and divided the infectious period into intervals to allow for changes in transmissibility by infection stage. We used a Bayesian melding approach to fit the model to HIV prevalence data collected between 1987 and 2005 at Lilongwe antenatal clinics. We assessed interventions that reduced the per-contact transmission probability to 0.00003 in people receiving them, and varied the proportion of individuals receiving the intervention in each stage.

FINDINGS

We estimated that 38.4% (95% credible interval 18.6-52.3) of HIV transmissions in Lilongwe are attributable to sexual contact with individuals with early infection. Interventions targeted at only early infection substantially reduced HIV prevalence, but did not lead to elimination, even with 100% coverage. Interventions targeted at only chronic infections also reduced HIV prevalence, but coverage levels of 95-99% were needed for the elimination of HIV. In scenarios with less than 95% coverage of interventions targeted at chronic infections, additional interventions reaching 25-75% of individuals with early infection reduced HIV prevalence substantially.

INTERPRETATION

Our results suggest that early infection plays an important part in HIV transmission in this sub-Saharan African setting. Without near-complete coverage, interventions during chronic infection will probably have incomplete effectiveness unless complemented by strategies targeting individuals with early HIV infection.

FUNDING

National Institutes of Health, University of North Carolina Center for AIDS Research.

Concurrency revisited: increasing and compelling epidemiological evidence

Multiple sexual partnerships must necessarily lie at the root of a sexually transmitted epidemic. However, that overlapping or concurrent partnerships have played a pivotal role in the generalized epidemics of sub-Saharan Africa has been challenged. Much of the original proposition that concurrent partnerships play such a role focused on modelling, self-reported sexual behaviour data and ethnographic data. While each of these has definite merit, each also has had methodological limitations. Actually, more recent cross-national sexual behaviour data and improved modelling have strengthened these lines of evidence. However, heretofore the epidemiologic evidence has not been systematically brought to bear. Though assessing the epidemiologic evidence regarding concurrency has its challenges, a careful examination, especially of those studies that have assessed HIV incidence, clearly indicates a key role for concurrency.Such evidence includes: 1) the early and dramatic rise of HIV infection in generalized epidemics that can only arise from transmission through rapid sequential acute infections and thereby concurrency; 2) clear evidence from incidence studies that a major portion of transmission in the population occurs via concurrency both for concordant negative and discordant couples; 3) elevation in risk associated with partner's multiple partnering; 4) declines in HIV associated with declines in concurrency; 5) bursts and clustering of incident infections that indicate concurrency and acute infection play a key role in the propagation of epidemics; and 6) a lack of other plausible explanations, including serial monogamy and non-sexual transmission. While other factors, such as sexually transmitted infections, other infectious diseases, biological factors and HIV sub-type, likely play a role in enhancing transmission, it appears most plausible that these would amplify the role of concurrency rather than alter it. Additionally, critics of concurrency have not proposed plausible alternative explanations for why the explosive generalized epidemics occurred. Specific behaviour change messaging bringing the concepts of multiple partnering and concurrency together appears salient and valid in promoting safer individual behaviour and positive social norms.

Concurrent sexual partnerships and primary HIV infection: a critical interaction

The combination of long-term concurrent sexual partnerships and high infectiousness early in HIV infection has been suggested as a key driver of the extensive spread of HIV in general populations in sub-Saharan Africa, but this has never been scientifically investigated. We use a mathematical model to simulate HIV spreading on sexual networks with different amounts of concurrency. The models show that if HIV infectiousness is constant over the duration of infection, the amount of concurrency has much less influence on HIV spread compared to when infectiousness varies over three stages of infection with high infectiousness in the first months. The proportion of transmissions during primary infection is sensitive to the amount of concurrency and, in this model, is estimated to be between 16 and 28% in spreading epidemics with increasing concurrency. The sensitivity of epidemic spread to the amount of concurrency is greater than predicted by models that do not include primary HIV infection.

Concurrent partnerships and HIV: an inconvenient truth

The strength of the evidence linking concurrency to HIV epidemic severity in southern and eastern Africa led the Joint United Nations Programme on HIV/AIDS and the Southern African Development Community in 2006 to conclude that high rates of concurrent sexual partnerships, combined with low rates of male circumcision and infrequent condom use, are major drivers of the AIDS epidemic in southern Africa. In a recent article in the Journal of the International AIDS Society, Larry Sawers and Eileen Stillwaggon attempt to challenge the evidence for the importance of concurrency and call for an end to research on the topic. However, their "systematic review of the evidence" is not an accurate summary of the research on concurrent partnerships and HIV, and it contains factual errors concerning the measurement and mathematical modelling of concurrency.Practical prevention-oriented research on concurrency is only just beginning. Most interventions to raise awareness about the risks of concurrency are less than two years old; few evaluations and no randomized-controlled trials of these programmes have been conducted. Determining whether these interventions can help people better assess their own risks and take steps to reduce them remains an important task for research. This kind of research is indeed the only way to obtain conclusive evidence on the role of concurrency, the programmes needed for effective prevention, the willingness of people to change behaviour, and the obstacles to change.

Empiricism and theorizing in epidemiology and social network analysis

The connection between theory and data is an iterative one. In principle, each is informed by the other: data provide the basis for theory that in turn generates the need for new information. This circularity is reflected in the notion of abduction, a concept that focuses on the space between induction (generating theory from data) and deduction (testing theory with data). Einstein, in the 1920s, placed scientific creativity in that space. In the field of social network analysis, some remarkable theory has been developed, accompanied by sophisticated tools to develop, extend, and test the theory. At the same time, important empirical data have been generated that provide insight into transmission dynamics. Unfortunately, the connection between them is often tenuous and the iterative loop is frayed. This circumstance may arise both from data deficiencies and from the ease with which data can be created by simulation. But for whatever reason, theory and empirical data often occupy different orbits. Fortunately, the relationship, while frayed, is not broken, to which several recent analyses merging theory and extant data will attest. Their further rapprochement in the field of social network analysis could provide the field with a more creative approach to experimentation and inference.

Timing is everything: international variations in historical sexual partnership concurrency and HIV prevalence

BACKGROUND

Higher prevalence of concurrent partnerships is one hypothesis for the severity of the HIV epidemic in the countries of Southern Africa. But measures of the prevalence of concurrency alone do not adequately capture the impact concurrency will have on transmission dynamics. The importance of overlap duration and coital exposure are examined here.

METHODOLOGY/PRINCIPAL FINDINGS

We conducted a comparison of data from three studies of sexual behavior carried out in the early 1990s in Uganda, Thailand and the US. Using cumulative concurrency measures, the three countries appeared somewhat similar. Over 50% of both Thai and Ugandan men reported a concurrency within the last three partnerships and over 20% reported a concurrency in the last year, the corresponding rates among US men were nearly 20% for Blacks and Hispanics, and about 10% for other racial/ethnic groups. Concurrency measures that were more sensitive to overlap duration, however, showed large differences. The point prevalence of concurrency on the day of interview was over 10% among Ugandan men compared to 1% for Thai men. Ugandan concurrencies were much longer duration - a median of about two years - than either the Thai (1 day) or US concurrencies (4-9 months across all groups), and involved 5-10 times more coital risk exposure with the less frequent partner. In the US, Blacks and Hispanics reported higher prevalence, longer duration and greater coital exposure than Whites, but were lower than Ugandans on nearly every measure. Together, the differences in the prevalence, duration and coital exposure of concurrent partnerships observed align with the HIV prevalence differentials seen in these populations at the time the data were collected.

CONCLUSIONS/SIGNIFICANCE

There were substantial variations in the patterns of concurrent partnerships within and between populations. More long-term overlapping partnerships, with regular coital exposure, were found in populations with greater HIV epidemic severity.

In the absence of marriage: long-term concurrent partnerships, pregnancy, and HIV risk dynamics among South African young adults

In KwaZulu/Natal, South Africa, where HIV prevalence is among the world's highest, a longitudinal qualitative study of partnership dynamics and HIV preventive behaviors was conducted. 47 young adults aged 18-24 participated in in-depth interviews, and 29 were re-interviewed 2 years later. Five analytical domains emerged: primary partnerships, love and romance; secondary partnerships; pregnancy/parenthood; condom use/prevention; and contextual influences, including schooling and future aspirations. Primary relationships were long-lasting, with most men and women in the same relationship at 2-year follow-up. Secondary, casual partnerships were common for men and women, although these were shorter and changed frequently. Love and marriage aspirations were not viewed as incompatible with secondary partners. Condom use increased over time in some primary relationships, but decreased in others, and was nearly universal with non-primary partners. Pregnancy, school drop-out, and economic need strongly influence young people's lifecourse. These findings suggest the need to focus prevention efforts on the partnership context, including partner reduction, and structural factors that impede or enhance prevention success.

Concurrent sexual partnerships do not explain the HIV epidemics in Africa: a systematic review of the evidence

The notion that concurrent sexual partnerships are especially common in sub-Saharan Africa and explain the region's high HIV prevalence is accepted by many as conventional wisdom. In this paper, we evaluate the quantitative and qualitative evidence offered by the principal proponents of the concurrency hypothesis and analyze the mathematical model they use to establish the plausibility of the hypothesis.We find that research seeking to establish a statistical correlation between concurrency and HIV prevalence either finds no correlation or has important limitations. Furthermore, in order to simulate rapid spread of HIV, mathematical models require unrealistic assumptions about frequency of sexual contact, gender symmetry, levels of concurrency, and per-act transmission rates. Moreover, quantitative evidence cited by proponents of the concurrency hypothesis is unconvincing since they exclude Demographic and Health Surveys and other data showing that concurrency in Africa is low, make broad statements about non-African concurrency based on very few surveys, report data incorrectly, report data from studies that have no information about concurrency as though they supported the hypothesis, report incomparable data and cite unpublished or unavailable studies. Qualitative evidence offered by proponents of the hypothesis is irrelevant since, among other reasons, there is no comparison of Africa with other regions.Promoters of the concurrency hypothesis have failed to establish that concurrency is unusually prevalent in Africa or that the kinds of concurrent partnerships found in Africa produce more rapid spread of HIV than other forms of sexual behaviour. Policy makers should turn attention to drivers of African HIV epidemics that are policy sensitive and for which there is substantial epidemiological evidence.