WaSH insecurity and anxiety among people who inject drugs in the Tijuana-San Diego border region

BACKGROUND

Water, sanitation, and hygiene (WaSH) insecurity increases the risk of water-related diseases. However, limited research has been conducted on psychosocial distress as it relates to WaSH insecurity, especially among people who inject drugs (PWID). We examined the relationship between WaSH insecurity and related anxiety among PWID living in different housing conditions along the US-Mexico border region.

METHODS

From 2020-2021, a cross-sectional study was conducted among 585 people who injected drugs within the last month in Tijuana (N = 202), San Diego (N = 182), and in both Tijuana and San Diego (N = 201). Participants underwent interviewer-administered surveys related to WaSH access, substance use, and generalized anxiety disorder (GAD-7). Quasi-Poisson regressions were used to assess associations between WaSH insecurity and anxiety in the prior 6-months.

RESULTS

Participants were 75% male, 42% were unhoused and 91% experienced WaSH insecurity in the prior 6-months. After adjusting for housing status, gender, and age, lack of access to basic drinking water (Adj RR: 1.28; 95% CI: 1.02-1.58), sanitation (Adj RR:1.28; 95% CI: 1.07-1.55), and a daily bath/shower (Adj RR: 1.38; 95% CI: 1.15-1.66) were associated with mild-severe anxiety. The number of WaSH insecurities was independently associated with a 20% increased risk of experiencing anxiety per every additional insecurity experienced (Adj RR: 1.20; CI: 1.12-1.27). We also found a significant interaction between gender and housing status (p = 0.003), indicating that among people experiencing sheltered/unsheltered homelessness, women had a higher risk of mild-severe anxiety compared to men (Adj RR: 1.55; 95% CI: 1.27-1.89). At the same time, among women, those who are unhoused have 37% increased risk of anxiety than those who live in stable housing conditions (Adj RR: 1.37; 95% CI: 1.01-1.89).

CONCLUSION

The lack of specific WaSH services, particularly lack of drinking water, toilets, and daily showers were associated with higher levels of anxiety among PWID in the Tijuana-San Diego border region. Women experiencing homelessness were especially vulnerable. WaSH interventions that provide safe, 24-h access may help to reduce anxiety and health risks associated with WaSH insecurity.

Novel Location-Based Survey Using Cognitive Interviews to Assess Geographic Networks and Hotspots of Sex and Drug Use: Implementation and Validation Study

BACKGROUND

The Ending the HIV Epidemic initiative in the United States relies on HIV hotspots to identify where to geographically target new resources, expertise, and technology. However, interventions targeted at places with high HIV transmission and infection risk, not just places with high HIV incidence, may be more effective at reducing HIV incidence and achieving health equity.

OBJECTIVE

We described the implementation and validation of a web-based activity space survey on HIV risk behaviors. The survey was intended to collect geographic information that will be used to map risk behavior hotspots as well as the geography of sexual networks in Los Angeles County.

METHODS

The survey design team developed a series of geospatial questions that follow a 3-level structure that becomes more geographically precise as participants move through the levels. The survey was validated through 9 cognitive interviews and iteratively updated based on participant feedback until the saturation of topics and technical issues was reached.

RESULTS

In total, 4 themes were identified through the cognitive interviews: functionality of geospatial questions, representation and accessibility, privacy, and length and understanding of the survey. The ease of use for the geospatial questions was critical as many participants were not familiar with mapping software. The inclusion of well-known places, landmarks, and road networks was critical for ease of use. The addition of a Google Maps interface, which was familiar to many participants, aided in collecting accurate and precise location information. The geospatial questions increased the length of the survey and warranted the inclusion of features to simplify it and speed it up. Using nicknames to refer to previously entered geographic locations limited the number of geospatial questions that appeared in the survey and reduced the time taken to complete it. The long-standing relationship between participants and the research team improved comfort to disclose sensitive geographic information related to drug use and sex. Participants in the cognitive interviews highlighted how trust and inclusive and validating language in the survey alleviated concerns related to privacy and representation.

CONCLUSIONS

This study provides promising results regarding the feasibility of using a web-based mapping survey to collect sensitive location information relevant to ending the HIV epidemic. Data collection at several geographic levels will allow for insights into spatial recall of behaviors as well as future sensitivity analysis of the spatial scale of hotspots and network characteristics. This design also promotes the privacy and comfort of participants who provide location information for sensitive topics. Key considerations for implementing this type of survey include trust from participants, community partners, or research teams to overcome concerns related to privacy and comfort. The implementation of similar surveys should consider local characteristics and knowledge when crafting the geospatial components.

Geographic mobility and its impact on sexual health and ongoing HIV transmission among migrant latinx men who have sex with men

An understudied social process that may determine variable HIV risk, testing, and linkage to care is geographic mobility, including immigration as well as short-term mobility, especially among sexual minority populations. We aimed to assess how geographic mobility over the lifecourse between Latin America and the U.S., and within the U.S., was linked to sexual risk and health behaviors among Latinx migrant men who have sex with men (MSM) in San Bernardino County, California. Qualitative analysis of 16 semi-structured interviews revealed four major domains of influence on participants' sexual risk behaviors. At the micro level, these included social environment/interpersonal factors (e.g., family and peer support) and geographic factors and pathways (e.g., migration journey to the U.S.). At the macro level data centered on cultural factors (e.g., gender norms in home country) and structural factors (e.g., HIV healthcare). Our results can illuminate and promote effective health policies and HIV reduction efforts for Latinx migrant MSM in metro areas.

Effective strategies to promote HIV self-testing for men who have sex with men: Evidence from a mathematical model

BACKGROUND

HIV testing is the gateway to HIV treatment and prevention. HIV self-testing (HIVST) has potential to increase testing; however, the potential population-level impact of HIVST on the HIV epidemic and the best strategies for promoting HIVST are unknown. Our aim is to inform public health approaches for promoting HIVST as part of a comprehensive strategy to reduce HIV incidence.

METHODS

Stochastic network-based HIV transmission models were used to estimate how different HIVST strategies would affect HIV incidence in Seattle and Atlanta over 10 years. We included four types of HIV testers and implemented nine replacement and eleven supplementation strategies for HIVST.

RESULTS

Replacement of clinic-based tests with HIVST increased HIV incidence in Seattle and Atlanta. The benefits of supplementary strategies depended on the tester type using HIVST. Targeting non-testers averted the highest number of cases per test. In Seattle 2.2 (95%SI=-77, 100.4) and 4.7 (95%SI=-35.7, 60.1) infections were averted per 1000 HIVST when non-testers used HIVST once or twice per year respectively. In Atlanta the comparable rates were 8.0 (95%SI=-60.3 to 77.7) and 6.7 (95%SI=-37.7, 41.0). Paradoxically, increasing testing among risk-based testers using HIVST increased incidence.

CONCLUSIONS

The population-level impact of HIVST depends on who is reached with HIVST, how kits are used, and by characteristics of the underlying epidemic and HIV care infrastructure. Targeted HIVST can be an effective component of a comprehensive HIV testing strategy. More work is needed to understand how to identify and target non-testers for self-testing implementation.

A call for epidemic modeling to examine historical and structural drivers of racial disparities in infectious disease

Since this is a commentary, there is no abstract.

Is It the Timing? Short-Term Mobility and Coital Frequency in Agbogbloshie, Ghana

Short-term mobility is often associated with increased sexual risk behavior. Mobile individuals often have higher rates of sexual risk behavior compared to non-mobile individuals, but the reasons why are not clear. Using monthly retrospective panel data from 202 men and 282 women in Agbogbloshie, Ghana, we tested whether short-term mobility was associated with changes in coital frequency, and whether the association was due to the act of travel in the given month (e.g., enabling higher risk behavior), the reason for travel, or an individual's travel propensity at other times in the year. Overnight travel specifically to visit family or friends, or for education, health, or other reasons, was associated with increased coital frequency for men. However, men with higher travel propensities had lower overall coital frequency and the act of traveling enabled more sex only for the most frequent male travelers. Men who seldom traveled had much higher coital frequency, but the act of traveling was not associated with additional sex acts. For women, travel for education, health, or other reasons increased coital frequency. Occasional female travelers had slightly more sex acts compared to non-mobile women, and the act of traveling for these women was associated with slight increases in coital frequency, supporting the enabling hypothesis. Highly mobile women had fewer sex acts per month on average. Our findings suggest that mobility characteristics measured on a broad temporal scale, as well as the reason for mobility, are important to understand the relationship between short-term mobility and sexual behavior.

Geographic Mobility, Place Attachment, and the Changing Geography of Sex among African American and Latinx MSM Who Use Substances in Los Angeles

The places that people go and interact with others, along with the characteristics of those places, determine degrees of sexual health risk and concomitant prevention opportunities for gay, bisexual, and other men who have sex with men (MSM). The objective of this paper is to use syndemic theory to guide analyses of 20 in-depth interviews with African American and Hispanic/Latinx MSM living in Los Angeles. We describe the places in which African American and Latinx MSM interviewees live and socialize, and how these places influence sexual behavior, drug use, and access to health care. We find common spatial patterns in mobility, incongruence in residential and sexual places, and differing geographic patterns of sex by men who use geo-social hook-up apps. Significant instability in home life and varying forms of mobility and risk-taking were a response to cumulative disadvantage and intersecting structural forces including poverty, racism, and homophobia. Our results strongly suggest that geographic mobility is a syndemic factor for HIV risk among MSM in Los Angeles, as mobility amplified negative impacts of other syndemic factors. Innovative place-interventions to reduce HIV incidence and disparities in HIV need to acknowledge the synergistic factors that drive higher HIV incidence among AA and Latinx MSM.

Immigrant Generational Differences in Social Support and Sexual Risk Behaviors Among Men Who Have Sex With Men in Seattle, Washington

Different immigrant generations may encounter distinct sexual opportunities with implications for HIV transmission. Yet, few studies have examined how immigrant generational status is associated with sexual risk behaviors among men who have sex with men (MSM). We explored relationships between immigrant generational status, social support, and sexual risk behaviors among English-speaking MSM using data from surveys conducted in Seattle, Washington, in 2014 (n = 323). We compared the sexual risk behaviors and social support of first-generation, second-generation, and third- and higher-generation MSM, and examined whether immigrant generational status and social support were associated with sexual risk behaviors using logistic regression models. Second-generation MSM reported lower friend social support than first- or third- and higher-generation MSM (p < .05). However, immigrant generational status was not associated with sexual risk behavior outcomes, even after accounting for social support. Results suggest that differences in immigration processes such as acculturation may be more predictive of risk behaviors than generational status alone.

A large-scale location-based social network to understanding the impact of human geo-social interaction patterns on vaccination strategies in an urbanized area

Cities play an important role in fostering and amplifying the transmission of airborne diseases (e.g., influenza) because of dense human contacts. Before an outbreak of airborne diseases within a city, how to determine an appropriate containment area for effective vaccination strategies is unknown. This research treats airborne disease spreads as geo-social interaction patterns, because viruses transmit among different groups of people over geographical locations through human interactions and population movement. Previous research argued that an appropriate scale identified through human geo-social interaction patterns can provide great potential for effective vaccination. However, little work has been done to examine the effectiveness of such vaccination at large scales (e.g., city) that are characterized by spatially heterogeneous population distribution and movement. This article therefore aims to understand the impact of geo-social interaction patterns on effective vaccination in the urbanized area of Portland, Oregon. To achieve this goal, we simulate influenza transmission on a large-scale location-based social network to 1) identify human geo-social interaction patterns for designing effective vaccination strategies, and 2) and evaluate the efficacy of different vaccination strategies according to the identified geo-social patterns. The simulation results illustrate the effectiveness of vaccination strategies based on geosocial interaction patterns in containing the epidemic outbreak at the source. This research can provide evidence to inform public health approaches to determine effective scales in the design of disease control strategies.

Development of an Agent-Based Model to Investigate the Impact of HIV Self-Testing Programs on Men Who Have Sex With Men in Atlanta and Seattle

BACKGROUND

In the United States HIV epidemic, men who have sex with men (MSM) remain the most profoundly affected group. Prevention science is increasingly being organized around HIV testing as a launch point into an HIV prevention continuum for MSM who are not living with HIV and into an HIV care continuum for MSM who are living with HIV. An increasing HIV testing frequency among MSM might decrease future HIV infections by linking men who are living with HIV to antiretroviral care, resulting in viral suppression. Distributing HIV self-test (HIVST) kits is a strategy aimed at increasing HIV testing. Our previous modeling work suggests that the impact of HIV self-tests on transmission dynamics will depend not only on the frequency of tests and testers' behaviors but also on the epidemiological and testing characteristics of the population.

OBJECTIVE

The objective of our study was to develop an agent-based model to inform public health strategies for promoting safe and effective HIV self-tests to decrease the HIV incidence among MSM in Atlanta, GA, and Seattle, WA, cities representing profoundly different epidemiological settings.

METHODS

We adapted and extended a network- and agent-based stochastic simulation model of HIV transmission dynamics that was developed and parameterized to investigate racial disparities in HIV prevalence among MSM in Atlanta. The extension comprised several activities: adding a new set of model parameters for Seattle MSM; adding new parameters for tester types (ie, regular, risk-based, opportunistic-only, or never testers); adding parameters for simplified pre-exposure prophylaxis uptake following negative results for HIV tests; and developing a conceptual framework for the ways in which the provision of HIV self-tests might change testing behaviors. We derived city-specific parameters from previous cohort and cross-sectional studies on MSM in Atlanta and Seattle. Each simulated population comprised 10,000 MSM and targeted HIV prevalences are equivalent to 28% and 11% in Atlanta and Seattle, respectively.

RESULTS

Previous studies provided sufficient data to estimate the model parameters representing nuanced HIV testing patterns and HIV self-test distribution. We calibrated the models to simulate the epidemics representing Atlanta and Seattle, including matching the expected stable HIV prevalence. The revised model facilitated the estimation of changes in 10-year HIV incidence based on counterfactual scenarios of HIV self-test distribution strategies and their impact on testing behaviors.

CONCLUSIONS

We demonstrated that the extension of an existing agent-based HIV transmission model was sufficient to simulate the HIV epidemics among MSM in Atlanta and Seattle, to accommodate a more nuanced depiction of HIV testing behaviors than previous models, and to serve as a platform to investigate how HIV self-tests might impact testing and HIV transmission patterns among MSM in Atlanta and Seattle. In our future studies, we will use the model to test how different HIV self-test distribution strategies might affect HIV incidence among MSM.

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.

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.

Estimating the impact of universal antiretroviral therapy for HIV serodiscordant couples through home HIV testing: insights from mathematical models

INTRODUCTION

Antiretroviral therapy (ART) prevents HIV transmission within HIV serodiscordant couples (SDCs), but slow implementation and low uptake has limited its impact on population-level HIV incidence. Home HIV testing and counselling (HTC) campaigns could increase ART uptake among SDCs by incorporating couples' testing and ART referral. We estimated the reduction in adult HIV incidence achieved by incorporating universal ART for SDCs into home HTC campaigns in KwaZulu-Natal (KZN), South Africa, and southwestern (SW) Uganda.

METHODS

We constructed dynamic, stochastic, agent-based network models for each region. We compared adult HIV incidence after 10 years under three scenarios: (1) "Current Practice," (2) "Home HTC" with linkage to ART for eligible persons (CD4 <350) and (3) "ART for SDCs" regardless of CD4, delivered alongside home HTC.

RESULTS

ART for SDCs reduced HIV incidence by 38% versus Home HTC: from 1.12 (95% CI: 0.98-1.26) to 0.68 (0.54-0.82) cases per 100 person-years (py) in KZN, and from 0.56 (0.50-0.62) to 0.35 (0.30-0.39) cases per 100 py in SW Uganda. A quarter of incident HIV infections were averted over 10 years, and the proportion of virally suppressed HIV-positive persons increased approximately 15%.

CONCLUSIONS

Using home HTC to identify SDCs and deliver universal ART could avert substantially more new HIV infections than home HTC alone, with a smaller number needed to treat to prevent new HIV infections. Scale-up of home HTC will not diminish the effectiveness of targeting SDCs for treatment. Increasing rates of couples' testing, disclosure, and linkage to care is an efficient way to increase the impact of home HTC interventions on HIV incidence.

Estimating PMTCT's Impact on Heterosexual HIV Transmission: A Mathematical Modeling Analysis

INTRODUCTION

Prevention of mother-to-child HIV transmission (PMTCT) strategies include combined short-course antiretrovirals during pregnancy (Option A), triple-drug antiretroviral treament (ART) during pregnancy and breastfeeding (Option B), or lifelong ART (Option B+). The WHO also recommends ART for HIV treatment and prevention of sexual transmission of HIV. The impact of PMTCT strategies on prevention of sexual HIV transmission of HIV is not known. We estimated the population-level impact of PMTCT interventions on heterosexual HIV transmission in southwestern Uganda and KwaZulu-Natal, South Africa, two regions with different HIV prevalence and fertility rates.

MATERIALS AND METHODS

We constructed and validated dynamic, stochastic, network-based HIV transmission models for each region. PMTCT Options A, B, and B+ were simulated over ten years under three scenarios: 1) current ART and PMTCT coverage, 2) current ART and high PMTCT coverage, and 3) high ART and PMTCT coverage. We compared adult HIV incidence after ten years of each intervention to Option A (and current ART) at current coverage.

RESULTS

At current coverage, Options B and B+ reduced heterosexual HIV incidence by about 5% and 15%, respectively, in both countries. With current ART and high PMTCT coverage, Option B+ reduced HIV incidence by 35% in Uganda and 19% in South Africa, while Option B had smaller, but meaningful, reductions. The greatest reductions in HIV incidence were achieved with high ART and PMTCT coverage. In this scenario, all PMTCT strategies yielded similar results.

DISCUSSION

Implementation of Options B/B+ reduces adult HIV incidence, with greater effect (relative to Option A at current levels) in Uganda than South Africa. These results are likely driven by Uganda's higher fertility rates.

Conceptual framework and research methods for migration and HIV transmission dynamics

Migration and mobility have had a profound influence on the global HIV epidemic. We propose a network-dyadic conceptual model to interpret previous literature and inform the development of future research with respect to study design, measurement methods, and analytic approach. In this model, HIV transmission is driven by risk behaviors of migrants that emerges and is enabled by mobility, the bridging of sub-epidemics across space and time, and the displacement effects on the primary residential sending community for migrants. To investigate these causal pathways, empirical study designs must measure the relative timing of migratory events, sexual risk behaviors, and incident HIV infections. Network-based mathematical models using empirical data on partnerships help gain insight into the dynamic disease transmission systems. Although the network-dyadic conceptual model and related network methods may not address all questions related to migration and HIV, they provide a unified approach for future research on this important topic.

Place and sexual partnership transition among young American Indian and Alaska native women

Multiple challenges expose American Indian and Alaska Native (AIAN) women to high-risk sexual partnerships and increased risk for HIV/STI. Using a unique sample of sexually-active young AIAN women (n = 129), we examined characteristics of last three partners and whether transitional partnerships were associated with different risk profiles, including where partners met, lived, and had sex. Respondents were more likely to have met their previous or current secondary partner (P2) at a friend's or family setting (versus work or social setting) (AOR = 3.92; 95 % CI 1.31, 11.70). Condom use was less likely when meeting a partner at friend's or family settings (AOR = 0.17; 95 % CI 0.05, 0.59). Sexual intercourse with P2 (compared to P1) usually took place in "riskier" settings such as a car, bar, or outside (AOR = 4.15; 95 % CI 1.59, 10.68). Perceived "safe" places, e.g., friend's or family's house, were identified with risky behaviors; thus, homogeneous messaging campaigns may promote a false sense of safety.

Seroadaptation among men who have sex with men: emerging research themes

Seroadaptation describes a diverse set of potentially harm-reducing behaviors that use HIV status to inform sexual decision making. Men who have sex with men (MSM) in many settings adopt these practices, but their effectiveness at preventing HIV transmission is debated. Past modeling studies have demonstrated that serosorting is only effective at preventing HIV transmission when most men accurately know their HIV status, but additional modeling is needed to address the effectiveness of broader seroadaptive behaviors. The types of information withwhichMSMmake seroadaptive decisions is expanding to include viral load, treatment status, and HIV status based on home-use tests, and recent research has begun to examine the entire seroadaptive process, from an individual's intentions to seroadapt to their behaviors to their risk of acquiring or transmitting HIV and other STIs. More research is needed to craft clear public health messages about the risks and benefits of seroadaptive practices.

Short-term Mobility and Increased Partnership Concurrency among Men in Zimbabwe

BACKGROUND

Migration has long been understood as an underlying factor for HIV transmission, and sexual partner concurrency has been increasingly studied as an important component of HIV transmission dynamics. However, less work has examined the role of short-term mobility in sexual partner concurrency using a network approach. Short-term mobility may be a risk for HIV for the migrant's partner as well either through the partner's risk behaviors while the migrant is away, such as the partner having additional partners, or via exposure to the return migrant.

METHODS

Using data from the 2010-11 Zimbabwe Demographic and Health Survey, weighted generalized linear regression models were used to investigate the associations between short-term mobility and partnership concurrency at the individual and partnership levels.

RESULTS

At the individual level, we find strong evidence of an association between short-term mobility and concurrency. Men who traveled were more likely to have concurrent partnerships compared to men who did not travel and the relationship was non-linear: each trip was associated with a 2% higher probability of concurrency, with a diminishing risk at 60 trips (p<0.001). At the partnership level, short-term mobility by the male only or both partners was associated with male concurrency. Couples in which the female only traveled exhibited less male concurrency.

CONCLUSIONS

Short-term mobility has the ability to impact population-level transmission dynamics by facilitating partnership concurrency and thus onward HIV transmission. Short-term migrants may be an important population to target for HIV testing, treatment, or social and behavioral interventions to prevent the spread of HIV.

Concurrent partnerships, acute infection and HIV epidemic dynamics among young adults in Zimbabwe

This paper explores the roles of acute infection and concurrent partnerships in HIV transmission dynamics among young adults in Zimbabwe using realistic representations of the partnership network and all published estimates of stage-specific infectivity. We use dynamic exponential random graph models to estimate partnership network parameters from an empirical study of sexual behavior and drive a stochastic simulation of HIV transmission through this dynamic network. Our simulated networks match observed frequencies and durations of short- and long-term partnerships, with concurrency patterns specific to gender and partnership type. Our findings suggest that, at current behavior levels, the epidemic cannot be sustained in this population without both concurrency and acute infection; removing either brings transmission below the threshold for persistence. With both present, we estimate 20-25% of transmissions stem from acute-stage infections, 30-50% from chronic-stage, and 30-45% from AIDS-stage. The impact of acute infection is strongly moderated by concurrency. Reducing this impact by reducing concurrency could potentially end the current HIV epidemic in Zimbabwe.

Change in sexual activity 12 months after ART initiation among HIV-positive Mozambicans

We assessed sexual behaviors before and 12-months after ART initiation among 277 Mozambicans attending an HIV clinic. Measured behaviors included the number of sexual partners, condom use, concurrent relationships, disclosure of HIV status, alcohol use, and partners' serostatus. Compared to before ART initiation, increases were seen 12 months after ART in the proportion of participants who were sexually active (48% vs. 64% respondents, P < 0.001) and the proportion of participants with HIV-negative or unknown serostatus partners (45% vs. 80%, P < 0.001). Almost all (96%) concurrent partnerships reported at 12 months formed after ART initiation. Although reported correct and consist condom use increased, the number of unprotected sexual relationships remained the same (n = 45). Non-disclosure of HIV-serostatus to sexual partners was the only significant predictor of practicing unprotected sex with partners of HIV-negative or unknown serostatus. Sexual activity among HIV-positive persons on ART increased 12 months after ART initiation. Ongoing secondary transmission prevention programs addressing sexual activity with multiple partners, disclosure to partners and consistent condom use with serodisconcordant partners must be incorporated throughout HIV care programs.

Population decline induced by gonorrhoea and tuberculosis transmission: Micronesia during the Japanese occupation, 1919-45

The islands of Yap in Micronesia survived a period of severe depopulation during the Japanese occupation from 1919 to 1945. Using data from historical documents, supplemented by ethnographic evidence, we calibrate a simulation model that accounts for this phenomenon. Our model tracks the reproduction histories of a synthetic cohort of women in Yap, including effects of infertility due to gonorrhoea as well as tuberculosis mortality, and predicts the net reproduction rate (NRR). In this particular case and throughout history, human migrations and associated social and cultural interactions have frequently been accompanied by dramatic changes in patterns of disease transmission and substantial demographic consequences. Despite the broad emphasis on mortality as a measure of demographic consequences in the historical and contemporary literature, there are important instances where life expectancy at birth, fertility rates, and total population size are important demographic consequences. We find that gonorrhoea may have significantly contributed to depopulation during the Japanese occupation of Micronesia, due to repeated infections and high risk of sterility. Results of our model suggest that gonorrhoea alone could have reduced the net reproduction rate by 82%, whereas deaths from tuberculosis may have contributed to a 17% decline.

Discussion and revision of the mathematical modeling tool described in the previously published article "Modeling HIV Transmission risk among Mozambicans prior to their initiating highly active antiretroviral therapy"

Mathematical models are increasingly used in social and behavioral studies of HIV transmission; however, model structures must be chosen carefully to best answer the question at hand and conclusions must be interpreted cautiously. In Pearson et al. (2007), we presented a simple analytically tractable deterministic model to estimate the number of secondary HIV infections stemming from a population of HIV-positive Mozambicans and to evaluate how the estimate would change under different treatment and behavioral scenarios. In a subsequent application of the model with a different data set, we observed that the model produced an unduly conservative estimate of the number of new HIV-1 infections. In this brief report, our first aim is to describe a revision of the model to correct for this underestimation. Specifically, we recommend adjusting the population-level sexually transmitted infection (STI) parameters to be applicable to the individual-level model specification by accounting for the proportion of individuals uninfected with an STI. In applying the revised model to the original data, we noted an estimated 40 infections/1000 HIV-positive persons per year (versus the original 23 infections/1000 HIV-positive persons per year). In addition, the revised model estimated that highly active antiretroviral therapy (HAART) along with syphilis and herpes simplex virus type 2 (HSV-2) treatments combined could reduce HIV-1 transmission by 72% (versus 86% according to the original model). The second aim of this report is to discuss the advantages and disadvantages of mathematical models in the field and the implications of model interpretation. We caution that simple models should be used for heuristic purposes only. Since these models do not account for heterogeneity in the population and significantly simplify HIV transmission dynamics, they should be used to describe general characteristics of the epidemic and demonstrate the importance or sensitivity of parameters in the model.

Mathematical models for HIV transmission dynamics: tools for social and behavioral science research

HIV researchers have long appreciated the need to understand the social and behavioral determinants of HIV-related risk behavior, but the cumulative impact of individual behaviors on population-level HIV outcomes can be subtle and counterintuitive, and the methods for studying this are rarely part of a traditional social science or epidemiology training program. Mathematical models provide a way to examine the potential effects of the proximate biologic and behavioral determinants of HIV transmission dynamics, alone and in combination. The purpose of this article is to show how mathematical modeling studies have contributed to our understanding of the dynamics and disparities in the global spread of HIV. Our aims are to demonstrate the value that these analytic tools have for social and behavioral sciences in HIV prevention research, to identify gaps in the current literature, and to suggest directions for future research.

Modeling HIV transmission risk among Mozambicans prior to their initiating highly active antiretroviral therapy

Understanding sexual behavior and assessing transmission risk among people living with HIV-1 is crucial for effective HIV-1 prevention. We describe sexual behavior among HIV-positive persons initiating highly active antiretroviral therapy (HAART) in Beira, Mozambique. We present a Bernoulli process model (tool available online) to estimate the number of sexual partners who would acquire HIV-1 as a consequence of sexual contact with study participants within the prior three months. Baseline data were collected on 350 HAART-naive individuals 18-70 years of age from October 2004 to February 2005. In the three months prior to initiating HAART, 45% (n = 157) of participants had sexual relationships with 191 partners. Unprotected sex occurred in 70% of partnerships, with evidence suggesting unprotected sex was less likely with partners believed to be HIV-negative. Only 26% of the participants disclosed their serostatus to partners with a negative or unknown serostatus. Women were less likely to report concurrent relationships than were men (21 versus 66%; OR 0.13; 95%CI: 0.06, 0.26). Given baseline behaviors, the model estimated 23.2 infections/1,000 HIV-positive persons per year. The model demonstrated HAART along with syphilis and herpes simplex virus type 2 (HSV-2) treatment combined could reduce HIV-1 transmission by 87%; increasing condom use could reduce HIV-1 transmission by 67%.

Population and Environment

The interactions between human population dynamics and the environment have often been viewed mechanistically. This review elucidates the complexities and contextual specificities of population-environment relationships in a number of domains. It explores the ways in which demographers and other social scientists have sought to understand the relationships among a full range of population dynamics (e.g., population size, growth, density, age and sex composition, migration, urbanization, vital rates) and environmental changes. The chapter briefly reviews a number of the theories for understanding population and the environment and then proceeds to provide a state-of-the-art review of studies that have examined population dynamics and their relationship to five environmental issue areas. The review concludes by relating population-environment research to emerging work on human-environment systems.

Overweight in the Pacific: links between foreign dependence, global food trade, and obesity in the Federated States of Micronesia

The Federated States of Micronesia (FSM) has received considerable attention for their alarming rates of overweight and obesity. On Kosrae, one of the four districts in the FSM, 88% of adults aged 20 or older are overweight (BMI > 25), 59% are obese (BMI > 30), and 24% are extremely obese (BMI > 35). Recent genetic studies in Kosrae have shown that obesity is a highly heritable trait, and more work is underway to identify obesity genes in humans. However, less attention has been given to potential social and developmental causes of obesity in the FSM. This paper outlines the long history of foreign rule and social change over the last 100 years, and suggests that a combination of dietary change influenced by foreigners, dependence on foreign aid, and the ease of global food trade contributed to poor diet and increased rates of obesity in Micronesia. The last section of the paper highlights the Pacific tuna trade as an example of how foreign dependence and global food trade exacerbates their obesity epidemic.

Do Migrants Degrade Coastal Environments? Migration, Natural Resource Extraction and Poverty in North Sulawesi, Indonesia

Recent literature on migration and the environment has identified key mediating variables such as how migrants extract resources from the environment for their livelihoods, the rate and efficiency of extraction, and the social and economic context within which their extraction occurs. This paper investigates these variables in a new ecological setting using data from coastal fishing villages in North Sulawesi, Indonesia. We do not find as many differences between migrant and non-migrant families regarding destructive fishing behavior, technology, and investment as might have been expected from earlier theories. Instead, the context and timing of migrant assimilation seems to be more important in explaining apparent associations of migration and environmental impacts than simply migrants themselves. This finding fits well with recent literature in the field of international migration and immigrant incorporation.