Social determinants of adult sex ratios and racial/ethnic disparities in transmission of HIV and other sexually transmitted infections in the USA

Inequity in US Racial/Ethnic Infant Health and Birth Outcomes: The Role of the Adult Sex Ratio as a Potential Indicator of Structural Anti-Black Racism

BACKGROUND

Structural racism accounts for inequity in health outcomes in ways that are difficult to measure. To conduct more actionable research and measure the impact of intervention programs, there is a need to develop indicator measures of structural racism. One potential candidate is the Adult Sex Ratio (ASR), which was identified by Du Bois as an important indicator of social life functioning over 100 years ago and has remained significant up to the present day. This study investigated the utility of this measure.

METHODS

We compared birth/infant health outcomes using the US 2000 Linked Birth/Infant Death Cohort Data Set matched with 2000 Census data on adult sex ratios in multilevel logistic regression models, stratified by the racial/ethnic category of the mothers.

RESULTS

In an adjusted model, the odds of infant death was 21% higher among non-Hispanic Black (NHB) women living in counties in the lowest ASR tertile category when compared to their counterparts in counties in the highest ASR tertile. Similarly, the odds of giving birth to a preterm or a low birth weight infant were each 20% higher among NHB women living in counties in the lowest ASR tertile compared to their counterparts in counties in the highest ASR tertile.

CONCLUSION

ASRs may serve as a useful indicator of anti-Black structural racism at the local level. More research is needed to determine the circumstances under which this factor may serve to improve assessment of structural racism and facilitate health equity research.

Sex ratios and gender norms: why both are needed to understand sexual conflict in humans

Sexual conflict theory has been successfully applied to predict how in non-human animal populations, sex ratios can lead to conflicting reproductive interests of females and males and affect their bargaining positions in resolving such conflicts of interests. Recently this theory has been extended to understand the resolution of sexual conflict in humans, but with mixed success. We argue that an underappreciation of the complex relationship between gender norms and sex ratios has hampered a successful understanding of sexual conflict in humans. In this paper, we review and expand upon existing theory to increase its applicability to humans, where gender norms regulate sex ratio effects on sexual conflict. Gender norms constrain who is on the marriage market and how they are valued, and may affect reproductive decision-making power. Gender norms can also directly affect sex ratios, and we hypothesize that they structure how individuals respond to market value gained or lost through biased sex ratios. Importantly, gender norms are in part a product of women's and men's sometimes conflicting reproductive interests, but these norms are also subject to other evolutionary processes. An integration of sexual conflict theory and cultural evolutionary theory is required to allow for a full understanding of sexual conflict in humans.

Reducing Human Immunodeficiency Virus and Sexually Transmitted Infections Risk in African American Women with At-Risk Male Partners: A Randomized Trial

Background: We examined the efficacy of the Females of African American Legacy Empowering Self (FemAALES) intervention in a cohort of 203 publicly insured Black women in Los Angeles. Materials and Methods: Women who reported recent sex with a male partner who was at increased risk for infection by human immunodeficiency virus (HIV) and sexually transmitted infections (STI) were randomized to the six-session FemAALES intervention or to a single client-centered family planning and STI/HIV counseling session. Participants were followed at 3 and 9 months post-intervention. To investigate between-group behavioral changes in condomless sex in the prior 90 days and other HIV/STI risks, we used generalized estimating equations that accounted for repeated observations in individuals. Results: Most participants (mean age 34 ± 11 standard deviation) were low-income and unemployed, despite three-quarters having completed high school or the equivalent. The most common HIV/STI risk factors among recent male partners were incarceration (58.8%) and concurrent sex with other women (72.2%). At 3 months, the FemAALEs group showed a larger increase in the odds of asking their partner to test (adjusted odds ratio = 2.14; 95% confidence interval [CI], 1.02-4.47; p = 0.0431) and in sexual health self-efficacy scores (adjβ = 1.82; 95% CI, 0.02-3.62; p = 0.0471) compared to the control group, although these changes did not hold at 9 months. Both groups showed statistically significant declines in the frequency of several sexual risk factors between baseline and 9 months. Conclusion: Although we did not find evidence that the FemAALES intervention was more efficacious than the less-intensive control condition in reducing sexual risk behaviors, the overall declines in risk behaviors we observed warrant further research. ClinicalTrials.gov (Identifier: NCT02189876).

The contingent effect of incarceration on state health outcomes

Introduction

This study examines how growth in the population of former prisoners affects rates of communicable diseases such as tuberculosis, syphilis, chlamydia, and HIV.

Methods

We estimate state-level fixed effects count models showing how the former prisoner population affected communicable disease in U.S. states from 1987 to 2010, a period of dramatic growth in incarceration.

Results

We find contingent effects, based on how specific diseases are recognized, tested, and treated in prisons. The rate of former prisoners increases diseases that are poorly addressed in the prison health care system (e.g., chlamydia), but decreases diseases that are routinely tested and treated (e.g., tuberculosis). For HIV, the relationship has shifted in response to specific treatment mandates and protocols. Data on prison healthcare spending tracks these contingencies.

Discussion

Improving the health of prisoners can improve the health of the communities to which they return. We consider these results in light of the relative quality of detection and treatment available to underserved populations within and outside prisons.

Diverging Neisseria gonorrhoeae Morbidity in Non-Hispanic Black and White Females: Application of Group-Based Trajectory Modeling to Trends in County-Level Morbidity 2003-2018

National trends in gonorrhea rates may obscure informative local variations in morbidity. We used group-based trajectory models to identify groups of counties with similar gonorrhea rate trajectories among non-Hispanic White (NHW) and non-Hispanic Black (NHB) females using county-level data on gonorrhea cases in US females from 2003 to 2018. We assessed models with 1-15 groups and selected final models based on fit statistics and identification of divergent trajectory groups with distinct intercepts and/or slopes. We mapped counties by assigned trajectory group and examined the association of county characteristics with group membership. We identified 7 distinct gonorrhea trajectory groups for NHW females and 9 distinct trajectory groups for NHB females. All identified groups for NHW female morbidity experienced increasing gonorrhea rates with a limited range (11.6-183.3/100,000 NHW females in 2018); trajectories of NHB female morbidity varied widely in rates (146.6-966.0/1000 NHB females in 2018) and included 3 groups of counties that experienced a net decline in gonorrhea rates. Counties with higher NHW female morbidity had lower adult sex ratios, lower health insurance coverage, and lower marital rates among NHW adults. Counties with higher NHB female morbidity were more urban, experienced higher rates of poverty, and had lower rates of marriage among NHB adults. Morbidity patterns did not always follow geographic proximity, which could be explained by variation in social determinants of health. Our results demonstrated a highly heterogenous gonorrhea epidemic among NHW and NHB US females, which should prompt further analysis into the differential drivers of gonorrhea morbidity.

Lifetime prevalence of syphilis infection among predominantly Black sexual and gender minorities living with HIV in Atlanta, Georgia: a cross-sectional analysis

OBJECTIVES

Syphilis infection disproportionately impacts Black sexual and gender minorities (SGM) in the United States. The extent of this impact among those living with HIV has been minimally examined. This study sought to examine lifetime syphilis prevalence and associated factors in a community sample of predominantly Black SGM living with HIV in the Southeastern US.

DESIGN

Participants (N = 174) enrolled in a stigma-mitigation trial for people living with HIV in Atlanta, Georgia, completed a sub-study involving testing for Treponema pallidum antibodies, indicative of lifetime syphilis infection. We performed chi-square and Fisher's exact tests to assess sociodemographic and healthcare differences by presence/absence of lifetime syphilis infection.

RESULTS

Most participants identified as non-Hispanic Black (n = 142/174; 81.6%) and cisgender male (n = 146/174; 83.9%). More than two thirds (n = 120/174) identified as gay/homosexual. We documented a 55.7% (n = 97/174) lifetime prevalence of syphilis infection and observed differences by sexual identity, with 77.3% (n = 75/97) of those screening positive reporting gay/homosexual identity relative to 58.4% (n = 45/77) of those screening negative (chi-square[1] = 7.8, p < 0.010).

CONCLUSION

Findings underscore how syphilis prevention efforts have missed the most marginalized, warranting a renewed, comprehensive strategy for improving the sexual health of Black SGM. Embedding targeted, respectful community engagement, expanded testing access, and healthcare provider training into broader sexual health and psychosocial wellness efforts is needed.

Adult sex ratios: causes of variation and implications for animal and human societies

Converging lines of inquiry from across the social and biological sciences target the adult sex ratio (ASR; the proportion of males in the adult population) as a fundamental population-level determinant of behavior. The ASR, which indicates the relative number of potential mates to competitors in a population, frames the selective arena for competition, mate choice, and social interactions. Here we review a growing literature, focusing on methodological developments that sharpen knowledge of the demographic variables underlying ASR variation, experiments that enhance understanding of the consequences of ASR imbalance across societies, and phylogenetic analyses that provide novel insights into social evolution. We additionally highlight areas where research advances are expected to make accelerating contributions across the social sciences, evolutionary biology, and biodiversity conservation.

Too Many Males or Too Many Females? Classroom Sex Ratio, Life History Strategies and Risk-Taking Behaviors

Prior research finds that sex ratio, defined as the proportion of males and females in a given context, is related to engagement in risk-taking behaviors. However, most research operationalizes sex ratio at a local context (e.g., regional or county), which fails to reflect with precision the sex ratios contexts of individuals at a closer level. Furthermore, the relationship between sex ratio and risk-taking behaviors may be affected by individuals’ life history strategy, with previous studies showing fast life history strategies linked to risk-taking behaviors, compared to slow life history strategies. The present study analyzes the relationship between classroom sex ratio and risk-taking behaviors and the interaction between classroom sex ratio and life history strategy in adolescents. The sample comprised 1214 participants nested in 57 classrooms, 49.75% females, 91.5% Spanish and a mean age of 16.15 years (SD = 1.23, range 14–21). Results from multilevel modeling showed a negative relation between classroom sex ratio and risk-taking behaviors in female adolescents with faster life history strategy. By contrast, classroom sex ratio in male adolescents related positively to risk-taking behaviors but did not interact with life history strategy. These findings underscore the importance of studying proximate sex ratio on risk-taking behaviors in adolescents and underline its potential influence in the development and expression of life history strategies.

An Analysis of Sex Practices and Behaviors Among African Americans in Sexually Concurrent and Sexually Exclusive Relationships

Historically, sexually concurrent relationships have been associated with increased risk for sexually transmitted infections (STIs), including HIV. Due to socio-structural factors, African Americans (AAs) have higher rates of STIs compared to other racial groups and are more likely to engage in sexually concurrent (SC) relationships. Current research has challenged the assumption that SC is the only risky relationship type, suggesting that both SC and sexually exclusive (SE) relationships are at equal risk of STI and HIV acquisition and that both relationship types should engage in safer sex practices. This study aimed to compare sex practices and behaviors among AA men and women in SC and SE relationships (N = 652). Results demonstrate differences in sexual practices and behaviors between SC and SE men and women. Overall, SC and SE women report condom use with male partners less frequently than SC and SE men. SC men were more likely to report substance use during sex compared to SC and SE women. Pre-exposure prophylaxis (PrEP) use did not differ across groups. SE men were less likely to report STI testing and diagnosis compared to SC women. Findings support the need to focus on culturally and gender-specific safer sex interventions among AAs.

The adult sex ratio of European regions predicts female, but not male, subjective well-being

In recent years, researc in subjective well-being has found several ecological factors that may underpin societal differences in happiness. The adult sex ratio, the number of males relative to females in an environment, influences many behaviours in both humans and non-human animals. However, the possible influence of the sex ratio on subjective well-being has received little attention. I investigated the relationship between the adult sex ratio and subjective well-being in over 29,000 respondents from 133 regions of Europe. I find that women report lower subjective well-being in areas with more female-biased sex ratios, but males’ well-being was unaffected. I did not find that the sex ratio influences the sex specific probability of marriage, or marriage rates overall. I also find that increased population density is associated with lower well-being. Drawing from sociological and evolutionary theories, I suggest that results may be due to females’ decreased bargaining power in the dating market.

Evidence for HIV transmission across key populations: a longitudinal analysis of HIV and AIDS rates among Black people who inject drugs and Black heterosexuals in 84 large U.S. metropolitan areas, 2008-2016

PURPOSE

To assess cross-population linkages in HIV/AIDS epidemics, we tested the hypothesis that the number of newly diagnosed AIDS cases among Black people who inject drugs (PWID) was positively related to the natural log of the rate of newly diagnosed HIV infections among Black non-PWID heterosexuals in 84 large U.S. metropolitan statistical areas (MSAs) in 2008-2016.

METHODS

We estimated a multilevel model centering the time-varying continuous exposures at baseline between the independent (Black PWID AIDS rates) and dependent (HIV diagnoses rate among Black heterosexuals) variables.

RESULTS

At MSA level, baseline (standardized β = 0.12) Black PWID AIDS rates and change in these rates over time (standardized β = 0.11) were positively associated with the log of new HIV diagnoses rates among Black heterosexuals. Thus, MSAs with Black PWID AIDS rates that were 1 standard deviation= higher at baseline also had rates of newly diagnosed HIV infections among Black non-PWID heterosexuals that were 10.3% higher. A 1 standard deviation increase in independent variable over time corresponded to a 7.8% increase in dependent variable.

CONCLUSIONS

Black PWID AIDS rates may predict HIV rates among non-PWID Black heterosexuals. Effective HIV programming may be predicated, in part, on addressing intertwining of HIV epidemics across populations.

The role of dispersal and school attendance on reproductive dynamics in small, dispersed populations: Choyeros of Baja California Sur, Mexico

Individuals from small populations face challenges to initiating reproduction because stochastic demographic processes create local mate scarcity. In response, flexible dispersal patterns that facilitate the movement of individuals across groups have been argued to reduce mate search costs and inbreeding depression. Furthermore, factors that aggregate dispersed peoples, such as rural schools, could lower mate search costs through expansion of mating markets. However, research suggests that dispersal and school attendance are costly to fertility, causing individuals to delay marriage and reproduction. Here, we investigate the role of dispersal and school attendance on marriage and reproductive outcomes using a sample of 54 married couples from four small, dispersed ranching communities in Baja California Sur, Mexico. Our analyses yield three sets of results that challenge conventional expectations. First, we find no evidence that dispersal is associated with later age at marriage or first reproduction for women. For men, dispersal is associated with younger ages of marriage than those who stay in their natal area. Second, in contrast to research suggesting that dispersal decreases inbreeding, we find that female dispersal is associated with an increase in genetic relatedness among marriage partners. This finding suggests that human dispersal promotes female social support from genetic kin in novel locales for raising offspring. Third, counter to typical results on the role of education on reproductive timing, school attendance is associated with younger age at marriage for men and younger age at first birth for women. While we temper causal interpretations and claims of generalizability beyond our study site given our small sample sizes (a feature of small populations), we nonetheless argue that factors like dispersal and school attendance, which are typically associated with delayed reproduction in large population, may actually lower mate search costs in small, dispersed populations with minimal access to labor markets.

Relationship of Racial Residential Segregation to Newly Diagnosed Cases of HIV among Black Heterosexuals in US Metropolitan Areas, 2008-2015

Social science and public health literature has framed residential segregation as a potent structural determinant of the higher HIV burden among black heterosexuals, but empirical evidence has been limited. The purpose of this study is to test, for the first time, the association between racial segregation and newly diagnosed heterosexually acquired HIV cases among black adults and adolescents in 95 large US metropolitan statistical areas (MSAs) in 2008-2015. We operationalized racial segregation (the main exposure) using Massey and Denton's isolation index for black residents; the outcome was the rate of newly diagnosed HIV cases per 10,000 black adult heterosexuals. We tested the relationship of segregation to this outcome using multilevel multivariate models of longitudinal (2008-2015) MSA-level data, controlling for potential confounders and time. All covariates were lagged by 1 year and centered on baseline values. We preliminarily explored mediation of the focal relationship by inequalities in education, employment, and poverty rates. Segregation was positively associated with the outcome: a one standard deviation decrease in baseline isolation was associated with a 16.2% reduction in the rate of new HIV diagnoses; one standard deviation reduction in isolation over time was associated with 4.6% decrease in the outcome. Exploratory mediation analyses suggest that black/white socioeconomic inequality may mediate the relationship between segregation and HIV. Our study suggests that residential segregation may be a distal determinant of HIV among black heterosexuals. The findings further emphasize the need to address segregation as part of a comprehensive strategy to reduce racial inequities in HIV.

States with higher minimum wages have lower STI rates among women: Results of an ecological study of 66 US metropolitan areas, 2003-2015

Prior research has found that places and people that are more economically disadvantaged have higher rates and risks, respectively, of sexually transmitted infections (STIs). Economic disadvantages at the level of places and people, however, are themselves influenced by economic policies. To enhance the policy relevance of STI research, we explore, for the first time, the relationship between state-level minimum wage policies and STI rates among women in a cohort of 66 large metropolitan statistical areas (MSAs) in the US spanning 2003-2015. Our annual state-level minimum wage measure was adjusted for inflation and cost of living. STI outcomes (rates of primary and secondary syphilis, gonorrhea and chlamydia per 100,000 women) were obtained from the CDC. We used multivariable hierarchical linear models to test the hypothesis that higher minimum wages would be associated with lower STI rates. We preliminarily explored possible socioeconomic mediators of the minimum wage/STI relationship (e.g., MSA-level rates of poverty, employment, and incarceration). We found that a $1 increase in the price-adjusted minimum wage over time was associated with a 19.7% decrease in syphilis rates among women and with an 8.5% drop in gonorrhea rates among women. The association between minimum wage and chlamydia rates did not meet our cutpoint for substantive significance. Preliminary mediation analyses suggest that MSA-level employment among women may mediate the relationship between minimum wage and gonorrhea. Consistent with an emerging body of research on minimum wage and health, our findings suggest that increasing the minimum wage may have a protective effect on STI rates among women. If other studies support this finding, public health strategies to reduce STIs among women should include advocating for a higher minimum wage.

Trends in Geographic Rates of HIV Diagnoses Among Black Females in the United States, 2010-2015

BACKGROUND

HIV diagnoses among females in the United States declined 22% from 2010 to 2015, including a 27% decline in diagnoses among black females. Despite this progress, disparities persist. Black females accounted for 60% of new HIV diagnoses among females in 2015. Geographic disparities also exist. This article describes geographic differences in HIV diagnoses among black females in the United States, from 2010 to 2015.

MATERIALS AND METHODS

We examined HIV surveillance data from 2010 to 2015 to determine in which geographic areas decreases or increases in HIV diagnoses occurred. We used data from the National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention's (NCHHSTP) AtlasPlus to calculate percent changes in HIV diagnosis rates by geographic region for black females ≥13 years of age.

RESULTS

The number of new HIV diagnoses declined 27% among black females from 2010 to 2015. The highest rates of HIV diagnosis per 100,000 population of black females, from 2010 to 2015, were in the Northeast and the South. In 2015, five of the eight states reporting the highest rates of HIV diagnosis (i.e., the highest quartile) were in the South.

CONCLUSIONS

HIV diagnosis rates decreased nationally among black females, but the decreases were not uniform within regions or across the United States. Some states experienced increases, and black females in the South and Northeast remain disproportionately affected. Additional research is needed to ascertain factors associated with the increases to continue progress toward reducing HIV-related disparities among females in the United States.

Sex roles and sexual selection: lessons from a dynamic model system

Our understanding of sexual selection has greatly improved during the last decades. The focus is no longer solely on males, but also on how female competition and male mate choice shape ornamentation and other sexually selected traits in females. At the same time, the focus has shifted from documenting sexual selection to exploring variation and spatiotemporal dynamics of sexual selection, and their evolutionary consequences. Here, I review insights from a model system with exceptionally dynamic sexual selection, the two-spotted goby fish Gobiusculus flavescens. The species displays a complete reversal of sex roles over a 3-month breeding season. The reversal is driven by a dramatic change in the operational sex ratio, which is heavily male-biased at the start of the season and heavily female-biased late in the season. Early in the season, breeding-ready males outnumber mature females, causing males to be highly competitive, and leading to sexual selection on males. Late in the season, mating-ready females are in excess, engage more in courtship and aggression than males, and rarely reject mating opportunities. With typically many females simultaneously courting available males late in the season, males become selective and prefer more colorful females. This variable sexual selection regime likely explains why both male and female G. flavescens have ornamental colors. The G. flavescens model system reveals that sexual behavior and sexual selection can be astonishingly dynamic in response to short-term fluctuations in mating competition. Future work should explore whether sexual selection is equally dynamic on a spatial scale, and related spatiotemporal dynamics.

Adult sex ratios and reproductive strategies: a critical re-examination of sex differences in human and animal societies

It is increasingly recognized that the relative proportion of potential mates to competitors in a population impacts a range of sex-specific behaviours and in particular mating and reproduction. However, while the adult sex ratio (ASR) has long been recognized as an important link between demography and behaviour, this relationship remains understudied. Here, we introduce the first inter-disciplinary collection of research on the causes and consequences of variation in the ASR in human and animal societies. This important topic is relevant to a wide audience of both social and biological scientists due to the central role that the relative number of males to females in a population plays for the evolution of, and contemporary variation in, sex roles across groups, species and higher taxa. The articles in this theme issue cover research on ASR across a variety of taxa and topics. They offer critical re-evaluations of theoretical foundations within both evolutionary and non-evolutionary fields, and propose innovative methodological approaches, present new empirical examples of behavioural consequences of ASR variation and reveal that the ASR plays a major role in determining population viability, especially in small populations and species with labile sex determination. This introductory paper puts the contributions of the theme issue into a broader context, identifies general trends across the literature and formulates directions for future research.This article is part of the themed issue 'Adult sex ratios and reproductive decisions: a critical re-examination of sex differences in human and animal societies'.

Adult sex ratio and social status predict mating and parenting strategies in Northern Ireland

Evidence from animal species indicates that a male-biased adult sex ratio (ASR) can lead to higher levels of male parental investment and that there is heterogeneity in behavioural responses to mate scarcity depending on mate value. In humans, however, there is little consistent evidence of the effect of the ASR on pair-bond stability and parental investment and even less of how it varies by an individual's mate value. In this paper we use detailed census data from Northern Ireland to test the association between the ASR and pair-bond stability and parental investment by social status (education and social class) as a proxy for mate value. We find evidence that female, but not male, cohabitation is associated with the ASR. In female-biased areas women with low education are less likely to be in a stable pair-bond than highly educated women, but in male-biased areas women with the lowest education are as likely to be in a stable pair-bond as their most highly educated peers. For both sexes risk of separation is greater at female-biased sex ratios. Lastly, our data show a weak relationship between parental investment and the ASR that depends on social class. We discuss these results in the light of recent reformulations of parental investment theory.This article is part of the themed issue 'Adult sex ratios and reproductive decisions: a critical re-examination of sex differences in human and animal societies'.