This study was the first to our knowledge to empirically examine the association of racial residential segregation with gonorrhea rates, the second most common STI, among Black persons in the United States. Isolation and unevenness and, to a lesser extent, centralization predicted gonorrhea rates, whereas other dimensions (i.e., concentration and clustering) did not. These findings partially coincide with Acevedo-Garcia's conceptual model, describing how segregation may affect infectious disease risk.22
The isolation index, which measures the extent to which Black people are exposed in large part to only other Black people, was associated with gonorrhea rates, and this association was modified by age. Conceptually, high isolation of Black persons from White persons may lead to increased rates of STIs among Black persons because those who are likely to acquire infection are sexual contacts of those already infected (i.e., those exposed to the infectious agent). Studies examining sexual networks and gonorrhea infection have found that high sexual isolation (i.e., the tendency of individuals to select sexual partners among members of the same group) maintains the presence of groups within which transmission occurs.22,45
Because individuals tend to select sexual partners in the area in which they live (i.e., spatial assortativity),46
sexual isolation may be affected by geographic isolation. As a result, isolation of infected and susceptible persons in a geographic area will increase the likelihood that core network members, or individuals at high risk for infection, will have sexual intercourse and spread the infection to individuals with few sexual partners within that area.5,22,31,46,47
Isolation may increase the risk for gonorrhea through its effect on social factors as well. Social norms—which also can be transmitted—have been shown to be associated with sexual risk among adolescents and among Black women.48–50
In isolated communities, within-group norms for risky sexual behavior might be strengthened.25
Age moderated the isolation–gonorrhea rate association; the association was stronger among the younger age groups. Because they are experiencing major transitions, the social environment may confer more influence for younger individuals.51
We hypothesized that concentration of Black individuals in more densely settled areas may lead to higher rates of STI transmission among Black individuals because of denser sexual networks (i.e., more interconnectedness between sexual contacts)46
and by concentrating economic and social disadvantage,9,24,29,31,37,52,53
but it was not associated with gonorrhea rates among Black individuals in our analysis.
Centralization—the tendency of Black residents to live nearer to the center of the MSA relative to White residents—was marginally associated with gonorrhea rates overall. High centralization, which may be an indicator for crowding, poor neighborhood environment, and, consequently, a lack of social control, can affect individual behaviors by encouraging risky behaviors, including crime, drug use, and risky sexual behaviors.9,22,25,31,54
This risky behavior may lead to higher rates of transmission of STIs among those confined to living in these areas. Several studies have found an association of neighborhood physical environment with gonorrhea rates in US cities.31,55,56
We did not find any evidence of an association between clustering and gonorrhea rates, which was consistent with Acevedo-Garcia's model. However, in contrast to the model, we did find that unevenness was associated with gonorrhea rates. Unevenness is conceptually related to isolation in that if an area is highly uneven, Black people are not distributed evenly across neighborhoods in an MSA and live in separate neighborhoods. Therefore, in highly uneven areas, Black persons live on average in neighborhoods with a high percentage of Black residents, resulting in Black people being isolated from White people. Additionally, isolation and unevenness capture a summary of the racial composition of neighborhoods in a metropolitan area, whereas the other dimensions capture the spatial distribution of these neighborhoods. Therefore, isolation and unevenness may be functioning similarly in this context. Interestingly, these dimensions are the most commonly tested in the health literature. Although the research on the segregation–sexual risk associations is still too nascent to exclude other mechanisms, this may suggest that testing these dimensions may be sufficient in the future.
Hypersegregation, which assumes that all dimensions are equally important, was not associated with gonorrhea rates. However, as shown by the results, certain dimensions were not associated with gonorrhea, so this measure may not be a meaningful summary of elevated risk in this context.
These associations of isolation, centralization, and unevenness with gonorrhea rates remained after adjusting for MSA-level covariates, including region, population size, density, socioeconomic position, and racial composition. This suggests that segregation is associated with gonorrhea rates above and beyond its effect on MSA socioeconomic position. Socioeconomic position was positively associated with gonor-rhea (RR = 1.05; 95% CI = 1.02, 1.08), and even though it may be a partial mediator, it did not completely explain the association between segregation and gonorrhea rates. This finding is supported by previous studies.24
Additionally, although neighborhood racial composition has been shown to be associated with rates of gonorrhea,57
in our analyses, MSA racial composition was not associated with gonorrhea among Black individuals, and models without MSA racial composition did not differ substantially from models with racial composition, suggesting that the observed associations were not artifacts of racial composition. This finding is supported by previous research among injection drug users58
and may indicate that the racial composition of neighborhoods and their spatial organization explain disparities in risk rather than simply the racial composition of the entire MSA.
Although this novel study was the first to use national data to directly assess the association of racial residential segregation with sexual risk in the United States, it had limitations. First, gonorrhea infections can be asymptomatic and therefore undiagnosed, and screening practices to detect infections may vary by gender and geography.8,59
Detected cases also may be underreported. For example, compared with White persons, minority persons more often seek STI care in public clinics, which may be more likely to report cases than would private providers.59
If differential diagnosis and reporting are also related to MSA racial residential segregation, then bias could be introduced. Because of our exclusion criteria, our sample may not be representative of all metropolitan areas in the United States. Additionally, this study examined only MSA-level covariates and did not include neighborhood-or individual-level measures of risk, which might help elucidate the mechanisms and account for potential confounding.24
Even though associations were seen even after adjusting for MSA-level variables, we may have underestimated the real effect because some of these variables (e.g., socioeconomic position) may be on the causal pathway.28
Finally, numerous comparisons were made, which could have resulted in significant findings by chance. However, because these findings were relatively consistent across strata of sex and age, these findings, taken as a whole, are not likely the result of chance alone.
Although this study was limited to Black people, the findings suggest that racial residential segregation, a characteristic that differentially affects Black and White persons, may help to explain the large racial disparity in gonorrhea rates, and future studies should aim to directly test this. Additionally, our findings suggest that interventions to reduce sexual risk that account for racial residential segregation may be needed. Interventions may have to be adapted in highly segregated communities to account for the social context that put individuals at risk for these infections. For example, an intervention to reduce STI prevalence among Black individuals living in segregated areas may include a focus on empowering individuals to make systemic changes in their community that aim to reduce racial residential segregation. Although structural interventions that directly address the factors that created or perpetuate racial residential segregation—such as programs that aim to reduce unfair housing policies and discriminatory practices in the housing market and increase affordable housing60,61
—are often seen as distal to health outcomes, they could have broad benefit by affecting sexual risk and reducing health disparities as well as other negative health, social, and economic outcomes.30