Kaplan, Mark S. DrPH*; Crespo, Carlos J. DrPH*; Huguet, Nathalie PhD*; Marks, Gary PhD†
SEXUALLY TRANSMITTED DISEASES (STDs) REMAIN an intractable public health problem in the United States.1 Nearly 19 million STDs occurred in the United States in 2000.2 The 2 most commonly reported infectious diseases in the United States are Chlamydia trachomatis and Neisseria gonorrhea. In 2006, there were 1,030,911 cases (347.8 per 100,000) of genital chlamydia infection and 358,366 cases (120.9 per 100,000) of gonorrhea reported in the United States.3 It is likely that both infectious diseases are substantially underdiagnosed and underreported.
Wide ethnic and racial disparities persist in the rates of reported STDs.3,4 According to the Institute of Medicine,1 serological population surveys of markers for STDs confirm higher prevalence of some STDs among black and Hispanics compared with the European-American population. Specifically, blacks and Hispanics have higher reported rates of chlamydia and gonorrhea than European Americans.1 Race and ethnicity are risk markers that correlate with other more fundamental determinants of health status such as poverty, access to quality health care, health care seeking behavior, illicit drug use, and other types of culturally influenced behaviors such as dietary practices.3
Over the years, a body of research has emerged pointing to a robust connection between conditions of the social environment and health status.5–7 One widely held view (“urban health penalty”) holds that segregated and impoverished inner-city neighborhoods lead to a disproportionate burden of poor health among racial and ethnic minority populations.8,9 Historically, the effect of poverty and segregation on a broad range of infectious diseases has been observed with tuberculosis, STD, and HIV.10 On the other hand, there is growing evidence that living in ethnically homogeneous urban communities might confer advantage by exposing residents to a salutogenic (i.e., health promoting) social environment. For example, Cagney et al.11 found that foreign-born Latinos embedded in a neighborhood that had a high percentage of foreign-born residents experienced a significantly lower prevalence of asthma and other breathing problems.
The purpose of this study was to examine the association of Hispanic and black community homogeneity with objectively measured incidence rates of 2 bacterial STDs (gonorrhea and chlamydia) in those communities. Our analysis statistically controlled for poverty level, unemployment, age, and education. Thus, our results may provide new insights on how neighborhood ethnic composition is related to health status apart from established neighborhood socioeconomic conditions.
Materials and Methods
The sample consisted of 77 community areas with relatively stable boundaries in Chicago, IL. These community areas, also referred to as neighborhoods, were developed based upon social, cultural, and geographic factors nearly 70 years ago by the University of Chicago Social Sciences Research Committee.12 We used gonorrhea and chlamydia incidence data for 2002 for the community areas (vital statistics obtained from Chicago Department of Public Health) and Chicago census data from 2000 to model several demographic factors in our analysis. Health care workers and laboratories are required to report all positive diagnoses of gonorrhea and chlamydia to the Chicago Department of Public Health (J. Broad, personal communication, October 2006).
The dependent variables were chlamydia and gonococcal incidence rates per 100,000 persons in 2002. The primary correlate of interest was percentage of the population in each of the 77 communities that was Hispanic or black in 2000. Owing to the relatively high level of collinearity (r = −0.59, P <0.001) between the percent Hispanic and the percent black in a community, a single variable with 3 subgroups was created. One subgroup represents relatively homogeneous Hispanic neighborhoods in which 60% or more of individuals are Hispanic (n = 10), a second subgroup represents relatively homogeneous black neighborhoods in which 60% or more are black (n = 29), and a third subgroup that represents neighborhoods with less than 60% Hispanic and less than 60% black (n = 38). This 60% cut-point has been previously used in studies examining incidence of cancer by neighborhood ethnic composition.13 Other demographic variables in our model, identified in previous research as risk factors for STDs, included the percent of community residents with incomes below the federally defined poverty level, the percent of residents aged 25 years and older who had received a high school diploma or its equivalent (high school graduates), the percent of residents aged 15 to 44 years, and the percent of residents aged 16 and older who were without work and actively seeking work (unemployed).
The analyses involved community-level demographic variables that were based on individual-level data obtained from census sources compiled by the Chicago Department of Public Health. A bivariate descriptive table displays the gonorrhea and chlamydia incidence rates per 100,000 by demographic subgroups from census tract information. Multiple linear regression analyses (one for each STD) examined the association of the demographic variables with the STD incidence rates. For the community ethnic-homogeneity variable, the subgroup representing homogeneous Hispanic communities served as the referent. Each of the other demographic variables was dummy coded in the regression analysis (cut-points can be seen in Table 1). The variables were included in the regression equation simultaneously; thus the finding for one variable was statistically adjusted for the effects of the others. We present unstandardized and standardized regression coefficients, standard errors, and an intercept value or constant for the equation. The R2 values reflecting the combined contribution of the independent variables are also provided. Because the gonorrhea and chlamydia incidence rates were not normally distributed across community areas, the rates were log transformed (base 10) in the regression analyses.14 Data were analyzed using SPSS version 14.0.
Gonorrhea and chlamydia incidence rates per 100,000 persons for the 77 community areas in 2002 were on average 503 and 766 per 100,000 populations, respectively. The STD rates across community areas ranged from 21 to 1,598 per 100,000 for gonorrhea and 42 to 2,340 per 100,000 for chlamydia.
Table 1 shows the incidence rates for chlamydia and gonorrhea according to demographic subgroups. The incidence of each of these 2 STDs was lower in communities where at least 60% of the residents reported being Hispanic compared with communities where at least 60% were black.
The STD incidence rates differed by other demographic factors. The incidence of gonorrhea and chlamydia were higher in communities where 20% or more of the residents had annual incomes below the poverty level, 10% or more were unemployed, and fewer than 45% were aged 15 to 44 years. It is important to note that communities with fewer than 45% aged 15 to 44 years were disproportionately homogeneous black communities. The incidence of chlamydia, but not gonorrhea, was higher in communities where fewer than 70% of the population had a high school education.
The results of the regression analysis (Table 2) revealed that the gonorrhea and chlamydia incidence rates in the communities were associated with racial/ethnic homogeneity after adjusting for poverty, unemployment, education, and age. Communities where at least 60% of the residents were black had significantly higher incidence rates of gonorrhea and chlamydia compared with communities where Hispanics comprised at least 60% of the residents. Communities where fewer than 60% blacks and fewer than 60% Hispanic had significantly higher incidence rates of gonorrhea compared to predominantly Hispanic neighborhoods.
Independent of ethnic/racial homogeneity, the incidence of these 2 STDs was higher in communities that had at least 20% of the residents living in poverty, at least 10% unemployed, and at least 45% between the ages of 15 to 44. Compared to the bivariate findings in Table 1, this age effect reversed after statistically controlling for the ethnic/racial homogeneity. In addition, the rates of chlamydia, but not gonorrhea, were higher in communities where fewer than 70% of the residents were high school graduates.
The community-level findings point to the importance of neighborhood racial/ethnic composition as a potential independent risk factor for the 2 STDs examined here. One epidemiologic explanation invokes sexual mixing patterns and numbers of sexual contacts among members of a community. Because sexual contacts occurring within a community typically follow a pattern of more within-race than between-race sexual mixing,15 a high rate of STDs can develop and be perpetuated within that racial group. Even if the prevalence of sexual risk behaviors and number of sexual contacts were comparable in 2 communities, the community with the higher background prevalence of STDs would increase the likelihood that sexual contact would expose a person to disease and, thus, sustain the epidemic. Although we do not have data on sexual behavior in this analysis, this sexual exposure theory may partially explain the differences in STD rates we observed in predominantly black communities compared with predominantly Hispanic communities. This explanation is supported by a recent review of empirical literature on the HIV epidemic, which shows that the incidence of HIV infection is considerably higher among black men who have sex with men (MSM) than Hispanic or white MSM.16 Although the prevalence of sexual risk behaviors is not appreciably higher among black MSM than other MSM,16,17 the background prevalence of HIV infection and the prevalence of unrecognized infection (i.e., those who are infected with HIV and unaware of it) are higher among black MSM, thus contributing to the higher incidence of new HIV infections in that population.18
In our study, the incidence rates of gonorrhea and chlamydia were lowest in communities in which at least 60% of the residents were Hispanic. This finding was independent of socioeconomic disadvantage (e.g., poverty, unemployment, lack of education). Homogeneous Hispanic communities are typically enclaves in which most residents identify strongly with traditional Hispanic beliefs and practices and most are minimally acculturated to mainstream US society. Indeed, in the Chicago communities with high concentration of Hispanic persons, almost all of the residents reported that they spoke Spanish as their primary language (data not shown). About our STD findings, it is possible that there are fewer sexual contacts occurring in these traditional Hispanic communities compared with other communities. Traditional Hispanic enclaves are likely to comprise strong familial traditions (familism) that encourage marriage, childbearing, and monogamy,19 practices that would be protective against contracting and transmitting STDs. Further, because the prevalence of gonorrhea and chlamydia are generally low in these traditional Hispanic communities, unprotected sex among persons residing in those communities carries less risk of exposure to these STDs.
A prior study20 examined incidence rates of primary- and secondary-stage syphilis from 1984 through 1993 using US counties as the unit of analysis. In a multivariate model, the mean rates increased significantly with the percent of non-Hispanic blacks in the county (the strongest correlate in the analysis); the rates also tended to increase with the percentage of Hispanics in the county. The finding for blacks is consistent with our findings, but the finding for Hispanics is at odds with our results. One possible reason for the inconsistency is the unit of analysis: countywide versus community area. Ethnic homogeneity may not be as high in a countywide area as it is in some of the community areas in Chicago. Community areas with almost all Hispanics had the lowest incidence rates of gonorrhea and chlamydia diagnoses of any of the 77 community areas in 2002 (data not shown). Within these highly homogeneous Hispanic enclaves there may be cultural attitudes and practices that protect against transmission of STDs. These culturally-based protective processes may become diluted in mixed community areas. Also, underdiagnosed and underreported STDs among undocumented Hispanic immigrants may contribute to the lower STD rate estimates. However, it is unclear if this explains the difference in our findings; thus we recommend more research on this issue.
Interestingly, the lower rates of gonorrhea and chlamydia observed in predominantly Hispanic communities in Chicago are consistent with studies that have examined other health outcomes. The incidence of several types of cancers (breast, colorectal, lung) was found to be lower in US census tracts in which 60% or more of the residents were Hispanic compared with US census tracts with fewer Hispanics.13 Another study found that prevalence of depressive symptoms, based on the Center for Epidemiologic Studies Depression Scale, was lower among Mexican Americans living in high-density Mexican American neighborhoods.21
We observed that several other demographic factors were independently associated with the incidence of gonorrhea and chlamydia. These 2 STDs were higher in communities that had more people living in poverty and more people who were unemployed. Communities that had at least 45% (vs. less than 45%) of the residents aged 15 to 44 years had higher gonorrhea and chlamydia rates after adjusting for the ethnic/racial homogeneity effect. This finding is not surprising if we assume that this age range captures individuals most likely to be sexually active. Finally, chlamydia rates were higher in communities where less than 70% (vs. 70% or more) of the residents were high school graduates. This finding suggests that public policy and targeted interventions that increase high school graduation rates may have the added benefit of lowering the incidence of chlamydia and, perhaps, other STDs within a community.
Our analysis is not without limitations. We were not able to directly compare the communities on prevalence of sexual activity because those data were not available. Nor did the database include measures of other potential explanatory variables such as cultural attitudes, values, and behavioral practices. Finally, caution must be used in generalizing the findings to other areas of the United States and elsewhere. Most (80%)22 of the Hispanic communities in Chicago comprise persons of Mexican ancestry. More research is needed to examine ethnic homogeneity in relation to STD risk among Cuban Americans, Puerto Ricans, and Mexican Americans in other US cities.
In summary, our analysis found that the incidence of gonorrhea and chlamydia infection in 2002 differed markedly between predominantly black and predominantly Hispanic neighborhoods in Chicago. The findings suggest that the challenge for public health authorities in Chicago and other metropolitan areas is to consider policy options that respond not only to sexual risk behaviors,23 but also to the contextual attitudes, cultural traditions, norms, and social circumstances24 in homogeneous communities that may affect the spread of STDs in disadvantaged urban populations.
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