Sexual Network Patterns Contribute to Racial Disparities in Disease Risk

Volume 31, No. 6, November/December 1999

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Sexual Network Patterns Contribute to Racial Disparities in Disease Risk

Racial and ethnic differences in sexual network patterns partly explain why black men and women are more likely than white and Hispanic people to have a history of sexually transmitted diseases (STDs). Among individuals who have had only one partner in the past year, black men and women are the most likely to have had intercourse with a member of their racial group who has had four or more partners, which increases the risk of infection. Further, because black men and women largely choose partners from their own racial group, STDs are more likely to stay within the black population than to spread to other groups. These are the major findings of an analysis of data from a nationally representative sample surveyed in 1992.¹

The National Health and Social Life Survey included data on 3,432 adults aged 18-59 living in the United States. Respondents were roughly evenly divided between men and women; 79% were white, 13% were black and 8% were Hispanic. In interviews that averaged 90 minutes, participants were questioned about their ethnicity, sexual activity and attitudes, history of STDs, and selected background and risk-related characteristics. The researchers used a variety of analytic techniques to assess individual risk factors for STDs and to examine the effects of sexual network patterns on that risk.

Some 18% of participants had ever had an STD--11% a bacterial infection and 8% a viral disease. Results of logistic regression analyses controlling for relevant risk factors indicated that compared with white respondents, black men and women were twice as likely to have had any STD (odds ratio, 2.2), while Hispanic participants had a significantly reduced risk (0.6). The odds of having had a bacterial STD were substantially elevated among black respondents (4.6), but both blacks and Hispanics were less likely than whites to have a history of viral STDs (0.5 for each).

To examine sexual network patterns, the researchers divided each racial or ethnic group into three groups, according to their level of sexual activity during the previous 12 months: those who had had only one partner, and were considered safe from STD infection (the peripheral group); those who had had 2-3 partners (the adjacent group); and those who had had four or more partners, and bore most responsibility for STD transmission within the population (the core group). Respondents were also asked for information on the sexual activity of two of their partners; on the basis of this information, these partners were assigned to the appropriate sexual activity group. The investigators constructed a matrix indicating patterns of sexual contact among the nine subgroups. They then conducted a log-linear analysis to examine the effects of sexual network patterns within each racial or ethnic group, and used a simulation to estimate the effects of patterns between groups.

Results of the log-linear analysis revealed very large differences between racial or ethnic groups in patterns of sexual activity. Black men and women are the least likely to restrict their sexual activity to partners of the same sexual activity group. The odds that an individual from the peripheral group has a partner from the core group are 4-5 times as high among blacks as among whites or Hispanics. As a result, even after the number of partners (a major risk factor for STDs) is controlled for, the STD infection rate is higher among black people in the peripheral group than among their white and Hispanic counterparts. In other words, the investigators point out, infections among black respondents are not limited to those engaging in the risk-taking behavior of having a large number of partners, but are spread throughout the black population.

The analysis of interracial networks revealed that black men and women are the least likely to have sexual partners outside their racial group. Consequently, the researchers observe, black individuals infected with an STD are likely to spread the infection within their community but not to other racial or ethnic groups. The analysts calculate that this factor alone makes black people 1.3 times as likely as whites to become infected with an STD.

According to the investigators, their findings regarding intraracial and interracial networks would not have been detected in a study of individual risk factors alone, but required a concentration on behavior patterns within populations and a focus on both infected and uninfected persons. An editorial accompanying the article noted that this approach represents "a paradigm shift for STD epidemiology...that may become predominant in the new millennium."²--M.L. O'Connor

References

1. Laumann EO and Youm Y, Racial/ethnic group differences in the prevalence of sexually transmitted diseases in the United States: a network explanation, Sexually Transmitted Diseases, 1999, 26(5):250-261.

2. Aral SO, Sexual network patterns as determinants of STD rates: paradigm shift in the behavioral epidemiology of STDs made visible, editorial, Sexually Transmitted Diseases, 1999, 26(5):262-264.

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