Sexually Transmitted Diseases

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Sexually Transmitted Diseases:
doi: 10.1097/01.olq.0000204549.79603.d6

Does Partner Selection Contribute to Sex Differences in Sexually Transmitted Infection Rates Among African American Adolescents in San Francisco?

Auerswald, Colette L. MD, MS*; Muth, Stephen Q. BA†; Brown, Beth MS, MPA‡; Padian, Nancy PhD‡§∥; Ellen, Jonathan MD¶

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From the *Division of Adolescent Medicine, Department of Pediatrics, the ‡Department of Obstetrics and Gynecology, and the ∥Center for Reproductive Health Research, University of California at San Francisco, San Francisco, California; †independent consultant, Colorado Springs, Colorado; the §School of Public Health, University of California, Berkeley, Berkeley, California; and the ¶Division of General Pediatrics and Adolescent Medicine, Department of Pediatrics, Johns Hopkins University School of Medicine, Baltimore, Maryland

The authors thank Ali Minnis, John Potterat, Mary Ott, and Matthew Kramer for their editorial suggestions. This endeavor would not have been possible without the cooperation of our adolescent subjects, for which the authors are grateful.

This research was supported by an award from NIAID (U01 AI47639) and from NICHD (1K23 HD01490). Research assistants Edward Cruz, Shira Rutman, and Drina Boban, MHA, interviewed and tracked the hard-to-reach subjects.

Correspondence: Colette L. Auerswald, MD, MS, Assistant Professor of Pediatrics, Division of Adolescent Medicine, University of California at San Francisco, Box 0503, San Francisco, CA 94143-0503. E-mail:

Received for publication August 2, 2005, and accepted December 13, 2005.

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Introduction: Little is known regarding whether partner characteristics explain sex differences in sexually transmitted infection (STI) rates in nonclinic-based, school-aged African American youth.

Materials and Methods: A random digit dial household sample of 14- to 19-year-old youth in San Francisco reported the total number, age, race, and perceived history of incarceration, gang membership, and level of sexual activity of their partners. Youth were tested for gonorrhea and chlamydia.

Results: Female participants were more likely than male participants to have a partner who was older or had been incarcerated and less likely to have a non-African American partner. Controlling for partner number, female's odds ratio (OR) for having an STI was 1.39 (95% confidence interval [CI] = 0.98–1.98; P = 0.07). Controlling for partner incarceration and number of partners, the borderline sex difference was eliminated (OR = 1.07; 95% CI = 0.70–1.63).

Conclusion: Sex differences in STI rates among African American adolescents may be determined more by the risk of the partner than the risk of the individual.

AFRICAN AMERICAN ADOLESCENTS EXPERIENCE DISPROPORTIONATE rates of sexually transmitted infections (STIs) relative to their white and Latino counterparts.1 Furthermore, African American females 15 to 19 years of age suffer disproportionately from STIs relative to their male counterparts. Nationally, African American females 15 to 19 years old have almost twice the rate of gonorrhea than their male peers (3495 vs. 1794 cases per 100,000).1 In San Francisco, the sex differential is similar (3363 vs. 1476 cases per 100,000).2 Although young females' increased biologic susceptibility to STIs has been documented,3,4 differences in sexual behavior are generally postulated to explain differences in rates of STIs. However, in the case of African American adolescents, differences in risky sexual behavior do not appear to explain differential morbidity by gender. The 2003 Youth Risk Behavior Survey found that 9th to 12th grade African American males were more likely than their female peers to have had sexual intercourse (73.8% vs. 60.9%), to have initiated sexual activity before the age of 13 years (31.8% vs. 6.9%), to have had greater than 3 lifetime sexual partners (41.7% vs. 16.3%), and to be currently sexually active (54.0% vs. 44.2%).5 These results would suggest a priori that African American adolescent males should have higher rates of STIs than their female counterparts rather than the opposite.

One explanation for this apparent paradox is that the difference in rates is the result of a difference in partner characteristics.6 Demographic and behavioral characteristics of partners have been shown to increase the risk for STIs. Having an older sex partner is correlated with earlier coiarche,7,8 decreased condom use,9,10 and increased risk of STIs11,12 and pregnancy.10,13,14 Given that incarceration15–17 and gang membership18 are associated with increased STI risk, individuals with partners who have been incarcerated or are members of a gang are at increased risk themselves for STIs as a result of greater likelihood of exposure to an infected partner.

Similarly, partner race has been postulated to affect likelihood of exposure and thus risk for STIs. Laumann and colleagues have suggested that African American adults are at higher risk for STI acquisition relative to adults of other ethnic groups because of greater proximity to members of core sexual networks characterized by multiple sexual partners.19 Ellen et al have suggested that the differential risk for STIs in African American adolescents in San Francisco may be the result of their proximity to core network members.20 Finally, Potterat et al have suggested that youth who select partners nonassortatively (i.e., teens who select partners of a different race) were at highest risk for an STI.21

Studies of partner selection and STIs in adolescents to date have only been conducted in school-based or high-risk clinic samples22,23 and have rarely been linked to biologically confirmed STIs. Little is known about whether sex differences in sexual partner characteristics explain sex differences in rates of STIs among a nonclinic sample of school-aged youth. Knowledge of the contribution of sexual partner characteristics to STI risk could inform interventions to prevent STIs among school-aged youth residing in high-prevalence communities. To the extent that partner characteristics matter, then efforts to reduce STIs in youth residing in high-prevalence communities would need to focus on sexual partner selection and on sex partners and their networks rather than continuing to only focus on individual behavior change such as condom use.

The objective of this study was to determine whether the demographic and behavioral characteristics of adolescents' sexual partners mediate the sex differences in rates of STIs.

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Materials and Methods


From July 2000 to August 2001, we recruited a random digit dial telephone household sample of 14- to 19-year-old African American youth who reside in the Bayview Hunter's Point District of San Francisco, California, a predominantly African American, economically marginalized and sociogeographically segregated district of San Francisco. The sample of telephone numbers was generated using a procedure called list-assisted random digit sampling. Approximately 40,000 phone numbers were dialed, of which 22,000 were identified as households. Ninety percent of households were excluded because they were out of the target area or did not host an eligible adolescent. A final sample of 673 teens living in 470 eligible households was identified. After excluding 93 duplicated respondents, 580 household youth were offered the interview. Three hundred fifty of the 580 household youth were interviewed (60.3% response rate). The distribution of the nonresponse rate among RDD index teens was: 20% guardian refusal, 13% respondent refusal, 4% informant refusal, and 3% respondent never available. Male adolescents and younger adolescents had higher refusal rates.

The focus of this article is on the adolescents who had had sex in the 3 months before recruitment. Of the 350 youth (205 females) in the cohort, 166 (99 female) had had sex in the prior 3 months, 133 (83 female) were virgins, 50 (23 female) had had sex outside of the 3 months, and one male youth declined to answer the question.

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Data Collection

Consent for participation was obtained from parents for all minor participants and directly from participants 18 years or older for participation in an adolescent health study that included interviews and STD testing for all participants. Minor study participants gave assent. Participating youth were interviewed and tested for Neisseria gonorrhea (GC) and Chlamydia trachomatis (CT). Interviews were conducted by telephone using computer-assisted telephone interview (CATI) technology. Eligible adolescents not reached by phone were located and interviewed by a field team using home visits, word-of-mouth referral, or information from public records, key informants, and community leaders. Field team interviews were also administered using CATI technology. Youth undergoing STI testing were met in the field by study staff who instructed youth on the use of tests and provided written instructions. Testing took place at a convenient location of the participant's choice such as their home, school, or workplace. Youth were reimbursed $25 for completion of the CATI interview and $10 for sexually transmitted disease testing.

The University of California at San Francisco Institutional Review Board approved all study procedures.

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Participants reported their age and the number and names of up to 6 of their sexual partners in the 3 months before being interviewed. Youth were asked to provide the names of partners because partners were subsequently offered participation in the study. Participants had the option of not giving a partner's name or not allowing a partner to be contacted. Only data from the original participants, not partner data, are reported here. Number of partners reported by the participant was treated as a continuous variable.

Partner age was reported by the participant. Age differences between the participants and each partner were calculated and dichotomized as greater than or equal to 5 years older (partner older than participant) or absolutely less than 5 years older (including cases when the partner is younger than the participant). The literature defines an older partner variously as greater than 2 years older and 5 years older or greater. Clinically, we are more concerned about the 15 year old partnering with the 20 year old than with a 17 year old so we chose the latter definition. Analyses performed with an age difference of 2 years yielded the same results.

Partner race was reported by the participant and then dichotomized as African American or not. This dichotomization was performed to measure nonassortative mixing by our all-African American index sample.

Partner incarceration was reported by the participant by asking: “Was [partner] ever in jail or juvenile hall?”

Partner gang membership was reported by the participant by asking: “Was [partner] ever in a gang or neighborhood crew?” “Neighborhood crew” is another term for gangs in the community.

Level of sexual activity of the partners was determined by asking: “Did [partner] have any other sex partners during the last 3 months?”

CT and GC infection were determined by obtaining a first-void urine from males or a self-administered vaginal swab from females, which were tested by ligase chain reaction (LCx; Abbott). STI tests were not obtained from 12.1% of the respondents because they could not be located or refused to provide a specimen after being interviewed by phone or in person. These missing results were recoded as negatives to bias effect estimates toward the null (results were the same when analyses were conducted with the missing tests deleted). Participants who tested positive for CT or GC were referred for care to their primary care provider or to a low cost or free adolescent-friendly clinic.

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Approach to Multiple Dyads per Participant.

Because we were interested in the summation of risk at the individual level, not the risk of individual partnerships at the dyadic level, we created a single record per index participant. The single record summarized the number of partners, the number of partners that were reported to have the specified characteristic (race of partner, older partner, perceived gang membership, perceived incarceration, and having other partners in specified period or not). We then recoded this to record whether the index had any partner with the specified characteristic.

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Statistical Methods

To test our hypothesis that the relationship between gender (our independent variable) and STI rates (our dependent variable) was mediated by partner characteristics (such as partner race, age, perceived incarceration or gang membership, or level of sexual activity), we performed the following 4-step regression approach to testing mediation effects as per Holmbeck24 using logistic regression. Our approach is also summarized in Figure 1.

Fig. 1
Fig. 1
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1. We determined that there were differences in the rate of STI diagnosis by gender even once the analyses were controlled for the potential confounding effect of number of sex partners;

2. We determined that there were gender differences in sexual partner characteristics (i.e., a difference by gender in having any partner with the characteristic of interest) and in number of partners;

3. We determined which sex partner characteristics were significantly associated with the diagnosis of STIs, controlling for number of sex partners; and

4. We demonstrated that the difference in the rate of STI diagnosis by gender is decreased when controlling for having any partner with a significant partner characteristic, even when controlling for the effect of partner number.

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The cohort included 99 sexually active female participants and 67 sexually active male participants of similar age (mean age, 17.6 years for females and 17.4 for males). All cohort members were African American. The mean number of partners reported by the males over the 3 months before being interviewed was 2.0 (range, 1–7). This was significantly greater than the mean of 1.3 partners reported by the females (range, 1–5; Wilcoxon 2-sample exact t test, P <0.0001). Only one youth reported more than 6 partners. No youth reported same sex sexual activity.

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Gender Differences in Sexually Transmitted Infections

The overall rate of positive STIs was 9.2%. As stated above, we were not able to collect tests from 12.2% of the sample. The rate of STIs was higher among females (12.1%; 12 of 99) than among males (4.5%; 3 of 67). The difference was not statistically significant (odds ratio [OR] = 1.31, 95% confidence interval [CI] = 0.95–1.81). However, when we controlled for number of sex partners, the difference bordered on significance (OR = 1.39, 95% CI = 0.98–1.96; P = 0.07).

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Gender Differences in Sexual Partner Characteristics

Partner demographics and high-risk characteristics by gender are summarized in Table 1. There were significant sex differences in demographic characteristics of partners. Female respondents were significantly more likely than male respondents to have an older partner (OR = 1.48; 95% CI = 1.08–2.03) and significantly less likely to have a non-African American partner (OR = 0.63; 95% CI = 0.51–0.77). Furthermore, female respondents were nearly twice as likely as male respondents to report that at least one sexual partner had been incarcerated (OR = 1.86; 95% CI = 1.50–2.29). There was no sex difference in rates of partners perceived to have a history of gang membership or in partners perceived to have had other partners.

Table 1
Table 1
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Sexual Partner Characteristics and Sexually Transmitted Infections

As shown in Table 2, the only partner characteristic associated with STI diagnosis was history of incarceration (OR = 6.56; 95% CI = 1.77–24.27). Number of sexual partners was not associated with STI diagnosis (OR = 1.09; 95% CI = 0.69–1.73).

Table 2
Table 2
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Impact of Sexual Partner Characteristics on Gender Differences in Sexually Transmitted Infections

Because the only partner characteristic to be associated with both gender and STI diagnosis was history of incarceration, we did not test the mediation effects of the other partner characteristics. Controlling for partner incarceration and number of partners, the sex difference in STI rates was eliminated (OR = 1.07; 95% CI = 0.70–1.63).

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This study showed that, although there were several gender differences in sexual partner characteristics, only having had a partner with a history of incarceration mediated gender differences in rates of STIs. This finding supports, although does not prove, our hypothesis that the higher rate of STIs among adolescent females relative to adolescent males, despite males' greater sexual risk behaviors, is related to partner selection.

In network terms, this suggests that the risk for contracting an STI is determined more by the risk of the partner than by the risk of the participant. Incarceration is associated with an increased risk of STIs and HIV.15–17,25,26 Incarceration may be a marker for STI risk and, in particular, for being a member of a core group for infection. Incarceration was correlated with having concurrent partners in a study of the partners of rural African Americans.27 As stated earlier, Laumann et al and Ellen et al have suggested that African American adults and adolescents are at higher risk for STI acquisition because of greater proximity to members of core sexual networks.19,20 This study supports these conclusions based on a random digit dial household sample of African American adolescents.

There are several limitations to our findings. First, the gender difference in the rate of STIs controlling for the number of sexual partners was of borderline significance. We report this finding nevertheless because of the small sample and the exploratory nature of this analysis. Second, the data regarding the partners are reported by the participants and not by the partners themselves. Third, the reporting may be subject to recall bias because of the time period (3 months) over which our adolescent participants were asked to report their activities. There may also be reporting bias as a result of the stigmatizing nature of the behaviors under study such as gang membership and incarceration of partners. Although the population-based sample is a strength of the study, youth without phones in the home could not be included in this random digit dial sample. However, the extensive telephone coverage of the Bayview District leads us to believe that the effect of these missing youth was not substantial. Finally, there were missing STI testing data on 12.1% of youth and, as mentioned previously, 40% of eligible adolescents failed to participate. The greater participation by females reflects the greater likelihood that females would be found at home versus males and the greater likelihood of male versus female refusals. Without data on the risk behavior of the male refusals, it is difficult to guess how this may have biased our findings. These data may have changed the overall findings, although as we have stated, we believe that by coding missing tests as negative, we biased our effect estimates toward the null hypothesis.

In conclusion, our findings suggest that African American females in an economically deprived community report significantly different patterns of partner selection relative to their male age mates, differences that appear to partially mediate their risk of STIs. Differences in individual behavior such as partner number did not alter the sex difference in STI rates. Sex differences in STI rates among African American adolescents may in part be the result of social contextual factors such as differences in partner characteristics. These differences may provide clues to interventions to improve the health of all African American adolescents.

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