Abstract
This national survey demonstrates age-disparate (≥5 years; AD-5) sexual partnerships remain common among males and females aged 20–29 years in the U.S. (2005–2016). Females reported more older AD-5 partners and males reported more younger AD-5 partners. Having AD-5 partners was associated with greater lifetime and recent number of sexual partners.
Keywords: Age-disparate partnerships, National Health and Nutrition Examination Surveys (NHANES), sexually transmitted infections, behaviors
Short Summary
A national survey of 20–29 year-olds in the U.S. found that sexual partnerships with a ≥5-year age difference between partners remain common and associated with other sexual behaviors.
Introduction
Sexual behaviors are key determinants of sexually transmitted infection (STI) transmission1,2. When sexual mixing occurs across different age groups, such as through age-disparate (AD) sexual partnerships, STIs that are also associated with age may move into susceptible populations. In the U.S. and globally, having an AD partner has historically been associated with prevalent C. trachomatis and N. gonorrhea infection among adolescent and adult females3,4 as well as HIV prevalence among adolescent and adult females5–7 and men who have sex with men8,9.
Since the late 1990s, global prevalence estimates of AD partnerships have ranged from 20% to almost 50%4,10–12. Britain’s third National Survey of Sexual Attitudes and Lifestyles found that approximately one-third of all participants aged 16–44 years had an AD partner in the past year13. Contemporary data describing the prevalence of AD partnerships in the U.S. are limited. This study uses data from the National Health and Nutrition Examination Surveys (NHANES) to describe trends in the prevalence of having age-disparate partners who were ≥5 years older or younger than the study participant (AD-5) in the past year and to characterize the sociodemographic and behavioral correlates of AD-5 partnerships.
Methods
Study design and population
Data were obtained from the continuous 2005–2016 NHANES, an annual complex survey conducted by the National Center for Health Statistics (NCHS), U.S. Centers for Disease Control and Prevention (CDC)14–18. Participants completed an in-home interview as well as additional interviews and a medical examination at a local mobile examination center (MEC). This cross-sectional analysis was conducted among sexually active participants aged 20–29 years who were examined at the MEC. All participants provided informed consent. Data collection was approved by the NCHS/CDC Research Ethics Review board and this analysis of publicly-available data was deemed “exempt from human research” by the Institutional Review Board of the Johns Hopkins University School of Medicine.
Questionnaire data
Sociodemographic characteristics were obtained by a trained interviewer using a computer-assisted personal interview system during an at-home interview. Participants were asked about their lifetime number of vaginal, anal, and oral sexual partners in a private room at the MEC using an audio- and computer-assisted self-interview system. Sexually active participants (those who reported ≥1 sex partner in the past 12 months) were asked, “of the persons you had sex with in the past 12 months, how many of them were five or more years older than you?” and “of the persons you had sex with in the past 12 months, how many of them were five or more years younger than you?” Data on condom use was ascertained among those who reported vaginal or anal sex in the past 12 months; participants who reported not always using a condom were categorized as inconsistent condom users. Participants were asked about their sexual orientation/identity. Participants who identified as anything other than heterosexual/straight or who were not sure of their sexual identity were considered sexual minorities and were collapsed into a single category owing to sample size limitations.
Statistical analysis
All data were analyzed using svy commands in Stata/MP, v15.1 (Statacorp LP, College Station, Texas), which account for the complex survey design and incorporate NCHS-derived MEC weights to generate nationally representative estimates. The MEC weights, which account for differential probability of selection, nonresponse, and adjustment to the noninstitutionalized U.S. civilian population, were pooled across the survey cycles, where appropriate19. Taylor series linearization was used to estimate design-adjusted standard errors (SE); 95% confidence intervals (CI) for prevalence estimates were calculated using the Korn-Graubard method.
The analytic sample was restricted to sexually active participants who responded regarding AD-5 partnerships. Analyses were stratified by sex. The study outcomes were the prevalence of reporting ≥1 older AD-5 partner in the past year and ≥1 younger AD-5 partner in the past year. Trends in each outcome were examined across four-year periods (i.e., 2005–2008, 2009–2012, 2013–2016). In the primary analysis (2005–2016), the prevalence of each outcome was estimated according to primary factors hypothesized a priori to be associated with past-year AD-5 partnerships including age, race/ethnicity, educational attainment, the annual family income-to-poverty ratio, marital status, sexual identity, age at sexual debut, and number of lifetime sexual partners20,21. Prevalence ratios (PR) were estimated by univariable modified Poisson regression. Adjusted PRs (aPR) were estimated from multivariable models that included all primary sociodemographic and behavioral factors of interest.
A secondary analysis examined associations of past-year AD-5 partnerships with past-year sexual behaviors, including reporting (1) multiple sexual partners and (2) inconsistent condom use. A separate multivariable model was used for each recent sexual behavior and included adjustment for all sociodemographic and behavioral covariates included in the primary analysis.
Subgroup analyses were conducted stratified by age group and race/ethnicity.
Results
The analytic sample included 2303 females and 1991 males aged 20–29 years. Excluded persons (720 females and 700 males), owing to missing data on the outcome or sexual activity status, were more likely to be a racial/ethnic minority, have a lower income-to-poverty ratio, and be unmarried (Supplemental.Digital.Content.Table.1). The prevalence of ≥1 older AD-5 partner in the past year was 32.4% (SE=1.1) in females and 21.2% (SE=1.0) in males. The prevalence of ≥1 younger AD-5 partner in the past year was 5.0% (SE=0.5) in females and 19.5% (SE=1.2) in males (Table.1). The prevalence of ≥1 older or younger AD-5 partner in the past year remained stable over time for both females and males (Supplemental.Digital.Content.Figure.1).
Table 1.
Prevalence of ≥1 past-year age-disparate (AD-5) partner among sexually active 20–29 year-olds, National Health and Nutrition Examination Survey 2005–2016.a
| Females | Males | ||||||||
|---|---|---|---|---|---|---|---|---|---|
| Characteristics | No.b | ≥1 Past-Year Older AD-5 Partner |
≥1 Past-Year Younger AD-5 Partner |
No.b | ≥1 Past-Year Older AD-5 Partner |
≥1 Past-Year Younger AD-5 Partner |
|||
| % (SE) | % (SE | % (SE | % (SE | ||||||
| Total | 2303 | 32.4 (1.1) | 5.0 (0.5) | 1991 | 21.2 (1.0) | 19.5 (1.2) | |||
| Age, years | |||||||||
| 20–24 | 1154 | 31.7 (1.6) | 2.9 (0.5) | 1014 | 22.8 (1.5) | 13.9 (1.4) | |||
| 25–29 | 1149 | 33.0 (1.7) | 7.1 (0.9) | 977 | 19.7 (1.4) | 24.8 (1.6) | |||
| Race/Ethnicity | |||||||||
| Non-Hispanic White | 910 | 29.4 (1.6) | 2.9 (0.5) | 761 | 15.9 (1.3) | 16.4 (1.6) | |||
| Non-Hispanic Black | 494 | 41.6 (2.3) | 8.5 (1.1) | 465 | 35.7 (2.5) | 25.3 (2.4) | |||
| Hispanic | 668 | 36.1 (2.0) | 8.4 (1.3) | 548 | 28.6 (2.2) | 23.6 (1.9) | |||
| Otherc | 231 | 31.7 (3.9) | 7.6 (2.3) | 217 | 20.3 (4.0) | 24.0 (3.9) | |||
| Educational Attainment | |||||||||
| Less than high school | 380 | 43.0 (2.7) | 7.3 (1.5) | 412 | 31.4 (2.7) | 27.2 (2.5) | |||
| High school or GED | 515 | 40.3 (2.4) | 5.9 (0.8) | 513 | 22.2 (2.0) | 23.9 (2.3) | |||
| Some college or more | 1408 | 28.0 (1.5) | 4.3 (0.7) | 1065 | 18.2 (1.2) | 15.6 (1.4) | |||
| Poverty-to-Income Ratio | |||||||||
| <1.0 | 655 | 38.8 (2.6) | 6.1 (1.0) | 514 | 28.6 (2.6) | 23.1 (2.8) | |||
| 1–2.9 | 897 | 32.8 (1.7) | 6.0 (1.0) | 771 | 19.3 (1.4) | 21.5 (1.9) | |||
| ≥3.0 | 618 | 27.7 (2.1) | 3.3 (0.8) | 557 | 18.6 (2.0) | 15.7 (1.8) | |||
| Marital Status | |||||||||
| Married | 734 | 25.4 (2.1) | 4.4 (0.9) | 476 | 10.7 (1.2) | 12.0 (1.8) | |||
| Unmarried | |||||||||
| Living with Partner | 447 | 32.0 (2.5) | 5.3 (1.1) | 382 | 18.8 (2.0) | 18.8 (2.6) | |||
| Never Married | 1027 | 36.6 (1.7) | 4.7 (0.6) | 1080 | 27.5 (1.6) | 21.9 (1.6) | |||
| Previously Married | 93 | 44.5 (5.7) | 11.0 (3.2) | 53 | 21.9 (7.2)d | 52.1 (7.8)d | |||
| Sexual Identity | |||||||||
| Heterosexual | 2039 | 31.0 (1.2) | 4.4 (0.5) | 1880 | 20.0 (0.9) | 19.3 (1.2) | |||
| Othere | 260 | 42.7 (3.2) | 9.7 (1.8) | 105 | 42.0 (4.8) | 20.5 (4.6) | |||
| Age at Sexual Debut, years | |||||||||
| ≤15 | 765 | 38.5 (2.1) | 5.3 (0.7) | 724 | 29.8 (2.0) | 23.6 (2.0) | |||
| 16–17 | 762 | 32.6 (2.0) | 4.6 (0.8) | 620 | 19.8 (1.7) | 16.0 (1.7) | |||
| ≥18 | 776 | 26.4 (2.1) | 5.2 (0.9) | 647 | 13.9 (1.3) | 18.5 (2.0) | |||
| Lifetime Number of Sex Partners | |||||||||
| 1–5 | 1271 | 24.3 (1.5) | 3.4 (0.6) | 834 | 10.9 (1.1) | 13.7 (1.6) | |||
| 6–10 | 539 | 31.3 (2.4) | 6.0 (1.0) | 489 | 17.3 (1.9) | 19.2 (2.0) | |||
| ≥11 | 440 | 51.6 (3.1) | 7.0 (1.3) | 642 | 39.0 (2.1) | 27.8 (2.3) | |||
| Number of Past-Year Sexual Partners | |||||||||
| 1 | 1665 | 26.1 (1.2) | 3.7 (0.6) | 1198 | 10.3 (0.9) | 13.9 (1.4) | |||
| ≥2 | 638 | 48.4 (2.5) | 8.2 (1.0) | 793 | 39.7 (2.1) | 28.9 (1.9) | |||
| Inconsistent Condom Use | |||||||||
| Consistently Used a Condom | 394 | 27.7 (2.8) | 5.1 (1.2) | 430 | 26.9 (2.6) | 19.7 (2.6) | |||
| Inconsistently Used a Condom | 1833 | 33.5 (1.3) | 5.0 (0.6) | 1469 | 20.0 (1.0) | 19.8 (1.4) | |||
All data are survey-weighted prevalence (%) and design-adjusted standard error (SE) estimates, unless otherwise noted.
Unweighted sample size.
Other race/ethnicity includes non-Hispanic Asian and multiracial persons.
RSE >30% or failed to meet NCHS standards.
Other sexual identity includes gay or lesbian, bisexual, something else, and responses of “Not sure” or “I don’t know.”
The prevalence of ≥1 older AD-5 partner in the past year varied by all primary sociodemographic and behavioral factors except age among females and males (Table.1). In primary multivariable analyses, minority race/ethnicity and increasing number of lifetime sexual partners were associated with increased prevalence of ≥1 older AD-5 partner and increasing educational attainment was associated with a decreased prevalence among males and females (Table.2).
Table 2.
Correlates of ≥1 past-year age-disparate partners (≥5-year age difference) among sexually active 20–29 year-olds, National Health and Nutrition Examination Survey 2005–2016.
| Characteristic | Females | Males | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| ≥1 past-year older AD-5 | ≥1 past-year younger AD-5 | ≥1 past-year older AD-5 | ≥1 past-year younger AD-5 | ||||||||
| PR (95% CI)a | aPR (95% CI)b | PR (95% CI)a | aPR (95% CI)b | PR (95% CI)a | aPR (95% CI)b | PR (95% CI)a | aPR (95% CI)b | ||||
| Age, years | |||||||||||
| 20–24 | Ref. | Ref. | Ref. | Ref. | Ref. | Ref. | Ref. | Ref. | |||
| 25–29 | 1.04 (0.90–1.21) | 1.09 (0.93–1.28) | 2.48 (1.69–3.64) | 2.58 (1.75–3.82) | 0.86 (0.71–1.05) | 0.99 (0.83–1.18) | 1.79 (1.46–2.19) | 2.04 (1.65–2.52) | |||
| Race/Ethnicity | |||||||||||
| Non-Hispanic White | Ref. | Ref. | Ref. | Ref. | Ref. | Ref. | Ref. | Ref. | |||
| Non-Hispanic Black | 1.42 (1.21–1.66) | 1.29 (1.11–1.49) | 2.90 (1.90–4.44) | 2.77 (1.77–4.31) | 2.24 (1.83–2.75) | 1.70 (1.40–2.07) | 1.54 (1.22–1.94) | 1.17 (0.92–1.50) | |||
| Hispanic | 1.23 (1.05–1.43) | 1.19 (1.01–1.41) | 2.85 (1.91–4.26) | 2.86 (1.85–4.44) | 1.80 (1.45–2.23) | 1.74 (1.39–2.19) | 1.44 (1.13–1.82) | 1.27 (0.97–1.65) | |||
| Otherc | 1.08 (0.83–1.40) | 1.18 (0.91–1.53) | 2.58 (1.30–5.15) | 2.81 (1.45–5.47) | 1.27 (0.84–1.92) | 1.45 (1.02–2.04) | 1.46 (1.02–2.09) | 1.66 (1.15–2.41) | |||
| Educational Attainment | |||||||||||
| Less than high school | Ref. | Ref. | Ref. | Ref. | Ref. | Ref. | Ref. | Ref. | |||
| High school or GED | 0.94 (0.77–1.14) | 1.02 (0.82–1.28) | 0.81 (0.49–1.35) | 1.00 (0.61–1.64) | 0.71 (0.57–0.88) | 0.76 (0.61–0.94) | 0.88 (0.67–1.15) | 0.92 (0.68–1.25) | |||
| Some college or more | 0.65 (0.56–0.76) | 0.73 (0.60–0.89) | 0.59 (0.36–0.98) | 0.70 (0.42–1.16) | 0.58 (0.46–0.73) | 0.70 (0.57–0.86) | 0.57 (0.44–0.74) | 0.61 (0.45–0.82) | |||
| Poverty-to-Income Ratio | |||||||||||
| <1.0 | Ref. | Ref. | Ref. | Ref. | Ref. | Ref. | Ref. | Ref. | |||
| 1–2.9 | 0.85 (0.71–1.003) | 0.90 (0.77–1.05) | 0.98 (0.63–1.53) | 1.05 (0.67–1.64) | 0.67 (0.53–0.85) | 0.83 (0.68–1.02) | 0.93 (0.71–1.22) | 1.03 (0.81–1.30) | |||
| ≥3.0 | 0.71 (0.59–0.87) | 0.85 (0.69–1.06) | 0.54 (0.30–0.95) | 0.62 (0.34–1.12) | 0.65 (0.48–0.87) | 0.91 (0.71–1.17) | 0.68 (0.50–0.91) | 0.79 (0.59–1.05) | |||
| Marital Status | |||||||||||
| Married | Ref. | Ref. | Ref. | Ref. | Ref. | Ref. | Ref. | Ref. | |||
| Unmarried | 1.41 (1.17–1.69) | 1.20 (0.995–1.45) | 1.19 (0.78–1.81) | 1.14 (0.74–1.74) | 2.34 (1.83–2.99) | 1.78 (1.38–2.29) | 1.84 (1.37–2.48) | 1.96 (1.44–2.69) | |||
| Sexual Identity | |||||||||||
| Heterosexual/straight | Ref. | Ref. | Ref. | Ref. | Ref. | Ref. | Ref. | Ref. | |||
| Otherd | 1.38 (1.16–1.64) | 1.06 (0.88–1.27) | 2.21 (1.41–3.47) | 1.78 (1.10–2.87) | 2.11 (1.64–2.70) | 1.77 (1.42–2.20) | 1.06 (0.68–1.65) | 0.87 (0.55–1.38) | |||
| Age at Sexual Debut, years | |||||||||||
| ≤15 | Ref. | Ref. | Ref. | Ref. | Ref. | Ref. | Ref. | Ref. | |||
| 16–17 | 0.85 (0.71–1.01) | 1.05 (0.87–1.27) | 0.86 (0.56–1.34) | 1.18 (0.72–1.92) | 0.66 (0.53–0.83) | 0.91 (0.73–1.14) | 0.68 (0.53–0.86) | 0.86 (0.68–1.08) | |||
| ≥18 | 0.69 (0.56–0.85) | 0.97 (0.77–1.22) | 0.98 (0.64–1.49) | 1.43 (0.92–2.23) | 0.47 (0.37–0.58) | 0.81 (0.62–1.06) | 0.78 (0.61–1.003) | 1.08 (0.82–1.43) | |||
| Lifetime Number of Sex Partners | |||||||||||
| 1–5 | Ref. | Ref. | Ref. | Ref. | Ref. | Ref. | Ref. | Ref. | |||
| 6–10 | 1.29 (1.05–1.58) | 1.25 (1.01–1.55) | 1.78 (1.09–2.91) | 1.92 (1.17–3.14) | 1.59 (1.16–2.20) | 1.23 (0.86–1.74) | 1.41 (1.04–1.91) | 1.22 (0.89–1.68) | |||
| ≥11 | 2.12 (1.78–2.54) | 2.02 (1.67–2.45) | 2.09 (1.23–3.54) | 2.02 (1.11–3.67) | 3.59 (2.84–4.54) | 2.85 (2.12–3.82) | 2.03 (1.54–2.68) | 1.78 (1.30–2.45) | |||
| Recent Number of Sex Partners | |||||||||||
| 1 | Ref. | Ref. | Ref. | Ref. | Ref. | Ref. | Ref. | Ref. | |||
| ≥2 | 1.85 (1.62–2.13) | 1.48 (1.25–1.75) | 2.20 (1.48–3.27) | 1.90 (1.21–2.98) | 3.85 (3.14–4.72) | 2.76 (2.09–3.65) | 2.09 (1.70–2.57) | 1.80 (1.39–2.34) | |||
| Recent Condom Use | |||||||||||
| Consistently Used | Ref. | Ref. | Ref. | Ref. | Ref. | Ref. | Ref. | Ref. | |||
| Inconsistently Used | 1.21 (0.97–1.52) | 1.20 (0.95–1.52) | 0.98 (0.59–1.63) | 0.99 (0.61–1.59) | 0.74 (0.60–0.91) | 0.71 (0.57–0.89) | 1.00 (0.75–1.34) | 1.05 (0.78–1.42) | |||
Crude prevalence ratios (PR) and corresponding 95% CI were estimated from weighted modified Poisson regression models.
Adjusted prevalence ratios (aPR) and corresponding 95% CI were estimated from weighted modified Poisson regression models that included the covariate of interest and adjustment for age group, race/ethnicity, educational attainment, family poverty to income ratio, marital status, sexual identity, age at sexual debut, and lifetime number of sexual partners.
Other race/ethnicity includes non-Hispanic Asian and multiracial persons.
Other sexual identity includes gay or lesbian, bisexual, something else, and responses of “Not sure” or “I don’t know.”
Among females, the prevalence of ≥1 younger AD-5 partner in the past year varied by age group, race/ethnicity, annual family poverty-to-income ratio, and sexual identity (Table.1). Among males, the prevalence of ≥1 younger AD-5 partner in the past year varied by all sociodemographic variables except for sexual identity. In primary multivariable analyses, older age and a higher number of lifetime sexual partners were among the factors associated with an increased prevalence of ≥1 past-year younger AD-5 partner among males and females (Table.2).
People with multiple sex partners in the past year had a higher prevalence of ≥1 older (females: aPR=1.48[95%CI=1.25–1.75]; males: aPR=2.76[95%CI=2.09–3.65]; Table.2) and younger AD-5 partner (females: aPR=1.90[95%CI=1.21–2.98]; males: aPR=1.80[95%CI=1.39–2.34]; Table.2). No association was observed between AD-5 partnerships and consistent condom use among females; however, males who used condoms consistently were more likely to report an older AD-5 partner (Table.2).
Subgroup analyses stratified by race/ethnicity and age-group demonstrated similar findings as observed in primary analyses (Supplemental.Digital.Content.Tables.3–6).
Discussion
Among 20–29 year-olds in the U.S., the prevalence of age-disparate sexual partnerships remained stable between 2005–2016. Females reported older AD-5 partners more than males, while males reported more younger AD-5 partners than females. Racial/ethnic minorities and those with a high number of lifetime sexual partners had a higher prevalence of ≥1 older AD-5 partner. The prevalence of ≥1 younger AD-5 partner was more prevalent in both racial/ethnic and sexual minority females, unmarried males, and persons with a higher number of lifetime sexual partners.
A robust relationship was seen between past-year AD-5 partnerships and multiple past-year sexual partners for both males and females, which remained significant after adjustment for lifetime sexual risk indicators. These results are consistent with other studies which saw associations between AD partnerships and other sexual risk behaviors22,23. While AD partnerships are common in this population, the majority of sexual partnerships occur among persons of similar age4,10,13. It is possible that those who select partners outside their age group have a propensity to engage in higher-risk behaviors which manifest as sexual health risks.
The prevalence of older AD-5 partners among females and younger AD-5 partners among males seen in this population is similar to other general populations, however many more males in this study had older AD-5 partners than seen in other populations. Survey data from the United Kingdom (U.K.) and Australia found that <10% of men reported sexual partners ≥5 years older10,13,24. The increased prevalence of older AD-5 partners among males may in part be due to more “casual” sex in the study population13. U.S.-based data on casual relationships and AD partnerships are limited, specifically among men, but U.S. men report more casual sexual partnerships than men in the U.K.10,25. Further, social differences may exist between U.S. and U.K. males that influence partner selection.
Males who consistently used condoms in the past year reported older AD-5 partners more than males who used condoms inconsistently. There was no association between past-year condom use and older AD-5 partnerships among females in this study, in contrast to the decreased condom use seen among adolescent females with older partners12,22. It is possible that females become more confident about negotiating condom use as they age into adulthood.
These data may be subject to recall bias as well as social desirability bias, particularly when reporting younger AD-5 partners. In the U.S., the age of consent ranges from 16–18 years and for those under the age of consent, many states define age differences at which sexual intercourse with an older individual is legal26. For many states with these laws, legal age differences are <5 years26. It is likely these laws partially explain why 20-to-24-year-old participants are much less likely to report a younger AD-5 partner than 25-to-29-year-olds.
This study has other limitations. While the cutoff in age difference for an AD partner in this study is more than twice the average partner age difference in other national surveys10,12,27, there may be important differences between those with a partner 5–9 years AD compared to ≥10 years that we were unable to capture. It should also be noted that these results may not necessarily be generalizable to the entire U.S. population or transferable to other populations.
A unique aspect of this study is the characterization of individuals who engage in sexual relationships with younger partners. Those with younger sexual partners have a higher number of lifetime and recent sexual partners than those without younger partners, which may put these young partners at an increased risk for STI. As educational attainment increased, the prevalence of AD-5 partnerships decreased, suggesting social context may also be an important factor in partner selection.
The independent association between AD-5 partnerships and established STI risk behaviors seen in this population highlights the need to better understand the relationship between sexual mixing in young adults who are most at-risk for many STI. Describing the prevalence and characteristics of AD partnerships may help to parameterize mathematical models for STI transmission, which are useful tools to approximate future infections and inform intervention strategies by designating risk groups and accurately informing mixing between those groups8,28,29. Additional research is needed to determine the impact of AD-5 partnerships on STI acquisition.
Supplementary Material
Financial support:
This work was supported in part by extramural support from the National Institutes of Health [R01AI120938 and R01AI128779 to A.A.R.T; U54EB007958 and U01068613 to C.A.G.; and T32AI102623 to E.U.P.] and the Division of Intramural Research, National Institute of Allergy and Infectious Diseases (T.Q.)
Footnotes
Potential conflicts of interest: All authors: No reported conflicts of interest.
Publisher's Disclaimer: Disclaimer: The content is solely the responsibility of the authors and does not necessarily represent the official views of the funders.
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