Abstract
Using data from the 2006–2010 National Survey of Family Growth, we found that lifetime number of vaginal sex partners is positively associated with the number of sex partners in the past 12 months and negatively associated with age at first vaginal intercourse among 15- to 44-year-old male and female respondents.
Studies have shown an association between lifetime sexual behaviors and age at sexual debut1,2 and recent sexual behaviors3; however, few studies have examined the relationship between these behaviors using data from national surveys. National data focusing on sexual behaviors are important to sexually transmitted infection (STI) research and prevention. Such data can be useful in many areas, including informing mathematical models of STIs, understanding epidemiological trends in STI incidence, and targeting prevention resources to those at highest risk for acquisition and transmission of STIs.4–6 For instance, as the use of mathematical modeling in the field of STI prevention has continued to grow in recent years,7 so has the need for data on sexual behavior to inform these models. The need for sexual behavior data is especially pronounced for individual-based models,8,9 which are becoming more common owing, in part, to the increased availability and affordability of faster, more powerful computers.10
The purpose of this study was to examine the distribution of sexual behaviors in the United States stratified by the lifetime number of vaginal sex partners. Our main contribution to the existing literature is use of recent, nationally representative data. Such data are useful (1) to illustrate heterogeneity in sexual behavior by sex, age, and lifetime number of sex partners to aid STI prevention efforts and (2) to inform mathematical models of STIs that often classify the population according to sexual activity level, based on the frequency at which people acquire new sex partners.6,10
We used data from the 2006–2010 National Survey of Family Growth (NSFG), a nationally representative, cross-sectional sample of men and women.11 The NSFG is a national probability sample of noninstitutionalized respondents aged 15 to 44 years interviewed in their homes from June 2006 to June 2010.11 Hispanics, blacks, and youth (age 15–24 years) were oversampled.11–13 There were 12,279 female respondents and 10,403 male respondents, with a response rate of 77%.12 Data included in this analysis were from an interviewer-administered computer-assisted personal interview.11 Data were analyzed using SAS version 9.3 (SAS Institute, Cary, NC) and SAS-callable SUDAAN 11.0 (Research Triangle Institute, Research Triangle Park, NC) to account for the complex sampling design.14,15
We created 5 sexual activity groups according to self-reported lifetime number of sex partners, where sex was defined as heterosexual vaginal intercourse and same-sex partners were excluded: sexual activity group 1 (0–1 lifetime sex partners), sexual activity group 2 (2–4 lifetime sex partners), sexual activity group 3 (5–9 lifetime sex partners), sexual activity group 4 (10–39 lifetime sex partners), and sexual activity group 5 (40+ lifetime sex partners). These groups are similar to those used in a recent individual-level model of human papillomavirus (HPV) vaccination and were modified based on previous research to be useful to other STI prevention and modeling efforts.9
We analyzed 3 sexual behavior measures. First, we examined the distribution of the population across the sexual activity groups, stratified by sex and age (using 5-year groupings). Second, for each sexual activity group, we calculated the mean number of recent vaginal sex partners (past 12 months), stratified by sex and age group. Third, for each sexual activity group, we examined age at first vaginal intercourse (among those aged 25–34 years) stratified by sex. We excluded older age groups from the “age at first vaginal intercourse” analysis to assess age at first vaginal intercourse in more recent years. Recent data are most useful for sexually transmitted disease prevention efforts including modeling. For all analyses, we calculated 95% confidence intervals (CIs) for estimates, and we examined overlap in CIs as a conservative estimate of statistical significance (CIs available in Appendix A).16
For the distribution of number of lifetime vaginal sex partners, we found similarities across age groups for male and female respondents, with a few minor exceptions. Among 15- to 24-year-olds, sexual activity group 1 (0–1 lifetime sex partners) was the most frequently reported sexual activity group for male (32.2%–70.5%) and female (34.7%–72.0%) respondents (Fig. 1A, B). For all age groups, sexual activity group 5 (40+ lifetime sex partners) was the least frequently reported sexual activity group for all male and female respondents. However, among women aged 25 to 44 years, sexual activity group 2 (2–4 lifetime sex partners) was the most frequently reported sexual activity group (30.3%–30.9%), whereas for men aged 25 to 44 years, sexual activity group 4 (10–39 lifetime sex partners) was the most frequently reported (27.8%–34.2%).
Figure 1.
A, Distribution of the number of lifetime sex partners among women by age group, NSFG 2006–2010 (n = 12,279). *Among women reporting 40 or more lifetime sex partners (age 15–19 years) the unweighted frequency (n) was less than 10; therefore, the results have been suppressed. Note: For clarity of illustration, the vertical axis was truncated at 40%. The actual value for 15- to 19-year-old girls who reported 0 to 1 lifetime sex partners is 72%. Confidence intervals can be found in Appendix A. B, Distribution of the number of lifetime sex partners among men by age group, NSFG 2006–2010 (n = 10,403). Note: For clarity of illustration, the vertical axis was truncated at 40%. The actual value for 15- to 19-year-old boys who reported 0 to 1 lifetime sex partners is 70.5%. Confidence intervals can be found in Appendix A.
The mean number of recent sex partners (past 12 months) varied according to lifetime number of sex partners; however, within sexual activity groups, we found few significant differences by age or sex (Fig. 2A, B). Overall, those in sexual activity group 1 (0–1 lifetime sex partners) had less than 1 recent sex partner on average, whereas respondents in sexual activity group 5 (40+ lifetime sex partners) reported a range of 1.5 (men, 40–44 years) to 5.1 recent partners (boys, 15–19 years). Although male respondents reported significantly more recent partners than female respondents overall (with the exception of those 15–19 years old), within a given sexual activity group, the reported numbers of recent vaginal sex partners did not significantly differ for male and female respondents by age group.
Figure 2.
A, Number of sex partners in the past 12 months among women by age group and sexual activity group (lifetime number of sex partners), NSFG 2006–2010 (n = 12,278). *Among women reporting 40 or more lifetime sex partners (age 15–19 years), the unweighted frequency (n) was less than 10; therefore, the results have been suppressed. Note: For clarity of illustration, the vertical axis was truncated at 3.5 partners. Confidence intervals can be found in Appendix A. B, Number of sex partners in the past 12 months among men by age group and sexual activity group (lifetime number of sex partners), NSFG 2006–2010 (n = 10,403). Note: For clarity of illustration, the vertical axis was truncated at 3.5 partners. The actual mean number of sex partners in the past 12 months for sexual activity group 5 (40+ lifetime sex partners) is 5.07 for 15- to 19-year-old boys and 3.72 for 20- to 24-year-olds. Confidence intervals can be found in Appendix A.
Age at first vaginal intercourse varied according to lifetime number of partners (Fig. 3A, B). In general, those with higher numbers of lifetime sex partners reported a younger age at first vaginal intercourse than those with lower numbers of lifetime sex partners. Male and female respondents reported similar ages at first vaginal intercourse for all sexual activity groups, except for sexual activity group 1 (0–1 lifetime sex partners). Within sexual activity group 1, more male respondents (88.6%) reported their first vaginal intercourse at age 18–24 years than female respondents (78.2%).
Figure 3.
A, Age at first vaginal intercourse among women aged 25 to 34 years by sexual activity group (lifetime number of sex partners), NSFG 2006–2010 (n = 4,090). *Among women reporting first vaginal intercourse at age 17 years, in the sexual activity group 4 (≥40 lifetime sex partners), the unweighted frequency (n) was less than 10; therefore, the results have been suppressed. Note: For clarity of illustration, the vertical axis was truncated at 60%. For sexual activity group 1 (0–1 lifetime sex partners), the actual value of first vaginal sex at age 18 to 24 years is 78.2%. Confidence intervals can be found in Appendix A. B, Age at first vaginal intercourse among men aged 25 to 34 years by sexual activity group (lifetime number of sex partners), NSFG 2006–2010 (n = 3,362). *Among men reporting first vaginal intercourse at age 10 to 14 or 15 years, in the sexual activity group 1 (0–1 lifetime sex partners), the unweighted frequency (n) was less than 10; therefore, the results have been suppressed. Note: For clarity of illustration, the vertical axis was truncated at 60%. For sexual activity group 1 (0–1 lifetime sex partners), the actual value of first vaginal sex at age 18 to 24 years is 88.6%. Confidence intervals can be found in Appendix A.
Our findings that lifetime number of sex partners is associated with (a) the number of recent sex partners and (b) age at sexual debut are supported by other studies.1–3,17–20 For example, in a study of US adults (age >18 years), early age at first intercourse (<14 years) was associated with more sex partners in the past year and the previous 5 years among men and women.2 Similarly, among nearly 65,000 Nordic women, women with younger age at first intercourse (<14 years) were 4 times more likely to report 10 lifetime partners and nearly twice as likely to report 2 or more recent sex partners (past 6 months) compared with older age at first intercourse (>14 years).1 Although the associations we report have been documented previously in other populations, our analysis offers additional insights into the use of lifetime number of sex partners as a sexual behavioral measure. A key theme of our results is that lifetime number of sex partners is a simple yet useful measure to capture heterogeneity in sexual activity. When controlling for lifetime number of sex partners (sexual activity groups 1–5 in our application), we found no significant differences between men and women in (a) reported number of recent sex partners and (b) age at sexual debut (except as noted above for sexual activity group 1).
The sexual activity groups we used were similar to, but not exactly the same as, the sexual activity groups used by Van de Velde and colleagues.9 However, the distribution of the population across sexual activity groups that we observed using US data is generally consistent with the distributions applied by Van de Velde and colleagues.9 Although our study is representative of the US general population aged 15 to 44 years, Van de Velde and colleagues9 used sexual behavior data from a Canadian multicenter clinical study.
Our analysis is subject to limitations. Responses to the interviewer-administered survey could be subject to social desirability bias. The measure for the number of sex partners in the past 12 months was top coded at 7, which could reduce the mean but also prevents extreme outliers from skewing the results. Sexual behaviors only included heterosexual vaginal sex partners in our analyses because we wanted to focus on vaginal sex in the lifetime; therefore, other sexual risk behaviors such as oral and anal sex were not accounted for in these analyses. Sample sizes precluded analyses by other sociodemographics. To facilitate the use of our results in future STI prevention efforts including models, the sexual activity groups we used were selected based on a recent model of HPV vaccination.9 Additional analyses are needed to examine alternate sexual activity classifications.
Despite these limitations, our analysis provides useful data on sexual behavior by age, sex, and lifetime number of vaginal sex partners. Furthermore, our analysis illustrates the potential usefulness of lifetime number of sex partners as a simple classification to reflect heterogeneity in other sexual behaviors. The examination of sexual behaviors by age groups and by sex is important for sex-specific, age-related recommendations and prevention programs (such as screening for chlamydial infection21,22 and HPV vaccination23,24). Our results can contribute to understanding trends in STI epidemiology, improvement of STI prevention strategies, and applications of mathematical models of STIs.25
Acknowledgments
This research was supported in part by an appointment to the Research Participation Program at the Centers for Disease Control and Prevention administered by the Oak Ridge Institute for Science and Education through an interagency agreement between the US Department of Energy and Centers for Disease Control and Prevention.
APPENDIX
TABLE A1.
Distribution of the Number of Lifetime Sex Partners, by Age Group and Sex, NSFG 2006–2010
| Age Group, y |
Lifetime Sex Partners |
Women (n = 12,279)
|
Men (n = 10,403)
|
||||||
|---|---|---|---|---|---|---|---|---|---|
| Unweighted n | Population Estimate |
% | 95% CI | Unweighted n | Population Estimate |
% | 95% CI | ||
| 15–19 | 0–1 partner | 1592 | 7,541,000 | 72.0 | 69.2–74.7 | 1581 | 7,627,000 | 70.5 | 67.9–73.1 |
| 2–4 partners | 435 | 1,805,0000 | 17.2 | 15.0–19.0 | 458 | 1,877,000 | 17.4 | 15.2–19.6 | |
| 5–9 partners | 191 | 828,000 | 7.9 | 6.4–9.8 | 200 | 722,000 | 6.7 | 5.2–8.2 | |
| 10–39 partners | 65 | 54,000 | 2.9 | 1.8–3.9 | 129 | 556,000 | 5.1 | 4.1–6.1 | |
| 40+ partners | —* | — | — | — | 10 | 35,000 | 0.3 | 0.0–0.6 | |
| 20–24 | 0–1 partner | 660 | 3,599,000 | 34.7 | 29.9–39.5 | 488 | 3,346,000 | 32.2 | 25.0–39.4 |
| 2–4 partners | 626 | 2,987,000 | 28.8 | 25.4–32.3 | 437 | 2,607,000 | 25.1 | 21.8–28.3 | |
| 5–9 partners | 487 | 2,425,000 | 23.4 | 20.3–26.5 | 393 | 2,119,000 | 20.4 | 16.7–24.1 | |
| 10–39 partners | 308 | 1,260,000 | 12.2 | 9.8–14.5 | 362 | 2,004,000 | 19.3 | 16.0–22.6 | |
| 40+ partners | 17 | 94,000 | 0.9 | 0.2–1.6 | 53 | 318,000 | 3.1 | 1.8–4.4 | |
| 25–29 | 0–1 partner | 555 | 2,625,000 | 24.9 | 21.7–28.2 | 318 | 1,849,000 | 17.2 | 14.5–19.9 |
| 2–4 partners | 712 | 3,219,000 | 30.6 | 27.6–33.5 | 427 | 2,757,000 | 25.6 | 22.1–29.2 | |
| 5–9 partners | 603 | 2,528,000 | 24.0 | 20.8–27.2 | 433 | 2,659,000 | 24.7 | 21.7–27.8 | |
| 10–39 partners | 444 | 1,955,000 | 18.6 | 15.8–21.3 | 535 | 2,986,000 | 27.8 | 24.6–31.0 | |
| 40+ partners | 52 | 208,000 | 2.0 | 1.1–2.8 | 94 | 509,000 | 4.7 | 3.5–6.0 | |
| 30–34 | 0–1 partner | 431 | 2,040,000 | 22.2 | 19.1–25.3 | 245 | 1,536,000 | 16.6 | 13.7–19.6 |
| 2–4 partners | 605 | 2,836,000 | 30.9 | 27.5–34.2 | 335 | 1,976,000 | 21.4 | 17.8–25.0 | |
| 5–9 partners | 521 | 2,268,000 | 24.7 | 21.6–27.7 | 341 | 1,843,000 | 20.0 | 16.5–23.4 | |
| 10–39 partners | 437 | 1,851,000 | 20.1 | 17.3–23.0 | 502 | 3,060,000 | 33.2 | 29.3–37.1 | |
| 40+ partners | 53 | 193,000 | 2.1 | 1.0–3.2 | 132 | 812,000 | 8.8 | 6.2–11.4 | |
| 35–39 | 0–1 partner | 379 | 2,454,000 | 23.3 | 20.4–26.2 | 207 | 1,691,000 | 16.3 | 13.4–19.1 |
| 2–4 partners | 550 | 3,188,000 | 30.3 | 26.9–33.6 | 308 | 2,235,000 | 21.5 | 18.6–24.3 | |
| 5–9 partners | 492 | 2,902,000 | 27.5 | 24.7–30.4 | 335 | 2,081,000 | 20.0 | 17.0–23.0 | |
| 10–39 partners | 339 | 1,839,000 | 17.5 | 14.9–20.0 | 522 | 3,556,000 | 34.2 | 30.9–37.4 | |
| 40+ partners | 38 | 154,000 | 1.5 | 0.8–2.2 | 128 | 843,000 | 8.1 | 5.7–10.5 | |
| 40–44 | 0–1 partner | 321 | 2,295,000 | 21.5 | 18.7–24.3 | 182 | 1,399,000 | 13.3 | 10.4–16.2 |
| 2–4 partners | 499 | 3,246,000 | 30.5 | 27.3–33.6 | 288 | 2,443,000 | 23.2 | 19.7–26.7 | |
| 5–9 partners | 504 | 3,141,000 | 29.5 | 26.2–32.8 | 323 | 2,552,000 | 24.2 | 20.8–27.7 | |
| 10–39 partners | 318 | 1,729,000 | 16.2 | 13.5–19.0 | 500 | 3,385,000 | 32.2 | 28.6–35.7 | |
| 40+ partners | 44 | 240,000 | 2.3 | 1.3–3.2 | 137 | 747,000 | 7.1 | 5.1–9.1 | |
Where the unweighted frequency (n) is less than 10, the results have been suppressed.
TABLE A2.
Number of Sex Partners in the Past 12 Months by Age Group, Sex, and Sexual Activity Group (Lifetime Number of Sex Partners), NSFG 2006–2010
| Age Group, y | Women (n = 12,278*)
|
Men (n = 10,403)
|
||
|---|---|---|---|---|
| Mean | 95% CI | Mean | 95% CI | |
| No. sex partners, past 12 mo (for all sexual activity groups) | ||||
| 15–19 | 1.56 | 1.45–1.67 | 1.69 | 1.58–1.80 |
| 20–24 | 1.31 | 1.25–1.38 | 1.65 | 1.54–1.76 |
| 25–29 | 1.17 | 1.13–1.22 | 1.35 | 1.27–1.44 |
| 30–34 | 1.07 | 1.01–1.12 | 1.27 | 1.19–1.35 |
| 35–39 | 0.99 | 0.96–1.02 | 1.15 | 1.09–1.20 |
| 40–44 | 0.94 | 0.91–0.98 | 1.07 | 1.01–1.13 |
| Sexual activity group 1 (0–1 lifetime sex partners) | ||||
| 15–19 | 0.86 | 0.81–0.91 | 0.82 | 0.76–0.88 |
| 20–24 | 0.86 | 0.81–0.90 | 0.78 | 0.68–0.88 |
| 25–29 | 0.90 | 0.86–0.94 | 0.84 | 0.77–0.92 |
| 30–34 | 0.90 | 0.86–0.95 | 0.91 | 0.86–0.96 |
| 35–39 | 0.90 | 0.85–0.94 | 0.88 | 0.82–0.93 |
| 40–44 | 0.89 | 0.85–0.93 | 0.91 | 0.85–0.97 |
| Sexual activity group 2 (2–4 lifetime sex partners) | ||||
| 15–19 | 1.47 | 1.36–1.59 | 1.35 | 1.25–1.44 |
| 20–24 | 1.12 | 1.04–1.19 | 1.07 | 0.99–1.15 |
| 25–29 | 0.98 | 0.94–1.01 | 0.90 | 0.82–0.98 |
| 30–34 | 0.92 | 0.89–0.96 | 0.92 | 0.85–0.99 |
| 35–39 | 0.95 | 0.89–1.02 | 0.91 | 0.86–0.96 |
| 40–44 | 0.86 | 0.82–0.91 | 0.86 | 0.79–0.94 |
| Sexual activity group 3 (5–9 lifetime sex partners) | ||||
| 15–19 | 2.58 | 2.30–2.86 | 2.70 | 2.45–2.95 |
| 20–24 | 1.49 | 1.36–1.62 | 1.76 | 1.55–1.97 |
| 25–29 | 1.18 | 1.11–1.25 | 1.25 | 1.17–1.33 |
| 30–34 | 1.03 | 0.98–1.07 | 1.07 | 1.02–1.11 |
| 35–39 | 1.00 | 0.97–1.03 | 1.04 | 0.99–1.09 |
| 40–44 | 0.93 | 0.89–0.98 | 1.02 | 0.90–1.13 |
| Sexual activity group 4 (10–39 lifetime sex partners) | ||||
| 15–19 | 2.90 | 2.24–3.56 | 3.45 | 2.97–3.94 |
| 20–24 | 2.09 | 1.80–2.38 | 2.66 | 2.38–2.94 |
| 25–29 | 1.64 | 1.49–1.80 | 1.75 | 1.56–1.95 |
| 30–34 | 1.37 | 1.20–1.53 | 1.43 | 1.29–1.56 |
| 35–39 | 1.09 | 1.00–1.18 | 1.27 | 1.18–1.36 |
| 40–44 | 1.09 | 0.98–1.21 | 1.22 | 1.07–1.37 |
| Sexual activity group 5 (40+ lifetime sex partners) | ||||
| 15–19 | —† | — | 5.07 | 4.18–5.96 |
| 20–24 | 2.89 | 2.11–3.66 | 3.72 | 2.77–4.67 |
| 25–29 | 2.57 | 1.83–3.31 | 3.32 | 2.64–4.00 |
| 30–34 | 2.28 | 0.90–3.66 | 2.56 | 1.94–3.19 |
| 35–39 | 1.97 | 1.30–2.64 | 1.98 | 1.66–2.29 |
| 40–44 | 1.61 | 1.16–2.07 | 1.54 | 1.26–1.82 |
The number of sex partners in the past 12 months is top coded at n = 7.
One participant was excluded from the analysis because she reported only 1 lifetime sex partner but also reported 60 sex partners in the past 12 months.
Where the unweighted frequency (n) is less than 10, the results have been suppressed.
TABLE A3.
Age at First Vaginal Intercourse for Those Aged 25 to 34 Years by Sex and Sexual Activity Group (Lifetime Number of Sex Partners), NSFG 2006–2010
| Age at First Vaginal Intercourse, y | Women (n = 4090)
|
Men (n = 3362)
|
||||||
|---|---|---|---|---|---|---|---|---|
| Unweighted n | Population Estimate | % | 95% CI | Unweighted n | Population Estimate | % | 95% CI | |
| Age at first vaginal sex (for all sexual activity groups) | ||||||||
| 10–14 | 684 | 2,778,000 | 15.1 | 13.2–17.1 | 673 | 3,638,000 | 19.8 | 17.7–21.9 |
| 15 | 583 | 2,670,000 | 14.6 | 12.8–16.3 | 429 | 2,744,000 | 14.9 | 13.1–16.8 |
| 16 | 742 | 3,518,000 | 19.2 | 17.1–21.2 | 525 | 3,317,000 | 18.1 | 16.2–19.9 |
| 17 | 587 | 2,489,000 | 13.6 | 11.8–15.3 | 455 | 2,862,000 | 15.6 | 13.7–17.5 |
| 18–24 | 1,494 | 6,892,000 | 37.6 | 34.7–40.4 | 972 | 5,797,000 | 31.6 | 28.8–34.4 |
| Sexual activity group 1 (0–1 lifetime sex partners) | ||||||||
| 10–14 | 15 | 32,000 | 0.9 | 0.3–1.5 | —* | — | — | — |
| 15 | 42 | 164,000 | 4.7 | 2.6–6.7 | —* | — | — | — |
| 16 | 52 | 241,000 | 6.9 | 3.9–9.8 | 12 | 48,000 | 2.5 | 0.2–4.7 |
| 17 | 74 | 329,000 | 9.4 | 6.3–12.5 | 19 | 108,000 | 5.6 | 2.0–9.1 |
| 18–24 | 539 | 2,746,000 | 78.2 | 73.8–82.6 | 255 | 1,720,000 | 88.6 | 83.6–93.6 |
| Sexual activity group 2 (2–4 lifetime sex partners) | ||||||||
| 10–14 | 128 | 539,000 | 9.1 | 6.7–11.4 | 73 | 318,000 | 6.9 | 4.1–9.7 |
| 15 | 160 | 796,000 | 13.4 | 10.6–16.2 | 79 | 591,000 | 12.8 | 8.6–17.0 |
| 16 | 235 | 1,222,000 | 20.5 | 17.0–24.1 | 115 | 679,000 | 14.7 | 10.4–19.0 |
| 17 | 219 | 982,000 | 16.5 | 13.1–19.9 | 121 | 831,000 | 18.0 | 13.7–22.3 |
| 18–24 | 548 | 2,410,000 | 40.5 | 36.5–44.5 | 348 | 2,193,000 | 47.6 | 41.2–53.9 |
| Sexual activity group 3 (5–9 lifetime sex partners) | ||||||||
| 10–14 | 228 | 834,000 | 17.5 | 14.4–20.5 | 159 | 926,000 | 20.7 | 16.2–25.2 |
| 15 | 207 | 955,000 | 20.0 | 16.2–23.8 | 108 | 612,000 | 13.7 | 9.8–17.5 |
| 16 | 255 | 1,203,000 | 25.2 | 20.9–29.5 | 154 | 1,063,000 | 23.8 | 19.5–28.0 |
| 17 | 177 | 721,000 | 15.1 | 11.8–18.4 | 154 | 882,000 | 19.7 | 15.6–23.8 |
| 18–24 | 244 | 1,058,000 | 22.2 | 17.8–26.6 | 195 | 990,000 | 22.1 | 18.0–26.3 |
| Sexual activity group 4 (10–39 lifetime sex partners) | ||||||||
| 10–14 | 261 | 1,205,000 | 32.4 | 26.0–38.7 | 316 | 1,772,000 | 29.4 | 24.9–34.0 |
| 15 | 161 | 684,000 | 18.4 | 13.8–23.0 | 202 | 1,255,000 | 20.8 | 16.7–25.0 |
| 16 | 184 | 783,000 | 21.0 | 16.3–25.8 | 211 | 1,295,000 | 21.5 | 17.3–25.7 |
| 17 | 108 | 406,000 | 10.9 | 8.0–13.8 | 140 | 865,000 | 14.4 | 11.0–17.7 |
| 18–24 | 153 | 644,000 | 17.3 | 13.5–21.1 | 160 | 838,000 | 13.9 | 10.8–17.0 |
| Sexual activity group 5 (40+ lifetime sex partners) | ||||||||
| 10–14 | 52 | 169,000 | 41.2 | 27.3–59.0 | 121 | 610,000 | 46.7 | 37.1–56.2 |
| 15 | 13 | 70,000 | 17.7 | 1.7–33.8 | 34 | 234,000 | 17.9 | 9.3–26.5 |
| 16 | 16 | 69,000 | 17.6 | 1.8–33.3 | 33 | 232,000 | 17.7 | 8.2–26.9 |
| 17 | —* | — | — | — | 21 | 175,000 | 13.4 | 6.8–20.0 |
| 18–24 | 10 | 35,000 | 8.8 | 2.1–15.6 | 14 | 56,000 | 4.3 | 1.1–7.5 |
Where the unweighted frequency (n) is less than 10, the results have been suppressed.
Footnotes
Disclosure: The findings and conclusions in this report are those of the authors and do not necessarily represent the official position of the Centers for Disease Control and Prevention.
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