Chlamydia trachomatis is the most commonly reported bacterial sexually transmitted disease (STD) in the United States. In women, chlamydial infections cause substantial morbidity, especially among those 15 to 24 years of age.1 Genital chlamydial infection in women may cause pelvic inflammatory disease, tubal infertility, ectopic pregnancy, and chronic pelvic pain2,3 and additionally may increase the risk for human immunodeficiency virus infection4,5 and cervical carcinoma.6,7 Two thirds of women with chlamydial infection in the cervix have no signs or symptoms of the infection.8 Because of the asymptomatic nature of the disease, screening and treatment programs for chlamydial infection constitute an important component of the prevention effort to reduce the disease burden.
The National Job Training Program (NJTP) is an occupational training program for socioeconomically disadvantaged aged 16 to 24 years old (i.e., high school dropouts, those in need of additional education, vocational training, or assistance to hold meaningful employment). In 1999, approximately 73% of the enrollees were from minority groups, 79% were high school dropouts, 62% had never been employed full time, and 26% were from families on public assistance.9 Because adolescent women have a lack of access to health care and are at high risk for chlamydial infection, the NJTP implemented universal chlamydia screening, starting in 1990, for females. This screening program is part of the entrance physical examination at approximately 110 program centers across the United States.
In previous analyses, Mertz et al.10 reported a decline in chlamydia prevalence in this population from 14.9% in May 1990 to 10.0% in June 1997. During this period (1990–1997), only Pathfinder Enzyme Immunoassay (EIA) (Sanofi Diagnostics Pasteur, Inc. Redmond, WA) was used to detect chlamydial infections. However, in 1998, a dioxyribonucleic acid (DNA) hybridization probe (GenProbe PACE 2, San Diego, CA), a more sensitive test, replaced the Pathfinder EIA test.11,12 Starting in 2000, a small proportion of women were tested by strand displacement assay (BDProbeTec ET, Becton-Dickinson, Sparks, MD). The objectives of this paper are to examine the trends of chlamydia prevalence in women after the introduction of the GenProbe test from 1998 to 2004 and to identify risk factors associated with chlamydial infection.
All women aged 16 to 24 years who were enrolled and screened at the training program from January 1998 through December 2004 were included in this analysis (106,377 women). Most women received pelvic examination within 14 days of enrollment. At most program centers, cervical specimens were obtained during this examination. These cervical specimens were sent to a contract laboratory for the detection of chlamydial infection by DNA hybridization probe (GenProbe PACE 2). Women who did not had a pelvic examination or did not provide urine specimens were excluded from the analysis. During the analysis period, GenProbe was used to detect chlamydial infections for 93.1% of women. In 2000, the strand displacement assay (BDProbeTec ET, Becton-Dickinson) was also used to detect genital chlamydial infection using urine specimens. A total of 3.6% of the women were tested by BDProbeTec test in 2000, 5.6% in 2001, 7.1% in 2002, 12.2% in 2003, and 17.4% in 2004. In addition to laboratory test results and type, information was collected about STD symptoms (symptomatic versus asymptomatic), demographic information (age, race/ethnicity, and state of residence), and year of test. No information on sexual behavior was collected.
We restricted our analysis to women whose specimens were labeled as “entrance examination” because these specimens constituted true screening. In the analysis, we used the following categories: age groups (16–17, 18–19, 20–21, 22–24 years), race/ethnicity (white, black, Hispanic, American Indian/Alaska Native, and Asian/Pacific Islander), state of residence, geographic region (Bureau of the Census regions: Northeast, South, Midwest, and West), presence of STD symptoms, type of chlamydia test, period of the test (1998–2000 and 2001–2004), and year of test. A total of 9062 women had missing race/ethnicity and 10,390 had missing state of residence. We excluded these women from the multivariate logistic regression analysis.
We used logistic regression to adjust the combined (1998–2004) chlamydial infection for age group, race/ethnicity, STD symptoms, type of test used, and period of the test; and computed the odds ratio (OR) and their 95% confidence intervals (CI). To compare prevalence by year, we used direct standardization to adjust the annual prevalence for age, race/ethnicity, and geographic region using the 1998 age group (16–17, 18–19, 20–21, 22–24 years), race/ethnicity (white, black, Hispanic, others), and region (South, Northeast, Midwest, and West) distributions as the “standard” population. The standard error of the annual prevalence and the relative decrease in prevalence from 1998 to 2004 was obtained using Taylor series approximation. The relative change (in percent) was computed as prevalence of the later year minus prevalence of the earlier year, divided by the prevalence of the earlier year. The significance of annual trends (treating year of test as an ordinal explanatory variable) was examined using logistic regression.13 A test is statistically significant if the P value <0.05.
Because changes in laboratory tests from a lower-sensitivity test (GenProbe) to a higher-sensitivity test (BDProbeTec) in the later years may spuriously increase the chlamydia prevalence, we adjusted the prevalence for changes in laboratory test sensitivity.14 In this adjustment, the reciprocal of the test sensitivity was used to estimate prevalence. We used sensitivity of 61.9% for the GenProbe test15 and of 83.0% for BDProbeTec test in the adjustment.16 We used SAS (SAS Institute, Inc, Cary, NC) and SUDAAN (SUDAAN, Research Triangle Institute, Research Triangle Park, NC) software for data analyses.
The total number of women who were screened in the National Job Training Program (NJTP) varied by year from 17,700 in 1998 to 19,198 in 2004, an average of 15,197 women per year. Screening coverage also varied by year from 88% in 1998 to 84% in 2003, a total coverage of 86%. Chlamydia prevalence decreased by age from 12.7% in women aged 16 to 17 years to 6.6% in women aged 22 to 24 years (Table 1). Black women had the highest prevalence (13.1%), followed by American Indian (11.1%), Asian/Pacific Islander (11.0%), Hispanic (9.6%), and white (6.8%) women. Women who resided in the South had the highest prevalence (12.6%), whereas women who resided in the West had the lowest prevalence (8.7%). Women who reported STD symptoms had a significantly higher prevalence than those who did not report having had symptoms (13.1% versus 10.8%, respectively). Women who were tested in the earlier period (1998–2000) had a significantly higher prevalence than women tested in the later period (2001–2004) (11.6% versus 10.8%, respectively). In the logistic regression analysis, factors associated with the chlamydial infection in the univariate analysis were also independently associated with the increased risk of chlamydial infection (young age, nonwhite race, Southern region only, presence of STD symptoms, and early period of the test [1998–2000]) (Table 1).
Chlamydia prevalence significantly decreased from 11.7% in 1998 to 10.0% in 2003, and then slightly increased, although not statistically significantly, from 2003 to 2004 (Fig. 1). A similar pattern was observed after standardization for age groups, race/ethnicity, and regions. From 1998 to 2003, the relative standardized prevalence decrease was 14.1% (95% CI, 7.9%–20.3%) and from 2003 to 2004, the relative standardized prevalence increase was 2.3% (95% CI, −3.7% to 9.0%). As expected, adjustment for the sensitivity of the laboratory tests resulted in higher prevalence for all years but a similar pattern of decline. The adjusted prevalence was 18.8% (1998), 18.7% (1999), 18.2% (2000), 17.6% (2001), 17.0% (2002), 15.8% (2003), and 16.0% (2004) (data not shown). A similar pattern of decline was observed after excluding women who were tested by BDProbeTec (11.7% in 1998, 11.7% in 1999, 11.4% in 2000, 10.7% in 2001, 10.6% in 2002, 9.7% in 2003, and 10.2% in 2004) (data not shown). Evaluation of trends stratified by sociodemographic characteristics indicated similar patterns as the overall trends, a decreased prevalence in all categories from 1998 to 2003, and a slightly increased or stable prevalence from 2003 to 2004 in most of the categories (Table 2). After adjustment for laboratory test sensitivity or after excluding women who were tested by BDProbeTec, similar trends in rates were observed (data not shown).
From 1990 to 1997 a 32.9% relative decline in the prevalence of chlamydia was found by Mertz et al.,10 compared to our data that showed a less pronounced relative prevalence decline (14.1%) from 1998 to 2003 and no decline from 2003 to 2004. Women in the younger age group (16–17 years) had more dramatic decline than in the older age groups. We speculate that the greater decline in younger age group (16–17 years) may be due to the higher baseline prevalence for this age group (14.0% in 16–17 years versus 6.9% in 22–24 years). The impact of intervention programs is usually more pronounced for those with higher rates than lower rates (more leeway for higher rates to drop than saturated lower rates). The overall decline in prevalence suggests that prevention activities may have reached the disadvantaged youth population and may be partly due to screening and treatment programs, which have been documented to reduce chlamydial infection in the community.17–19 However, the reason for stabilized prevalence in 2003 and 2004 is unclear at this time. Only continued monitoring of these trends will be able to determine if this is a random fluctuation or the beginning of stabilization.
To our knowledge, this analysis is the only recent assessment of trends of chlamydia prevalence in socioeconomically disadvantaged young women. A screening program that was implemented at an earlier period of time (1996 to 1998) among Army female recruits demonstrated a sustained high prevalence of chlamydia.20 The Chlamydia Prevalence Monitoring Surveillance System (CPMSS) has shown an increase in chlamydia positivity from 5.6% in 1998 to 7.2% in 2003 in Health and Human Services (HHS) region X among young women (15–24 years) who attended family planning clinics.21 Of the 10 HHS regions, from 1998 to 2003, chlamydia decreased in 5 regions (regions I, III, IV, V, and VI) and increased in others regions (regions II, VII, VIII, IX, and X).21 Unlike CPMSS, we computed chlamydia prevalence (number of women with positive tests divided by total number of women) instead of chlamydia positivity (number of positive tests divided by number of total tests; 1 woman may have more than 1 test) and reported chlamydia prevalence by age groups, race/ethnicity, and regions over the time period.
Although screening and treatment efforts may have reduced the prevalence in this group of young women, the overall prevalence, 10.3%, is still very high and the annual prevalence is persistently high. This persistently high prevalence makes this advantaged population a cost-effective venue for chlamydia screening.22,23 The persistent high prevalence and the less pronounced decline seen in recent years may be due to relatively low chlamydia screening coverage for adolescent women and limited screening in men. Screening and treatment of chlamydia in men have the potential to reduce the chlamydia reservoir in the community and reduce the incidence and prevalence of recurrent infection in women.24 Although the Centers for Disease Control and Prevention (CDC)25 and the U.S. Preventive Services Task Force26 have recommended universal chlamydia annual screening for adolescent women, the estimated national screening coverage for women aged 15 to 19 years in 2000 was only 60%.27 Other studies reported even lower chlamydia screening coverage than the national estimate of 60%.28,29 A study among young female enrollees (aged 16–26 years) in commercial and Medicaid health plans documented low and minimal increase in screening coverage of chlamydia.28 The screening coverage for commercial health plans increased from 20% in 1999 to 26% in 2001, and for Medicaid plans, from 28% in 1999 to 38% in 2001. The National Longitudinal Study of Adolescents also reported a low coverage of annual STD screening (22%) among a large nationally representative sample of adolescents.29 Several regional studies reported that many adolescent women did not receive annual chlamydia screening.30–32
Our study showed race/ethnicity and geographical differences. Blacks had chlamydia prevalence 2 times higher than whites. Previous studies among other populations of young women, including the general population and Army recruits, reported higher prevalence of chlamydia in blacks than whites.10,20,33–35 Among all 3 populations (general, Army recruits, and NJTP populations) there was a consistence of race/ethnicity differences, with the largest differences in the general population (14.0% in blacks versus 2.5% in whites),35 followed by the Army recruits (14.9% versus 5.5%)33 and the NJTP (13.1% versus 6.8%). Although race/ethnicity differences existed in all the 3 populations, the prevalence in blacks was similarly high across the 3 populations (14.9%, 14.0%, and 13.1%). In addition to race/ethnicity differences, we also found geographical differences, with the highest prevalence of chlamydia among women from the South (12.6%). Several studies among young women supported our findings of geographical differences.10,20,34,35 Similar prevalence trends in race/ethnicity and regional differences were also observed over the time period. A variety of complex factors such as social networks, sexual behavior, economic and social inequalities, and lack of access to prevention and treatment services might explain these race/ethnicity and geographical differences.
There are several limitations in this analysis. First, although our findings documented a decline of prevalence among disadvantaged youth in NJTP, the findings might not be generalizable to other women who did not participate in the NJTP. Second, chlamydia test results were available for 86% of the participants. Test results were not available if they were performed by a noncontract laboratory, if women had dropped out of the program before undergoing the physical examination, or if they denied being sexually active.34 Third, a number of records did not include race/ethnicity (8.5%) or state of residence (9.8%). The chlamydia prevalence in women with missing race/ethnicity was similar to those without missing race/ethnicity (10.7% versus 10.9%). Similar findings were not observed by state of residence (12.3% for missing residence versus 10.8% for nonmissing residence). Although we excluded the missing records in our multivariate analysis, we did not exclude these records in our trend analysis. However, trends should not be affected by either of the limitations. Last, starting in 2000, a more sensitive test was used.36 Because changes in laboratory tests from a lower-sensitivity test to a higher-sensitivity test may spuriously increase the chlamydia prevalence, we adjusted the prevalence for changes in laboratory test sensitivity.14 After the sensitivity adjustment, similar patterns of decline from 1998 to 2003 and slightly increased or stable prevalence from 2003 to 2004 were also observed.
In summary, the findings of a persistent high prevalence and minimal decrease in prevalence, especially among young black women, have implications for STD prevention and control. Prevention programs should include testing and treatment, safe-sex education, and partner notification and treatment targeted to disadvantaged out-of-school or out-of-workplace adolescents. Special attention should be focused on young black women. Health care providers should be encouraged to follow the CDC recommendation for at least annual chlamydia screening for young adolescent women. In addition, the Institute of Medicine recommendation for STD comprehensive services in nontraditional high-risk settings that lack access to clinical services should be implemented.37
1. Weinstock H, Berman S, Cates W Jr. Sexually transmitted diseases among American youth: incidence and prevalence estimates, 2000. Perspect Sex Reprod Health 2004; 36:6–10.
2. Cates W Jr, Wasserheit JN. Genital chlamydial infections: epidemiology and reproductive sequelae. Am J Obstet Gynecol 1991; 164(6 pt 2):1771–1781.
3. Westrom L, Eschenbach D. Pelvic inflammatory disease. In: Holmes KK, Mardh PA, Sparling PF, et al., eds. 3rd ed. New York, NY: McGraw-Hill, 1999:783–809.
4. Fleming DT, Wasserheit JN. From epidemiological synergy to public health policy and practice: the contribution of other sexually transmitted diseases to sexual transmission of HIV infection. Sex Transm Infect 1999; 75:3–17.
5. Royce RA, Sena A, Cates W Jr, et al. Sexual transmission of HIV. N Engl J Med 1997; 336:1072–1078.
6. Wallin KL, Wiklund F, Luostarinen T, et al. A population-based prospective study of Chlamydia trachomatis
infection and cervical carcinoma. Int J Cancer 2002; 101:371–374.
7. Samoff E, Koumans EH, Markowitz LE, et al. Association of Chlamydia trachomatis
with persistence of high-risk types of human papillomavirus in a cohort of female adolescents. Am J Epidemiol 2005; 162:668–675.
8. Stamm WE. Chlamydia trachomatis
infections of the adult. In: Holmes KK, Mardh PA, Sparling PF, et al., eds. 3rd ed. New York, NY: McGraw-Hill; 1999:407–422.
9. U.S. Department of Labor. Job Corps Annual Report, Program Year 1999. Washington, DC: U.S. Department of Labor, 2000.
10. Mertz KJ, Ransom RL, St. Louis ME, et al. Prevalence of genital chlamydial infection in young women entering a national job training program, 1990–1997. Am J Public Health 2001; 91:1287–1290.
11. Black CM. Current methods of laboratory diagnosis of Chlamydia trachomatis
infections. Clin Microbiol Rev 1997; 10:160–184.
12. Newhall WJ, Johnson RE, DeLisle S, et al. Head-to-head evaluation of five chlamydia tests relative to a quality-assured culture standard. J Clin Microbiol 1999; 37:681–685.
13. Schlesselman JJ. Case-Control Studies. New York, NY: Oxford University Press, 1982.
14. Dicker LW, Mosure DJ, Levine WC, et al. Impact of switching laboratory tests on reported trends in Chlamydia trachomatis
infections. Am J Epidemiol 2000; 151:430–435.
15. Black CM, Marrazzo J, Johnson RE, et al. Head-to-head multicenter comparison of DNA probe and nucleic acid amplification tests for Chlamydia trachomatis
infection in women performed with an improved reference standard. J Clin Microbiol 2002; 40:3757–3763.
16. Van Der PB, Ferrero DV, Buck-Barrington L, et al. Multicenter evaluation of the BDProbeTec ET system for detection of Chlamydia trachomatis
and Neisseria gonorrhoeae
in urine specimens, female endocervical swabs, and male urethral swabs. J Clin Microbiol 2001; 39:1008–1016.
17. Centers for Disease Control and Prevention. Chlamydia prevalence and screening practices: San Diego County, California, 1993. MMWR Morb Mortal Wkly Rep 1994; 43:366–369, 375.
18. Bachmann LH, Macaluso M, Hook EW III. Demonstration of declining community prevalence of Chlamydia trachomatis
infection using sentinel surveillance. Sex Transm Dis 2003; 30:20–24.
19. Mertz KJ, Levine WC, Mosure DJ, et al. Trends in the prevalence of chlamydial infections: the impact of community-wide testing. Sex Transm Dis 1997; 24:169–175.
20. Gaydos CA, Howell MR, Quinn TC, et al. Sustained high prevalence of Chlamydia trachomatis
infections in female army recruits. Sex Transm Dis 2003; 30:539–544.
21. Division of STD Prevention. Sexually Transmitted Disease Surveillance 2003. Atlanta, GA: Centers for Disease Control and Prevention, 2004.
22. Hu D, Hook EW III, Goldie SJ. Screening for Chlamydia trachomatis
in women 15 to 29 years of age: a cost-effectiveness analysis. Ann Intern Med 2004; 141:501–513.
23. Kraut-Becher JR, Gift TL, Haddix AC, et al. Cost-effectiveness of universal screening for chlamydia and gonorrhea in US jails. J Urban Health 2004; 81:453–471.
24. McConnell JK, Packel L, Biggs MA, et al. Integrating Chlamydia trachomatis
control services for males in female reproductive health programs. Perspect Sex Reprod Health 2003; 35:226–228.
25. Centers for Disease Control and Prevention. 1998 Guidelines for treatment of sexually transmitted diseases. MMWR Recomm Rep 1998; 47:1–111.
26. Screening for chlamydial infection: recommendations and rationale. US Preventive Services Task Force. Am J Prev Med 2001; 20(3 suppl):90–94.
27. Levine WC, Dicker LW, Devine O, et al. Indirect estimation of Chlamydia
screening coverage using public health surveillance data. Am J Epidemiol 2004; 160:91–96.
28. Centers for Disease Control and Prevention. Chlamydia screening among sexually active young female enrollees of health plans: United States, 1999–2001. MMWR Morb Mortal Wkly Rep 2004; 53:983–985.
29. Fiscus LC, Ford CA, Miller WC. Infrequency of sexually transmitted disease screening among sexually experienced U.S. female adolescents. Perspect Sex Reprod Health 2004; 36:233–238.
30. Ellen JM, Lane MA, McCright J. Are adolescents being screened for sexually transmitted diseases? a study of low income African American adolescents in San Francisco. Sex Transm Infect 2000; 76:94–97.
31. Mangione-Smith R, McGlynn EA, Hiatt L. Screening for chlamydia in adolescents and young women. Arch Pediatr Adolesc Med 2000; 154:1109–1113.
32. St. Lawrence JS, Montano DE, Kasprzyk D, et al. STD screening, testing, case reporting, and clinical and partner notification practices: a national survey of US physicians. Am J Public Health 2002; 92:1784–1788.
33. Gaydos CA, Howell MR, Pare B, et al. Chlamydia trachomatis
infections in female military recruits. N Engl J Med 1998; 339:739–744.
34. Lifson AR, Halcon LL, Hannan P, et al. Screening for sexually transmitted infections among economically disadvantaged youth in a National Job Training Program. J Adolesc Health 2001; 28:190–196.
35. Miller WC, Ford CA, Morris M, et al. Prevalence of chlamydial and gonococcal infections among young adults in the United States. JAMA 2004; 291:2229–2236.
36. Pollara C, Terlenghi L, De Francesco MA, et al. Comparative evaluation of BDProbeTec ET, LCx and PACE 2 assays for the detection of Chlamydia trachomatis
in urogenital specimens. Eur J Clin Microbiol Infect Dis 2003; 22:512–514.
© Copyright 2006 American Sexually Transmitted Diseases Association
37. Institute of Medicine. In: Eng TR, Butler WT, eds. The Hidden Epidemic: Confronting Sexually Transmitted Diseases. Washington, DC: National Academy Press, 1997.