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Infrequent Chlamydial Testing Among Young Adults: Financial and Regional Differences

Nguyen, Trang Quyen PhD, MPH*; Ford, Carol A. MD; Kaufman, Jay S. PhD*; Leone, Peter A. MD; Suchindran, Chirayath PhD§; Miller, William C. MD, PhD, MPH*‡

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Sexually Transmitted Diseases: August 2008 - Volume 35 - Issue 8 - p 725-730
doi: 10.1097/OLQ.0b013e318170588c
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THE NATIONAL PREVALENCE OF CHLAMYDIAL INFECTION (Ct) among young adults is estimated to be 4.19%. Regionally, prevalence is highest in the South (5.39%) when compared with the Midwest (3.95%), West (3.17%), and Northeast (2.39%).1 Most chlamydial infections are asymptomatic2–4 and are often undiagnosed,5 resulting in ongoing transmission. Routine Ct screening among women, first widely recommended in 1989, is cost-effective because of the high prevalence in this population. 6–10 Guidelines do not consistently suggest Ct screening for males, although screening asymptomatic males has been shown to reduce infections among females.11

In 1988, federal monitoring of Ct screening and prevalence began in the Northwest. This program was phased in nationally, representing a major public health effort to reduce prevalence of Ct infection. The South was one of the last US regions that received funding for this program in 1995.12 In 2000, the Health Plan Employee Data and Information Set added annual chlamydia screening for women between the ages of 15 and 25 as a measure of healthcare quality, highlighting efforts to encourage Ct screening of young women in both private and public clinical settings. Yet, economic disparities persist in Ct prevalence among adolescents and young adults,13 who represent 75% of all chlamydial infections.14–16 People at highest risk of infection often lack a source of regular care17 and might not be getting tested as regularly as needed.

Despite the funding and guidelines that were meant to increase Ct testing and reduce Ct prevalence among women nationwide, infection rates remain high among women, particularly in the South. In this study, we describe the prevalence of Ct testing among a representative sample of young adults in the United States, assess regional testing variation, and examine the associations between income, insurance status, and testing.


Study Design

The National Longitudinal Study of Adolescent Health (Add Health) is a prospective cohort study following approximately 20,000 individuals who enrolled in 1994 when they were adolescents. Our study includes cross-sectional analyses of wave III data, collected in 2001–2002 when respondents were young adults (age, 18–26 years). The University of North Carolina Institutional Review Board approved all study procedures.

The sampling design for Add Health has been described in detail elsewhere.18 Briefly, all public and private high schools in the United States registered in the Quality Education Database served as the primary sampling unit. In 1994, systematic sampling methods and implicit stratification were used to select a nationally representative sample of 80 high schools and 52 middle schools, ensuring a representative group with respect to the region of the country, degree of urbanicity, school type, ethnicity, and school size.

During wave I, all adolescents from the selected schools (n = 90,118) were asked to complete a brief in-school interview. Then, a random subsample of 17,600 students and certain systematically oversampled groups were selected to complete the wave I in-home interview. The oversampled groups included 4 ethnic groups (blacks from well-educated families, Chinese, Cuban, Puerto Rican), all students in 16 schools (to enable complete social network analysis), disabled students, and sibling pairs living in the same household. Design effects and unequal probability of selection were corrected to ensure a nationally representative sample. For wave III, from August 2001 until April 2002, Add Health attempted to re-interview all original wave I respondents currently living in the continental US, HI, or Alaska. We used poststratification weights in analyses to account for individuals who could not be located or refused to participate.


An interviewer traveled to the home or another suitable location to meet with contacted persons. After obtaining written consent, interviewers conducted approximately 90-minute interviews in a private area. Respondents’ answers about less sensitive topics were recorded in a laptop by the interviewer. For sensitive questions, respondents entered answers directly in the laptop using a Computer-Assisted Self-Interview program.

Population for Analysis

We conducted all analyses among sexually experienced respondents, defined as anyone who responded positively when asked “Have you ever had vaginal intercourse? (Vaginal intercourse is when a man inserts his penis into a woman's vagina.)”



Testing for chlamydial infection in the past 12 months was measured by self-report. Responses were coded as yes or no.

Main Factors of Interest

Geographic Region.

Respondents were interviewed in or near their residence. We coded the zip codes of their interview locations as being in the Northeast, South, Midwest, or West, as defined by the Centers for Disease Control and Prevention for national surveillance of communicable diseases.

Insurance Status.

Based on responses to “Which of the following best describes your current health insurance situation?,” respondents’ insurance status was coded as being public (i.e., Medicaid or Indian Health Service), private (i.e., parent's, spouse's, work, union, school, active-duty military, or self-pay insurance) or none.


We created a measure of functional income based on the ability of the respondent or the respondent's household to pay the full amount of 1) rent or mortgage or 2) bills for gas, electricity, or oil in the past year. If the respondent reported an inability to pay either at any time during the year, then income was defined as nonfunctional; all others were coded as having a functional income.

Other Characteristics and Behaviors

We evaluated if any respondent characteristics or behaviors modified the main relationships between testing and each financial resource (i.e., insurance status or income). Demographic variables we considered were gender, age, educational attainment, student enrollment status, employment status, and marital status (currently and ever). Self-reported race/ethnicity was categorized as white (white non-Hispanic), black (black non-Hispanic), Asian or Pacific Islander, Native American or Alaskan, and Latino/a (Hispanic of any race). To define sexual orientation, respondents were given 6 statements to select from, ranging from “100% heterosexual (straight)” or “100% homosexual (gay)” to not sexually attracted to either males or females. Based on responses, we categorized respondents as being either 100% heterosexual or not.

Sexual history and healthcare variables included age at first sex, number of lifetime sexual partners, frequency of sex in the past year, having sex with an STD-infected person in the past year, condom use at most recent sex, dripping or oozing from the penis or vagina in the past year, and use of medications for infections or birth control.


We used Stata, version 7.0 (College Station, TX, 2002) to account for the complex survey design of Add Health, incorporating the school as the primary sampling unit, region as a stratification variable, and poststratification weights. We stratified analyses by gender because of differences between men and women in national Ct prevalence estimates. Because screening guidelines exist only for women, our estimates of testing reported by women represent the degree to which practices match national guidelines.

After we calculated the prevalence of Ct testing in the US and for each region, we estimated testing prevalence by region, stratified by insurance status and income. Then, using logistic regression for survey data, we evaluated whether any characteristics or behaviors altered the main association between income or insurance status and Ct testing. Finally, we calculated nationally representative prevalence odds ratios and 95% confidence intervals for Ct testing.


Study Population

Of the wave I adolescent sample (n = 18,924), 14,322 young adults (75.7%) were located and agreed to participate in wave III. Six percent (n = 1109) refused participation and 18.5% (n = 3493) could not participate or be located.

Eighty-six percent of wave III respondents (n = 12,334) reported having participated in vaginal intercourse by the time of the interview and served as the analytical sample. Of these sexually experienced young adults, 49.7% were female. The majority (67.9%) was white, 16.6% were black, and 15.0% did not have a functional income (Table 1). Most young adults (67.8%) reported private insurance, whereas approximately 26% were uninsured and 7% were publicly insured. More than half (58.4%) did not use a condom during their most recent sexual intercourse and 2.5% experienced the symptom most often associated with chlamydial infection—dripping or oozing from the penis or vagina—in the past 12 months.

Characteristics of Add Health Respondents Who Reported Ever Having Vaginal Intercourse at Wave III (2001–2002)

Testing by Region—Women

Among women, Ct testing in the past year was low (27.3%; 95% CI, 25.5–29.2%) and varied regionally (Table 2). The lowest prevalence of reported chlamydia testing among women was in the South (24.8%; 95% CI, 22.0–27.8%), which was significantly lower than the prevalence of testing by women in the West (P <0.01) and Northeast (P <0.01).

Prevalence of Reported Testing for Chlamydial Infection in the Past 12 mo by Region, Among Add Health Respondents Who Reported Ever Having Vaginal Intercourse at Wave III (2001–2002)

Testing by Financial Resources—Women

In multivariable analyses, only race/ethnicity altered the association between insurance status and testing (Table 3). After adjusting for race/ethnicity, privately insured (OR, 0.72; 95% CI, 0.57–0.92) and uninsured females (OR, 0.63; 95% CI, 0.48–0.88) were less likely to report Ct testing when compared with publicly insured female young adults.

Prevalence, OR, and 95% CI Estimates for the Association Between Current Insurance Status and Testing for Chlamydial Infection by Region, Among Add Health Respondents Who Reported Ever Having Vaginal Intercourse at Wave III (2001–2002) (n = 13,659)

No demographic or behavioral variables modified the association between income and testing among women. The lowest prevalence of reported testing was among those with a functional income in the South (23.6%; 95% CI, 20.7–26.9%) (Table 4). Young women without a functional income were more likely to report Ct testing in the last year than those with a functional income (OR, 1.36; 95% CI, 1.12–1.66). These trends were consistent within each region.

Prevalence, OR, and 95% CI Estimates for the Association Between Current Functional Income and Testing for Chlamydial Infection Among Add Health Respondents Who Reported Ever Having Sexual Intercourse at Wave III (2001–2002) (n = 13,731)

Testing Among Males

The proportion of men who reported Ct testing was much lower than that among women, both nationally (8.9%; 95% CI, 7.7–10.2%) and regionally (Table 2). Regional differences were indiscernible. Prevalence was uniformly low across insurance and income levels. Though trends by financial status and region among men were similar to patterns of testing by women, estimates were imprecise (Tables 3 and 4) due to the small number of men who reported a history of Ct testing.


The South has the highest chlamydial infection prevalence and the lowest levels of Ct testing in the United States. To reduce prevalence and prevent poor health outcomes, Ct screening should be conducted at least once a year among young women who engage in sex, which was not borne out of our findings. More than a decade after recommendations were made for routine Ct testing of sexually experienced adolescent and young adult women, testing was low overall while national prevalence levels of chlamydial infection steadily increased.5 Five years after the federal program for Ct screening was phased-in to include the South, women in the South have the highest prevalence levels. In light of the dedicated resources and explicit guidelines to increase testing among women, our finding that women in the South reported lower levels of testing than in any other region was unexpected. On the other hand, the low level of testing reported by men was expected. In the absence of routine screening recommendations, most men who seek Ct testing do so because of symptoms or a referral by an infected partner. Reasons for low levels of testing by women and men are likely multifactorial, including patient and provider behaviors and limitations to individual finances and the public health infrastructure. Yet, our results indicate that an inverse relationship exists between testing and prevalence by region, highlighting the potential to further reduce prevalence via increased testing.

Despite the national focus on increasing testing within vulnerable populations, financial disparities in testing persist. To enhance our understanding of the role of finances, instead of using measures of total income that young adults might have calculated variably (e.g., inconsistently including student loans, parents, or employment wages), we used functional income to directly define the ability of respondents to pay for services after household expenditures. Young adults lacking financial resources (i.e., having public insurance or low income) reported more (albeit a low level of) testing than those with resources, which could reflect a measurable effect of federally funded public Ct programs within poorer communities. Regardless of any relative success, testing is low overall and most young adults are privately insured and are not being tested.

Differences in testing by financial status might be further exacerbated by personal and provider assumptions that financially stable young adults are at low risk.19,20 Providers have a unique opportunity to engage patients in discussions about sexual health, STD prevention, and screening.21 Yet, many primary care providers feel uncomfortable about obtaining a sexual history, lack the experience or willingness to conduct Ct tests, and are unaware of current guidelines and the availability of laboratory tests that do not require a urethral or vaginal swab.22–24 In 2003, only 40% of top-performing managed care organizations and Medicaid plan providers reported screening sexually experienced women aged 16 to 26 years for chlamydial infection.24 Providers might require additional directives, training, and resources to increase testing levels.

The South is in greatest need of testing, yet barriers related to confidentiality and stigma prevail.25 Of concern is the parallel increase of HIV in the South, revealing similar disparities in rates of infection by gender and financial status.26 In addition, mathematical modeling determined that 64% of HIV infections that were attributable to STDs resulted from a concurrent chlamydial infection.27 Attempts to improve testing and reduce transmission of Ct and HIV face similar challenges: lack of funding for additional testing sites; limited transportation options to reach distant healthcare sites in rural or suburban areas; and a dearth of sex education in schools and communities. Our findings support the need for region-focused policies for Ct prevention and testing guidelines to reduce Ct prevalence, which might also reduce HIV transmission.

Increasing federal funding, particularly in the South, to improve and increase Ct preventive services could have a significant impact on prevalence levels, given the reduction in incidence due to testing.28 The effectiveness of testing to reduce chlamydial infection prevalence has not been sufficiently studied prospectively nor have changes to population prevalence been well monitored.28 Funding for gonorrhea, though, resulted in a marked reduction of prevalence that was cost-effective.29 Program costs were lower than the expenditures that would have been required to treat gonorrheal infections and resultant sequelae.30 In time, the savings exceeded the costs of gonorrhea prevention, which would be expected of sufficient funding for Ct prevention. Although a preliminary analysis of the current chlamydial infection status of Add Health participants revealed a higher prevalence among those who reported a testing history when compared with those who did not, evaluations of current Ct program funding should be conducted, including an analysis of the effect that increased funding could have on Ct prevalence by region, age, and financial status.

An important limitation of this study is that participants, particularly women, might have misreported their Ct testing history. Urine testing for chlamydial infection in women was not being used widely in clinical settings at the time of this study, so testing would have required a pelvic examination. Pelvic examinations are easy to recall, but women might not be aware of the type of tests ordered by their physicians (e.g., a pap smear with or without a Ct test). If we have underestimated the prevalence of Ct testing, even by 100-fold, reported screening is still not above 50% in the South. If we overestimated the true prevalence of testing, then providers are insufficiently screening/testing their patients to an even larger degree than we identified. Overall for both men and women, the observed pattern that young adults with few financial resources were more likely to report testing than those with greater financial resources would still hold despite any over or underestimation.

Strategies to increase Ct testing, particularly in the South where prevalence is high, need to be identified, implemented, and evaluated. Recommendations for regularly testing men should be incorporated into testing guidelines because men are more commonly asymptomatic than symptomatic. Undiagnosed infections in men can lead to repeat infections among women. In particular, increasing testing in the South should favorably influence transmission dynamics and levels of infection in sexual networks. Confidential testing for adolescents and young adults could be offered in schools or testing vans. Incentives such as coupons from local music or food stores, or raffle giveaways might entice people to seek testing.

To reduce the overall prevalence of infection, chlamydial screening for men and women could be integrated as part of routine care for anyone over the age of 16, thereby avoiding the need for providers and patients to discuss sexual activity and removing the stigma associated with risk-based testing. Finally, and most importantly, education about the need for routine testing should not depend solely on providers but could be enhanced outside of the school systems, such as at movie theaters, sports venues, and through local radio, television, and school papers. A holistic approach will be necessary to improve the healthcare practices and Ct screening of this vulnerable population, who are just beginning to acquire the knowledge, skills, and capacity to assume responsibility of their health needs.


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