THE EPIDEMIC of Chlamydia trachomatis is well studied. Acute infections and chronic sequelae caused by this sexually transmitted disease (STD) have substantial public health consequences. In 1995, there were 477,638 cases of chlamydia infection reported in the United States; 383,956 of these cases were diagnosed in women.1 Studies examining C. trachomatis among growing populations such as urban Hispanic groups have not yet been reported. It is important to examine risk profiles for understudied populations such as these.
The purpose of this study was to determine the prevalence of genital chlamydial disease among women attending two community-based university-affiliated clinics in New York City in 1994. We sought to determine if previously established risk factors and risk markers for chlamydia were present in this Hispanic population and if novel risk factors for C. trachomatis could be found. Because the relationship between oral contraceptives and C. trachomatis has been inconsistent,2–5 this was also examined here.
Patients were enrolled into this retrospective study from either the Family Planning Clinic or the Young Adult Clinic of Columbia Presbyterian Medical Center's Ambulatory Network, located in Washington Heights, New York City. Immigrants from the Dominican Republic represent the largest segment of the population served by these clinics, which provide services free of charge and are closely linked to the school-based health clinics and local emergency rooms. Young women are evaluated for pregnancy, provided with contraceptives, treated for STDs, and given general physical examinations. STD testing is done routinely at annual examinations and additionally if indicated by patient complaints. In this way, these clinics serve as primary care facilities for obstetric and gynecologic care.
Selection of Patients and Control Subjects
Women 30 years of age and younger were eligible for enrollment into this study. Patients were excluded if their medical records were unavailable. Although women may have been tested more than once during the year, study participants could only be enrolled once during the study year. Chlamydia cases were enrolled at the time of their first positive test. Of the 227 positive tests for C. trachomatis, 200 represented women met the enrollment criteria for patients. Control subjects were systematically sampled from a computer-generated list of women who tested negative for chlamydia during 1994. Control subjects were matched to patients by clinic attended and month of testing. The 1:3 patient to control subject ratio and sample size was selected to have 80% power to detect a doubling in the risk of chlamydia for exposures with a prevalence of 10% or greater in the control group (Epi Info 6, Centers for Disease Control and Prevention; Atlanta, GA).
Cervical samples were tested for chlamydia by either the Cancer Screening Services (North Hollywood, CA) or by the Columbia Presbyterian Medical Center microbiology laboratory. The California site used Chlamydiazyme (Abbott Diagnostics, Chicago, IL) and the medical center used Gen-Probe (Pace 2 System, San Diego, CA). Approximately 25% of the chlamydia samples were sent to California. The choice of screening test used was not based on patient demographics.
Data were compiled from standardized data collection instruments used in both clinics. These forms consisted of the New York State Family Planning Reporting System data sheet, a risk assessment survey for STDs in use at the clinic, and a provider encounter form that described the physical examination and treatment regimens. Demographic information, sexual and STD history, human immunodeficiency virus (HIV) risk factors, exposure to physical and sexual abuse, drug and alcohol use, and physical examination findings were extracted from patient records and entered directly into a computer database (Microsoft Excel; Richmond, WA). The accuracy of the data was reviewed periodically throughout the study. Past STD testing was verified by review of the hospital's microbiology log book and the computerized clinical information system.
Demographic information, reason for visit to the clinic, behavioral risk factors, and physical examination findings were the independent variables used as predictors of a positive chlamydia test. The result of the chlamydia test was the dependent variable studied. Risk markers were analyzed and included concurrent evidence of gonorrhea and abnormal gynecologic findings. Differences between the means of continuous variables were assessed for statistical significance using student's t tests. Categoric variables were assessed using chi-square tests. Differences between patients and control subjects were presented as odds ratios with 95% confidence intervals using Cochran-Mantel-Haenszel tests. Logistic regression was used to develop a predictive model for a chlamydial infection. All tests used a significance level of 0.05 (SAS statistical package, SAS Institute; Cary, NC).
Disease Prevalence and Patient Demographics
Two hundred twenty-seven of 4,190 screening tests done were positive for chlamydia for an annual prevalence of 5.4%. Because of possible differences in chlamydia test sensitivities and demographics in the two clinics studied, we stratified our analysis by clinic. No differences were found, and test results were subsequently pooled for analyses. As expected, the study population was primarily Hispanic (76%). Twenty-three percent of women were African-American and only 1% was white. Sixty-one percent of the study group received Medicaid insurance and the remainder of the population used the clinic free of charge.
Reason for Patient Visit
We evaluated the study population's stated reason for visiting the clinic. Just over half of the patients presented for a general physical examination (57%), only 10% had genitourinary symptoms, 16% sought a birth control method, 9% wanted a pregnancy test, and 8% came for a postpartum visit. Patients had significantly different reasons for visiting the clinic than control subjects (chi-square2df = 23.5; P < 0.001). More patients presented for pregnancy testing, but fewer patients presented for a birth control method than control subjects.
Table 1 illustrates the differences between patients and control subjects with regard to age, sexual experience, and pregnancy history. Patients were younger than control subjects and experienced their first intercourse earlier. Although the number of children was not different between patients and control subjects, patients were more likely to be pregnant at the time of testing for chlamydia.
Overall, 19% of the women reported that they did not use any contraceptive method (22% of patients and 18% of control subjects). Of those reporting contraceptive use, 70% (581/823) used condoms. Although 24 women reported using the sponge, only 3 used it without condoms. Likewise, 16 women reported using a diaphragm, but only 1 did not also use a condom. Therefore, subsequent analysis of “barrier methods” was collapsed into one group: condoms, sponge, or diaphragm. Regarding hormonal birth control, 132 women reported using the oral contraceptive pill, 67 reported using Depo-Provera (Upjohn; Kalamazoo, MI), and 36 reported using Norplant (Wyeth-Ayerst; Philadelphia, PA). These hormonal categories were collapsed into one group for analysis as well.
We compared the contraceptives used by patients and control subjects, and significant differences were found (Table 2). Surprisingly, women using hormonal contraception alone (without a barrier method) were one third as likely to be infected with chlamydia than those using no protection. Barrier methods alone did not prove to be protective when compared with using no contraception. However, women using a barrier method plus a hormonal contraception were less than half as likely to be infected with chlamydia than those using no protection.
History of Sexually Transmitted Diseases, Human Immunodeficiency Virus Testing, and Concurrent Sexually Transmitted Disease
There was no difference in the proportion of patients and control subjects previously diagnosed with an STD (Table 3). However, 35% of the women in the study had a past history of chlamydia or another STD. More patients were unaware of their HIV status than control subjects; 63% of the patients did not know their HIV status compared with 53% of control subjects (P < 0.0001). Only one of the 842 study patients was HIV seropositive, and she was infected with C. trachomatis. Concurrent genital gonorrhea was significantly associated with chlamydial infection because it occurred in 3.5% of patients compared with 1% of control subjects (P = 0.01).
Abnormal Clinical Findings. Physical examination findings in the study population included abnormal cervical findings, vaginal discharge, or a tender uterus and/or adenexa (Table 3). Cervical abnormalities included provider reports of abnormal cervical appearance, friability, inflammation, and cervical discharge. Providers documented vaginal discharge independently of cervical findings. Thirty-nine percent of women diagnosed with chlamydia infection had no abnormalities reported on physical examination. Conversely, 20% of patients with negative C. trachomatis tests had physical examination findings suggestive of genital infection.
High-Risk Social Exposures
There were no differences between patients and control subjects with respect to exposure to violence, risky sexual behavior, or drug use. Twenty-three percent of our study population had a history of exposure to violence by a sexual partner (e.g., touched in an uncomfortable way, forced to have sex, or beaten). Other high-risk sexual practices, such as sex with a partner with HIV, sex with a drug user, or sex with a man who has sex with men, were reported by 4% of the total study population. Drug use (crack, cocaine, heroine, or other) was reported by only 2% of the total population. Thus, these social exposures were not found to be risk factors for chlamydial infection.
Regression Model for Predicting Chlamydia Infection
As previously described, it is difficult for the health care provider to accurately diagnose chlamydial infection using signs and symptoms alone. Therefore, we applied a regression analysis to investigate factors associated with chlamydia. Eight independent variables previously published as factors associated with chlamydia infection were included in a stepwise regression model. Three of these variables remained significant in our population at the 0.20 level: positive pregnancy test at the time of visit, vaginal discharge on pelvic examination, and self-reported current drug use. We compared this predictive model with the impressions or diagnosis of the clinic practitioners before confirmation with chlamydia test results. The positive predictive value of diagnosing an infection increased from 50% using the clinical impressions of the providers to 61% with this model.
We observed a 5.4% prevalence of C. trachomatis genital infection in women attending our young adult clinics despite using C. trachomatis diagnostic tests that, although widely used, may fail to detect a substantial proportion of infections. To see if this prevalence rate was consistent with that reported in the literature, we performed a MEDLINE review and found an estimated mean chlamydia prevalence of 8% in North American women attending non-STD clinics.2,3,5–16 Recent Centers for Disease Control and Prevention analysis of chlamydia prevalence among women of reproductive age in 5 U.S. cities showed an estimated mean prevalence of 4.5% in family planning clinics.17 Therefore, the chlamydia prevalence reported in our population reflects the national trend of lowered prevalence, perhaps due to the initiation of enhanced screening programs to detect asymptomatic chlamydial disease.16,17
Our study confirmed previously established risks for chlamydia infection in women: young age, early age at first coitus, and physical examination findings consistent with a genital tract infection. In addition, 16% of our population had adenexal tenderness suggestive of early pelvic inflammatory disease. By enhancing efforts at early diagnosis and treatment of chlamydia, we could potentially decrease the incidence of pelvic inflammatory disease in our population.18
Pregnancy was found to be a risk factor for C. trachomatis in this population. There may be an ascertainment bias in this finding because it is known that pregnant women are more likely to be positive for an STD than nonpregnant women9; the association between chlamydia infection and pregnancy may be confounded by lack of contraception. However, we did not detect any significant differences in contraceptive use among pregnant chlamydia-positive women. Nonetheless, the many requests for pregnancy tests (9% of all women specifically requested testing) and the actual pregnancy rate of 5% indicate a lack of contraceptive use in this young population. These findings highlight the need for enhanced STD screening in young women, especially in women currently pregnant and those seeking pregnancy.
Although most women reported using condoms (70%), barrier methods were not found to be protective against chlamydial infection in this population. Studies showed that failure of barrier methods to protect against STDs may be due to their inconsistent and incorrect use, or mechanical defects.19 Our study could not assess the appropriateness of barrier use, because this information was unavailable in the medical records. Hormonal contraceptives were found to be protective, but condom use did not increase the protective value of hormones. This finding, however, may simply reflect differences in sexual risk-taking behavior or access to preventive care because women on hormonal contraceptives may be seen more regularly in clinic. Because our study was retrospective, we were unable to ascertain differences in current sexual practices.
Recent studies explored the relationship between HIV and STDs, including C. trachomatis. 20 However, we were unable to study the interactions between C. trachomatis and HIV seroprevalence because only one woman in our study was known to be HIV infected. The rates of STDs and HIV in this specific social and cultural community still need to be explored.
With our data we attempted to develop a predictive model for identifying chlamydial infection. Our model indicated that if the following criteria were used-a positive pregnancy test, vaginal discharge on examination, and a report of drug use-clinicians could increase their ability to diagnose chlamydia without laboratory confirmation by 11%, an increase from 50% to 61%. However, the risk factors found to predict chlamydia in our clinic population may not be generalizable to other populations. This type of analysis could be useful in other practice settings as a guide for clinical programs.
In conclusion, although this retrospective study has limited generalizability, it is important to study growing populations such as young Hispanic women who are at increased risk for STDs. The detection of C. trachomatis using technologic innovations such as ligase chain reaction and polymerase chain reaction in our clinic population would allow earlier more accurate diagnosis and hopefully more timely treatment, thereby limiting costly sequelae.
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