Chlamydia trachomatis is the most common sexually transmitted bacterial infection in adolescent girls and women in the United States.1,2 Previous research has shown that a high percentage of females test positive for Chlamydia infection a few months after treatment of a previous infection, due to reinfection by infected but untreated partners or an infected new partner, or occasionally, due to treatment failures.3–7 Repeat infections are associated with increased risk for long-term sequelae, such as ectopic pregnancy.8–10 Guidelines from the Centers for Disease Control and Prevention (CDC) recommend that women with Chlamydia infection should be rescreened 3 months after treatment.11
Adherence to Chlamydia infection rescreening is poor. The time and effort needed for patients to return to the clinic are believed to contribute to the poor adherence. In addition, in the United States, many females at high risk for repeat Chlamydia infection may not have a stable medical “home” for follow-up care, and some healthcare providers may not view Chlamydia infection rescreening as a priority.4,12 With the advent of nucleic acid amplification testing for Chlamydia infection, mailed specimens have been shown to be a reliable alternative to clinic-based testing,13–15 and many studies have used specimens obtained at home and mailed to the laboratory for analysis.6,7,16–21 Although the uptake of home-based screening is relatively low in men and in nonclinic populations,16–20 the strategy involving self-obtained, mailed specimens is more promising for rescreening in women treated for Chlamydia infection.6,7,21
The objectives of this study were to determine whether the use of home-based, self-obtained vaginal swabs among women who were treated for Chlamydia infection can increase rescreening rates in comparison with clinic-based rescreening, and to identify subgroups in which rescreening could be enhanced using self-obtained vaginal swabs.
MATERIALS AND METHODS
Two randomized trials were conducted: one with enrollment in sexually transmitted disease (STD) clinics and the other in family planning clinics. Although both STD and family planning clinics serve low-income individuals, the rate of rescreening was expected to be higher in women from family planning clinics. The two trials followed a common protocol and both trials enrolled participants from clinics in the cities of New Orleans, Louisiana, St Louis, Missouri, and Jackson, Mississippi, from 2005 through 2007. After informed consent, eligible participants were randomly assigned to the clinic group, in which participants were given an appointment to return to the clinic for rescreening for Chlamydia infection, or to the home group, in which women were mailed a vaginal swab kit for self-collection at home and return the specimen via the U.S. Postal Service. For women in both trials, rescreening was scheduled for 3 months after treatment.
In the STD clinics, female clients were tested for Chlamydia infection regardless of age and risk behaviors, but in the family planning clinics, a Chlamydia test was provided annually to women younger than 26 years of age and to older women with high sexual risk behavior. In all study clinics, women who tested positive for Chlamydia infection were typically treated with single-dose azithromycin, and their sex partners were empirically treated if they would visit the clinic. The consent process and enrollment procedure varied according to when the woman was treated: for women who had been empirically treated in the clinic or for whom a prescription had been telephoned in to a pharmacy, enrollment was offered by phone when the woman's Chlamydia test was known to be positive. Verbal consent was obtained and the subsequent interview was conducted by phone. The consent was verified by a witness and a printed copy of the consent form was mailed to the participant. For women who returned to the clinic for treatment after notification of a positive Chlamydia screening test, written informed consent and face-to-face interviews were conducted in the clinic. Enrollment procedures differed substantially by clinic type because most women in the STD clinics were empirically treated and tested for Chlamydia infection during the initial visit and were enrolled by phone, whereas most women in family planning clinics were enrolled when they presented for treatment in the clinic when a screening Chlamydia test was known to be positive.
Females were invited to participate if they had a genital infection with Chlamydia infection detected by a U.S. Food and Drug Administration (FDA)–cleared test. The lower age limit of inclusion was 18 years in New Orleans and 16 years in St. Louis and Jackson. Individuals were excluded if they were pregnant or trying to conceive, planning to move in the following 3 months, living outside the study areas, not able to understand spoken English adequately to assure informed consent, known to be infected with human immunodeficiency virus (HIV), or had other serious illnesses.
Randomization was conducted after informed consent and the initial interview. Women were randomly assigned to the clinic group or the home group (1:1 ratio). The group assignment was determined by opening an envelope that was numbered sequentially with the participant's study identification numbers marked on the front. Each envelope contained the participant's group assignment according to a random number generator (clinic or home) and study identification labels to be placed on the participant's questionnaires and specimens. The envelopes were centrally stuffed at the CDC and each clinic was instructed to use the envelopes sequentially. Two series of envelopes were prepared for each clinic, one for in-person enrollment and the other for enrollment by phone. Randomization was conducted independently for each series, with a block size of 12.
We attempted to place a reminder call to all women, regardless of group assignment. The reminder call was approximately 2 weeks before the date of scheduled rescreening. We used a reminder call log to keep track of the reminder calls and to standardize the intensity of the calls. We made three to five attempts over 1 week; calls were made at different times of day, including evenings. For each attempt we tried to use all the numbers provided by the participant at enrollment, including the participant's cell phone number and the phone number of a close friend or relative. When answering machines were encountered, a generic voice message was left only if the participant had given permission during enrollment to do so.
When the participant was reached, her identity was verified by at least three questions, including the date of clinic visit. For women assigned to the clinic group, a clinic appointment was scheduled for rescreening. For women assigned to the home group, the participant's home address was confirmed, and a specimen collection kit with instructions on how to obtain a vaginal swab was mailed to the participant's home (or her preferred address). Women assigned to the home group could also elect to pick up the collection kit from the clinic. After specimen collection, participants were asked to return the specimen in a postage-paid, preaddressed mailing tube, along with the follow-up questionnaire. Although only participants reached by phone were provided specimen collection kits (home group) or clinic appointments (clinic group), participants in either group could return to the clinic for rescreening. Among those reached by the first reminder call, second and final reminder calls were made if the participant's clinic visit was more than 7 days overdue or if a swab had not been returned 14 days after the scheduled self-collection date.
The endpoint was Chlamydia infection rescreening approximately 3 months after treatment. The primary endpoint was rescreening within a 7-week window, defined as 1 week (7 days) before to 6 weeks (42 days) after the target date that marked 3 months after the initial treatment (day 90). Rescreening rates in other periods, during a 4-week window (1 week before to 3 weeks after the targeted rescreening date) or anytime after enrollment were also determined. We analyzed rescreening rates among all participants (ie, intent-to-treat analyses) in these time periods and among the population reached by reminder call(s) (ie, per-protocol analyses) in the 7-week window.
We used the APTIMA COMBO 2 assay, which was the only FDA-cleared test for Chlamydia infection nucleic acid using vaginal swab specimens at the time. Specimens were transported or mailed to the laboratory in the Gen-Probe specimen collection kit.
In calculating sample sizes, we assumed the rescreening rates would be 25% in the clinic group from STD clinics and 50% from the family planning clinics. For STD clinics, the hypothesis was that the percentage rescreened would be higher (superior) in the home group compared with that in the clinic group. The target sample size for STD clinics was 720 participants to detect a difference of at least 10%, given the type I error (α) at .05, the type II error (β) at .20. For family planning clinics, the hypothesis was that the percentage of women rescreened in the home group would not be inferior to that in the clinic group22; noninferiority margin was set at 10%. With the type I error (α) at .05, and the type II error (β) at .20, the sample size needed was 858. Because of the higher rescreening rates found in the home group in the family planning clinic participants and for simplicity, in the final analysis, we assessed the superiority of home-based rescreening in both STD and family planning clinics.
We compared demographic and other relevant factors between home group and clinic group using χ2 for categorical variables and t test for continuous variables. Rescreening rates were also compared by study site, key demographics, and behavioral factors to identify subpopulations in which rescreening rates in the home group were significantly higher. We used the χ2 or Fisher exact test, when appropriate, to compare rescreening rates. We defined a P<.05 as statistically significant. All sample size calculations were performed with NQuery Advisor 5.0. All statistical analyses were done using SAS 9.2. This study was approved by the ethics review boards of Louisiana State University Health Sciences Center (New Orleans, LA), Washington University (St Louis, MO), University of Mississippi State Department of Health (Jackson, MS), and the CDC (Atlanta, GA).
From STD clinics, we enrolled a total of 880 participants from October 2004 through August 2007. Because of Hurricane Katrina, we had to exclude 69 participants who were enrolled from New Orleans after May 15, 2005, because the follow-up protocol was disrupted. The final analysis included a total of 811 participants: 408 were randomized to the home group and 403 to the clinic group (Fig. 1A). Most of the STD participants were African American; the mean age was 22 years. At enrollment, there were no statistically significant differences in demographic characteristics between the home and clinic groups (Table 1).
From family planning clinics, we enrolled a total of 412 participants. The trial was not fully enrolled because of low patient volumes at enrollment sites and the closure of the family planning clinic in New Orleans after Hurricane Katrina. After excluding eight participants because of Hurricane Katrina, the final analyses included 404 participants, and 196 were randomized to the home group and 208 to the clinic group (Fig. 1B). The home and clinic groups had comparable characteristics (Table 1). Most participants from the family planning clinic were also African American. Compared with STD participants, family planning clinic participants overall were more likely to have education beyond high school (23.3% compared with 17.4%, P<.02) and were more likely to work or attend school full-time (41.1% compared with 33.9%, P<.02) (data not shown).
We compared rescreening rates in home group and clinic group by clinic type (Table 2). In STD clinics, rescreening rates were higher in the home group than in the clinic group (26.7% compared with 19.1%, P=.01) during the 7-week period surrounding the targeted rescreening date (Table 2). In family planning clinics, the rescreening rates were also significantly higher in the home group than in the clinic group (40.8% compared with 20.7%, P<.001). During other follow-up window periods (4-week or anytime), the rescreening rates were higher among those assigned to the home group in both clinic populations. When the analysis was limited to women who were reached by the reminder call(s) (per-protocol population), rescreening rates were also significantly higher in the home group than in the clinic group: 43.5% compared with 33.0% in STD clinic participants and 59.2% compared with 37.8% in family planning clinic participants (Table 2).
In STD clinic participants, the rescreening rates in the home group ranged from 18.2% at the New Orleans site to 33.3% at the St. Louis site (Table 3). In subgroups of women younger than 22 years, with at most a high school education, and of African American race, the rescreening rates in the home group were in the upper 20% range and were significantly higher than those in the clinic group, although the improvement compared with the rates in the clinic group was modest (absolute improvement of 7–9%). Improvements of similar magnitude were found in other subgroups of women defined by working or school hours, living with parents, and behavioral factors. The largest difference in rescreening rates was 16.4% (32.6% compared with 16.2%), observed in women who reported that their partners did not have other sex partners (exclusive partnership) (Table 3).
The rescreening rates in family planning participants assigned to the home group ranged from 37.0% to 50.0% (Table 3). Rescreening rates were significantly higher (P<.05) in the home group among all the demographic and behavioral subgroups examined except in women with some college or more education and non–African American women (Table 3). In the family planning clinics, the differences in rescreening rates between the home and clinic groups were larger than those in STD clinics, and the largest difference was 35.3% (Table 3).
Rescreening rates were high in both STD and family planning participants who were reached by reminder call(s) (Table 3). In STD clinics, 44.6% of women in the home group and 35.1% in the clinic group were rescreened after they were reached by the reminder call(s), and the corresponding percentages in the family planning clinic clients were even higher. In both home and clinic groups, a small number of participants decided to withdraw when reached by the call. The rescreening rates among participants who were not reached was low (less than 5%) among both STD and family planning clinic participants. Of note, the proportion of participants reached by reminder call(s) was higher among those assigned to the home group than in the clinic group: 58.6% (239/408) compared with 51.1% (239/408) in STD clinics and 66.3% (130/196) compared with 53.4% (111/208) in family planning clinics (both P<.05) (Fig. 1). It should be noted, however, that when limited to women who were reached by reminder call(s), rescreening rates were still significantly higher in the home group in both the STD and family planning populations (both P<.05) (Table 3).
We compared rates of reinfection, measured as test positivity rates, by study population and participants' group assignment (Table 4). The rates were high in both clinic populations and in both study groups, ranging from 12.9% to 19.4%. The differences between home group and clinic group were not statistically significant (P≥.3) (Table 4).
In STD and family planning clinic clients, home-based, self-collected vaginal swabs clearly provide an alternative to clinic-based Chlamydia infection rescreening. In STD clinic participants, home-based testing resulted in modest but significant increases in rescreening rates compared with rescreening in the clinic. In women enrolled from family planning clinics, rescreening rates were almost twice as high in the home group as in the clinic group. In various subpopulations defined by demographic and behavioral characteristics, rescreening rates were consistently improved by use of home-based specimen collection, suggesting the potential for a broad application of this tool in facilitating Chlamydia infection rescreening.
Our findings are supported by other randomized trials of home-based screening in the United States. In a small trial involving 122 patients from an urban STD clinic, 45% of women who were given the option of either rescreening in the clinic or home-based testing and 32% of those assigned to clinic-based rescreening were rescreened within 28 days of enrollment.21 In women using long-acting reversible contraceptive methods, use of self-collected vaginal swabs significantly increased testing rates of Chlamydia infection and gonorrhea compared with clinic-based testing (56% compared with 25% during 12 months).23 In high-risk young women, Cook et al reported that serial mailing of home-based kits significantly increased the use of Chlamydia and gonorrhea testing (82% in the home group and 61% in the clinic group had at least one test during the 2-year follow up).24 Our study extends findings from other studies and demonstrates benefits of using home-based testing in two populations that are at high risk for Chlamydia infection long-term sequelae but typically are hard to reach for Chlamydia infection rescreening.
As seen in numerous other studies, we found high reinfection rates in women at about 3 months after treatment of a previous Chlamydia infection. New tools for primary prevention of reinfection, such as through patient-delivered partner therapy, have been shown to be effective and should be widely used.25,26 Home-based specimen collection is a potential new tool for secondary prevention through rescreening. Allowing women to choose between methods may help to increase overall rescreening adherence.21 For patients who are motivated and can keep the specimen collection kit for 3 months, giving patients the kit in advance may be a better alternative than mailing.
This study has several limitations. First, because of Hurricane Katrina, we had to exclude some participants after randomization, which could have compromised the comparability of the two study groups. However, we found no differences by study group in the participants included in the final analyses. Second, there were appreciable differences in rescreening rates across the three study sites, with the rates higher in both the home and clinic groups at the Jackson site, suggesting that factors other than group assignment, such as clinic operation and patient trust, can significantly influence compliance with rescreening. Third, study personnel who made the reminder calls knew the patient's group assignment; this lack of blinding may have led to differential efforts in making the reminder calls, differences in communication during the reminder calls, or both, and thus led to different rescreening rates by study group. In addition, women enrolled in the trials may have higher rescreening rates than the general clinic populations because these women volunteered to participate in a study about home-based testing. Last, our study did not assess the potential opportunity costs associated with home-based testing, including the opportunity for risk reduction counseling in the clinic.
Future studies should focus on cost-effectiveness analyses comparing home- with clinic-based rescreening, and on determining nonclinic settings where self-collection is appropriate.27,28 Currently, several Chlamydia tests are approved for use on self-collected vaginal swabs but none is approved by FDA for use in nonclinical settings.27 Our study adds to the literature that supports the role for home-based specimen collection for Chlamydia infection rescreening. Studies that would further strengthen the case for FDA's clearance of home-based specimen collection, such as stability studies of mailed specimens, should also be among priority areas for future research.
In this study, the rates of rescreening among those who could not be reached by reminder calls were very low. Although we collected multiple phone numbers at enrollment from each subject and made multiple attempts to call, a significant proportion of study participants was not reached by reminder call(s). Findings from our study emphasize the importance of identifying better ways to remind patients of either home-based specimen collection or clinic appointments.29 Determining the reasons for not reaching patients by telephone call and exploring other reminder strategies could have major implications for Chlamydia control programs.
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© 2011 by The American College of Obstetricians and Gynecologists.
Figure. No caption available.