A Randomized Trial of Clinician-Delivered Interventions Promoting Barrier Contraception for Sexually Transmitted Disease Prevention

Artz, Lynn MD, MPH*; Macaluso, Maurizio MD, DrPH*; Meinzen-Derr, Jareen MPH*; Kelaghan, Joseph MD†; Austin, Harland SD‡; Fleenor, Michael MD§; Hook, Edward W. III MD§¶; Brill, Ilene MPH*


Objective: The objective of this study was to compare 2 interventions promoting condoms and vaginal microbicides to prevent sexually transmitted disease (STD).

Study: Women (N = 427) attending an STD clinic were randomly assigned to 2 clinician-delivered interventions and followed up monthly to assess condom/microbicide use and incidence of gonorrhea, chlamydia, and syphilis.

Results: During follow up, condom use rates were 69% (enhanced) and 49% (basic) and microbicide use rates were 44% and 29%, respectively. STD rates did not significantly differ between intervention groups. Perfect condom use (regardless of intervention arm) was associated with a 3-fold decrease in STD rates (relative risk [RR], 0.3; 95% confidence interval [CI], 0.1–0.8). Using a vaginal microbicide during ≥50% of the acts of intercourse was associated with reduced STD rates (RR, 0.5; 95% CI, 0.3–1.0) across intervention groups and condom use categories.

Conclusions: The enhanced intervention increased use of condoms and vaginal microbicide; however, STD rates did not decrease because a protective effect was seen only among perfect barrier users, and the enhanced intervention only modestly increased perfect use.

In a randomized trial with sexually transmitted disease (STD) clinic clients, women who received an intensive clinician-delivered intervention were more likely to use condoms and microbicides. The intervention did not seem to decrease STD rates, but consistent and correct condom users had fewer STDs.

From the *Department of Epidemiology and International Health, School of Public Health, University of Alabama at Birmingham, Birmingham, Alabama; †Contraceptive and Reproductive Evaluation Branch, National Institute of Child Health and Human Development, Bethesda, Maryland; ‡Department of Epidemiology, Rollins School of Public Health, Emory University, Atlanta, Georgia; §Jefferson County Department of Health, Birmingham, Alabama; and ¶Division of Infectious Diseases, Department of Medicine, School of Medicine, University of Alabama at Birmingham, Birmingham, Alabama

*Currently affiliated with the Centers for Disease Control and Prevention, Atlanta, Georgia.

Correspondence: Dr. Maurizio Macaluso, Division of Reproductive Health, NCCDPHP, CDC, 4770 Buford Highway, Mail Stop K-34, Atlanta, GA 30341-3724. E-mail: mmacaluso@cdc.gov.

Received for publication September 23, 2004, and accepted April 4, 2005.

Article Outline

SEXUALLY TRANSMITTED DISEASES (STDs) threaten the health of many young women. Women are more likely to acquire STDs than men, and these infections may lead to pelvic inflammatory disease, infertility, ectopic pregnancy, and cervical cancer. In addition, AIDS has become the fourth leading cause of death for U.S. women aged 25 to 44, and heterosexual transmission is now the most frequent route of HIV infection in women.

In recent years, there has been increased effort to develop risk-reduction interventions for young adult women, especially minority women. Although most interventions address multiple risk behaviors, the main focus is typically condom promotion. The majority of interventions for women has been evaluated using quasiexperimental methods1 and have evaluated intervention effectiveness using behavioral intention,2–4 self-reports of condom use,5–8 or condom acquisition.9–12 Some of these interventions have failed to produce any significant change in behavior.11,13,14 Some have failed to change the behavior of women even when they have changed the behavior of men.15,16 Among tested interventions reporting success in increasing condom use among women, condom use increased from 26% to 56% of acts,6 condom use at last intercourse was 68% compared with 49% for controls,17 and 100% consistent condom use increased from 35% to 47% with no change for controls.5

Fewer studies with women have evaluated intervention effectiveness using STD outcomes. When STD outcomes alone have been considered, postintervention decreases in STD reinfection rates have been found for men but not for women.18–20 Four randomized intervention trials have recently examined both behavioral and STD outcomes among women.15,21–23 One small trial failed to find changes in either outcome,15 whereas 3 large-scale trials have demonstrated that it is possible to reduce the incidence of STD and HIV in high-risk groups through behavioral interventions that promote consistent condom use.21–23 Although condom use rates increased in these studies, however, the risk reduction attained was not very large, possibly because consistent condom use is difficult to achieve and to maintain over an extended time period.

Most tested STD/HIV risk-reduction interventions for women involve multiple intervention sessions, typically 4 or 5 sessions lasting 1 to 2 hours each.5–8,15 Effective condom promotion interventions usually include skill-building elements.1,24,25 Most interventions have been delivered by peer educators5,6,8 or health educators, social workers, and psychologists.4,7,11,15,22,26,27 Almost no tested interventions have been delivered by clinicians. The exception was a comparison of 2 brief (5- to 10-minute) interventions to increase knowledge about HIV transmission, one delivered by clinicians and one delivered by peer educators.14 Neither intervention was effective in changing condom use behavior, possibly as a result of the brevity of the interventions and their focus on information transfer.

Still clinicians are being urged to counsel patients about STD/HIV preventive behavior,28 and the credibility and influence of clinicians have been underused in STD/HIV preventive efforts to date. Therefore, we have applied what has been learned from other studies to develop a practical clinician-delivered intervention to promote safer sex among women at risk of STD. Furthermore, we have evaluated effectiveness using a randomized, controlled intervention trial that examines both behavioral and STD outcomes.

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Materials and Methods

Study Design

This intervention trial was nested within a prospective observational study of the prophylactic efficacy of male latex condoms and vaginal microbicide (i.e., nonoxynol-9-based contraceptive jelly, foam, suppositories, and film).29 The objective of the observational study was to evaluate condoms and vaginal microbicide (used alone and in combination) for preventing STDs. The first 450 women enrolled in the study were asked to participate in a randomized trial comparing the effectiveness of 2 clinician-delivered interventions designed to promote barrier contraception.

The eligibility criteria, the recruitment and follow-up procedures, and the laboratory methods used in the study are described in detail elsewhere.29 Briefly, women attending the metro STD clinic in Birmingham, Alabama, were eligible for enrollment if they were 18 to 35 years old, had not had a hysterectomy, were not pregnant, did not want to become pregnant in the next 6 months, and were not on long-term antibiotic therapy. Study participants attended an initial study visit and were asked to return for 6 monthly follow-up visits. During the initial visit, subjects were randomly assigned to an intervention group using a randomization scheme that ensured balanced assignment of subjects to the 2 intervention arms within any given day. Next, participants completed a baseline interview, participated in an intervention, received a pelvic examination, and were taught to keep a sexual diary. At each follow-up visit, participants were interviewed and examined, and their sexual diaries were reviewed. All study procedures were reviewed and approved by the Institutional Review Board of the University of Alabama at Birmingham.

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Intervention Methods

The goal of both interventions was to encourage consistent and correct use of barrier contraception (preferably condoms and vaginal microbicide in combination) for STD prevention. The counseling interventions were scripted and 8 STD clinic nurse-clinicians were trained to deliver the interventions verbatim. A counseling flip chart helped to assure a standardized intervention across nurses. Clinicians went through a certification process, including one-on-one training sessions with a behavioral scientist (LA), videotaped role-playing sessions to rehearse possible counseling dynamics, and systematic feedback to ensure consistent delivery of the intervention.

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Basic Intervention.

The 5- to 10-minute basic intervention consisted of information about the effectiveness of barrier contraceptives, a clear recommendation to use condoms and vaginal microbicide to prevent STDs, free supplies of barrier contraceptives, and 2 brochures on how to use condoms and vaginal microbicide products correctly.

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Enhanced Intervention.

This intervention included a 19-minute videotape, a 30-minute skills-oriented counseling session with a nurse clinician, free supplies of barrier contraceptives, and assorted take-home items. The videotape, whose concept was developed by a local production firm after extensive formative evaluation, and was tested among potential study participants, promoted safer sex as the new norm and modeled effective condom negotiation strategies. During the counseling, the clinician briefly reviewed important information about STDs and recommended sexual abstinence or consistent use of protection. The effectiveness of condoms and vaginal microbicide was discussed, joint use of condoms and microbicide was recommended as likely to provide the greatest protection, and microbicide alone was recommended only as a last resort. The nurse then taught the woman how to use condoms and microbicide correctly using anatomic models (penis model: Ansell Medical Products; female pelvis model: SIMA Model 60-27CS, Gaumard Scientific Company, Inc.) to review relevant anatomy, demonstrate correct use, and allow the client to practice the skill. The counseling then shifted to partner communication and how to persuade a partner to use condoms. Clients practiced requesting condom use and responding to common objections. They were reassured that a request is often sufficient. If objections were encountered, they were advised to avoid long arguments and insist on condoms (i.e., “no condom, no sex”). Once familiar with all of the products and how to negotiate condom use, the participant was asked to choose the kind of protection she wanted to use—condoms and microbicide together, condoms alone, or microbicide alone. Finally, the participant signed a “promise” to use her chosen method every time she had sex until her next visit.

Before leaving the clinic, the client received a 6-week supply of her chosen barrier method and an assortment of take-home items designed to encourage, facilitate, and support condom and microbicide use after the counseling session. These included 4 illustrated brochures that reviewed information from the counseling session, 4 greeting card-style condom cards to give to partners to request condom use, and a packet of information and product samples to give to her best female friend. Also included were a safer sex comic book, a medical “prescription” to “use condoms,” “use spermicide,” and “avoid unprotected sex,” and a condom wallet to carry condoms discreetly. A few days after her initial visit, the client was mailed a supportive letter signed by her nurse. At the first follow-up visit, subjects in the enhanced intervention group observed a second videotape (“Let’s Do Something Different,” Education Development Center, Newton, MA) that promoted condoms and modeled effective condom negotiation skills.

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Data Collection Methods and Measures

Interview Data.

Before the intervention, subjects participated in a 30-minute structured interview that collected sociodemographic, medical, behavioral, and psychosocial data. Participants reported on their sexual activities and their use of condoms and vaginal microbicide during the preceding 30 days. They also reported on behaviors that facilitate condom use such as whether they kept a supply of condoms, carried condoms, and requested condom use in the prior month. The same information was collected at each follow-up visit.

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Sexual Diary and Product Count.

Between study visits, subjects recorded daily information about number and type of sexual partners, coital frequency, types of sexual activities, and barrier use in a pocket-sized diary. Problems such as condom breakage and slippage were also noted. At each follow-up visit, the diary was reviewed by the interviewer and unused products and product wrappers (i.e., condom, film, and suppository wrappers) were counted. Jelly tubes and foam cans were weighed to estimate the number of applications used.

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Physical Examination.

At each visit, the nurse conducted a directed genital examination that included inspection of the external genitalia, bimanual examination, and a vaginal speculum examination. Clinical findings were recorded, and endocervical specimens were obtained for gonorrhea and chlamydia cultures. Wet preps, Gram stains of cervical secretions, rectovaginal examination, and a urinary human chorionic gonadotropin test for pregnancy were performed if clinically indicated. Blood specimens were obtained and stored for serologic tests, and a rapid plasma reagin (RPR) test for syphilis was done when clinically indicated. The laboratory methods for detecting gonorrhea, chlamydia, syphilis, and pregnancy at entry and during follow up were described in a previous report.29 We note that the study was carried out before the advent of nucleic acid amplification tests, and both chlamydia and gonorrhea were detected by culture. Also, whereas gonorrhea, chlamydia, and syphilis were the primary biologic outcomes and were screened for at each follow-up visit, budget constraints did not allow pursuing systematically other potentially interesting outcomes such as unintended pregnancy or other infections. For the latter, diagnosis was pursued only when there was clinical suspicion.

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Data Analysis

The objectives of the analyses were 1) to evaluate the effectiveness of the intervention in modifying intermediate behaviors such as carrying condoms and asking a man to use a condom; 2) to describe patterns of sexual activity and condom use during the 6-month follow-up period; and 3) to describe STD and pregnancy outcomes observed during follow up. Frequency distributions and univariate descriptive statistics were used for preliminary analyses. In simple analyses, standard contingency table techniques were used to compare the distribution of categorical characteristics between groups. STD incidence rates were computed by dividing the number of new infections by the number of months of follow up accumulated in the appropriate category. The epidemiologic measure of association used was the rate ratio (RR). Mantel-Haenszel summary estimates of the RR and the 95% confidence interval (CI) of the RR were computed to make inference about the association between STD incidence and potential determinants of risk, including the intervention and consistency of condom and microbicide use.

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Recruitment into the prospective study began on June 2, 1992, and ended on March 31, 1995; follow up continued through February 1, 1996, to maximize the number of individuals with complete follow up. Approximately 41% of the women who were eligible for enrollment participated in an initial study visit. A previous report addressed differences between participants and nonparticipants.29 Briefly, participants did not differ substantially from women who were scheduled for an initial visit but did not participate. Participants appeared to be slightly more educated than nonparticipants but to have lower income, a larger number of partners, and more frequently reported a history of STD. Thus, the recruitment may have selected women at higher risk of STD who presumably were more motivated to participate.29 Because participants were randomly assigned to the intervention arms, selection was not a likely source of bias for the most important comparisons.

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Study Subjects

The first 450 women who attended the initial study visit were randomly assigned to either the enhanced or the basic intervention. Twenty-three were found to be ineligible or declined to further participate in the study before the end of the initial visit. The present analysis is limited to 427 participants. Participants were young (median age, 25 years), mostly single or not currently married (88%), and predominantly black (88%). Most had completed high school (median number of years in school, 12). The median per capita household income was $150 per month and 47% of the participants received food stamps.

Seventy-two percent of the women reported prior STDs, 79% a previous pregnancy, and 71% had children. The median age at first intercourse was 16. The median lifetime number of sex partners at recruitment was 6. At entry into the study, 34% of the women were using hormonal methods of birth control, usually oral contraceptives, and 29% were surgically sterilized, whereas 15% reported not using any method of birth control. In the month preceding study entry, most women were using male condoms inconsistently (34%) or not at all (44%).

Two hundred thirteen women received the enhanced intervention and 214 women received the basic intervention. There were no statistically significant differences between groups for any of the baseline variables described here (Table 1). Of the 427 women enrolled in the trial, 357 (84%) returned for at least one follow-up visit and 249 (58%) returned for all 6 follow-up visits. The median number of follow-up visits was 4. Attrition was slightly higher for the basic intervention group (RR, 1.1; 95% CI, 0.9–1.3), but the difference was not statistically significant (P = 0.37). Analysis of potential baseline and time-dependent predictors of withdrawal from follow up (data not shown) indicate that women at highest risk for STDs tended to drop out of follow up earlier than other women, but did so at similar rates in the 2 intervention groups.

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Behaviors Facilitating Condom Use

Of 213 women in the enhanced intervention arm, 204 returned a signed behavioral contract: of these, 4 promised to abstain from sexual intercourse, 191 promised to use condoms with or without microbicides, and 9 promised to use microbicides alone. It is unclear whether the 9 women who did not sign a promise were actually asked. Throughout follow up, compared with the basic intervention group, recipients of the enhanced intervention were more likely to keep condoms at home and to carry condoms on their person (Table 2). They were also more likely to have asked a man to use a condom and to have put a condom on a sex partner. Although both intervention groups performed these behaviors more frequently after intervention than at study entry, the increased performance of these behaviors during follow up was more marked for the enhanced intervention group. The proportion of women keeping and carrying condoms remained very high over time, and the difference between intervention arms was still statistically significant during the last month of follow up, whereas the proportion reporting other facilitating behaviors generally declined over time, and the between-arm differences were weakened during the last month (results not shown in detail).

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Sexual Behavior Other Than Barrier Use

Only 10% of women abstained from vaginal intercourse during any given follow-up month. The proportion of women practicing abstinence after the intervention was not different from the proportion reporting abstinence before entry into the study and did not differ between intervention groups during follow up.

Before intervention, 25% of the women reported having more than one sexual partner. Among women with multiple partners at baseline, the number of partners did not decrease after either intervention. During follow-up, the mean number of unique sex partners was 3 for the enhanced intervention group and 2.8 for the basic intervention group (Table 4).

The frequency of vaginal intercourse during follow up did not differ between the 2 intervention groups, and it was not different from the frequency reported at entry. The median number of acts of vaginal intercourse per month of follow up was 6 for both intervention groups (Table 4).

Oral sex was infrequently practiced and anal intercourse was a rare event during follow up for both groups. There appeared to be no change in the frequency of these practices after intervention and no significant differences between intervention groups during follow up.

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Use of Barrier Protection

During follow up, women in the enhanced intervention group were more likely to use barrier protection and less likely to have unprotected intercourse than women in the basic intervention group. The average proportion of sex acts protected using a condom during follow up was 69% in the enhanced group and 49% in the basic intervention group, a highly significant difference in analyses stratified by month of follow up (results not shown in detail). The average proportion of sex acts protected using a vaginal microbicide was 44% in the enhanced group and 29% in the basic intervention group. The overall proportion of unprotected sex acts was 21% in the enhanced intervention group compared with 35% in the basic intervention group.

The distribution of acts of intercourse according to method of protection used by intervention group before the intervention (as reported by interview) and during follow-up (as reported in diaries) is displayed in Figure 1. Although the proportion of acts protected by condoms alone during follow up was about the same in the 2 groups, the proportion of acts protected using both a condom and vaginal microbicide increased from 3% to 34% in the enhanced intervention group and from 1% to only 13% in the basic intervention group. In contrast, the proportion of acts protected using only a vaginal microbicide increased more in the basic intervention group (from 1% to 16%) than in the enhanced intervention group (from 0.5% to 10%). Thus, reported barrier use patterns suggest that the enhanced intervention achieved its intended effect of increasing simultaneous use of condoms and vaginal microbicide.

Analyses that evaluated the distribution of women according to consistency of barrier use (not presented in detail) yielded similar results. Approximately two thirds of the women in the enhanced intervention group and half of the women in the basic intervention group used barrier protection for every act of vaginal intercourse during a follow-up month. The proportion of women using no barrier was twice as high among women in the basic intervention group. Women in the basic intervention group rarely used condoms and vaginal microbicide in combination. Two thirds never did and only approximately 5% did so for all acts of intercourse during a given month. In contrast, the majority of the women in the enhanced intervention group used condoms and vaginal microbicide together at least once, and approximately 20% of the women in this group used the 2 barrier methods in combination for all acts of vaginal intercourse.

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Biologic Outcomes

Despite the large difference between the 2 intervention groups about the behavioral outcomes, there was no proportionate reduction in the rates of STD (gonorrhea, chlamydia, and syphilis combined) or pregnancy during follow-up (Table 3). There was an excess of STD cases and pregnancies (15 and 4 cases, respectively, not included in Table 3) in the enhanced intervention group as compared with the basic intervention group (7 and 1, respectively, not included in Table 3) during the first month of follow up (15 cases), which declined in subsequent months. Because the excess incidence during the first month of follow-up may be the effect of carryover of infections that were present at entry into follow-up, the first month was excluded from subsequent analyses. The results of analyses restricted to months 2 to 6 are compatible with no between-group differences in an array of conditions, including gonorrhea, chlamydia, syphilis, trichomonas, candida, bacterial vaginosis, and pregnancy (Table 3).

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Effectiveness of Perfect Condom Use

Further analyses were carried out to clarify the apparent lack of intervention effectiveness in reducing STD rates despite the large increase in the number of women who reported consistent condom use. Simple subgroup analyses that compared the STD rates of consistent condom users with the rates of inconsistent users did not show a protective effect of consistent condom use. Next, information from the sexual diaries and from the follow-up interviews was used to determine whether reported condom use was reliable and whether any use problems were experienced during each month of follow-up. During follow-up, if interview information or the comparison of supplies distributed and returned suggested that condom use was overreported in a sexual diary, the diary was classified as unreliable. This would occur, for example, when the number of returned wrappers was lower than the reported number of condoms used during the interval, or when the participant admitted to having had unprotected intercourse in the retrospective interview while the diary reported consistent condom use. In addition, if user problems such as condom breakage, slippage, and incorrect use were reported either in the diary or during the interview, the diary was classified as associated with condom use problems. Thus, for each month of follow-up, condom use was reclassified as: 1) consistent condom use, reliable diary, no reported problems; 2) consistent condom use, reliable diary, problems reported; 3) consistent condom use, unreliable diary (including diaries in which problems were also reported); and 4) inconsistent condom use (including unreliable diaries and diaries in which problems were reported). When perfect condom use was reported, the rate of first infection (gonorrhea, chlamydia, or syphilis, whichever the earliest) was lower than for inconsistent condom use in both intervention groups (Mantel-Haenszel rate ratio [RR], stratified by intervention group: 0.3; 95% CI, 0.1–0.8). The time intervals in which condom use was reported as consistent, but use problems were also reported or the reliability of reporting was questionable, were associated with STD incidence rates comparable to those of inconsistent users (Table 4).

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Effect of Combining Vaginal Microbicide Use and Condom Use

Among women in both the enhanced intervention and basic intervention groups, the incidence of STD was considerably lower when a vaginal microbicide was used in at least 50% of the acts of intercourse, as compared with time intervals when microbicide use was less frequent (Table 4). The effect of microbicide use is likely to be confounded by condom use, because the main objective of the intervention was to promote joint use of condom and vaginal microbicide. After stratification by pattern of condom use and by intervention group, the comparison of high frequency of microbicide use versus low frequency of use yielded a Mantel-Haenszel RR estimate of 0.5 (95% CI, 0.3–1.0) (Table 4).

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Skills-oriented counseling by clinicians had a greater effect on participants’ behavior than clinicians’ advice about how to reduce risk (given free supplies for both conditions). Women in the enhanced intervention group were significantly more likely to use any barrier, to use condoms, and to use condoms and vaginal microbicide in combination—and were more likely to do so for all acts of vaginal intercourse. This is consistent with the observation that effective condom promotion interventions usually include skill-building elements.1,24,25 The fact that women in the enhanced intervention group were also more likely to perform skills such as requesting condom use and putting condoms on men supports the contention that the skills orientation was responsible for the observed difference in barrier use between groups.

The effectiveness of the enhanced intervention in increasing barrier use was comparable to that reported by the most effective of rigorously evaluated intervention studies for women conducted to date.5,6,17 Unlike prior studies in which interventions were delivered in multiple sessions often totaling 8 to 10 hours, however, most of the enhanced intervention was delivered in a single session with limited booster activities (one video and ad hoc discussions with the clinician) during follow-up. This suggests that either clinicians substantially boost the effectiveness of single-session interventions or that it may be possible to teach critical skills in less time than is typically expended. This finding is supported by another recent study that compared the effectiveness of 2 brief, skills-oriented interventions—one involving a 20-minute session followed by 3 60-minute sessions and one involving 2 20-minute sessions—and found that the interventions were equally effective in increasing condom use.22

Although the enhanced intervention in this study is considerably shorter than is typical, even a 30-minute individual counseling intervention may seem impractical for clinicians given the usual time allotted for patient visits. It is possible that similar outcomes could be achieved with an even less intensive intervention. This study was not designed to evaluate the independent contribution of intervention components to the outcome, however, and cannot identify components that could be omitted to improve cost-effectiveness.

The contribution of free supplies to the effect on behavior cannot be estimated. Although both groups received free supplies, it may be that free supplies are relatively more important when combined with intensive skills training. Interventions that have largely or exclusively focused on increasing condom availability have typically reported only small increases in condom use.30,31

The main objective of the larger-scale prospective study was to measure the effectiveness of condom and vaginal microbicides in reducing the acquisition of STD. Thus, the focus of intervention development was on promoting condom and microbicide use to sexually active women. It is not surprising that our interventions did not increase sexual abstinence, reduce number of sex partners, or change patterns of sexual activity, even if sexual behavior changes were recommended to participants in the enhanced intervention. Our findings are consistent with other studies of STD/HIV risk-reduction interventions for young adult women. Interventions often fail to change these behaviors even when condom use increases.6,8 It may be that these behaviors are more resistant to change or merely that interventions typically focus on condom promotion. To increase abstinence or change numbers of partners and patterns of sexual activity, an intervention would probably have to include a compelling rationale (given the availability of condoms), identify acceptable alternatives, address cultural norms, teach required skills, and include relevant intervention materials.

Although the enhanced intervention achieved its intended effect of increasing use of condoms and vaginal microbicide, it failed to produce a commensurate decrease in STD rates. Subgroup analyses documented a clear protective effect only when perfect condom use was achieved, i.e., when a woman not only reported 100% use, but also 1) the diary report was in agreement with other sources of information on condom use during the same period; 2) no user problems (e.g., slippage or breakage) were reported; and 3) there was no indication of incorrect condom use. STD incidence was 3 to 4 times lower during months of perfect condom use than during other months of follow-up.

Although the enhanced intervention considerably increased consistency of condom use, it had only a relatively modest effect in increasing perfect use. Among women in the enhanced intervention followed for 2 or more months, 202 of 573 months of follow-up were classified in the category of perfect use, whereas 119 of 628 months of perfect use were recorded in the basic intervention group. Thus, although there was a between-group difference, it was much less remarkable than the difference in other indicators of condom use, including a simple assessment of consistency of use.

The proportion of perfect users, although larger in the enhanced intervention group than in the basic intervention group, was too small to produce a significant difference in group-specific STD rates. Using the STD incidence rates during imperfect use months to compute the number of STD cases expected in months of perfect use, we estimate that 5 STD cases were prevented in the enhanced intervention group. In other words, the enhanced intervention caused a 14% reduction of the incidence that the group would have experienced in the absence of an intervention effect. This difference was too small for the overall between-group difference in STD rates to be statistically significant and is well within the 95% confidence interval of the ratio of the intervention-specific incidence rates.

Finally, this study suggests that use of vaginal microbicides containing nonoxynol-9, in combination with condoms, further reduces STD acquisition rates in women, at least when used at the relatively low frequency and dosage of this study group. The public health significance of this finding is unclear, because other studies have indicated that nonoxynol-9 does not provide protection against HIV acquisition,32,33 and weak34 or no35 protection against gonorrhea and chlamydia.

In conclusion, this study demonstrates that a skills-oriented intervention, including a 30-minute counseling session delivered by a nurse-clinician, video viewing, and take-home materials, can substantially increase barrier use for STD prevention among women at high STD risk. Second, this study shows that whereas perfect condom use is associated with significantly reduced STD rates, perfect use is difficult to achieve. Although the enhanced intervention was successful in increasing condom use as compared with the basic intervention, it only modestly increased the frequency of perfect use, and the study failed to document a difference in STD rates between the intervention groups. The findings of this study indicate that evaluating the effectiveness of interventions based only on behavioral outcomes may inaccurately predict effectiveness in reducing biologic outcomes.

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