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Sexually Transmitted Disease Clinic Clients at Risk for Subsequent Gonorrhea and Chlamydia Infections

Possible ‘Core’ Transmitters

Gunn, Robert A. MD, MPH*†; Fitzgerald, Star BA; Aral, Sevgi O. PhD*

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Sexually Transmitted Diseases: July 2000 - Volume 27 - Issue 6 - p 343-349
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DURING THE LAST DECADE, gonorrhea (GC) incidence has been declining in most areas of the United States, and currently, many cases are reported among inner-city minority populations.1 It is postulated that sexual networks of persons who have repeated GC infections and multiple sex partners-so called high-frequency or “core” transmitter networks-maintain endemic foci of GC.2 Trends in chlamydia (CT) incidence are more difficult to determine because reported prevalence and incidence vary considerably based on screening practices of community clinicians. However, some data suggest that CT incidence may be declining3 and that, in some geographic areas, cases of CT may be becoming concentrated in core transmitter groups.4 Core group theory suggests that controlling GC/CT within core groups can have a marked impact on overall community incidence.5 However, from a sexually transmitted disease (STD) control perspective, developing a practical way to identify core transmitters-persons who could be candidates for enhanced intervention-has been difficult.

Identifying persons who meet a specific definition of a core transmitter6 requires a considerable amount of information about sex-partner networks and infection rates-a task beyond the capabilities of most STD control programs. Moreover, such networks are fluid and may evolve and change before interventions can be implemented. As an indirect way to address this issue, we conducted a study to identify STD clinic clients who, at their current visit, were at an increased risk of being involved in GC or CT transmission in the subsequent year. Such persons may be core transmitters, especially if they have had GC/CT in the recent past or at the current STD clinic visit. These potential core transmitters would be candidates for enhanced intervention that could include periodic visits for client-centered risk reduction, counseling for STD symptom recognition, STD screening, and preventive treatment-the essential elements of what could be considered as STD-prevention case management services. In addition, field investigators could interview potential core transmitters to identify sexual network members who could be screened and preventively treated, and to delineate target areas for other community-level interventions.

For a practical application of the findings of this evaluation, the information collected was used to determine the risk profile of persons likely involved in GC or CT transmission in the subsequent year. Using the risk profile, persons seeking services could be assigned to various levels of intervention ranging from minimal (basic STD health education) to intensive, such as prevention case management. This approach should improve the efficiency and possibly the effectiveness of STD clinic-based intervention activities.


All clients with a new problem attending the main San Diego County STD clinic between February 23 and July 31, 1995 were eligible for enrollment. Each client was asked to complete a one-page risk assessment form (English or Spanish) that covered the number and types of sex partners, condom use, STD history, and questions about perceived risk (e.g., did the clients think they had been exposed to an STD or had an STD themselves, and if so, did they know the source person or think they had spread the STD?). They were also asked whether they thought they would get an STD in the next 2 years. The form was reviewed by the clinic clinician who also asked a few additional questions about drug use and trading sex for drugs or money. In some instances the clinician corrected client responses and helped complete questions not answered by the client initially.

After the current clinic visit, the medical record was abstracted to determine the final diagnosis for the visit. A recent STD history was defined as having an STD in the past 5 years that was determined by a patient self-report, clinic record documentation, or a current visit diagnosis. One year after the current visit, the medical record of each client was reviewed for evidence of a visit during the 1-year follow-up period, and the medical record was abstracted for each visit. In addition, the names of all clients enrolled were matched with the STD program case and sex-partner interview database and with the overall county-wide STD case-reporting surveillance database (to identify persons diagnosed with reportable STDs in other medical settings).

During the 1-year follow-up period, a subsequent STD was defined as a bacterial STD (GC, CT, or syphilis), bacterial-related STD syndrome (nongonococcal urethritis or pelvic inflammatory disease), newly diagnosed viral STD (genital herpes, or human papillomavirus), trichomoniasis, or a sex partner contact to any bacterial STD (GC, CT, or syphilis) reported by the client or communicable disease investigator. The subsequent STD had to occur between 45 and 365 days after enrollment. The primary outcome of interest, subsequent GC/CT, was limited to clients having either GC or CT or being a sexual contact to a person with either infection.

Data were analyzed using EpiInfo 6.0 (Centers for Disease Control and Prevention, Atlanta, GA). Because more than 85% of the clients did not require assistance (completion or correction) with their questionnaire responses, only the original client responses were analyzed.


During the enrollment period, 2637 clients were eligible, and 2612 (99%) were given a risk assessment form. Of those, 30 persons declined to complete the form and 6 persons reported that someone else completed the form for them. These records were excluded, leaving 2576 records (99%) for analysis.

Of the 2576 enrolled clients, 204 (7.9%) had a subsequent STD during the 1-year follow-up period. Of the 204 clients, 20 (9.8%) were identified through the county-wide STD case-reporting surveillance system. The 204 subsequent STD clients had, at minimum, 242 clinical visits for an STD evaluation, 170 had one visit, 21 had two visits, six had three visits, and three clients had four visits (number of visits per persons identified through the county-wide STD case-reporting surveillance system could not be determined and were assigned as having had one visit). These 242 medical encounters identified 260 STD conditions (Table 1). Nongonococcal urethritis was the most common subsequent diagnosis; five men had three or more episodes of nongonococcal urethritis during the 1-year follow-up period.

STD Clinic Clients (N = 204)* With Subsequent STDs

Subsequent GC/CT occurred in 79 clients (3.1%) clients, of whom 68 had GC or CT, 32 had GC, 32 had CT, and four clients had GC and CT at some time during the follow-up period. Eleven clients reported sexual contact with a person with either GC or CT, but were not themselves identified as infected during the follow-up period. Only 2 of the 36 persons with GC and 2 of the 36 persons with CT were infected more than once.

Overall, the strongest predictor of subsequent GC/CT was a recent history of GC/CT or current visit diagnosis of GC/CT infection (6.1% subsequent GC/CT rate, P < 0.001) (Table 2). Having a recent history or current clinic visit of an STD other than GC or CT increased the risk of subsequent GC/CT slightly. A recent history or current clinic visit diagnosis of GC/CT was strongly predictive for both females (6.3%) and heterosexual males (6.3%) but not among men who had sex with men (MSM), which includes men identifying as gay or bisexual (Table 2). However, MSM as a group had a 5.2% (14 of 271 persons) subsequent GC/CT rate, which was similar to the subsequent GC/CT rate for heterosexual males and females with a recent history or current visit diagnosis of GC or CT (6.3%).

Recent History and Current Visit Diagnosis of STDs Predictive of Subsequent Gonorrhea or Chlamydia*

A medical record documentation of recent history of a GC or CT infection or a client's report of having ≥2 GC or CT infections in the recent past (5 years) was a stronger predictor of a subsequent GC/CT than a self-reported client history of only one GC or CT infection in the recent past. Table 3 shows combinations of client history, medical record documentation, and current STD clinic visit of GC/CT that predicted a subsequent GC/CT rate of more than 10%. Having a recent history and current STD visit diagnosis of GC/CT infection predicted a 15% to 24% subsequent GC/CT rate. The few patients with two or more GC documented in the clinic medical record had >50% subsequent GC/CT rate.

Recent History and Current Visit Diagnosis of Gonorrhea or Chlamydia Infections Predicting > 10% Subsequent Gonorrhea or Chlamydia Risk*

Among the stratum of heterosexual males who had a recent history or current clinic visit diagnosis of GC or CT, we wanted to determine if there were additional factors that further increased the risk of subsequent GC/CT. Among these males (n = 507), there were no demographic (age, race, ethnicity, area of residence), behavioral (number of sex partners, new sex partner, condom use, alcohol or drug use, or trading sex for drugs or money), or history of other STDs that substantially increased the risk of subsequent GC or CT. Of the small number of men (n = 42) who thought they had an STD and spread it to someone else, the subsequent GC/CT rate was 14.3% (P = 0.05). Among all MSMs (n = 271), no demographic, behavioral, or other STD history substantially increased the risk of subsequent GC or CT; however, MSM who thought they had an STD (n = 113) or those who thought they knew the source of their STD (n = 51) had an elevated subsequent GC or CT rate (8.0%, P = 0.08; 15.5%, P < 0.01, respectively).

Among females who had a recent history or current clinic visit diagnosis of GC or CT (n = 239), no behavioral or perception of risk variables substantially increased the risk of subsequent GC or CT. However, black women (n = 82) in this group had a more than threefold increased risk of having a subsequent GC or CT than women of other races (12.2% versus 3.2%; RR = 3.8, P < 0.01).

Criteria for identifying clients for various levels of prevention and risk-reduction counseling were developed based on the subsequent GC/CT rate (Table 4). Clients reporting a history of two or more episodes either of of GC or of CT during the past 5 years or having a GC or CT infection documented in the clinic medical record during the past 5 years (n = 227) accounted for 9% of clinic clients and had a 10.1% subsequent GC/CT rate. These clients would possibly be candidates for enhanced intervention (prevention case management). Clients with lesser subsequent GC/CT risk (25% of clinic clients with a 4.7% subsequent GC/CT rate) could receive less-intensive interventions, with a large proportion of clients (66% of clinic clients with a 1.5% subsequent GC/CT rate) needing only basic STD health education and prevention information.

Criteria for Identifying Clients for Various Levels of Prevention/Risk Reduction Counseling*


This 1995 to 1996 study in San Diego, CA, showed that among STD clinic clients, almost 1 in 12 (7.9% subsequent STD rate) were involved in STD transmission during the 1-year follow-up period after their initial STD clinic visit, and approximately half of these clients (3.1% subsequent GC/CT rate) were involved in GC or CT transmission. In the San Diego STD clinic, the 1-year overall subsequent STD rate (7.9%) was similar to that found in a 1993 study7 in Dallas, TX (6.0%) and a 1994 to 995 National Institute of Mental Health8 multisite study (9.4%), but lower than a 1987 study9 in Dade County, FL (18.5%), a 1988 to 1989 study10 in Baltimore, MD (20%), and a 1992 study11 in New York City (approximately 15%). Because subsequent STD rates are, to some extent, a reflection of the community prevalence of STDs, the somewhat higher rates seen in studies performed in the late 80s and early 90s compared with the more recent studies are partially explained by the higher STD prevalence during those years. Overall, these subsequent STD rates indicate that many persons attending STD clinics are likely involved in high-risk core sexual networks and repeatedly present for treatment at STD clinics where interventions could be initiated.

In this study, the strongest predictor of subsequent GC or CT was having had GC or CT within the past 5 years (history or current visit diagnosis). Those persons reporting having had two or more episodes of either GC or CT or having a medical record documented history of GC or CT had a higher risk of subsequent GC/CT, and those with two or more episodes of GC documented in their medical record had a more than 50% risk of subsequent GC/CT. It appears that the more frequently a person acquires these infections, the more likely they will continue to do so in the future, and suggests that such persons, especially persons with two or more episodes, are members of core GC/CT sexual networks.

Several studies of gonococcal infections in the 1970s showed the importance of persons with repeat GC infections in overall GC incidence.12–14 One investigator proposed that intensive follow-up evaluation of the small number of high-risk populations and their contacts could result in major reductions in the number of reported cases of gonorrhea.12

In the 1987 Dade County STD clinic-based study of subsequent STDs, the same risk factor-a past history or current visit diagnosis of an STD-was the strongest predictor of a 1-year subsequent STD.9 The authors suggested that these patients be targeted for intervention, and mentioned that a 6-month STD rescreening with intensive counseling be considered as a potential intervention.

Our study suggests that much of the risk of subsequent GC/CT among STD clinic clients results from having sex with partners who have a high likelihood of having GC or CT. This contention is supported by the fact that among persons with a recent history or current visit diagnosis of GC/CT, reported unsafe sexual behaviors did not further increase the risk of subsequent GC/CT; actually, those who used condoms more frequently had a slightly higher subsequent GC/CT rate (data not shown). Other studies of persons at risk for STDs, especially those who have repeat episodes, have shown that sociodemographic factors (e.g., race, ethnicity, age, gender, social groups) rather than individual risky behaviors (e.g., multiple partners, infrequent condom use) are stronger predictors of STD acquisition, particularly the acquisition of GC or CT.15–20

In our study, high-risk clients may have appreciated the risk their partners presented, but more-frequent condom use could not counteract the effect of a high prevalence of GC/CT infection among their partners. Further supporting the concept that persons with a high risk of subsequent GC/CT were involved in sexual networks with a high prevalence of GC/CT is that persons in some subgroups who perceived that they spread an STD or knew the source of their infection had a substantially higher subsequent GC/CT rate. This suggests that these persons were familiar with STD symptoms and risk behaviors.

In lower-prevalence populations, such as among persons attending family planning or general primary care in urban areas, sexual behaviors and condom use are likely more important in determining the risk of acquiring an STD.21–23 In the lowest-prevalence populations in which STDs are rare, the risk of unsafe sexual behavior and infrequent condom use may be difficult to determine because the probability of being exposed to an STD is low. Therefore, the relative predictive value of risk behaviors and the recent history of GC/CT in determining subsequent risk will likely vary based on the prevalence of GC/CT in the community-at-large, as well as in the group being evaluated.

Because our STD clinic serves subgroups of high-risk clients, clients can be classified regarding their subsequent risk of GC/CT and the type of intervention needed. From our data, two thirds of our clients had a low risk of subsequent GC/CT and are in need of minimal intervention (basic STD health education). The other one third of clients at higher risk could be identified based on their STD history and current visit diagnosis and without using information about sexual or other behaviors, except that MSM had a higher risk regardless of STD history. We recommend the STD history (in particular, GC- and CT-documented positive tests and patient-reported GC and CT history) and sexual orientation, be obtained from clients seeking STD care or HIV counseling and testing and be recorded in an easily identifiable location in their clinical record. This information should be used to direct patients to the appropriate level of intervention, reserving intensive interventions such as periodic risk reduction and STD screening (prevention case management) for those at the greatest risk.

We are in the process of evaluating a prevention case management program for clients with a history of two or more documented GC/CT infections in the past 12 months (high risk for subsequent GC/CT). Although it is a resource-intensive intervention, core STD transmission theory suggests that decreasing prevalence through periodic screening and treatment of asymptomatic infections that would normally not be identified, rapidly treating symptomatic infections (prevention case management clients have special “no wait” STD clinic appointments), and improving sexual behavior among core transmitters, may have a population-level effect. We encourage further evaluation of STD-prevention case management in various settings and communities.

One limitation of using data obtained at the STD clinic to identify possible core transmitters is that some core transmitters will be missed and others will be erroneously classified as such. Almost 30% of persons with subsequent GC/CT did not have a recent history of GC/CT; such clients may be new members of core groups but would not be identified at the current clinic visit. Likewise, more than 90% of the persons with recent history or current visit GC/CT infection did not develop a recognized subsequent GC/CT; some of these clients may be leaving the core groups or were never core group members. Nevertheless, clients with two or more GC/CT infections in the recent past may be, for practical purposes, classified as potential core transmitters to prioritize intervention resources.

Besides the individual-level prevention case management approach to reducing the GC/CT among possible core group members, interventions directed toward identifying sexual networks that may be supporting transmission should be considered. Clients who are candidates for prevention case management could also be interviewed to obtain information about sexual networks and named partners. In some settings, interview techniques should be evaluated that are modified to focus on identifying networks without trying to elicit named partners. Once sexual networks have been identified, field and outreach techniques need to be developed to accomplish screening and preventive treatment of network members, even in field settings.24–26 Infections identified can lead to further identification of additional networks. Many of these approaches need evaluation through pilot and feasibility studies.

Other public health programs, such as those providing mental health services, domestic violence prevention, and tuberculosis control, have identified subgroups of persons who have repeated and difficult-to-solve problems and consume a disproportionate amount of intervention resources. In tuberculosis control, those with a high risk of transmitting infection have been identified and considerable resources have been invested (i.e., directly observed therapy) to cure infections and prevent transmission within the community. Those involved in preventing HIV transmission have also developed guidance on prevention case management for persons infected with HIV who are having difficulty in maintaining safe sexual behavior.27,28 We recommend that STD prevention and control programs consider a similar approach that explicitly evaluates interventions aimed at identifying and preventing STDs among persons in high-risk sexual networks, with the end result possibly being a marked decrease in overall community STD incidence.


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