Sexually Transmitted Diseases:
STD Prevention: Effectively Reaching the Core and a Bridge Population With a Four‐Component Intervention
Van Dam, Johannes C. MD, MSc*; Holmes, King K. MD, PhD†
*From the Population Council, Horizons Project, Washington, DC; and the †Center for AIDS and STD, University of Washington, Seattle, Washington
Reprint requests and correspondence: King K. Holmes, MD, PhD, Harborview Medical Center, Box 359931, 325 9th Avenue, Seattle, WA 98014. E‐mail: email@example.com.
Received for publication October 12, 1999, and accepted October 13, 1999.
THE NEED FOR prevention and control of sexually transmitted diseases (STDs) has been underscored by the role conventional STDs are considered to play in the acquisition and transmission of HIV infection.1 Whereas control programs in many industrialized countries have succeeded in reducing the prevalence of gonorrhea, bacterial genital ulcer diseases (GUD), and trichomoniasis to historically low values,2 these curable STDs continue to be a large public health problem in many parts of the developing world.3
In the absence of inexpensive, accurate, and simple diagnostic and screening tests, the comparatively high prevalence of STDs in the developing world is due in part to (1) the lack of systematic application of effective algorithms for syndromic management of STDs; (2) the frequently asymptomatic nature of sexually transmitted infections (STIs) especially, but not exclusively, in women; and (3) the failure to target feasible interventions to populations most likely to acquire and transmit STIs.2,4,5 Resource constraints severely limit the diagnostic and screening options available for the management of symptomatic and asymptomatic STDs in both men and women. Selective mass treatment of female sex workers6 has been shown to reduce gonorrhea prevalence rapidly; however, rates of infection returned to preintervention levels in a period of weeks, and a community‐level, randomization trial involving the mass treatment of the general population of the Rakai district of rural Uganda every 10 months failed to demonstrate an impact of the intervention on rates of gonorrhea, chlamydial infection, serologic evidence of active syphilis, or symptoms of GUD.7
In this issue of Sexually Transmitted Diseases, Steen et al8 report on a four‐component STD intervention program for female sex workers. This landmark study used a mobile clinic to deliver (1) monthly, selective mass treatment for bacterial STDs with a directly observed 1‐g dose of azithromycin; (2) syndromic management of vaginal discharge and genital ulcers; (3) regular serologic tests for syphilis, with treatment of persons who tested seropositive; and (4) counseling and condom promotion. The prevalence of gonorrhea and chlamydial infection declined by 77% in women who attended the clinic on at least four occasions (from 24.9% to 5.7%), and the prevalence of clinical evidence of genital ulcers in these women declined by 86% (from 6.4% to 0.9%). Cross‐sectional surveys among miners living near the intervention site were conducted before and 9 months after the start of the intervention. The prevalence of gonorrhea and chlamydial infections declined by 43%, and clinical evidence of genital ulcers was reduced by 77%. The authors also stratified miner hostels by distance from the intervention site, and observed for each stratum the number of miners seeking STD consultation as a proportion of all outpatient department visits by miners, both before and after the intervention. An inverse relationship was noted between distance of the hostels from the sex worker intervention site and the reduction in the number of STD consultations among miners; the proportion of outpatient visits for STDs actually increased among miners living more than 5 km from the intervention site. Essentially, the surveys of the strata of miners over time could be viewed as three concurrent time‐series studies in a quasi‐experimental design.
This study raises a number of further questions. Although the impact of the program on STD prevalence in participating sex workers was impressive, reinfection rates were very high initially, declining from more than 12% for gonorrhea and chlamydia in the first month to less than 6% for women who made three follow‐up visits. A treatment interval of less than 1.3 months led to significant reductions in the prevalence of gonorrhea, chlamydia, and genital ulcers, thereby underscoring the efficacy of regular participation in the program.
However, an important aspect of this setting was the relatively stable residential status of the male client population, and the availability of medical STD care provided by their occupational health system. Although the miners represent a migrant work force who periodically return home, thereby serving as a “bridge population” for transmission of STD to spouses and regular partners, they remain at the work site for months at a time. Thus, it cannot be assumed that a similar intervention would produce a similar decline in prevalence of STD and in incidence of STD reinfection among sex workers serving less stable populations. For example, sex workers in port cities or along urban transport routes, where reinfection pressures presumably would remain high despite these interventions, might require more frequent intervention to achieve comparable prevalence.
In the study population, the considerable reduction in STD prevalence illustrates the quandary of a successful program; when prevalence levels decrease, the specificity of the approach is reduced, leading to reductions in cost‐effectiveness and to increased rates of overtreatment (with both mass treatment and syndromic treatment).
The reduced reinfection rates in sex workers who participated in this study coincided with an increase in condom use with casual sex partners (2% to 33%); thus, the impact of the program cannot be attributed either to periodic, selective presumptive treatment or syndromic treatment alone. The rapid decline in the number of women who continue to participate in the program also raises a concern; among enrolled women, 42% returned for two follow‐up visits, and 26% returned for three follow‐up visits. The total number of sex workers in the area is not provided, and is undoubtedly difficult to determine; therefore, it is not clear what percent‐age of the sex workers were covered by the intervention. Despite this uncertainty, a surprisingly large population effect was observed in terms of reduced STD rates in miners.
The current study provides strong evidence of the validity of core‐group theory,9 albeit in the unique, if not uncommon, setting of migrant labor camps. The impact on STD prevalence in miners suggests that in some situations, a targeted program can have a substantial impact at the population level, despite only partial and unsustained coverage of the core‐group; however, it is relevant to ask whether other factors or a combination of factors could help to explain the size of the reduction of STD rates in miners. For example, miners in the intervention may have adopted safer sex behaviors and increased their use of condoms, either as a result of sex worker counseling and condom promotion or in reaction to mine‐based health education programs. The subset of sex workers who dropped out of the intervention program may have included many who moved out of the immediate intervention area, thereby reducing the risk of exposure of miners at the site to nonparticipating sex workers. New sexual partnerships or networks may have formed as miners who were aware of the ongoing intervention could have increasingly sought sexual partners among women participating in the intervention. Finally, it would be of interest to assess, through mathematical modeling, under what assumptions the reduction of STD prevalence and increased condom use in a subset of sex workers for a finite period would lead to the observed decline in STD clinic consultations among these men.
Where does this leave us? The four‐component program reported in the study by Steen et al represents one approach to ensure case management of both symptomatic and asymptomatic STDs. Providing mobile clinics and monthly mass treatment may not be affordable in many resource‐constrained settings; nevertheless, the study results illustrate the importance of bringing services to those who need them, especially in areas with marginalized and disempowered residents. Future evaluations of similar approaches in different settings must formally assess not only the impact on STD rates and on antimicrobial resistance of STD pathogens or other organisms, but the acceptability and the voluntary nature of participation in such interventions.
An alternative approach, which has been equally successful in lowering STD prevalence in female sex workers in other settings, involves periodic screening for and specific treatment of STDs, coupled with syndromic treatment (e.g., genital ulcers) and counseling, and condom promotion and provision.8,9,10 The choice between periodic presumptive treatment versus periodic screening and treatment of specific infections rests on further comparative analyses of costs, feasibility, and other factors.
Finally, to achieve the greatest long‐term success in STD control, interventions to reduce STD prevalence in core‐group members need to be combined with good‐quality clinical services that involve (1) syndromic treatment algorithms and feasible screening tests (e.g., syphilis serology) for bridge populations (as in the setting studied by Steen et al); and (2) effective, sustained behavior change interventions to prevent the transmission of STIs. Programs for syndromic management of STDs in the general population have been shown to reduce STI and HIV rates.13 Such programs, together with behavior change interventions in the general population, are particularly important where patterns of sexual behavior do not involve core groups.14 Further operational‐intervention studies based on the combination of targeted and general‐population approaches are warranted, ideally to (1) measure the impact on HIV and STD; (2) understand and optimize the implementation of such programs in different settings; and (3) assess their effect on HIV transmission. Reaching the core is an essential first step in many settings.
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3. World Health Organization. An Overview of Selected Curable Sexually Transmitted Diseases. Geneva: World Health Organization, 1995.
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6. Holmes KK, Johnson DW, Kvale PA, et al. Impact of a gonorrhea control program, including selective mass treatment, in female sex workers. J Infect Dis 1996; 174(suppl 2):230–239.
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9. Thomas JC, Tucker MJ. The development and use of the concept of a sexually transmitted disease core. J Infect Dis 1996; 174(suppl 2):S134-S143
10. Laga M, Alary M, Nzila N, et al. Condom promotion, sexually transmitted diseases treatment, and declining of HIV infection in female Zairian sex workers. Lancet 1994; 344:246–248.
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13. Grosskurth H, Mosha F, Todd J, et al. Impact of improved treatment of sexually transmitted diseases on HIV infection in rural Tanzania: randomized controlled trial. Lancet 1995; 346:530–536.
14. van Vliet C, Holmes KK, Singer B, Habbema JDF. The effectiveness of HIV prevention strategies under alternative scenarios: evaluation with the STDSIM model. In: Ainsworth M, Fransen L, Over M, eds. Confronting AIDS: Evidence from the Developing World. The European Commission, 1998:207–237.
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