Can behavior change explain increases in the proportion of genital ulcers attributable to herpes in sub-Saharan Africa? A simulation modeling study

Costing of National STI Program Implementation for the Global STI Control Strategy for the Health Sector, 2016-2021

Introduction

In 2016 the World Health Assembly adopted the global strategy on Sexually Transmitted Infections (STI) 2016–2021 aiming to reduce curable STIs by 90% by 2030. We costed scaling-up priority interventions to coverage targets.

Methods

Strategy-targeted declines in Chlamydia trachomatis, Neisseria gonorrhoeae, Treponema pallidum and Trichomonas vaginalis were applied to WHO-estimated regional burdens at 2012. Syndromic case management was costed for these curable STIs, symptomatic Herpes Simplex Virus 2 (HSV-2), and non-STI vaginal syndromes, with incrementally expanding etiologic diagnosis. Service unit costs were multiplied with clinic attendances and people targeted for screening or prevention, by income tier. Human papilloma virus (HPV) vaccination and screening were costed for coverage increasing to 60% of 10-year-old girls for vaccination, and 60% of women 30–49 years for twice-lifetime screening (including clinical follow-up for positive screens), by 2021.

Results

Strategy implementation will cost an estimated US$ 18.1 billion over 2016–2021 in 117 low- and middle-income countries. Cost drivers are HPV vaccination ($3.26 billion) and screening ($3.69 billion), adolescent chlamydia screening ($2.54 billion), and antenatal syphilis screening ($1.4 billion). Clinical management—of 18 million genital ulcers, 29–39 million urethral discharges and 42–53 million vaginal discharges annually—will cost $3.0 billion, including $818 million for service delivery and $1.4 billion for gonorrhea and chlamydia testing. Global costs increase from $2.6 billion to $ 4.0 billion over 2016–2021, driven by HPV services scale-up, despite vaccine price reduction. Sub-Saharan Africa, bearing 40% of curable STI burdens, covers 44% of global service needs and 30% of cost, the Western Pacific 15% of burden/need and 26% of cost, South-East Asia 20% of burden/need and 18% of cost.

Conclusions

Costs of global STI control depend on price trends for HPV vaccines and chlamydia tests. Middle-income and especially low-income countries need increased investment, innovative financing, and synergizing with other health programs.

Incidence of herpes simplex virus type 2 infections in Africa: a systematic review

The burden of HSV type 2 varies substantially by region, with the highest incidence and prevalence in sub-Saharan Africa. We undertook a systematic review to identify studies reporting prospective data on incidence rates in men and women in Africa. Of 18 eligible studies, 7 were conducted in high-risk populations. Among women, incidence rates appeared to be higher in those with high-risk sexual behavior, with rates ranging from 3 to 23 per 100 person-years. In contrast, incidence rates in men appeared to be lower, ranging from 1 to 12 per 100 person-years. Risk factors for HSV-2 in women included prevalent human immunodeficiency virus (HIV) infection, younger age at sexual initiation, and sexual activity. Among men, condom use and circumcision had a protective effect, whereas prevalent HIV increased the risk of HSV-2 acquisition. This review draws attention to the high HSV-2 acquisition rates reported in Africa, thereby identifying an efficient setting for preventative HSV-2 vaccine trials.

Elimination of HIV in South Africa through expanded access to antiretroviral therapy: a model comparison study

BACKGROUND

Expanded access to antiretroviral therapy (ART) using universal test and treat (UTT) has been suggested as a strategy to eliminate HIV in South Africa within 7 y based on an influential mathematical modeling study. However, the underlying deterministic model was criticized widely, and other modeling studies did not always confirm the study's finding. The objective of our study is to better understand the implications of different model structures and assumptions, so as to arrive at the best possible predictions of the long-term impact of UTT and the possibility of elimination of HIV.

METHODS AND FINDINGS

We developed nine structurally different mathematical models of the South African HIV epidemic in a stepwise approach of increasing complexity and realism. The simplest model resembles the initial deterministic model, while the most comprehensive model is the stochastic microsimulation model STDSIM, which includes sexual networks and HIV stages with different degrees of infectiousness. We defined UTT as annual screening and immediate ART for all HIV-infected adults, starting at 13% in January 2012 and scaled up to 90% coverage by January 2019. All models predict elimination, yet those that capture more processes underlying the HIV transmission dynamics predict elimination at a later point in time, after 20 to 25 y. Importantly, the most comprehensive model predicts that the current strategy of ART at CD4 count ≤350 cells/µl will also lead to elimination, albeit 10 y later compared to UTT. Still, UTT remains cost-effective, as many additional life-years would be saved. The study's major limitations are that elimination was defined as incidence below 1/1,000 person-years rather than 0% prevalence, and drug resistance was not modeled.

CONCLUSIONS

Our results confirm previous predictions that the HIV epidemic in South Africa can be eliminated through universal testing and immediate treatment at 90% coverage. However, more realistic models show that elimination is likely to occur at a much later point in time than the initial model suggested. Also, UTT is a cost-effective intervention, but less cost-effective than previously predicted because the current South African ART treatment policy alone could already drive HIV into elimination. Please see later in the article for the Editors' Summary.

The impact of mobility on HIV control: a modelling study

Mobility is associated with HIV due to more risky sexual behaviour of mobile groups such as travellers and migrants. Limited participation of such groups may reduce the effectiveness of HIV interventions disproportionally. The established STDSIM model, which simulates transmission and control of HIV and STD, was extended to simulate mobility patterns based on data from Tanzania. We explored the impact of non-participation of mobile groups (travellers and recent migrants) on the effectiveness of two interventions: condom promotion and health education aiming at partner reduction. If mobile groups do not participate, the effectiveness of both interventions could be reduced by 40%. The impact of targeting travellers with a combined HIV campaign is close to that of a general population intervention. In conclusion, it is important to account for possible non-participation of migrants and travellers. If non-participation is substantial, impact of interventions can be greatly improved by actively approaching these people.

Modelling the interactions between herpes simplex virus type 2 and HIV: implications for the HIV epidemic in southern India

BACKGROUND

The role of herpes simplex virus type 2 (HSV-2) in the HIV epidemic and the potential impact of HSV-2 suppressive therapy have previously been explored only within the context of sub-Saharan Africa. In this analysis, modelling is used to estimate the contribution of HSV-2 to HIV transmission from clients to female sex workers (FSW) in a southern Indian setting and the maximum potential impact of 'perfect' HSV-2 suppressive therapy on HIV incidence.

METHODS

A dynamic HSV-2/HIV model was developed, parameterised and fitted to Mysore data. The model estimated the attributable fractions of HIV infections due to HSV-2. Multivariate sensitivity analyses and regression analyses were conducted.

RESULTS

The model suggests that 36% (95% CI 22% to 62%) of FSW HIV infections were due to HSV-2, mostly through HSV-2 asymptomatic shedding. Even if HSV-2 suppressive therapy could eliminate the effect of HSV-2 on HIV infectivity among all co-infected clients, only 15% (95% CI 3% to 41%) of HIV infections among FSW would have been averted. 36% (95% CI 18% to 61%) of HIV infections among HSV-2-infected FSW could have been averted if suppressive therapy reduced their risk of HIV acquisition to that of HSV-2-uninfected FSW.

CONCLUSIONS

HSV-2 contributes substantially to HIV in this southern Indian context. However, even in the best case scenario, HSV-2 suppressive therapy is unlikely to reduce HIV transmission or acquisition by more than 50% (as aimed for in recent trials), because of the limited strength of the interaction effect between HSV-2 and HIV.

HSV-2 serology can be predictive of HIV epidemic potential and hidden sexual risk behavior in the Middle East and North Africa

BACKGROUND

HIV prevalence is low in the Middle East and North Africa (MENA) region, though the risk or potential for further spread in the future is not well understood. Behavioral surveys are limited in this region and when available have serious limitations in assessing the risk of HIV acquisition. We demonstrate the potential use of herpes simplex virus-2 (HSV-2) seroprevalence as a marker for HIV risk within MENA.

METHODS

We designed a mathematical model to assess whether HSV-2 prevalence can be predictive of future HIV spread. We also conducted a systematic literature review of HSV-2 seroprevalence studies within MENA.

RESULTS

We found that HSV-2 prevalence data are rather limited in this region. Prevalence is typically low among the general population but high in established core groups prone to sexually transmitted infections such as men who have sex with men and female sex workers. Our model predicts that if HSV-2 prevalence is low and stable, then the risk of future HIV epidemics is low. However, expanding or high HSV-2 prevalence (greater than about 20%), implies a risk for a considerable HIV epidemic. Based on available HSV-2 prevalence data, it is not likely that the general population in MENA is experiencing or will experience such a considerable HIV epidemic. Nevertheless, the risk for concentrated HIV epidemics among several high-risk core groups is present.

CONCLUSIONS

HSV-2 prevalence surveys provide a useful mechanism for identifying and corroborating populations at risk for HIV within MENA. HSV-2 serology offers an effective tool for probing hidden sexual risk behaviors in a region where quality behavioral data are limited.

Dynamic modeling of herpes simplex virus type-2 (HSV-2) transmission: issues in structural uncertainty

The sexually transmitted infection (STI) Herpes simplex virus type-2 (HSV-2) is of public health concern because it is a very common frequently unrecognized lifelong infection, which may facilitate HIV transmission. Within HIV/STI modeling, structural uncertainty has received less attention than parametric uncertainty. By merging the compartments of a "complex" model, a "simple" HSV-2 model is developed. Sexual interactions between female sex workers (FSWs) and clients are modeled using data from India. Latin Hypercube Sampling selects from parameter distributions and both models are run for each of the 10,000 parameter sets generated. Outputs are compared (except for 2,450 unrealistic simulations). The simple model is a good approximation to the complex model once the HSV-2 epidemic has reached 60% of the equilibrium prevalence (95% of the 7,550 runs produced <10% relative error). The simple model is a reduced version of the complex model that retains details implicitly. For late-stage epidemics, the simple model gives similar prevalence trends to the complex model. As HSV-2 epidemics in many populations are advanced, the simple model is accurate in most instances, although the complex model may be preferable for early epidemics. The analysis highlights the issue of structural uncertainty and the value of reducing complexity.

Population-level effect of potential HSV2 prophylactic vaccines on HIV incidence in sub-Saharan Africa

Herpes simplex virus type-2 (HSV2) infection increases HIV transmission. We explore the impact of a potential prophylactic HSV2 vaccination on HIV incidence in Africa using STDSIM an individual-based model. A campaign that achieved 70% coverage over 5 years with a vaccine that reduced susceptibility to HSV2 acquisition and HSV2 reactivation by 75% for 10 years, reduced HIV incidence by 30-40% after 20 years (range 4-66%). Over 20 years, in most scenarios fewer than 100 vaccinations were required to avert one HIV infection. HSV2 vaccines could have a substantial impact on HIV incidence. Intensified efforts are needed to develop an effective HSV2 vaccine.

Population-level effect of HSV-2 therapy on the incidence of HIV in sub-Saharan Africa

BACKGROUND

Herpes simplex virus type 2 (HSV-2) infection increases acquisition and transmission of HIV, but the results of trials measuring the impact of HSV-2 therapy on HIV genital shedding and HIV acquisition are mixed, and the potential impact of HSV-2 therapy on the incidence of HIV at the population level is unknown.

METHODS

The effects of episodic and suppressive HSV-2 therapy were simulated using the individual-level model STDSIM fitted to data from Cotonou, Benin (relatively low HIV prevalence) and Kisumu, Kenya (high HIV prevalence). Clinician- and patient-initiated episodic therapy, started when symptomatic, were assumed to reduce ulcer duration. Suppressive therapy, given regardless of symptoms, was also assumed to reduce ulcer frequency and HSV-2 infectiousness.

RESULTS

Clinician-initiated episodic therapy in the general population had almost no effect on the incidence of HIV. The impact of patient-initiated therapy was higher because of earlier treatment initiation, but still low (<5%) unless symptom recognition and treatment-seeking behaviour were very high. Suppressive therapy given to female sex workers (FSW) in Kisumu had little effect on population HIV incidence. In Cotonou, suppressive therapy in FSW with high coverage and long duration reduced population HIV incidence by >20% in the long term. Impact was increased in both cities by also treating a proportion of their clients. Long-term suppressive therapy with high coverage in the general population could reduce HIV incidence by more than 30%.

CONCLUSIONS

These results show that HSV-2 therapy could potentially have a population-level impact on the incidence of HIV, especially in more concentrated epidemics. However, a substantial impact requires high coverage and long duration therapy, or very high symptom recognition and treatment-seeking behaviour.

Genital herpes has played a more important role than any other sexually transmitted infection in driving HIV prevalence in Africa

Background

Extensive evidence from observational studies suggests a role for genital herpes in the HIV epidemic. A number of herpes vaccines are under development and several trials of the efficacy of HSV-2 treatment with acyclovir in reducing HIV acquisition, transmission, and disease progression have just reported their results or will report their results in the next year. The potential impact of these interventions requires a quantitative assessment of the magnitude of the synergy between HIV and HSV-2 at the population level.

Methods and Findings

A deterministic compartmental model of HIV and HSV-2 dynamics and interactions was constructed. The nature of the epidemiologic synergy was explored qualitatively and quantitatively and compared to other sexually transmitted infections (STIs). The results suggest a more substantial role for HSV-2 in fueling HIV spread in sub-Saharan Africa than other STIs. We estimate that in settings of high HSV-2 prevalence, such as Kisumu, Kenya, more than a quarter of incident HIV infections may have been attributed directly to HSV-2. HSV-2 has also contributed considerably to the onward transmission of HIV by increasing the pool of HIV positive persons in the population and may explain one-third of the differential HIV prevalence among the cities of the Four City study. Conversely, we estimate that HIV had only a small net impact on HSV-2 prevalence.

Conclusions

HSV-2 role as a biological cofactor in HIV acquisition and transmission may have contributed substantially to HIV particularly by facilitating HIV spread among the low-risk population with stable long-term sexual partnerships. This finding suggests that prevention of HSV-2 infection through a prophylactic vaccine may be an effective intervention both in nascent epidemics with high HIV incidence in the high risk groups, and in established epidemics where a large portion of HIV transmission occurs in stable partnerships.

Possible reasons for an increase in the proportion of genital ulcers due to herpes simplex virus from a cohort of female bar workers in Tanzania

OBJECTIVES

To determine trends in the prevalence and aetiological distribution of genital ulcer syndrome (GUS) in a cohort of female bar workers and to assess factors associated with these trends.

METHODS

An open cohort of 600 women at high risk of HIV and sexually transmitted infection (STI) was offered screening and treatment for STI at 3-month intervals. The prevalence of GUS and associated aetiological agents (Herpes simplex virus (HSV), Treponema pallidum and Haemophilus ducreyi) were monitored over 27 months through clinical examination, dry lesion swabbing and multiplex polymerase chain reaction. The effects of HIV status and other factors on the prevalence trends of STI were assessed.

RESULTS

A total of 753 women were recruited into the cohort over 10 examination rounds. At recruitment, the seroprevalence was 67% for HIV and 89% for HSV type 2 (HSV-2). During follow-up, 57% of ulcers had unknown aetiology, 37% were due to genital herpes and 6% to bacterial aetiologies, which disappeared completely in later rounds. The absolute prevalence of genital herpes remained stable at around 2%. The proportion of GUS caused by HSV increased from 22% to 58%, whereas bacterial causes declined. These trends were observed in both HIV-negative and HIV-positive women.

CONCLUSIONS

The changes observed in the frequency and proportional distribution of GUS aetiologies suggest that regular STI screening and treatment over an extended period can effectively reduce bacterial STI and should therefore be sustained. However, in populations with a high prevalence of HSV-2, there remains a considerable burden of genital herpes, which soon becomes the predominant cause of GUS. Given the observed associations between genital herpes and HIV transmission, high priority should be given to the evaluation of potential interventions to control HSV-2 either through a vaccine or through episodic or suppressive antiviral therapy and primary prevention.

Herpes simplex virus type 2: epidemiology and management options in developing countries

Genital herpes simplex virus type 2 (HSV2) is highly prevalent worldwide and an increasingly important cause of genital ulcer disease (GUD). Continued HSV2 transmission is facilitated by the large number of undiagnosed cases, the frequency of atypical disease and the occurrence of asymptomatic shedding. The lack of easy, affordable diagnostic methods and specific antiviral treatment in countries with low and middle income is of great concern, given the ability of GUD to enhance HIV transmission and acquisition. With rising HSV2 prevalence contributing to an increase in the proportion of GUD attributed to genital herpes in high-HIV prevalence settings, a safe and effective HSV vaccine is urgently needed. Meanwhile, multifaceted interventions are required to improve recognition of genital herpes, to prevent its spread and also to prevent its potential to promote HIV transmission in developing countries.

Country-wide distribution of the nitrile female condom (FC2) in Brazil and South Africa: a cost-effectiveness analysis

OBJECTIVE

To evaluate the cost-effectiveness and potential impact of expanded female condom distribution.

DESIGN

Cost-effectiveness analysis assessing HIV infections averted annually and incremental cost per HIV infection averted for country-wide distribution of the nitrile female condom (FC2) among sexually active individuals, 15-49 years, with access to publicly distributed condoms in Brazil and South Africa.

RESULTS

In Brazil, expansion of FC2 distribution to 10% of current male condom use would avert an estimated 604 (5-95th percentiles, 412-831) HIV infections at 20,683 US dollars (5-95th percentiles, 13,497-29,521) per infection averted. In South Africa, 9577 (5-95th percentiles, 6539-13,270) infections could be averted, at 985 US dollars (5-95th percentiles, 633-1412) per infection averted. The estimated cost of treating one HIV-infected individual is 21,970 US dollars (5-95th percentiles, 18,369-25,719) in Brazil and 1503 US dollars (5-95th percentiles, 1245-1769) in South Africa, indicating potential cost savings. The incremental cost of expanded distribution would be reduced to 8930 US dollars (5-95th percentiles, 5864-13,163) per infection averted in Brazil and 374 US dollars (5-95th percentiles, 237-553) in South Africa by acquiring FC2s through a global purchasing mechanism and increasing distribution threefold. Sensitivity analyses show model estimates to be most sensitive to the estimated prevalence of sexually transmitted infections, total sexual activity, and fraction of FC2s properly used.

CONCLUSIONS

Expanded distribution of FC2 in Brazil and South Africa could avert substantial numbers of HIV infections at little or no net cost to donor or government agencies. FC2 may be a useful and cost-effective supplement to the male condom for preventing HIV.

Empirical Observations Underestimate the Proportion of Human Immunodeficiency Virus Infections Attributable to Sexually Transmitted Diseases in the Mwanza and Rakai Sexually Transmitted Disease Treatment Trials: Simulation Results

BACKGROUND AND OBJECTIVES

Population attributable fractions (PAF) from observational studies may under- or overestimate the contribution of cofactor sexually transmitted disease (STD) to human immunodeficiency virus (HIV) spread. Empirical PAF estimates from the Mwanza and Rakai trials indicated the proportion of HIV infections attributable to STDs was higher in Mwanza than Rakai.

GOAL OF THIS STUDY

Estimate the "true" proportion (PAFM) of HIV infections attributable to STDs in the Mwanza and Rakai STD trial populations and explore how the evaluated interventions prevented HIV infections.

STUDY DESIGN

The STDSIM model was used to simulate the 2 populations at the baseline of the trials (with no STD treatment interventions) and counterfactual scenarios in which STD cofactor effects on HIV spread were removed either at the start of the trials or 2, 10, and 20 years into the HIV epidemics. Similar methods were used to quantify the contribution of the cure of each STD to overall HIV impact in each site.

RESULTS

: In Mwanza, the highest PAFM for the effect of any single STD over the 2 years of the trial was due to chancroid (40%). The PAFM for all curable STD was 65%. In Rakai, herpes simplex virus type 2 (HSV-2) was the most important STD (PAFM = 23%); the PAFM for curable STD was 20%. In both sites, the proportion of new infections due to treatable STD decreased over time. The decrease was greater for Rakai, where a behavioral risk reduction that preceded the trial reduced STD prevalence. In both sites, the importance of HSV-2 increased later in the HIV epidemics and STD increased transmission of HIV more than acquisition of HIV. In the Mwanza trial, treatment of chancroid contributed most to preventing new HIV infections.

CONCLUSIONS

PAFs calculated from empirical data underestimated the contribution of STD to HIV spread in the Mwanza and Rakai trial populations because STD effects on HIV transmission (as opposed to acquisition) were not captured in the observationally based studies.

Can population differences explain the contrasting results of the Mwanza, Rakai, and Masaka HIV/sexually transmitted disease intervention trials?: A modeling study

OBJECTIVE

To determine whether population differences can explain the contrasting impacts on HIV observed in the Mwanza trial of sexually transmitted disease (STD) syndromic treatment (ST), the Rakai trial of STD mass treatment (MT), and the Masaka trial of information, education, and communication (IEC) with and without ST as well as to predict the effectiveness of each intervention strategy in each population.

METHODS

Stochastic modeling of the transmission of HIV and 6 STDs was used with parameters fitted to demographic, sexual behavior, and epidemiological data from the trials and general review of STD/HIV biology.

RESULTS

The baseline trial populations could be simulated by assuming higher risk behavior in Uganda compared with Mwanza in the 1980s, followed by reductions in risk behavior in Uganda preceding the trials. In line with trial observations, the projected HIV impacts were larger for the ST intervention in Mwanza than for the MT intervention in Rakai or the IEC and IEC + ST interventions in Masaka. All 4 simulated intervention strategies were more effective in reducing incidence of HIV infection in Mwanza than in either Rakai or Masaka.

CONCLUSIONS

Population differences in sexual behavior, curable STD rates, and HIV epidemic stage can explain most of the contrast in HIV impact observed between the 3 trials. This study supports the hypothesis that STD management is an effective HIV prevention strategy in populations with a high prevalence of curable STDs, particularly in an early HIV epidemic.

Aetiology of sexually transmitted infections and response to syndromic treatment in southwest Uganda

OBJECTIVE

To determine the aetiology of genital ulcers and discharges in rural south western Uganda and to assess response to syndromic treatment.

METHOD

A longitudinal, prospective study using laboratory testing and questionnaires to evaluate 561 adult men and women presenting with clinically verified genital ulcers, urethral, or vaginal discharge at a general outpatient clinic and two health centres between December 1999 and July 2001.

RESULTS

One third of patients had genital ulcers and two thirds discharges. There was good response to treatment in 461/508 patients (90.7%). Herpes simplex virus type 2 was found in 95/217 (43.8%) genital ulcers. In 24.1% of ulcer cases there was also a genital discharge. HIV seropositivity was high in ulcer cases (63.2%), with significantly more HSV2 and secondary bacterial infection than in seronegative cases. Neisseria gonorrhoeae was found in 135/204 (66.2%) male genital discharges. Female genital discharges were mostly associated with bacterial vaginosis (36.1%), Trichomonas vaginalis (18.9%), and candidiasis (18.6%).

CONCLUSIONS

The aetiological pattern of STI syndromes reported will help inform revision of national STI guidelines. The importance of herpes simplex virus type 2, the variation in causes of genital ulcers according to HIV serostatus, the high frequency of multiple infections and secondary bacterial contamination of genital ulcers are notable. These results help explain the lack of effect of an STI intervention on HIV incidence in a recent trial in this area.

Changes in the Etiology of Sexually Transmitted Diseases in Botswana between 1993 and 2002: Implications for the Clinical Management of Genital Ulcer Disease

BACKGROUND

In recent years, increasing evidence has accumulated that suggests the majority of cases of genital ulcer disease in sub-Saharan Africa are due to viral and not bacterial infections. Although many cross-sectional studies support such a trend, few serial cross-sectional data are available to show the evolution of genital ulcer disease over time.

METHODS

We surveyed the prevalence of sexually transmitted diseases (STDs) among patients with STD symptoms and women recruited from family planning clinics in 3 cities in Botswana in 2002 and compared our findings with those from a survey of a similar population conducted in 1993.

RESULTS

The observed proportion of cases of genital ulcer disease due to chancroid decreased from 25% in 1993 to 1% in 2002, whereas the proportion of ulcers due to herpes simplex virus increased from 23% in 1993 to 58% in 2002. Although the proportion of ulcers due to syphilis was similar for both surveys, the rate of positive serologic test results for syphilis among patients with genital ulcer disease decreased from 52% in 1993 to 5% in 2002. During this period, decreases in the prevalence of gonorrhea, syphilis-reactive serologic findings, chlamydial infection, and trichomoniasis were also detected among patients with STDs and women from family planning clinics. These changes remained significant after estimates were adjusted for the sensitivity and specificity of diagnostic tests.

CONCLUSIONS

Our findings suggest a decrease in the prevalence of bacterial STDs and trichomoniasis, a reduction in the proportion of ulcers due to bacterial causes, and an increase in the proportion of ulcers due to herpes simplex virus during the period 1993-2002. These changes should be taken into consideration when defining new guidelines for the syndromic management of genital ulcer disease.

Determinants of the impact of sexually transmitted infection treatment on prevention of HIV infection: a synthesis of evidence from the Mwanza, Rakai, and Masaka intervention trials

Community-randomized trials in Mwanza, Tanzania, and Rakai and Masaka, Uganda, suggested that population characteristics were an important determinant of the impact of sexually transmitted infection (STI) treatment interventions on incidence of human immunodeficiency virus (HIV) infection. We performed simulation modeling of HIV and STI transmission, which confirmed that the low trial impact in Rakai and Masaka could be explained by low prevalences of curable STI resulting from lower-risk sexual behavior in Uganda. The mature HIV epidemics in Uganda, with most HIV transmission occurring outside core groups with high STI rates, also contributed to the low impact on HIV incidence. Simulated impact on HIV was much greater in Mwanza, although the observed impact was larger than predicted from STI reductions, suggesting that random error also may have played some role. Of proposed alternative explanations, increasing herpetic ulceration due to HIV-related immunosuppression contributed little to the diminishing impact of antibiotic treatment during the Ugandan epidemics. The strategy of STI treatment also was unimportant, since syndromic treatment and annual mass treatment showed similar effectiveness in simulations of each trial population. In conclusion, lower-risk behavior and the mature HIV epidemic explain the limited impact of STI treatment on HIV incidence in Uganda in the 1990s. In populations with high-risk sexual behavior and high STI rates, STIs treatment interventions may contribute substantially to prevention of HIV infection.

HIV dynamics and behaviour change as determinants of the impact of sexually transmitted disease treatment on HIV transmission in the context of the Rakai trial

OBJECTIVE

To assess how the impact of sexually transmitted disease (STD) treatment on HIV incidence varies between stages of the HIV epidemic.

METHODS

We simulated the spread of curable STD, herpes simplex virus type 2 and HIV in the dynamic transmission model. Parameters were quantified to represent a severe HIV epidemic as in Rakai, Uganda, using demographic, behavioural and epidemiological data from a recent STD treatment trial.

RESULTS

The model fitted the HIV epidemic in Rakai if we assumed a considerable behavioural risk reduction, starting at the end of the Ugandan civil war in 1986. An improvement in STD treatment reduced HIV incidence in this population by 35% over 2 years if implemented in 1981, but only by 11 and 8% in 1988 or 1998. This trend resulted partly from the hypothesized behaviour change, which markedly reduced the prevalences of bacterial STD. In a simulated epidemic without behavioural change, the corresponding treatment impacts in 1988 and 1998 would be 19 and 15%. Enhanced herpetic ulceration in immunocompromised HIV patients contributed little to the reduced impact of treatment of bacterial STD over time.

CONCLUSION

In HIV epidemics beyond the first decade, the impact of STD treatment programmes on HIV transmission may depend more on behavioural risk reduction than on the stage of the epidemic. Preceding behavioural change associated with restored civil stability may have contributed to the lack of impact of STD treatment on HIV in the Rakai trial. In advanced epidemics with less behaviour change, STD treatment may still be important for HIV prevention.