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Sexually transmitted infections (STIs) and bacterial vaginosis (BV), a common infection of the vagina, are widespread globally. These conditions have important health consequences, including genital symptoms, pregnancy complications, infertility, enhanced HIV transmission, and psycho-social effects. The World Health Organization estimated that, in 2012, there were 357 million new episodes of four curable STIs (chlamydia, gonorrhea, syphilis, and trichomoniasis) and 417 million people had infection with herpes simplex virus type 2 (HSV-2). Global estimates of BV occurrence have never been made.
The WHO Global Health Sector Strategy on STIs, 2016-2021 provides goals, targets, and priority actions for stemming the STI epidemic. As data on STI burden are critical for efforts to prevent, control, and manage STIs, the first strategic direction of the Global Strategy is to increase information, including STI prevalence estimates, for focused public health action. Estimating the global burden of STIs is hampered by the limited availability of STI diagnostic testing and surveillance and a scarcity of high-quality published studies of STI prevalence in low- and middle-income countries. Given these limitations, a WHO consultation highlighted the importance of exploring potential data available through clinical research studies and trial networks that gather baseline data on STIs, even when estimating STI prevalence is not the primary study objective.
In a study recently published in PLOS Medicine, investigators heeded this call to action by using combined data from 18 HIV prevention studies, including more than 37 000 women in sub-Saharan Africa, to estimate the prevalence of chlamydia, gonorrhea, syphilis, trichomoniasis, HSV-2, and BV.
The study revealed age-, region- and population-specific patterns in prevalence of these infections. It indicated a higher prevalence of STIs among younger (15–24 year-old) compared with older (25–49 year-old) women. It also suggested a generally higher STI prevalence in clinic or community-based populations in South Africa than among similar populations elsewhere in southern or eastern Africa, and greater prevalence among higher-risk populations for certain STIs (e.g., gonorrhea and syphilis), but not for others (e.g., HSV-2 and BV, which had high prevalence across all population types).
These findings strengthen our understanding of STI and BV epidemiology among sub-Saharan African women, and will help to inform decisions on the public health actions required to address the high burden of STIs in this region. For example, the high STI prevalence among young people highlights the need for global efforts to improve sexual and reproductive health among this group and particularly among adolescent girls and young women.
In addition to highlighting populations that are especially vulnerable, the study helps to identify where efforts need to be focused. Women enrolled from clinic or community-based settings in South Africa had particularly high prevalence of STIs. For chlamydia, prevalence was similar to or even greater than among women in eastern Africa recruited from higher-risk settings such as where transactional sex frequently occurs. However, in clinic or community-based populations elsewhere in southern or eastern Africa, the estimated chlamydia prevalence was lower and similar to that of high-income countries in Europe and in the United States of America with well-established chlamydia control programs. HSV-2 and BV prevalence was relatively high across all regions and population types. STI control efforts are particularly important in areas that also have high HIV prevalence as it is known that having an STI increases the risk of acquiring HIV.
Unlike the other STIs studied, gonorrhoea and syphilis were primarily concentrated among women from higher-risk settings, which in this study were all in eastern Africa. This suggests that targeting interventions to both populations and geographic regions will be important in controlling the spread and impact of gonorrhoea, particularly in stemming the threat of gonococcal antimicrobial resistance, and in reducing mother-to-child transmission of syphilis and HIV. Controlling gonorrhoea and syphilis are two of the three main areas of intervention focus for the Global Health Sector Strategy on STIs. The third main area of focus, fully utilizing human papillomavirus (HPV) vaccines, was not addressed in this analysis due to a lack of HPV data in the 18 studies evaluated.
Collecting new STI data is challenged by resource and logistical constraints. By leveraging existing data, this analysis provides a new approach to obtaining critically needed information on the epidemiology of STIs in low- and middle-income countries. Better data on STI burden are valuable not just for designing and implementing prevention and control programs in different settings, but also for monitoring program impact. Affordable, feasible point-of-care tests are needed to facilitate the collection of STI data and improve testing and treatment. Looking to the future, a global roadmap for accelerating the development of STI vaccines outlines how better data on STI burden in low- and middle-income countries are critical for catalyzing investment in new vaccine development and guiding future vaccine implementation and evaluation.