Trichomonas vaginalis (TV) and bacterial vaginosis (BV) are highly prevalent vaginal infections. Both are associated with pelvic inflammatory disease and HIV acquisition and transmission, though the underlying mechanisms are incompletely understood. We characterized the effect of TV and BV infection on inflammatory markers in the vagina among reproductive-aged women in Atlanta, Georgia. Cervicovaginal lavage specimens were collected from HIV seronegative women at a baseline visit and again three months later. Eighteen individual cytokines, 17 T cell subsets, BV, and TV were measured at both timepoints. After natural log transformation, the median cytokine concentration and number of T cells were compared by infection status statistically using the Kruskal-Wallis test. A cytokine inflammation score and a T cell score were created using principal components analysis. The scores were then used as outcomes in separate linear mixed regression models with a random intercept. Sixty women had baseline data and 43 were seen for follow-up. The median age was 30 years, 78% self-reported Black race. TV and BV prevalence at the baseline visit was 15% and 37%, respectively. The concentration of 16 out of 18 cytokines differed by infection status. In multivariable modeling, neither TV nor BV were associated with cytokine score. Most CD4+ T cell subsets (7 out of 9) differed by infection status. In a multivariable model, TV infection was associated with a higher T cell score (1.54; 95%CI 0.00, 3.08). BV was not associated with a higher T cell score. Increased concentration of vaginal mucosal T cells may explain the observed association between TV infection and HIV risk.

PURPOSE: To examine differences in unstable housing and health-risk behaviors and experiences by sexual identity among U.S. high school students. METHODS: Using data from the 2021 Youth Risk Behavior Survey, a nationally representative survey of U.S. high school students, we calculated prevalence estimates and prevalence ratios of unstable housing by sexual identity (lesbian, gay, bisexual, questioning, and other-identifying [LGBQ+] vs. heterosexual). Among students experiencing unstable housing, we calculated prevalence estimates and prevalence ratios by sexual identity for substance use, violence victimization, mental health, and suicidal behaviors. RESULTS: LGBQ+ students were twice as likely to experience unstable housing, including sleeping in shelters or emergency housing, compared to heterosexual students. Among students experiencing unstable housing, LGBQ+ students were more likely to use substances and experience violence victimization, poor mental health, and suicide ideation and attempts. DISCUSSION: LGBQ+ youth experience a disproportionate burden of unstable housing and related health-risk behaviors and experiences.

The Youth Risk Behavior Surveillance System (YRBSS) is a set of surveys that tracks a broad range of behaviors, experiences, and conditions that can lead to poor health among high school students. The system includes a nationally representative Youth Risk Behavior Survey (YRBS) and separate school-based YRBSs conducted by states, tribes, territories, and local school districts. For the 2023 national YRBS, CDC made changes to the sampling method, survey administration mode, and questionnaire. Specifically, the sampling design added an American Indian or Alaska Native (AI/AN) supplemental sample so that separate, precise estimates could be made for AI/AN high school students, in addition to the usual sample designed to provide nationally representative data for the population of students in grades 9-12. To decrease the time needed to collect and process data, CDC changed the survey administration mode from paper-and-pencil scannable booklets to a tablet-based electronic survey. To provide national data on topics of emerging interest, CDC added new questions to the questionnaire. These new questions assessed social media use, experiences of racism at school, adverse childhood experiences, transgender identity, consent for sexual contact, and unfair discipline at school. Public health practitioners and researchers can use YRBSS data to examine the prevalence of youth health behaviors, experiences, and conditions; monitor trends; and guide interventions. This overview report describes 2023 YRBSS survey methodology, including sampling, data collection, data processing, weighting, and data analyses. The 2023 YRBS participation map, survey response rates, and a detailed examination of student demographic characteristics are included in this report. During 2023, in addition to the national YRBS, 68 site-level surveys were administered to high school students in 39 states, three tribal governments, five territories, and 21 local school districts. These site-level surveys use site-specific questionnaires that are similar to the national YRBS questionnaire but are modified to meet sites' needs. This overview and methods report is one of 11 featured in this MMWR supplement, which reports results from the 2023 national YRBS but does not include data from the 68 site-level surveys. Each report is based on data collected using methods presented in this overview report. A full description of YRBSS results and downloadable data are available (https://www.cdc.gov/yrbs/index.html).

Relatively little is known about the association between school discipline and student health and well-being. Using CDC's 2023 Youth Risk Behavior Survey, CDC analyzed the prevalence of report of unfair discipline at school and associations with experiences at school, mental health, suicidal thoughts and behaviors, and health risk behaviors among high school students overall and stratified by race and ethnicity. Prevalence estimates, prevalence differences, and prevalence ratios adjusted for race (in overall models), grade, and sex were calculated. Overall, 19.3% of students reported receiving unfair discipline during the previous 12 months; Black or African American students had a higher prevalence (23.1%) compared with Hispanic or Latino students (18.4%) and White students (18.1%). Unfair discipline was reported among a majority of students who describe their sexual identity in some other way (besides gay, heterosexual, lesbian, bisexual, or questioning) for American Indian or Alaska Native (81.7%) and multiracial (57.1%) subgroups. Overall, report of unfair discipline was associated with every health risk behavior and experience examined, including being bullied at school or electronically, skipping school due to feeling unsafe, carrying a weapon at school, prescription opioid misuse, poor mental health, persistent feelings of sadness or hopelessness, seriously considered attempting suicide, and attempted suicide. This pattern of association was similar among most student groups in models stratified by race and ethnicity. This analysis is the first to demonstrate, among a nationally representative sample of high school students, that reports of unfair discipline are associated with various health risk behaviors and experiences. With these findings, public health and education practitioners can create interventions that equitably promote safe, supportive, and inclusive school environments for student health.

Racism is a fundamental determinant of health inequities among racial and ethnic groups and is understudied among adolescents. In 2023, the national Youth Risk Behavior Survey questionnaire included an item assessing experiences of racism in the school setting among students in grades 9-12 in the United States. This report estimates the prevalence of students who reported ever having experienced racism in school and compares prevalence by racial and ethnic groups. For each racial and ethnic group, prevalence differences and prevalence ratios were estimated comparing the prevalence of indicators of poor mental health, suicide risk, and substance use among students who reported that they have ever versus never experienced racism in school. In 2023, approximately one in three high school students (31.5%) said that they had ever experienced racism in school. Reported experiences of racism were most prevalent among Asian (56.9%), multiracial (48.8%), and Black or African American (Black) (45.9%) students and least prevalent among White students (17.3%). Black and Hispanic or Latino (Hispanic) students who reported experiencing racism had a higher prevalence of all health risk behaviors and experiences investigated, including indicators of poor mental health, suicide risk, and substance use compared with students of their racial and ethnic group who reported never experiencing racism. Many of these associations were also found among multiracial and White students. Student reports of racism were associated with indicators of mental health and suicide risk among American Indian or Alaska Native (AI/AN) and Asian students. Among students of color, including AI/AN, Asian, Black, Hispanic, and multiracial students, the prevalence of seriously considering and attempting suicide was more than two times higher among students who ever compared with never experienced racism. These findings demonstrate that racism in the school setting is experienced by high school students attending public and private schools and continues to disproportionately affect students of color. Students who reported experiencing racism had a higher prevalence of indicators of poor mental health, suicide risk, and substance use. Schools can incorporate policies and practices to prevent unfair treatment on the basis of race and ethnicity and offer resources to help students cope with these experiences.

Transgender high school students (those whose gender identity differs from their sex assigned at birth) experience disparate health outcomes and challenges in school, including violence and discrimination, compared with cisgender students (those whose gender identity aligns with their sex assigned at birth). Until recently, population-based data describing the experiences of transgender students and students questioning whether they are transgender (questioning) have been limited. In 2023, the national Youth Risk Behavior Survey assessed transgender identity, providing the first nationally representative data about transgender students. This report describes the demographic characteristics of transgender and questioning high school students and examines differences in the prevalence of experiences of violence, poor mental health, suicidal thoughts and behaviors, school connectedness, and unstable housing among transgender, questioning, and cisgender high school students nationwide. In 2023, 3.3% of U.S. high school students identified as transgender, and 2.2% identified as questioning. Transgender and questioning students experienced a higher prevalence of violence, poor mental health, suicidal thoughts and behaviors, and unstable housing, and a lower prevalence of school connectedness than their cisgender peers. Compared with 8.5% of cisgender male students, 25.3% of transgender students and 26.4% of questioning students skipped school because they felt unsafe. An estimated 40% of transgender and questioning students were bullied at school, and 69% of questioning students and 72% of transgender students experienced persistent feelings of sadness or hopelessness, a marker for experiencing depressive symptoms. Approximately 26% of transgender and questioning students attempted suicide in the past year compared with 5% of cisgender male and 11% of cisgender female students. Intervention opportunities for schools to create safer and more supportive environments for transgender and questioning students can help address these disparities. The findings of this report suggest that more effort is necessary to ensure that the health and well-being of youths who are socially marginalized is prioritized.

Adverse childhood experiences (ACEs) are preventable, potentially traumatic events occurring before age 18 years. Data on ACEs among adolescents in the United States have primarily been collected through parent report and have not included important violence-related ACEs, including physical, sexual, and emotional abuse. This report presents the first national prevalence of self-reported ACEs among U.S. high school students aged <18 years, estimates associations between ACEs and 16 health conditions and risk behaviors, and calculates population-attributable fractions of ACEs with these conditions and behaviors using cross-sectional, nationally representative 2023 Youth Risk Behavior Survey data. Exposures were lifetime prevalence of individual (emotional, physical, and sexual abuse; physical neglect; witnessed intimate partner violence; household substance use; household poor mental health; and incarcerated or detained parent or guardian) ACEs and cumulative ACEs count (zero, one, two or three, or four or more). Health conditions and risk behaviors included violence risk factors, substance use, sexual behaviors, weight and weight perceptions, mental health, and suicidal thoughts and behaviors. Bivariate analyses assessed associations between individual and cumulative ACEs and demographics. Adjusted prevalence ratios assessed associations between cumulative ACEs and health conditions and risk behaviors, accounting for demographics. Population-attributable fractions were calculated to determine the potential reduction in health conditions and risk behaviors associated with preventing ACEs. ACEs were common, with approximately three in four students (76.1%) experiencing one or more ACEs and approximately one in five students (18.5%) experiencing four or more ACEs. The most common ACEs were emotional abuse (61.5%), physical abuse (31.8%), and household poor mental health (28.4%). Students who identified as female; American Indian or Alaska Native; multiracial; or gay or lesbian, bisexual, questioning, or who describe their sexual identity in some other way experienced the highest number of ACEs. Population-attributable fractions associated with experiencing ACEs were highest for suicide attempts (89.4%), seriously considering attempting suicide (85.4%), and prescription opioid misuse (84.3%). ACEs are prevalent among students and contribute substantially to numerous health conditions and risk behaviors in adolescence. Policymakers and public health professionals can use these findings to understand the potential public health impact of ACEs prevention to reduce adolescent suicidal behaviors, substance use, sexual risk behaviors, and other negative health conditions and risk behaviors and to understand current effects of ACEs among U.S. high school students.

Breakfast consumption is positively associated with academic achievement and diet quality among students, whereas skipping breakfast has been linked with poor mental health. Data from CDC's 2023 nationally representative Youth Risk Behavior Survey were used to describe how often high school students ate breakfast in the past 7 days and the associations between skipping breakfast every day (ate breakfast on 0 of the past 7 days), experiencing persistent feelings of sadness or hopelessness, school connectedness, and self-reported grades. Prevalence estimates and corresponding 95% CIs were calculated, and t-tests were used to identify differences within demographic groups (e.g., sex, race and ethnicity, and sexual identity). Logistic regression analyses were conducted to calculate prevalence ratios describing breakfast skipping, adjusting for demographics, and stratified by sex and race and ethnicity. Most students missed breakfast ≥1 time in the past 7 days (72.6%), and 17.9% of students skipped breakfast every day, with differences by sex, sexual identity, and race and ethnicity. Overall, and among both males and females, students who experienced persistent feelings of sadness or hopelessness were more likely to skip breakfast every day. The association between feelings of sadness and hopelessness and skipping breakfast was generally consistent across racial and ethnic groups. In contrast, greater levels of school connectedness and earning mostly As or Bs were inversely associated with skipping breakfast. Students who had higher school connectedness were approximately 30% less likely to skip breakfast on all 7 days. Skipping breakfast and poor mental health co-occur among many adolescents and might impede students' readiness to learn. School efforts to make breakfast accessible and appealing to high school students might yield multiple benefits and help reinforce school administrators' efforts to recover student learning losses that occurred during the COVID-19 pandemic. Parents, school decision-makers, and organizations that partner with schools and families can use these findings to guide efforts to promote breakfast consumption.

Schools are in a unique position to offer opportunities for students to be physically active throughout the school day and promote health and well-being. However, experiences that threaten safety or perceptions of safety might affect students' physical activity behaviors. Using the 2023 national Youth Risk Behavior Survey, six physical activity behaviors and five negative safety and violence experiences were examined from a nationally representative sample of U.S. high school students. This report updates national estimates for physical activity behaviors overall and by sex, grade, race and ethnicity, and sexual identity. In addition, associations between negative experiences and physical activity behaviors were examined, stratified by sex, via unadjusted and adjusted prevalence ratios. Regardless of negative safety and violence experiences, male students had a higher prevalence of meeting aerobic, muscle-strengthening, and both aerobic and muscle-strengthening physical activity guidelines compared with female students. In adjusted models among female students, a positive association was observed between being threatened or injured with a weapon at school and meeting the aerobic guideline, meeting the muscle-strengthening guideline, and playing on ≥1 sports team. Among male students, positive associations were observed between witnessing neighborhood violence and meeting the aerobic guideline and the muscle-strengthening guideline. A negative association was observed between attending physical education classes on all 5 days and witnessing neighborhood violence among female students and being bullied electronically among male students. Physical activity might serve as a mechanism that students employ to cope with negative safety and violence experiences. Understanding current physical activity behaviors among students with these negative experiences will be useful for school leaders, teachers, and public health practitioners who influence physical activity infrastructure and programming in schools and work to support safe, supportive, and inclusive school environments for student health. Although future research is needed to further explore these associations, physical activity continues to be an important behavior to prioritize for adolescent health in the school setting.

PURPOSE: Transgender youths (those whose gender identity differs from their sex assigned at birth) experience stigma and discrimination that can place them at increased risk for poor health outcomes compared with cisgender youths (those whose gender identity aligns with their sex assigned at birth). Limited population-based data exist on disparities among transgender and cisgender youths. METHODS: We examined differences in experiences of violence, substance use, mental health, suicide, sexual behavior, unstable housing, parental monitoring, and school connectedness among 98,174 transgender and cisgender high school students using data from 18 states that included an item to assess transgender identity on their 2021 Youth Risk Behavior Survey. RESULTS: Overall, 2.9% of students identified as transgender and 2.6% questioned whether they were transgender. Among transgender students, 71.5% reported that their mental health was not good, 32.3% had attempted suicide, and 29.0% experienced sexual violence. Transgender students were more likely than cisgender students to report experiences of violence, substance use, poor mental health, suicide risk, some sexual risk behaviors, and unstable housing, and were less likely to report feeling connected to others at school. CONCLUSIONS: Interventions that can address the causes of these adverse outcomes and promote the health and wellbeing of transgender youths are warranted.

The Youth Risk Behavior Surveillance System (YRBSS) is the largest public health surveillance system in the United States, monitoring a broad range of health-related behaviors among high school students. The system includes a nationally representative Youth Risk Behavior Survey (YRBS) and separate school-based YRBSs conducted by states, tribes, territories, and local school districts. In 2021, these surveys were conducted during the COVID-19 pandemic. The pandemic underscored the importance of data in understanding changes in youth risk behaviors and addressing the multifaceted public health needs of youths. This overview report describes 2021 YRBSS survey methodology, including sampling, data collection procedures, response rates, data processing, weighting, and analyses. The 2021 YRBS participation map, survey response rates, and a detailed examination of student demographic characteristics are included in this report. During 2021, in addition to the national YRBS, a total of 78 surveys were administered to high school students across the United States, representing the national population, 45 states, two tribal governments, three territories, and 28 local school districts. YRBSS data from 2021 provided the first opportunity since the onset of the COVID-19 pandemic to compare youth health behaviors using long-term public health surveillance. Approximately half of all student respondents represented racial and ethnic minority groups, and approximately one in four identified as lesbian, gay, bisexual, questioning, or other (a sexual identity other than heterosexual) (LGBQ+). These findings reflect shifts in youth demographics, with increased percentages of racial and ethnic minority and LGBQ+ youths compared with previous YRBSS cycles. Educators, parents, local decision makers, and other partners use YRBSS data to monitor health behavior trends, guide school health programs, and develop local and state policy. These and future data can be used in developing health equity strategies to address long-term disparities so that all youths can thrive in safe and supportive environments. This overview and methods report is one of 11 featured in this MMWR supplement. Each report is based on data collected using methods presented in this overview. A full description of YRBSS results and downloadable data are available (https://www.cdc.gov/healthyyouth/data/yrbs/index.htm).

Youths experiencing unstable housing face higher risks for poor physical, mental, and sexual health outcomes and increased risk for suicide compared with their peers experiencing stable housing. In addition, youths of color and sexual minority youths are disproportionately more likely to experience homelessness. For the first time, in 2021, the nationally representative Youth Risk Behavior Survey included an item assessing housing stability, or nighttime residence among students in grades 9-12 in the United States. During 2021, 2.7% of U.S. high school students experienced unstable housing. Among racial and ethnic subgroups, Native Hawaiian or other Pacific Islander youths were most likely to experience unstable housing, followed by American Indian or Alaska Native and Black youths. Sexual minority (lesbian, gay, bisexual, and questioning or other) youths were more likely to experience unstable housing compared with their heterosexual peers. Compared with students who were stably housed, students who were unstably housed were more likely to engage in risky sexual behaviors, substance use, and suicide ideation and attempts, and to experience violence. These findings highlight which adverse health risks and behaviors are elevated among youths experiencing housing insecurity. Focused public health interventions are required to address the disproportionate burden of health risks prevalent among youths who are unstably housed.

Genital inflammation (GI) undermines topical HIV pre-exposure prophylaxis (PrEP) efficacy through unknown mechanisms. Here, associations between activated endocervical CD4+ T cell numbers and higher deoxyadenosine triphosphate (dATP) concentrations suggest that competition for intracellular metabolites within HIV target cells may reduce the efficacy of antiretroviral-based PrEP in women with GI.

BACKGROUND: Sexually transmitted infections (STIs) and Human immunodeficiency virus (HIV) share a complex bidirectional relationship, however, population prevalence and the association between the presence of STIs and HIV in a high HIV burden district in KwaZulu-Natal, South Africa is not known. METHODS: A total of 9812 participants aged 15-49 years were enrolled in a cross-sectional population-based household survey. Participants completed a structured questionnaire and provided first-pass urine (males) or self-collected vulvo-vaginal swabs (females) for the detection of STIs. RESULTS: Prevalence of herpes simplex virus type-2 (HSV-2) was 57.8%, syphilis was 1.6%, Neisseria gonorrhoeae was 2.8%, Chlamydia trachomatis was 7.1%, Trichomonas vaginalis was 9.0%, Mycoplasma genitalium was 5.5% and HIV was 36.3%. HIV positive status was associated with an increased probability of having M. genitalium (aPR = 1.49, 95% CI 1.02-2.19) among males and syphilis (aPR = 2.54, 95% CI 1.32-4.86), N. gonorrhoeae (aPR = 2.39, 95% CI 1.62-3.52), T. vaginalis (aPR = 1.70, 95% CI 1.43-2.01) and M. genitalium (aPR = 1.60, 95% CI 1.15-2.22) among females. HIV viral load >/=400 copies per mL was associated with an increased probability of N. gonorrhoeae (aPR = 1.91, 95% CI 1.36-2.70), C. trachomatis (aPR = 1.52, 95% CI 1.12-2.05) and M. genitalium (aPR = 1.83, 95% CI 1.27-2.63). CONCLUSIONS: The high prevalence of STIs and the association between STIs and HIV, and HIV viral load underscores the public health implications of sustained transmission risk of STIs and HIV. These findings highlight the urgent need for expanding STI surveillance and implementing interventions to monitor and reduce the STI burden.

Despite the increasing use of human rights-based approaches to health, the Centers for Disease Control and Prevention (CDC) does not routinely train its staff in the use of such approaches as a part of public health practice. We conducted a training needs assessment among CDC locally employed staff working outside of the United States through eight key informant interviews and an online survey from June to December 2015. Key informants revealed an awareness that rights violations negatively affect access to health services and supported implementation of formal training among CDC staff. Most (82%) survey respondents felt that the CDC should do more to address health and human rights issues in its programs, policies and research. However, 72% of respondents did not feel they had adequate knowledge to address human rights in their work. In particular, 86% of participants had no knowledge of the Siracusa Principles (criteria for human rights restrictions) and only 2% of participants had received any training on international human rights treaties related to the duties of public health professionals. Our findings inform and support the need to design a training on human rights-based approaches to health, focused on the knowledge and skill needs of CDC locally employed staff.

Several clinical trials have demonstrated that antiretroviral (ARV) drugs taken as pre-exposure prophylaxis (PrEP) can prevent HIV infection, with the magnitude of protection ranging from -49 to 86% (refs. ). Although these divergent outcomes are thought to be due primarily to differences in product adherence, biological factors likely contribute. Despite selective recruitment of higher-risk participants for prevention trials, HIV risk is heterogeneous even within higher-risk groups. To determine whether this heterogeneity could influence patient outcomes following PrEP, we undertook a post hoc prospective analysis of results from the CAPRISA 004 trial for 1% tenofovir gel (n = 774 patients), one of the first trials to demonstrate protection against HIV infection. Concentrations of nine proinflammatory cytokines were measured in cervicovaginal lavages at >2,000 visits, and a graduated cytokine score was used to define genital inflammation. In women without genital inflammation, tenofovir was 57% protective against HIV (95% confidence interval (CI): 7-80%) but was 3% protective (95% CI: -104-54%) if genital inflammation was present. Among women who highly adhered to the gel, tenofovir protection was 75% (95% CI: 25-92%) in women without inflammation compared to -10% (95% CI: -184-57%) in women with inflammation. Immunological predictors of HIV risk may modify the effectiveness of tools for HIV prevention; reducing genital inflammation in women may augment HIV prevention efforts.

BACKGROUND: South Africa has over 6,000,000 HIV infected individuals and the province of KwaZulu-Natal (KZN) is the most severely affected. As public health initiatives to better control the HIV epidemic are implemented, timely, detailed and robust surveillance data are needed to monitor, evaluate and inform the programmatic interventions and policies over time. We describe the rationale and design of the HIV Incidence Provincial Surveillance System (HIPSS) to monitor HIV prevalence and incidence. METHODS/DESIGN: The household-based survey will include a sample of men and women from two sub-districts of the uMgungundlovu municipality (Vulindlela and the Greater Edendale) of KZN, South Africa. The study is designed as two sequential cross-sectional surveys of 10,000 randomly selected individuals aged 15-49 years to be conducted one year apart. From the cross sectional surveys, two sequential cohorts of HIV negative individuals aged 15-35 years will be followed-up one year later to measure the primary outcome of HIV incidence. Secondary outcomes include the laboratory measurements for pulmonary tuberculosis, sexually transmitted infections and evaluating tests for estimating population-level HIV incidence. Antiretroviral therapy (ART) access, HIV-1 RNA viral load, and CD4 cell counts in HIV positive individuals will assess the effectiveness of the HIV treatment cascade. Household and individual-level socio-demographic characteristics, exposure to HIV programmatic interventions and risk behaviours will be assessed as predictors of HIV incidence. The incidence rate ratio of the two cohorts will be calculated to quantify the change in HIV incidence between consecutive samples. In anticipation of better availability of population-level HIV prevention and treatment programmes leading to decreases in HIV incidence, the sample size provides 84 % power to detect a reduction of 30 % in the HIV incidence rate between surveys. DISCUSSION: The results from HIPSS will provide critical data regarding HIV prevalence and incidence in this community and will establish whether HIV prevention and treatment efforts in a "real world", non-trial setting have an impact on HIV incidence at a population level. Importantly, the study design and methods will inform future methods for HIV surveillance.

Despite the well-known benefits of youths engaging in 60 or more minutes of daily physical activity, physical inactivity remains a significant public health concern. The 2008 Physical Activity Guidelines for Americans (PAG) provides recommendations on the amount of physical activity needed for overall health; the PAG Midcourse Report (2013) describes effective strategies to help youths meet these recommendations. Public health professionals can be dynamic change agents where youths live, learn, and play by changing environments and policies to empower youths to develop regular physical activity habits to maintain throughout life. We have summarized key findings from the PAG Midcourse Report and outlined actions that public health professionals can take to ensure that all youths regularly engage in health-enhancing physical activity.

Accurate program planning for populations most at risk for HIV/STI acquisition requires knowledge of the size and location where these populations can best be reached. To obtain this information for sex workers operating at 137 hotspots in the central business district (CBD) in Nairobi, Kenya, we utilized a combined mapping and capture-recapture enumeration exercise. The majority of identified hotspots in this study were bars. Based on this exercise, we estimate that 6,904 male and female sex workers (95% confidence intervals, 6690 and 7118) were working nightly in the Nairobi CBD in April 2009. Wide ranges of captures per spot were obtained, suggesting that relatively few hot spots (18%) contain a relatively high proportion of the area's sex workers (65%). We provide geographic data including relatively short distances from hotspots to our dedicated sex worker outreach program in the CBD (mean<1 km), and clustering of hotspots within a relatively small area. Given the size covered and areas where sex work is likely taking place in Nairobi, the estimate is several times lower than what would be obtained if the entire metropolitan area was enumerated. These results have important practical and policy implications for enhancing HIV/STI prevention efforts.