Hepatitis Prevalence Among Key Populations in Nigeria: A Scoping Review

Study design and reporting

This scoping review was conducted following the methodological framework developed by Arksey and O’Malley (2005) and subsequently refined by Levac, Colquhoun, and O’Brien (2010) and Peters et al. (2020).^12-14 The six-stage framework includes: (1) Identifying the research question, (2) identifying relevant studies, (3) study selection, (4) charting the data, (5) collating, summarizing, and reporting results, and (6) consultation with stakeholders. Reporting followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews checklist.¹⁵

Research questions

The primary research question was: “What is the current evidence on hepatitis prevalence among KPs in Nigeria?” Secondary questions included: (1) What hepatitis types have been studied among KPs? (2) Which KP groups have been studied and in what geographic locations? (3) What methodological approaches have been used? (4) What is the quality of existing evidence? (5) What evidence exists for hepatitis-HIV co-infection? (6) What are the main knowledge gaps and research priorities?

Information sources and search strategy

A comprehensive search strategy was developed combining three main concept groups using Boolean operators. Electronic databases searched included PubMed/MEDLINE, Embase, Web of Science Core Collection, Cochrane Library, African Index Medicus, and Global Health. Gray literature sources included the World Health Organization (WHO) institutional repository, the Nigeria Centre for Disease Control reports, Joint United Nations Programme on HIV/AIDS (UNAIDS) country reports, Federal Ministry of Health policy documents, and conference abstracts.

Search terms combined

• Hepatitis: MeSH terms “Hepatitis B”(Mesh), “Hepatitis C”(Mesh), “Hepatitis D”(Mesh), “Hepatitis E”[Mesh]; free text terms hepatitis B, hepatitis C, HBV, HCV, HDV, HEV, HBsAg, anti-HBc, anti-HCV, “viral hepatitis”

• KPs: MeSH terms “Sex Workers”(Mesh), “Sexual and Gender Minorities”(Mesh), “Homosexuality, Male”(Mesh), “Substance Abuse, Intravenous”(Mesh), “Prisoners”(Mesh); free text terms “sex worker*,” “men who have sex with men,” MSM, transgender*, “people who inject drugs,” PWID, prisoner*, “key population*”

• Nigeria: MeSH terms “Nigeria”(Mesh); free text terms Nigeria, Nigerian, “West Africa”

The search covered publications from January 2008 to December 2024, with no initial language restrictions.

Eligibility criteria

Study selection and data extraction

Study selection followed a systematic two-stage process conducted by two independent reviewers using Covidence software. Inter-rater reliability was assessed using Cohen’s kappa coefficient. A standardized data extraction form was developed based on the Joanna Briggs Institute template and pilot tested. Extracted data included study characteristics, population demographics, hepatitis outcomes, and methodological details.

Quality assessment

Quality assessment was conducted using criteria adapted from the Joanna Briggs Institute Critical Appraisal Checklist for Studies Reporting Prevalence Data.¹⁶ The assessment included nine criteria covering sample frame appropriateness, sampling methods, sample size adequacy, participant description, data analysis coverage, valid identification methods, standardized measurement, statistical analysis, and response rate adequacy. Overall quality was categorized as high (7–9 criteria met), moderate (4–6 criteria met), or low (0–3 criteria met).

Data synthesis

Data synthesis followed a narrative approach appropriate for scoping reviews, given anticipated heterogeneity. Descriptive analysis of study characteristics and quality, narrative synthesis of prevalence estimates by KP and hepatitis type, geographic mapping of study locations, temporal analysis of publication trends, and thematic analysis of knowledge gaps were conducted. Prevalence estimates were presented as ranges and medians with confidence intervals (CIs) when available.

Search results and study selection

As shown in Figure 1, the comprehensive search strategy yielded 1,270 records from electronic databases and 47 additional records from grey literature sources. After removing 234 duplicates, 1,083 records underwent title and abstract screening. Inter-rater reliability for initial screening was substantial (κ = 0.84, 95% CI: 0.79–0.89). Following screening, 178 records were selected for full-text review. After full-text assessment, 25 studies met the inclusion criteria. The most common exclusion reasons were: lack of KP-specific data (n = 67, 43.8%), studies conducted outside Nigeria (n = 34, 22.2%), and absence of hepatitis prevalence outcomes (n = 30, 19.6%).

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Figure 1: PRISMA chat.

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Study characteristics

The 25 included studies were published between 2008 and 2025, with 72% published after 2015. Study designs included cross-sectional surveys (72%), systematic reviews (16%), national surveillance reports (8%), and cohort studies (4%). Sample sizes ranged from 89 to 4,568 participants (median: 387, Interquartile range: 200-850). Geographic distribution covered 12 of Nigeria’s 36 states (33% coverage), with the highest concentration in Lagos State (n = 8, 32%), Enugu State (n = 6, 24%), and the Federal Capital Territory (n = 5, 20%). Northern states were notably underrepresented, with only Borno State and Nasarawa State having dedicated studies. All five KP groups were represented: sex workers (9 studies, 36%), people in prisons (6 studies, 24%), PWID (5 studies, 20%), MSM (4 studies, 16%), and transgender people (3 studies, 12%). The majority of studies (84%) focused on HBV, while HCV was examined in 32%, HDV in 12%, and HEV in 8% of studies.

Quality assessment results

Quality assessment revealed significant methodological heterogeneity. Of 21 primary studies, 9 (43%) were rated high quality, 8 (38%) moderate quality, and 4 (19%) low quality. Common limitations included convenience sampling (67%), inadequate sample sizes (52%), poor response rate reporting (43%), suboptimal laboratory methods (33%), and insufficient statistical analysis (29%).

HBV prevalence by KP

Transgender people

Data on hepatitis prevalence among transgender people in Nigeria are extremely limited, representing one of the most significant knowledge gaps identified in this review. Only three studies provided relevant information, and none reported separate prevalence estimates specifically for transgender populations.

The Innocent-Adiele et al study included transgender women alongside MSM but did not disaggregate results by gender identity, reporting combined prevalence estimates.¹⁹ This methodological approach, while common in KP research, obscures the specific burden and risk factors among transgender people, who may face distinct vulnerabilities related to gender identity, hormone use, and gender-affirming procedures.

The lack of transgender-specific data in Nigeria reflects broader challenges in conducting research with this population, including stigma, discrimination, legal barriers, and difficulties in recruitment and retention. The criminalization of same-sex relationships under Nigerian law may particularly affect transgender women, who are often conflated with MSM in legal and social contexts. In addition, the lack of legal recognition of gender identity creates barriers to healthcare access and may contribute to elevated health risks.

PWIDs

Five studies examined hepatitis prevalence among PWID in Nigeria, providing data on both HBV and HCV infections. The most recent and methodologically rigorous study by Orabueze et al. (2024) assessed 200 illegal drug users in Enugu State, reporting HBV prevalence of 7.0% (95% CI: 3.8–12.0%).²⁰ This study employed systematic sampling methods and used ELISA testing for HBV diagnosis, representing current best practices in prevalence estimation among this population.

The Orabueze study identified several important risk factors for HBV infection among PWID. Male gender was associated with increased risk (OR: 2.3, 95% CI: 1.1–4.8, p = 0.03), as was young age (18–25 years vs. >35 years: OR: 2.8, 95% CI: 1.2–6.5, p = 0.02). Single marital status showed elevated risk compared to married participants (OR: 1.9, 95% CI: 1.0–3.6, p = 0.05). Most importantly, frequent injecting behavior (daily vs. weekly: OR: 3.4, 95% CI: 1.6–7.2, p = 0.001) and sharing of injection equipment (OR: 4.2, 95% CI: 2.1–8.4, p < 0.001) were strongly associated with HBV infection.

The study documented patterns of risk behavior among PWID participants. Syringe sharing was reported by 34.5% (95% CI: 28.1–41.4%) of participants, with higher rates among younger participants and those injecting daily. Sharing of other injection equipment (cookers, filters, water) was even more common, reported by 52.0% (95% CI: 45.1–58.9%) of participants. These findings highlight the urgent need for expanded harm reduction services in Nigeria.

The Enugu study documented extremely low uptake of harm reduction services among PWID participants. Only 12% reported ever receiving clean needles from harm reduction programs, and HBV vaccination coverage was extremely low at 3.5%. These findings underscore the urgent need for expanded harm reduction services and targeted prevention interventions for PWID in Nigeria.

People in prisons and closed settings

Six studies examined hepatitis prevalence among incarcerated populations in Nigeria, revealing the highest and most variable prevalence rates among all KPs studied. HBV prevalence ranged from 7.9% to 23.0% across different correctional facilities and time periods, representing a nearly three-fold variation that suggests significant heterogeneity in transmission dynamics and risk factors across facilities.

The most recent facility-specific study by Ajakaye and Omidele (2024) assessed 139 inmates at Owo Correctional Facility in Ondo State, reporting HBV prevalence of 7.9% (95% CI: 4.2–13.4%).²¹ This study also examined co-infection with Plasmodium falciparum, finding that 23.0% (95% CI: 16.4–31.0%) of inmates had malaria-HBV co-infection, highlighting the complex health challenges facing incarcerated populations in Nigeria.

A broader systematic review by Scott et al. (2025)²² examined hepatitis burden across African prisons, reporting 15% HBV prevalence among Nigerian inmates based on pooled analysis of available studies.²² This review emphasized the “silent crisis” of viral hepatitis in correctional settings, noting inadequate screening, limited treatment access, and poor infection control measures as contributing factors to high transmission rates. The review identified several facility-level factors associated with higher hepatitis prevalence, including overcrowding (>150% capacity), limited healthcare staffing, and the absence of harm reduction programs.

Geographic coverage of prison studies included facilities in Ondo State, the Federal Capital Territory, Nasarawa, and Borno, providing insights into regional variations. The highest prevalence (23.0%) was reported from a facility in Borno State, which may reflect regional differences in background prevalence, facility conditions, or population characteristics. However, significant gaps remain in coverage of Nigeria’s 244 correctional facilities, limiting the generalizability of findings to the entire prison population.

Several studies documented risk factors for hepatitis transmission in correctional settings. Overcrowding was consistently associated with higher prevalence, with facilities operating at >150% capacity showing 2.3-fold higher HBV prevalence compared to less crowded facilities. The duration of incarceration was positively associated with infection risk, with inmates incarcerated >2 years showing a higher prevalence than those with shorter sentences. A history of injecting drug use before incarceration was strongly associated with both HBV and HCV infection.

HCV prevalence

HCV data among KPs in Nigeria are notably limited compared to HBV, representing one of the most significant knowledge gaps identified in this review. Only eight studies (32%) provided HCV prevalence estimates. They most relied on self-reported data rather than laboratory confirmation, creating substantial uncertainty about the true burden of HCV infection among these vulnerable populations.

Among PWID, HCV prevalence estimates ranged from 2.3% to 3.3% based on self-reported data from Harm Reduction International (2023).²³ However, the lack of laboratory-confirmed HCV data among Nigerian PWID represents a critical gap, particularly given the global recognition of PWID as the population at highest risk for HCV infection. Global studies consistently report HCV prevalence >50% among PWID in many settings, suggesting that Nigerian estimates may significantly underestimate the true burden. The reliance on self-reported data is particularly problematic for HCV, as many infected individuals remain asymptomatic for years and may be unaware of their infection status.

For other KPs, HCV data were extremely sparse. No studies provided laboratory-confirmed HCV prevalence estimates specifically for sex workers, MSM, or transgender people in Nigeria. This contrasts sharply with global data showing elevated HCV prevalence among these populations, particularly MSM in high-income countries where HCV outbreaks have been documented. The absence of HCV data among sex workers is particularly concerning given documented sexual transmission risks, especially among those engaging in high-risk practices or experiencing intimate partner violence.

The limited HCV data may reflect several interconnected factors that highlight broader challenges in Nigeria’s hepatitis response. Higher cost and complexity of HCV testing compared to HBV create barriers to routine screening, particularly in resource-constrained settings. Limited laboratory capacity for HCV diagnosis across Nigeria restricts access to confirmatory testing, with many facilities lacking the infrastructure for HCV RNA testing required for definitive diagnosis. Historical focus on HBV, given its higher background prevalence, may have diverted attention and resources from HCV surveillance and prevention efforts.

In addition, lack of awareness about HCV among healthcare providers and KPs may contribute to underdiagnosis and underreporting. Unlike HBV, which has established vaccination programs and greater clinical recognition, HCV remains less well-understood among frontline healthcare workers, potentially leading to missed opportunities for testing and diagnosis. The absence of routine HCV screening protocols in most healthcare settings further compounds this challenge.

This knowledge gap has important implications for prevention and treatment programs, particularly given the availability of highly effective direct-acting antiviral treatments for HCV that can achieve >95% cure rates with 8–12-week treatment courses. The potential for HCV elimination among KPs through targeted testing and treatment programs cannot be assessed without accurate prevalence data, representing a missed opportunity for significant public health impact.

Geographic distribution and regional variations

The geographic distribution of studies revealed significant coverage gaps across Nigeria’s 36 states and the Federal Capital Territory, with important implications for understanding the true national burden of hepatitis among KPs. Only 12 states (33%) were represented in the literature, with a heavy concentration in urban centers and southern regions, which may not accurately reflect the actual distribution of KPs or their hepatitis burden nationally.

Southern Nigeria was heavily represented, with Lagos State having the highest number of studies (n = 8), followed by Enugu State (n = 6). These states are major urban centers with established research institutions, well-developed HIV programs, and greater accessibility for researchers, which may facilitate KP research. However, this concentration may not reflect the distribution of KPs nationally and could introduce geographic bias in understanding hepatitis epidemiology.

Northern Nigeria was notably underrepresented despite having higher general population HBV prevalence rates documented in national surveys. Only Borno State in the northeast and the Federal Capital Territory had studies specifically examining KPs. This geographic gap is particularly concerning given that the 2018 NAIIS documented the highest HBV prevalence in northern regions (North West: 12.1%, North East: 11.2%) compared to the southern areas (South East: 5.8%, South West: 4.1%).⁷ The absence of KP data from high-prevalence northern states represents a critical knowledge gap that may mask significant disease burden.

Rural areas were severely understudied, with most research concentrated in state capitals or major urban centers. Only the Enugu State study by Aniche et al. (2022) included smaller towns and peri-urban areas, revealing important sub-regional variations in prevalence.¹⁷ This urban bias limits understanding of hepatitis burden among rural KPs, who may face different risk environments, healthcare access patterns, social dynamics, and structural barriers compared to their urban counterparts.

Regional comparison with other African countries provides an important context for interpreting Nigerian findings. Compared to other West African countries, Nigerian KP hepatitis prevalence appears consistent with regional patterns. A systematic review by Stockdale et al. (2020) reported HBV prevalence among KPs in West Africa ranging from 8 to 15%, with Nigeria falling within this range.²⁴ However, direct comparisons are limited by methodological differences, varying KP definitions across studies, and different healthcare system contexts.

East African data from countries such as Kenya and Uganda suggest higher HCV prevalence among PWID (15–25%) compared to Nigerian estimates. However, this may reflect differences in drug use patterns, harm reduction service availability, diagnostic methods, or genuine epidemiological differences.^25,26 The higher HCV prevalence in East African PWID populations may also reflect different injection practices, drug types, or social networks that facilitate transmission.

Southern African studies from South Africa and Botswana report similar HBV prevalence among MSM (8–12%) but higher HCV prevalence among PWID (20-30%), again suggesting potential underestimation in Nigerian data or genuine regional differences in transmission dynamics.^27,28 The more developed healthcare systems and harm reduction programs in some Southern African countries may also contribute to better surveillance and more accurate prevalence estimates.

Knowledge gaps and research limitations

This comprehensive review identified several critical knowledge gaps that significantly limit understanding of hepatitis epidemiology among KPs in Nigeria and impede the development of evidence-based interventions and policies.

Summary of key findings

This comprehensive scoping review provides the first systematic synthesis of evidence on hepatitis prevalence among KPs in Nigeria, revealing a substantial disease burden that consistently exceeds general population estimates across all studied groups. The findings demonstrate a complex epidemiological landscape characterized by significant inter-population variations, geographic disparities, and critical knowledge gaps that limit comprehensive understanding of hepatitis transmission dynamics among Nigeria’s most vulnerable populations.

The most striking finding is the consistently elevated HBV prevalence among all KPs compared to general population estimates. While the 2018 NAIIS reported national HBV prevalence of 8.1% among adults,⁶ KPs demonstrated prevalence rates ranging from 4.0% among sex workers in Enugu to 23.0% in select prison facilities. This pattern aligns with global evidence documenting disproportionate hepatitis burden among KPs, reflecting shared behavioral, biological, and structural risk factors that facilitate transmission.^29,30

Prison populations emerged as the group with the highest and most variable HBV prevalence, ranging from 7.9% to 23.0% across different facilities. This finding is consistent with global literature documenting elevated hepatitis prevalence in correctional settings, attributed to factors including overcrowding, limited healthcare access, high-risk behaviors, inadequate infection control measures, and concentrated populations of individuals with pre-existing risk factors.^31,32 The substantial variation between facilities suggests that local factors, including facility management practices, healthcare provision, population characteristics, and regional background prevalence, significantly influence transmission dynamics.

Public health implications and policy considerations

The elevated hepatitis burden among KPs in Nigeria has profound implications for public health policy and program development at national, state, and local levels. The documented prevalence rates suggest that KPs serve as important reservoirs for ongoing hepatitis transmission, with potential for spillover into general populations through sexual and social networks.³² This epidemiological reality necessitates targeted prevention and treatment interventions that address the specific needs, vulnerabilities, and structural barriers faced by each KP group.

The intersection of hepatitis and HIV epidemics among KPs creates additional complexity requiring integrated service delivery approaches. The Adeyemi study’s documentation of 25.3% HIV prevalence among MSM, combined with 10.0% HBV prevalence and 15.8% co-infection rate, illustrates the syndemic nature of these infections and the potential for significant morbidity and mortality among co-infected individuals.³³ Hepatitis-HIV co-infection accelerates liver disease progression, increases the risk of hepatotoxicity from antiretroviral therapy, and complicates clinical management, requiring specialized expertise and coordinated care approaches.

The geographic concentration of studies in urban centers and southern states, while reflecting research capacity and population accessibility, may mask a significant burden in underserved regions. The higher general population HBV prevalence documented in northern Nigeria compared to southern regions suggests that KPs in northern areas may face even greater hepatitis risks than currently documented.⁷ This geographic disparity has important implications for resource allocation, program planning, and health equity considerations.

Research gaps and future directions

Policy and program recommendations

Strengths and limitations

Strengths include a comprehensive search strategy across multiple databases, standardized data extraction and quality assessment, inclusion of all KPs and hepatitis types, and systematic gap identification. Limitations include study heterogeneity limiting quantitative synthesis, predominance of convenience sampling affecting representativeness, potential publication bias, and methodological limitations in many included studies affecting the precision of estimates.