The prevalence of HIV infection was relatively high in inmates currently incarcerated in the state prisons of Lome and Dakar and independently associated with liver fibrosis. Indeed, reported HIV prevalence from these state prisons, were two to four times higher than the respective prevalence of HIV infection in the general adult population of Togo and Senegal [28]. Although sparse data exist on HIV prevalence in prisoners in these countries, our results are in accordance to a previous report from Togo where HIV prevalence in incarcerated men was estimated at 4.0 % [29]. Together with the fact that only one out of the 18 patients identified as HIV-infected was aware of its status; these results emphasize the need to promote HIV screening and access to care in prisons in sub-Saharan Africa.

The independent association between HIV infection and liver fibrosis has already been reported in sub-Saharan Africa. Stabinski et al conducted a case-control study on the association between HIV infection and severe liver fibrosis using the same non-invasive approach in Uganda [30]. Adjusted for various risk factors including HBV infection, HIV infection was significantly associated with liver fibrosis (OR = 1.5 [95 % CI 1.1–2.1]). Potential reasons for this association are numerous; various unmeasured tropical hepatotoxic infectious agents such as schistosomiasis may have synergistically interacted with HIV infection in the development of liver fibrosis. Our population of HIV-infected patients was mostly unaware of their HIV status and potentially had uncontrolled HIV replication. The direct toxicity of HIV on liver cells has been reported in previous studies through several mechanisms including, stellate cells activation, apoptotic effect on hepatocytes and immune activation [31–34]. A recent cohort study exploring factors associated with the occurrence of liver fibrosis in more than 14 000 HIV-infected persons identified HIV viral load as a main and independent determinant of progression to liver fibrosis [35]. Therefore, the high prevalence of liver fibrosis among HIV-infected persons reported in Uganda, Nigeria and in our study using the same methodological approach might be partly mediated by the direct toxicity of HIV itself [36]. Further etiologic and prospective studies will need to explore the exact mechanisms leading to liver fibrosis in HIV-infected persons without HBV or HCV in sub-Saharan Africa.

Both HBV and HCV infections were independently associated with severe liver fibrosis. The high prevalence of HBV infection was consistent with the prevalence of HBs antigen positivity in the general population in West Africa [37]. In addition, we provide here one of the rare reports of the impact of HBV infection on the liver. Almost 10 % of inmates positively screened for HBV were diagnosed with severe liver fibrosis making them potentially eligible to antiviral treatment regardless of other biomarkers. More than one-third of HBV-infected inmates harbored a high HBV DNA replication (>20 000 UI/ml), a well-known negative prognostic factor in HBV infection, regardless of the presence or absence of severe liver fibrosis. In a context of limited access to antiviral treatment for HBV-infected persons living in sub-Saharan Africa, the availability of reliable and appropriate tools for the assessment of liver fibrosis is of paramount importance to identify and prioritize patients in need for treatment.

A low prevalence of HCV infection was observed in our study sample, even lower than the available regional estimates [2.8 % (95%CI 2.4–3.3)] from West Africa [38]. However, this previous estimates from West Africa relied on a limited number of studies with selected populations and no information was available for several countries including Togo [39]. Prevalence studies among blood donors in Senegal reported prevalence of positive HCV serology of 0.7 % and 0.5 % [40, 41]. Therefore, the prevalence of HCV infection in West Africa is probably not homogenous according to countries and deserves more well conducted representative prevalence studies. As HCV prevalence increases with age, the fact that half of our population was under 30 might partly explain this low HCV prevalence. However, previous surveys among incarcerated people in Ghana and Nigeria have found particularly high HCV prevalence (over 10 %) [17, 18]. The spread of the HCV epidemic is mainly driven by blood exposure including intravenous drug use and unsafe medical practices through none adapted or inexistent sterilization process. In light of the marginal reporting of injected drug-use in our study sample, HCV was unlikely to have spread through this mode. Accurate estimates of HCV infection are currently limited by the availability of reliable serological assays and would benefit from larger standardized prevalence studies. Indeed, previous reports have highlighted the high rates of false positive results using the classical immunoassay techniques for the screening of HCV infection [42, 43]. Thus, the good sensitivity and specificity of the Oraquick® test used in our study might partly explain the discrepancy between our findings and previous reports on HCV prevalence in West Africa [20, 21]. While new potent but expensive cure strategies are emerging for HCV infection, a better knowledge of the epidemiology of HCV infection is urgently needed in low-income countries.

Use of herbal medicines was not uncommon in our study population and was associated with severe liver fibrosis. This finding confirmed the result from a report in Uganda where an in-depth assessment of herbs consumed showed that the Asteraceae family was associated with liver fibrosis [44]. There is a need to explore the types of herbs in relation to liver fibrosis in order to provide herb safety recommendations in the context of traditional medicine use in West Africa. Alcohol use was not associated with liver fibrosis in our report. The role of alcohol use in the development of liver fibrosis has been extensively demonstrated in high-income settings. The assessment of alcohol exposure through the AUDIT score did not capture the lifetime exposure to alcohol use which might be more relevant as liver fibrosis is a relatively long process. After adjusting for all important confounders, a fraction of the observed geographical variation in the prevalence of liver fibrosis remains unexplained. Unmeasured exposures to environmental risk factors could have played a role. For example, aflatoxin exposure which has been already linked to liver fibrosis might not be equally distributed throughout West Africa [45]. Additional investigations should explore the role of environmental factors in the occurrence of liver fibrosis and ultimately cirrhosis.

Our study population might not be representative of all prisons in these two countries as we only focused on selected civil prisons from the two main urban areas in Togo and Senegal. Indeed, the diversity of prison facilities needs to be addressed as wide variations in the prevalence of viral hepatitis infections have been reported elsewhere. Aside tobacco use, other addictive behaviors were prohibited in these prison facilities. This might have underestimated the self-reported use of drugs and alcohol. Although transient elastography is a technique rapidly mastered and easy to reproduce, it remains an operator-dependent procedure. An inadequate use of the device can lead to the overestimation of LSM. In order to provide better estimates of the burden of liver disease, larger studies with standardized procedures are needed throughout the African continent. In its latest guideline for the prevention, care and treatment of HBV infection, the WHO underlined to need to use inexpensive non-invasive approaches to assess the extent of liver fibrosis in resource-limited settings. However, they also recommend to use alternative approaches such as transient elastography wherever available. Although being initially expensive, the cost of transient elastography compared to alternative non-invasive biological tests for the evaluation of liver fibrosis remains to be assessed in the long term. Finally, the cross-sectional nature of the study limits our ability to draw any causal relation between liver fibrosis and associated factors. Nevertheless, several factors including HIV infection or the use of herbal medicines have been previously incriminated in previous cross-sectional studies. A longitudinal assessment of the impact of these factors on liver fibrosis will ultimately be needed.