This study has important implications for public health. The prevalence of HCV exposure of 2.4% (95% CI 1.9–2.9) was approximately two times higher than among the general population (1.38%) and 14 times higher than among the blood donors (0.17%) of Campo Grande, Mato Grosso do Sul [12,13].

Otherwise, this prevalence is not consistent with previous studies conducted among inmates in Brazil, such as in Sergipe (3.1%), São Paulo (9.0%) and Campo Grande, MS, (4.8%) and higher than in Espírito Santo (1.0%) [14–17]. Although this prevalence is greater than the prevalence in the general population, the low prevalence found may be due to current low prevalence of HCV exposure in the Midwest region. Additionally, the difference between the prevalence of HCV exposure found in this study compared with the study conducted in the same region by Pompilio et al. (2011) may be explained by the decline in the frequency of injection drug users (10.6% to 1%) [16]. In fact, in recent years, the pattern of drug use in Brazil has changed, resulting in a smaller proportion of IDU which was largely replaced by smoked or inhaled crack cocaine [18–20].

When compared to international studies, the prevalence of HCV found in our study was lower than in California (34.3%), Indonesia (34.1%), Italy (22.4%), Iran (7.4%) and Lebanon (3.4%), which could be explained by the low frequency of injecting drug users (1%) in male and female prisoners [21–24]. In addition to that, there is a law prohibiting the use of illicit drugs in Brazil, inside and outside prisons, leading those who use drugs illegally in prisons to punishment such as increased imprisonment time [25].

There was a significant difference in HCV exposure between male and female prisoners (p<0.01), with a higher prevalence among males (2.7%) than females (0.6%). This result is similar to those observed by Flisiak et al. (2011) in Poland, probably because males are more exposed to risk factors for infection with hepatitis C than females [26]. Despite comparable rates of reported IDU, a higher percentage of male prisoners reported previous incarceration (62% vs. 40%; p<0.01) and mean (±SD) of length of incarceration (20±27 vs. 12±12 months; p<0.01). This result differs from other studies that reported a predominance of HCV exposure among female inmates [27–29].

Increasing age was associated with HCV among male inmates, probably due to prolonged exposure to HCV infection presenting risk behaviors throughout life, which was observed in other vulnerable population groups such as health care professionals, homeless people, drug users, as well as inmates [16,30–34].

In this study, injection drug use was associated with HCV exposure in male inmates as described in other studies with similar populations [22,35,36]. In a meta-analysis study, male inmates and injecting drug users were 24 times more likely to be HCV positive than non-injecting drug users [29]. Despite correctional system prohibitions against injection drug use, this practice occurs among male prisoners (2%). Even if the injection drug use may have been omitted by most inmates, because of the stigma, fears of recrimination and punishment, this risk factor was strongly associated with HCV exposure.

High-risk activities such as sharing of sharps for making tattoos and injection drug use are common practices carried out within the prisons [6]. Despite the prohibition, a few prisoners have access to tools for injection drug use, increasing the risk of acquiring blood-borne diseases such as HCV by sharing needles and syringes [37]. In this context, it is not surprising to find that, in our study, syringe and needle sharing remained independently associated with HCV exposure among male inmates.

The longer the incarceration is, the higher the risk of acquiring new infections due to inconsistent condom use or sharing of contaminated needles and syringes [38]. Long imprisonment periods and previous incarcerations may create even more opportunities for HCV acquisition and transmission [37,39]. Moreover, poor diagnosis and lack of knowledge regarding HCV transmission or medical treatment might influence the risk for HCV. In fact, this is consistent with our results which found association between HCV exposure and longer than 48-mounth incarceration period and, also observed new cases of HCV infection during the cohort study.

Moreover, this study demonstrated a high prevalence rate of HCV/HIV coinfection (11.1%) among male inmates probably due to the similarity in the transmission routes of these infections. Prisoners are known to engage in various activities that are considered risk factors for HCV/HIV coinfection, including high-risk sexual behaviors, sharing of needles/syringes and several types of paraphernalia for tattoos and drug use [16,40,41].

This is the first study of incidence of HCV infection involving Brazilian prison inmates. Despite of the low incidence rate, this data demonstrates that high-risk behavior already occur and highlight the importance of the prevention of this infection inside prisons [42,43]. The potential to identify the exact mechanism through which seven inmates were infected was limited by our study design, and by self-reported risk behaviors, such as drug use. [42,44]. Nevertheless, risk behaviors reported by new HCV cases should be interpreted with caution.

A study conducted in Scottish prisons found that the availability of needles and syringes at harm reduction programs for intravenous drug use, reflected in a lower incidence and thus lower prevalence of HCV [43]. Unfortunately, Brazilian prisons have not yet recognized the importance of access to effective prevention strategies to reduce the transmission of blood-borne infections in the facilities. This is because drug use prevention initiatives in prisons are implemented from a repressive perspective and not from a public health one [45].

Furthermore, the Brazilian criminal code includes neither death penalty nor life sentence. The prison system, with rare exceptions, fails to rehabilitate and reinsert prisoners into society. Indeed, a high rate of recidivism (above 60%) was found in our study starting the cycle anew. Therefore, due to the high turnover of inmates between prisons and the community, the epidemics of HCV infection combined with injection drug use among this population becomes a public health problem [46,47].

There were some strengths and limitations to this study. Some behavior risks may have been under-reported due to discrimination and stigma, leading to underestimating potential risk factors associated with HCV exposure. Moreover, this cross sectional survey was not designed to provide the temporal relationship between risky behaviors and HCV exposure in the male inmate population. Moreover, the small number of HCV exposure among female inmate population affected the analysis of risk factors among them. The limited number of positive cases in incidence study might also complicate the determination of risk factors. Despite these limitations, our study, having a large sample size, is representative of this population group and has important implications which would contribute to a clearer scenario of the most relevant risk factors for HCV exposure.

The new cases detected inside prisons reinforce the urgent need to plan effective prevention strategies and control HCV infection in the prison system environment in order to reduce the susceptibility for this infection, given the crowded conditions, uncontrolled exposure to illicit drugs and absence of serological screening at the time of imprisonment. The screening serological test and monitoring of IDUs in the prison system, making possible assess implementation of harm reduction strategies (exchange of syringes/needles). In addition, it is necessary to take health education measures directed to the prison population on risk factors associated to viral hepatitis. Finally, studies using phylogenetic analysis will also help to understand HCV transmission routes within this population.