Amid the hepatitis C endemic among PWIDs and individuals enrolled in OAT programs in Sweden and Norway, the study has revealed a large increase in DAA treatment uptake among OAT patients in both countries from 2014 to 2017. As such, our findings reflect the immense progress, which has been achieved in HCV treatment during the recent years with almost a complete shift from interferon-based treatment to solely treatment with DAAs among OAT patients. The cumulative frequency of HCV treatment in the OAT population was 15% and 16% in Sweden and Norway, respectively. When adjusted for estimated prevalence and incidence the cumulative HCV treatment uptake was higher in Norway with almost 32% during the study period. DAA treatment was associated with increased age and dispensation of drugs used in diabetes in Sweden. Dispensations of lipid modifying agents and antibacterials were associated with lower odds in Norway. Being female was associated with decreased odds for treatment in both countries.
Even if considerable advances have been made in recent year with the introduction of interferon-free treatment regimens for HCV, few have actually engaged in treatment . Several studies have demonstrated continued low treatment uptake among PWIDs and OAT patients [19, 26]. However, concerns about DAA treatment to people who use drugs seems unwarranted as both adherence and high SVR rates in this group have been validated in randomized controlled trials [27, 28]. Our study suggests an increase in HCV treatment in Sweden and Norway, attributed by a complete shift to interferon-free treatment regimens among OAT patients. Treatment with DAAs in Sweden and Norway were previously limited by strict eligibility criteria based on stage of liver fibrosis. However, since 2017 and 2018 in Sweden and Norway, respectively, DAA treatment has been offered as universal health coverage to all HCV patients regardless of genotype and level of liver fibrosis [20, 29]. Treatment demand has naturally soared, especially among former PWIDs , while people who are still using drugs have seemingly not been fully able to benefit from the increased accessibility . Arguably, this opts for considering all models of onsite HCV care to people who use drugs in OAT programs, which despite ongoing drug use, may still result in high SVR [14, 18].
Even if the cumulative frequency of DAA treatment uptake seems to be similar in Sweden and Norway, there may still be discrepancy not fully captured in our results. Estimated HCV treatment uptake is at best imprecise as accurate prevalence and incidence data among OAT individuals from Sweden do not exist to our knowledge. In Norway it is estimated that mean prevalence among OAT patients was 52% and 43% in 2014 and 2017, respectively, with annual incidence of chronic HCV among PWIDs around 400 per year [7, 11]. However, if we consider the prevalence of Anti-HCV among PWIDs it seems higher in Sweden with 82% compared to 63% among PWIDs in Norway [31, 32]. Secondly, the coverage of OAT seems dissimilar. Sweden, with similar demography and roughly twice the general population compared to Norway has significantly less patients enrolled in OAT programs. Waal et al. estimate an overall OAT coverage around 60% among people with opioid dependence in Norway  compared to 10–50% OAT coverage in Sweden . Part of the answer may lay in the current guidelines. Norway altered its OAT guidelines in 2010, making opioid addiction the absolute criteria for inclusion and being retained in treatment, however in Sweden, current OAT guidelines allow lower thresholds for OAT cessation in the case of repeated illicit drug use [11, 12]. Hence, it is not unlikely that the Swedish OAT population represents a remarkably smaller and more selected group of patients with less ongoing drug use and may for this reason be viewed more eligible for HCV treatment.
With the provision of DAA treatment available for all Norwegian and Swedish patients, it may be tempting to argue that this is the beginning of the end for the HCV endemic in Sweden and Norway. In addition to OAT, by maintaining a high coverage of needle and syringe availability in these countries, together with continued scale-up of DAA treatment, it may be possible to reduce incidence by 90% by 2030 as shown in a modeling study from the UK . However, on the other hand it may still seem embryonic without sufficient surveillance and monitoring of the disease. HCV has been notified to The Norwegian Surveillance System for Communicable Diseases since 1990, yet, there has been no distinction between anti-HCV, HCV RNA or HCV core antigen reporting before 2016, it is therefore impossible to assess whether cases were acute or chronic, or whether patients achieved SVR on their own, or how many cases were actually notified . The result is that accurate HCV prevalence and incidence data prior to 2016 are not readily available. Furthermore, in order to eliminate HCV as a public health treat by 2030, which both countries have embraced, a coherent and structured national plan seems essential. The Norwegian Health Ministry introduced a national hepatitis C strategy in 2016, and was later revised in 2018, which focuses on DAA treatment, HCV surveillance, and prevention, and aims to reduce HCV incidence by 90% within 2023 . On the contrary, there is not yet established an ambitious national Swedish hepatitis C plan . Coupled with lower OAT coverage and a higher Anti-HCV prevalence, HCV elimination may seem more challenging and distant in Sweden compared to Norway.
Our findings suggest few intercountry differences in dispensed drugs among those treated with DAAs and not, except for drugs used for diabetes in the Swedish cohort, which was significantly higher and a predictor for DAA treatment. Chronic HCV might be a risk factor for developing immune system disorders, heart disease and diabetes, especially diabetes type II as the viral infection may increase insulin resistance [38, 39]. This finding was not mirrored in the Norwegian cohort however. Even if dispensed drugs can serve as a proxy for co-morbidity it is well established that both somatic and especially mental illness are underdiagnosed and undertreated among individuals with substance use disorders , and does not explain the vast differences we observed among dispensations of benzodiazepines, z-hypnotics, and antidepressants comparing Sweden and Norway. Older patients are more likely to have cirrhosis and longer HCV treatment courses compared to younger patients, which may explain the reported association between DAA treatment among patients aged 46–55 in Sweden. Although, a reason for the observed age difference with regard to being treated for HCV may be that the younger patients are usually harder to reach due to an unstable life situation and drug abuse related behavior. Similarly, the analyzes point toward that women are less likely to be treated for HCV, however, this could just as much be that women having lower prevalence and incidence of chronic HCV.