In analyzing this case register, we aimed to identify ethnic- and gender-specific differences in the prevalence of HIV among heroin users receiving opioid maintenance treatment in the canton of Zurich, Switzerland. Overall, we found a significant decrease in the prevalence of HIV among opioid-maintained patients, regardless of gender and nationality, during the first years after initiation of the register in 1991. The following years were associated with a more stable prevalence of HIV in this subgroup.
These findings are in line with previously available data from the Swiss Federal Office of Public Health and the SWISS HIV Cohort Study [19, 24, 26] and underline the effectiveness of measures that have been taken since HIV/AIDS became a major public health concern in the context of open drug scenes that developed in Switzerland’s largest cities in the early 1980s. Between 1985 and 1995, HIV/AIDS incidence and prevalence rates were the highest in Europe [56, 57]. Virus transmission by contaminated syringes and needles among an estimated 3,000 IDUs contributed significantly to this crisis . Although methadone prescription and maintenance treatment had been introduced almost a decade earlier and all physicians could prescribe methadone until 1975, controlled-substance legislation was inconsistent and oscillated between liberal and restrictive approaches . In the face of this heroin and HIV/AIDS epidemic, a harm-reduction-friendly policy was adopted in 1991 at the federal level [21, 57], which formally permitted the implementation of low-threshold methadone programs, needle- and syringe-exchange services, supervised consumption rooms, and heroin-assisted treatments .
When this legislation was implemented in cantonal practice in 1991, administrative barriers in Zurich (and other Swiss cities) were greatly reduced , since it was recognized that high-entry barriers keep opiate-dependent users from seeking admission to OMT. Since then, this finding has been widely and repeatedly replicated [60–63]. Furthermore, studies from Canada show that limited provision of addiction treatment may result not just in a missed opportunity to reduce HIV transmission behavior among IDUs  but could lead to increased HIV-related expenditures for the general public .
Other than suffering from an opiate dependence, there were no further prerequisites to enter treatment. Furthermore, medical care and prescription of opioids such as methadone and buprenorphine were covered by mandatory health insurance, and sufficient OMT providers were involved to avoid waiting lists. The introduction of an on-call service, staffed 24/7, allowed the admission of opiate-dependent patients into an OMT and the dispensation of a first dosage of methadone without delay. Both cantonal and private treatment institutions offered multidisciplinary approaches and were usually staffed by psychiatrists and internal medicine specialists with nurses, as well as social workers, to provide widespread support [21, 57]. Special attention was given to pregnant women suffering from opioid dependence to ensure easy access to OMT during pregnancy and after childbirth .
It was estimated that OMT attracts around 64% of Zurich’s opioid-dependent patients . Furthermore, every second individual with a problematic use of opioids will, regardless of gender, seek admission into a program within 2–3 years after developing dependency .
Despite this low-threshold approach, our findings suggest that gender and migration background influence the risk of being HIV positive. Different access to treatment and different exposure risk characteristics for certain subgroups may offer possible explanations for these findings [67–69]. A recent review identified pregnancy, lack of services for pregnant women, fear of losing custody for a newborn, or fear of prosecution, coupled with lack of childcare outside of treatment, to be gender-specific barriers keeping women from entering treatment for substance use disorders in general [70–72]. Additionally, women may not just lack social support, but experience greater social stigma and discrimination than their male counterparts, when entering such treatment [70, 73, 74]. Women have also been reported to articulate more negative expectations about treatment than males [70, 75]. A number of studies documented systematic barriers—irrespective of gender—related to the policies and procedures of OMT . They include multiple requirements for treatment initiation or modification (including waiting lists), rules regarding abstinence, requirements of established health insurance, hidden or collateral fees, requirements to prove identification, limited take-home dose availability, and a lack of information regarding treatment options [77, 78]. One aspect may be that drug-related services in Switzerland do not tend to be culture-specific, so as not to specifically arrange services for certain migrant subgroups, which may have the effect of increasing the likelihood of cultural misperception and overlook social variables. Previous studies elsewhere showed that migrants without legal documentation might avoid seeking medical advice or entering treatment services because of fear of expulsion from the country [27, 79]. Furthermore, some authors reported a more serious progression of opioid dependence in an immigrant population (leading to the acquisition of multiple infections) and interpreted this finding as part of a multifaceted acculturation problem .
In addition, the higher risk for native women and for women with a migration background warrants further research and should identify what factors deter women from using available HIV-prevention measures, as well as whether these measures need to be better adapted to high-risk groups. This becomes even more apparent in light of a recent study among a Canadian cohort of HIV-positive individuals in IDUs, which identified female gender as an additional barrier to access and adherence to antiretroviral therapy once women had been infected—a finding that was independent of drug use and other socio-behavioral and clinical characteristics .
We acknowledge the limitations of our study. First, Switzerland’s immigration policy is strictly controlled, especially in relation to individuals from non-EU member states and relies on a system of quotas and permits (short-term permit (L), initial residence permit (B), permanent residence permit (C), and cross border commuter permits (G)) and may prevent naturalization for two or more generations . Our calculations might therefore have falsely categorized individuals as non-native who were actually born and raised in Switzerland (i.e., granting nationality on the basis of jus sanguinis (‘right of blood’), as compared to those granting it on the grounds of jus soli (‘right of soil’), such as the USA.
Second, because of our small sample size, we cannot provide a finer breakdown for analysis than Swiss and non-Swiss; therefore, the latter is an extremely heterogeneous group that includes individuals from the majority of European and Eastern European countries, as well as a few subjects of Arabic or African ethnic background. Nevertheless, our database of OMT is one of the oldest in existence and is the largest of its kind in Europe, so our findings might still be useful when comparing HIV prevalence rates internationally, especially in relation to gender and immigration background.