METHADONE TREATMENT AND RISK OF HIV-INFECTION IN DRUG-USERS WITHOUT LEGAL ACCESS TO CLEAN INJECTION EQUIPMENT

The particular situation of the Swiss canton of Vaud (population 550 0 00) provides favourable observational conditions to assess the efficac y of a methadone treatment scheme inn reducing the risk of human immun odeficiency virus (HIV) infection among drug users. On the one hand, t he canton has a long tradition of methadone treatment dispensed by med ical practitioners. On the other hand, no legal access to clean inject ion equipment was provided up to 1989. For the 754 addicts having ente red at least one course of treatment at the end of 1988, HIV status wa s assessed through two surveys conducted at mid-1986 and at end 1988 a mong the private practitioners and in the screening centers, hospitals , medico-social institutions and prisons. The overall annual HIV seroc onversion rate shifted only slightly from 13% in the first study perio d (1984 to mid-1986) to 11 % in the second period (mid-1986 to end 198 8). In both periods, patients no longer on treatment mostly stable abs tainers, were the less exposed to HIV infection with a relative risk o f 0.65 (p < 0.05). For those still on treatment, the risk of infection was associated directly (p < 0.001) with the frequency of courses and inversely (p < 0.001) with the duration. Between patients with more t han 18 months spent on treatment and those with less than 6 months, th e relative risk gradient was 0.8 and 1.4 before mid-1986 and widened o ut to 0.3 and 2.1 later on. This is mainly due to an increasing HIV in cidence among newcomers into treatment. In conclusion, methadone treat ment has contributed to a significant risk reduction both through deto xication processes and in long-term maintenance, but facilitated acces s to sterile injection equipment is needed urgently for patients with poor attendance or new to treatment.