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The detected incidence of hepatitis C among injecting drug users in Dublin, Ireland is higher than corresponding figures from surveys in similar settings elsewhere. It contrasts with a comparatively low incidence of HIV.
Between 1992 and 1998, attenders at a drug treatment centre were encouraged to consent to testing for evidence of hepatitis C infection. The incidence of infection was calculated using the person years method. The date of a first negative test represented the starting point for all patients when calculating their person years at risk. The end point was the date of the last negative test if they remained seronegative or the midpoint of the last negative and first positive test for those who seroconverted.
Sixty seven of 100 patients retested seroconverted during the study period—an overall incidence of 66/100 person years (CI 51–84). A history of imprisonment was associated with a higher incidence while the group who usually smoked heroin and only occasionally injected had a lower incidence. Repeat testing for HIV in 164 patients uncovered two who seroconverted. The incidence of HIV was 0.7/100 person years (CI 0.1–2.5).
The authors considered the high hepatitis C incidence related to the fact that the cohort was young (median age 20.5y) and were mostly recent injectors (median six months). The reason for the extra risk posed by imprisonment is unclear: it predated entry to the study so could not have been causal but might reflect a lifestyle that involves generally increased risk taking behaviour.
Strategies to halt the spread of hepatitis C need to target drug users who have recently started injecting as well and to deflect heroin smokers from moving on to injecting.