Estimating the prevalence of problem opioid use in Copenhagen 1997-1998

Estimates of the prevalence of drug use in Denmark were, until 1999, based on the mortality multiplier method. This paper presents a study estimating the prevalence of problem opioid use in the Greater Copenhagen region using the capture-recapture method.

Records from the prehospital mobile emergency care unit, The Copenhagen Prehospital Research Database, were searched with a particular focus on treatment of opioid overdose. In addition, data from The National Register of Drug Users in Treatment in Greater Copenhagen were analysed for the years 1997 and 1998. Four samples were used within the capture-recapture analysis, ie the Prehospital Research Database for 1997/1998 and the Register of Drug Users in Treatment for the same period.

The estimates from the stratified capture-recapture analyses, when summed up, suggest that there is a hidden population of 4116 and thus a total population of 6992 opioid users in Greater Copenhagen (population approx 700,000). This corresponds to a rate of 10 per 1000 inhabitants aged 15-54 years. The 95% confidence attached to this estimate is 5787 to 10,885.

The prevalence rate of 10 per 1000 inhabitants aged 15-54 years is comparable to figures found in similar cities in Europe. A previous study of Central Copenhagen calculated the rate to be 12.4 per 1000 inhabitants between 15 and 59 years. It seems reasonable that the estimate of prevalence of problem drug use in Greater Copenhagen is lower than the prevalence in Central Copenhagen, as the city area is more urbanised and has a slightly different demographic and socio-economic profile. About 75% of all opioid overdose incidents are assumed to occur in the central district of the city during the observed period.