|STEP 1:||Imputation by Chained Equations: missing risk factor information|
|Missing risk factor information was imputed using Imputation by Chained Equations. The imputation model contains the variables: injecting drug use, sex, nationality, year at registration and age at registration. The imputation results in one complete dataset X k , containing original and imputed values.|
|STEP 2:||Stochastic Mortality Modeling: lacking follow-up of the HIV + /AIDS – cases|
For a complete dataset k, the number of registered HIV-cases for whom injecting drug use was the most probable route of transmission and who were alive at time t is calculated as
where I i indicates the ‘vital’ status with I i = 1 if person i is still alive and living in Belgium and I i = 0 otherwise, where r i is the number of years since HIV registration or r i = t − t hi and where p d is the annual non-AIDS mortality rate among seropositive IDUs with p d ~ betapert*(0.58%, 1.08%, 1.58%).
|STEP 3:||Benchmark-multiplier method: population size estimation|
|The number of ever-injecting drug users being alive at time t is given by with obtained from step 2, and n = 639.|