New opiate and crack-cocaine users: characteristics and trends 13 
 
population there exists a small group of frequent repeat users. 1,828 individuals (1.7% of this 
population) accounted for just over ten per cent of all positive tests (30,471 tests in total). These 
individuals provided between 16 and 57 positive tests over the period 2004 to 2013. 
Figure 4: Proportion of positive tests by number of times an individual tested positive.  
 
The age and year-of-birth distributions for the 104,817 individuals reveals a similar profile to the 
distribution for total tests (Figures 5 and 6).