# Forecasting epidemic trajectories if IDU populations change

Page last updated: 2009

The mathematical transmission model was also used to calculate projections of the expected number of HIV and HCV cases in the future if the number of IDUs in Australia changed (by the stated amount in the figure captions over a ten year period).

• IDU population decreases by 25% (see Figure 13)
• IDU population decreases by 10% (see Figure 14)
• IDU population increases by 10% (see Figure 15)
• IDU population increases by 25% (see Figure 16)
We found that incidence of HCV is very sensitive to any change in the number of current injectors. Similarly, we found that the relatively large drop in the number of HCV cases at the beginning of the last decade (Figure 2) was predominantly due to a decrease in the number of injectors and not due to any particular injecting-related behaviour.

## Figure 13: Projected HIV and HCV cases among Australian IDUs if the size of the IDU population decreases by 25% (2010-2019)  Top of page

### Text version of Figure 13

Figures in this description are approximate as they have been read from the graph.

Figure 13 consists of two graphs:
• Projected annual HIV incidence among Australian IDUs if the size of the IDU population decreases by 25% (2010-2019)

• The 100 model simulations decrease gradually from a range of 10-42 in 2009 to a range of 8-32 in 2010 and decrease steadily to 5-22 in 2020.

• The median of the model simulations decreases gradually from 25 in 2009 to 18 in 2010 and decreases steadily to 11 in 2020.

• The lower quartile of the model simulations decreases gradually from 18 in 2009 to 14 in 2010 and decreases steadily to 9 in 2020.

• The upper quartile of the model simulations decreases gradually from 32 in 2009 to 25 in 2010 and decreases steadily to 16 in 2020.

• Projected annual HCV incidence among Australian IDUs if the size of the IDU population decreases by 25% (2010-2019)

• The 100 model simulations decrease dramatically from a range of 7,800-16,200 in 2009 to a range of 1,800-5,500 in 2010 and increase gradually to 5,500-11,800 in 2020.

• The median of the model simulations decreases dramatically from 11,800 in 2009 to 3,600 in 2010, before increasing gradually to 8,000 in 2020.

• The lower quartile of the model simulations decreases dramatically from 10,500 in 2009 to 3,100 in 2010, before increasing gradually to 7,800 in 2020.

• The upper quartile of the model simulations decreases dramatically from 13,000 in 2009 to 4,000 in 2010, before increasing gradually to 9,000 in 2020.

## Figure 14: Projected HIV and HCV cases among Australian IDUs if the size of the IDU population decreases by 10% (2010-2019)  ### Text version of Figure 14

Figures in this description are approximate as they have been read from the graph.
Top of page
Figure 14 consists of two graphs:
• Projected annual HIV incidence among Australian IDUs if the size of the IDU population decreases by 10% (2010-2019)

• The 100 model simulations decrease gradually from a range of 10-42 in 2009 to a range of 9-39 in 2010 and decrease steadily to 6-27 in 2020.

• The median of the model simulations decreases gradually from 24 in 2009 to 21 in 2010 and decreases steadily to 13 in 2020.

• The lower quartile of the model simulations decreases gradually from 18 in 2009 to 16 in 2010 and decreases steadily to 11 in 2020.

• The upper quartile of the model simulations decreases gradually from 30 in 2009 to 28 in 2010 and decreases steadily to 18 in 2020.

• Projected annual HCV incidence among Australian IDUs if the size of the IDU population decreases by 10% (2010-2019)

• The 100 model simulations decrease dramatically from a range of 7,800-16,200 in 2009 to a range of 5,500-11,500 in 2010 and increase gradually to 7,500-15,000 in 2020.

• The median of the model simulations decreases dramatically from 11,800 in 2009 to 9,000 in 2010, before increasing gradually to 11,000 in 2020.

• The lower quartile of the model simulations decreases dramatically from 10,500 in 2009 to 7,200 in 2010, before increasing gradually to 10,000 in 2020.

• The upper quartile of the model simulations decreases dramatically from 13,000 in 2009 to 9,000 in 2010, before increasing gradually to 12,000 in 2020.

## Figure 15: Projected HIV and HCV cases among Australian IDUs if the size of the IDU population increases by 10% (2010-2019)  ### Text version of Figure 15

Figures in this description are approximate as they have been read from the graph.
Top of page
Figure 15 consists of two graphs:
• Projected annual HIV incidence among Australian IDUs if the size of the IDU population increases by 10% (2010-2019)

• The 100 model simulations increase slightly from a range of 10-42 in 2009 to a range of 12-48 in 2010, before decreasing gradually to 10-38 in 2020.

• The median of the model simulations increases slightly from 25 in 2009 to 27 in 2010, before decreasing gradually to 22 in 2020.

• The lower quartile of the model simulations increases slightly from 18 in 2009 to 20 in 2010, before decreasing gradually to 17 in 2020.

• The upper quartile of the model simulations increases slightly from 31 in 2009 to 34 in 2010, before decreasing gradually to 30 in 2020.

• Projected annual HCV incidence among Australian IDUsif the size of the IDU population increases by 10% (2010-2019)

• The 100 model simulations increases sharply from a range of 7,800-16,500 in 2009 to a range of 10,800-22,500 in 2010 and decrease gradually to 19,800-10,000 in 2020.

• The median of the model simulations increases sharply from 11,900 in 2009 to 16,500 in 2010 and decreases gradually to 14,800 in 2020.

• The lower quartile of the model simulations increases sharply from 10,800 in 2009 to 14,500 in 2010 and decreases gradually to 13,5000 in 2020.

• The upper quartile of the model simulations increases sharply from 13,000 in 2009 to 18,000 in 2010 and decreases gradually to16,200 in 2020.

## Figure 16: Projected HIV and HCV cases among Australian IDUs if the size of the IDU population increases by 25% (2010-2019)  ### Text version of Figure 16

Figures in this description are approximate as they have been read from the graph.
Top of page
Figure 16 consists of two graphs:
• Projected annual HIV incidence among Australian IDUsif the size of the IDU population increases by 25% (2010-2019)

• The 100 model simulations increase from a range of 10-42 in 2009 to a range of 12-55 in 2010 and decreases slightly to 10-50 by 2020.

• The median of the model simulations increases from 25 in 2009 to 30 in 2010 and dcreases slightly to 17 by 2020.

• The lower quartile of the model simulations increases from 18 in 2009 to 24 in 2010 and decreases slightly to 20 by 2020.

• The upper quartile of the model simulations increases from 32 in 2009 to 40 in 2010 and decreases slightly to 35 by 2020.

• Projected annual HCV incidence among Australian IDUs if the size of the IDU population increases by 25% (2010-2019)

• The 100 model simulations increase dramatically from a range of 8,000-16,500 in 2009 to a range of 14,000-32,000 in 20101 and decrease gradually to 12,800-23,000 in 2020.

• The median of the model simulations increases dramatically from 12,000 in 2009 to 23,500 in 2010, before decreasing gradually to 14,000 in 2020.

• The lower quartile of the model simulations increases dramatically from 11,000 in 2009 to 21,000 in 2010, before decreasing gradually to 16,000 in 2020.

• The upper quartile of the model simulations increases dramatically from 13,000 in 2009 to 26,000 in 2010, before decreasing gradually to 19,000 in 2020.