Part of the recent decrease in the San Francisco AIDS death rate could be attributable to the effect of combination antiretroviral therapy (ART, also known as highly active antiretroviral therapy (HAART)) decreasing disease progression rates. However, because treated individuals are like to retain some degree of infectivity, it is possible that ART/HAART could lead to an increase in the incidence rate. Furthermore drug-resistant HIV strains (that are less responsive to therapy) have emerged, and risky behavior has begun to increase in the gay community in San Francisco. Therefore, whether the epidemic-level effect of ART will be beneficial or detrimental is unclear.
We have developed a mathematical model that includes treatment effects of ART/HAART (in terms of decreased infectiousness and increased survival), increase in risky behavior, and emergence of drug-resistant strains. Full details, and several analyses of this model can be found in:
Blower, Gershengorn and Grant. 2000. A tale of two futures: HIV and
antiretroviral therapy in San Francisco. Science. Volume 287: 650 -
654 [Abstract] [Full Text]
Here we allow you to use the model yourself to explore the effect of
changes in treatment strategies and/or in risk behavior on the HIV
epidemic in the gay community in San Francisco. The current HIV
prevalence in this community
is 30%.
For those of you interested in the technical details, here are is a link with important information
concerning the differential equations from the paper.
Instructions
We have set things up so you can use the model to see the effects of
treatment with ART/HAART on the % AIDS deaths averted
(Applet 1) and the % infections prevented (Applet 2).
First, please note that these applets are viewed best at resolutions of 800 x 600 or higher. If you are having a hard time running these applets because they don't fit on the screen, try clicking the 'Open without Frames' button at the bottom of this page. Also some browsers, such as the internet explorer have full screen modes, which enable more of a page to be displayed (for IE 5.0 the F11 key switches to the full screen mode).
We have set things up so you can do several things:
1. Evaluate the effects of both an optimistic and a pessimistic strategy on the % AIDS deaths averted (Applet 1) and the % infections prevented (Applet 2). To run these two strategies simply click on the 'Graph' button. These two strategies differ in only two parameters. The optimistic strategy assumes that the average number of new risky sex partners is low (~1.6 per year) whereas the pessimistic strategy assumes that the average number of new risky sex partners is high (3.0 per year). The second difference in parameters is that there is a smaller proportion of ART/HAART cases per year who develop acquired drug resistance in the optimistic (0.1) compared to the pessimistic (0.5) strategy.
To see a list of all of the parameters used in these simulations and their values click the 'Parameters' button.
2. Use the model to see the effect on the % AIDS deaths averted and % AIDS infections prevented under a variety of different conditions. Here you can change the following five parameters:
To run simulations with custom parameters you must change either strategy A or B to 'Custom treatment'. Once set on this value note that the greyed out dropbox, text field, and button become accessible. Choose the parameter(s) to change in the second drop box, enter the new value in the text field, then click on either 'Set A' or 'Set B' buttons depending upon which baseline strategy you are changing.
If you wish to change how long time is plotted (in years), then choose a different time final value and click the 'Set' button (the default is 10.0 years). The model will continue to graph time as long as you want, however if you want to restart the model to its initial state then click 'Refresh' or 'Reload' on your browser.