Modelling AIDS reduction strategies

Mathematical models of the AIDS epidemic have not been able to give accurate predictions about the size of the epidemic because it is not possible to obtain sufficiently accurate measurements of the factors that enable HIV transmission. The uncertainties inherent in models of the AIDS epidemic appear to limit their relevance to epidemiologists. However, it is shown here that the uncertainties need not prevent models being used to make reliable decisions about which preventive strategy will be most effective.

A range of strategies are simulated in a model of the AIDS epidemic. The simulations are repeated as the value of what seems to be the most important uncertain factor, is varied. The effect of this variation on the effectiveness of each strategy is noted. In principle, the process could be repeated whilst all other uncertain factors are varied as well.

Although varying one uncertain factor created enormous variation in the size of the epidemic, it is remarkable that for most preventive strategies the relative effectiveness of the strategies was barely altered. Hence for the most part the ranking of strategies in order of effectiveness is not affected by the area of uncertainty explored here. The results also highlight the potential effectiveness not only of general condom promotion, but also the use of circumcision and spermicides and general screening or targetted screening in sexually transmitted disease clinics.

Epidemiological modelling may accurately rank the effectiveness of interventions although it may fail to predict the size of the epidemic.