Epidemiology is the study of disease at the population level. That is a different angle than is traditionally used to study medicine. Indeed, most individuals are used to the clinical angle where analysis is based on the individual (case study). The main difference between the two lies in perspective: Epidemiology is interested in finding common factors (variables) in populations that may cause disease. Clinical medicine, on the other hand, is concerned with diagnosing (and hopefully curing) diseases in individuals in that population.
HIV/AIDS, although much progress has been made in pharmacological treatments for the disease, still poses a great threat to certain sub-populations. Indeed, due to strenuous prevention efforts, HIV/AIDS’s rate of incidence has notably decreased over time. Incidence is the number of new cases of a disease. On the other hand, the rate of prevalence has not noticed a similar, notable decline. This is because prevalence not only includes new cases (which are declining), but also existing cases of HIV that have not been cured as of yet. There are two main ways that prevalent cases leave the population: death or a cure. In the 1980s, when a HIV/AIDS diagnosis effectively served as death sentence, the incidence rate was high and the prevalence rate was low; this was because most of the individuals diagnosed with the disease died within a 5-10 year time frame. As AZT and other pharmacological became more widespread, the incidence rate witnessed a minor decrease, but the prevalence rate skyrocketed as people did not die of the disease any more. These developments mean the mortality rate for HIV has decreased as well. Whereas previously many died of the disease, current uses of medication can keep them alive longer. Although the epidemiology of HIV/AIDS has radically changed over the past 30 years, work still remains to be done: Pockets of HIV still remain in the southern parts of the US, and abroad. Only continued efforts will help to bring down the incidence and mortality rates of this disease.
Gordis, L. (2005). Epidemiology.
Brown, L. (2001). Epidemiology.