It took, however, less time to identify that both male and female injection drug abusers, recipients of blood transfusions and patients with hemophilia, all are prone to this disease. As Berer (2004) has pointed out, these all point to an epidemiologic pattern, which indicated that the disease agent, most probably microscopic organisms are transmitted through both homo and heterosexual contacts and blood and blood products are the suspected etiologic agent. By the time this was known, AIDS became an epidemic (Berer, 2004).
Epidemiology of AIDS and HIV infection took strongholds since this disease seemed very difficult to be conquered despite tremendous advancement of technology, diagnostic measures, and epidemiologic strategies. As Lashley (2006) has pointed out, the main reasons for this most contemporary failure of modern medicine were perhaps multifactorial; however, as things progressed, many unknown information unveiled themselves. In 1985, a sensitive enzyme-linked immunosorbent assay (ELISA) was developed, which led to an appreciation of the scope and evolution of the HIV epidemic at first in the United States and other developed nations and finally among developing nations worldwide. Now AIDS is considered to be a pandemic throughout the world (Lashley, 2006).
With the growth of the epidemic, there has been a proportionate explosion of information and a huge volume of research and resultant literature in the areas of HIV virology, both immunologic and virologic pathogenesis, antiretroviral treatment of the disease, management of diseases that occur from the opportunistic pathogens but associated with this disease, and development of vaccines. In this assignment, the most current information on epidemiologic principles of this disease has been discussed in these areas to explore the state of the art approaches to this epidemic mainly in the USA and some in other countries to be able to compare the status.
In 1982, the new and frightening "acquired immune deficiency syndrome" (AIDS) was defined as "a disease at least moderately predictive of a defect in cell-mediated immunity occurring in a person with no known cause for diminished resistance to that disease. Such diseases include Kaposi's sarcoma, Pneumocystis carinii pneumonia and serious opportunistic infections" (CDC, 1982a). Following that, a list of specific AIDS-related and -defining conditions was elucidated with the addition of some new conditions based on additionally available evidence from advanced epidemiology of the disease, which led to changes in diagnostic practice since new serologic tests for the AIDS virus were available.
As expected, the case definition has changed and has undergone many revisions. The definition of AIDS is complex. As mentioned in Schneider et al. (2008) The clinician should not focus only on whether AIDS is present but should view HIV disease as a spectrum ranging from primary infection with or without the acute syndrome, to the asymptomatic stage, to advanced disease. The definition of AIDS was established not for the practical care of patients but for surveillance purposes. The current classification system provided by CDC includes both the criteria of clinical condition and CD4+ T lymphocyte count. As it appears from CDC criteria, this diagnostic system is based on three ranges of CD4+ T lymphocyte