Epidemiology and the emergence of human immunodeficiency virus and acquired immune deficiency syndrome

Although acquired immune deficiency syndrome (AIDS) was first described in the USA in 1981, there is evidence that individual cases occurred considera bly earlier in Central Africa, and serological and virological data show hu man immunodeficiency virus (HIV) was present in the Democratic Republic of Congo (DRC) as far back as 1959. It is likely that HIV-1 infection in human s was established from cross-species transmission of simian immunodeficienc y virus of chimpanzees, but the circumstances surrounding this zoonotic tra nsfer are uncertain. This presentation will review how causality is establi shed in epidemiology, and review the evidence (a putative ecological associ ation) surrounding the hypothesis that early HIV-1 infections were associat ed with trials of oral polio vaccine (OPV) in the DRC. From an epidemiologi cal standpoint, the OPV hypothesis is not supported by data and the ecologi cal association proposed between OPV use and early HIV/AIDS cases is unconv incing. It is likely that Africa will continue to dominate global HIV and A IDS epidemiology in the near to medium-term future, and that the epidemic w ill evolve over many decades unless a preventive vaccine becomes widely ava ilable.