In 1982, the Centers for Disease Control (CDC) acknowledged that there was an epidemic, and formally defined the 'acquired immune deficiency syndrome' (AIDS). The number of people who developed AIDS seemed to be doubling every six months in the United States and AIDS was soon found in every part of the country.

Early explanations broke into two main camps, single agent theories and 'immune overload' theories.

Single agent

It was observed very early in the epidemic that the gay men who were developing AIDS tended to have had many more sexual partners than gay men who were healthy. It had already been established that the number of sexual partners was the main risk factor for sexually transmitted diseases such as hepatitis B. It was therefore logical to believe that AIDS was caused by an agent that could be sexually transmitted. This theory was reinforced in the years before HIV was isolated by the occurrence of AIDS in injecting drug users and recipients of blood products donated by gay men, mimicking the transmission patterns of hepatitis B.

Early theories proposed viruses such as cytomegalovirus, African swine fever virus and Epstein-Barr virus and then ruled them out, instead considering that a new agent was responsible.

Immune overload

Particular lifestyle factors were blamed for damaging the immune system: use of poppers (amyl or butyl nitrite) or other recreational drugs, number of sexual partners, a preference for receptive anal intercourse, a history of various sexually transmitted diseases, or a combination of all these in the notion of `fast-lane living'.