Subjects are recruited through local physician networks and are interviewed over the telephone to be sure they meet the appropriate disease definition (multiply-exposed, acute seroconvertor, or long-term survivor). If the history matches the disease definition to be studied, they are scheduled for a visit at which time more extensive history is obtained, informed consent is signed, and screening blood tests are drawn. The blood tests vary based upon the disease state that is being studied. For instance, in acute seroconvertors, we look for evidence of falling viral load and an increasing immune response; in long-term survivors we look for low viral load and normal CD4 cell counts in someone with documented infection for >10 years; in exposed-uninfected subjects we look for evidence of sero-negativity in someone with a documented history of multiple high risk exposures. Once a subject meets the specific disease definition, he or she is asked to return for further phlebotomy.