The study of individuals at opposite ends of the HIV clinical spectrum can provide
invaluable insights into HIV biology. Heterogeneity in criteria used to define these
individuals can introduce inconsistencies in results from research and make it difficult
to identify biological mechanisms underlying these phenotypes. In this systematic
review, we formally quantified the heterogeneity in definitions used for terms referring
to extreme phenotypes in the literature, and identified common definitions and
components used to describe these phenotypes. We assessed 714 definitions of HIV
extreme phenotypes in 501 eligible studies published between 1 January 2000 and
15 March 2012, and identified substantial variation among these. This heterogeneity in
definitions may represent important differences in biological endophenotypes and
clinical progression profiles of individuals selected by these, suggesting the need for
harmonized definitions. In this context, we were able to identify common components
in existing definitions that may provide a framework for developing consensus
definitions for these phenotypes in HIV infection.