What do multiple letters representing a subtype mean?
Multiple letters indicate that the sequence is a recombinant of parental viruses originating from 2 or more clades. For example, AGI indicates that it is thought that three subtypes recombined to form the sequenced virus: A, G, and I. The subtypes are listed alphabetically. The regions of the genome that are derived from a particular subtype are not indicated by the name, because of the recombinants show complex patterns of breakpoints, and often a single gene can contain several subtypes. Intersubtype recombinant genomes become designated as “circulating recombinant forms” (CRF) if 3 or more people with no known epidemiological linkage are infected with HIV-1 strains which share the same recombination breakpoints (i.e., are derived from the same ancestral recombinant genome). CRFs are named with a number (e.g., 01_AE or 02_AG). We maintain a current list of specific CRFs: HIV-1 Circulating Recombinant Forms.
