BACKGROUND: In Western Europe, a previously subtype B HIV-1 restricted area, BC 
recombinants have been rarely reported.
OBJECTIVE: To describe an outbreak of HIV-1 BC recombinants in southern Italy.
STUDY DESIGN: We analyzed pol (protease/reverse transcriptase) sequences from 
135 newly diagnosed HIV-1-infected patients during the years 2009-2011. For 
phylogenetic relationships, sequences were aligned to the most recent reference 
data set from the Los Alamos database using BioEdit (version 7.1.3). The 
resulting alignment was analyzed with the Phylip package (version 3.67) building 
a neighbor-joining tree based on the Kimura two-parameter substitution model. 
The reliability of the tree topology was assessed through bootstrapping using 
1000 replicates. The recombination pattern was characterized using SimPlot 3.5.1 
and SplitsTree 4.
RESULTS: At phylogenetic analysis, 22 (16.2%) isolates whose sequences were not 
unequivocally assigned to a pure subtype or known CRF, formed a distinct 
monophyletic clade (100% of bootstrap value). For these isolates, the 
recombination analysis identified a BC mosaic pattern with two breakpoints at 
positions 2778±5 and 3162±8 (HXB2 numbering) which differed from those of known 
BC CRFs. All patients from whom these sequences were derived were highly 
educated youth Italians, 91% males and 82% MSM. Sequences of pol integrase, 
gp120 and gp41 from these same patients were classified as C subtype.
CONCLUSIONS: This outbreak which further reflects the increasing heterogeneity 
of HIV epidemic in our country is the first report of an Italian outbreak of a 
BC recombinant, possibly a novel candidate CRF.