The Multi-faceted Dynamics of HIV-1 Transmission in Northern Alberta: A Combined Analysis of Virus Genetic and Public Health Data

Molecular epidemiology has become a key tool for tracking infectious disease epidemics. Here, the spread of the most prevalent HIV-1 subtypes in Northern Alberta, Canada, was characterized with a Bayesian phylogenetic approach using 1146 HIV-1 pol sequences collected between 2007 and 2013 for routine clinical management purposes. Available patient metadata were qualitatively interpreted and correlated with onwards transmission using Fisher exact tests and logistic regression. Most infections were from subtypes A (n=36), B (n=815) and C (n=211). Africa is the dominant origin location for subtypes A and C while the subtype B epidemic was seeded from the USA and Middle America and, from the early 1990s onwards, mostly by interprovincial spread. Subtypes A (77.8%) and C (74.0%) were usually heterosexually transmitted and circulate predominantly among Blacks (61.1% and 85% respectively). Subtype B was mostly found among Caucasians (48.6%) and First Nations (36.8%), and its modes of transmission were stratified by ethnic origin. Compared to subtypes A (5.6%) and C (3.8-10.0%), a larger portion of subtype B patients were found within putative provincial transmission networks (20.3-29.5%), and this almost doubled when focusing on nationwide transmission clusters (37.9-57.5%). No clear association between cluster membership and particular patient characteristics was found. This study reveals complex and multi-faceted transmission dynamics of the HIV-1 epidemic in this otherwise low HIV prevalence population in Northern Alberta, Canada. These findings can aid public health planning.