Harm reduction interventions have dramatically reduced HIV incidence among people who inject drugs (PWID). In Glasgow, <10 infections/year have been diagnosed since the mid-90s. However in 2015 a sharp rise in HIV diagnoses was noted among PWID: all were subtype C with two identical drug resistant mutations and some displayed low avidity, suggesting the infections were linked and recently acquired. The outbreak follows reports of recent PWID outbreaks in Greece, Romania, Ireland, and the USA.
We collected pol sequences from all subtype C HIV diagnoses from Glasgow since 2010 (n=228). In parallel, we obtained sequences from the UK HIV Drug Resistance Database (UKRDB) which contains sequences from all UK patients diagnosed until 2013. We blasted the Glasgow sequences against the UKRDB and the Los Alamos National Laboratory (LANL) database and selected the ten closest matches from either database to each Glasgow sequence. A maximum likelihood phylogeny was reconstructed comprising 228 Glasgow sequences, 762 UKRDB and 1144 LANL. The outbreak cluster was identified and extracted from the tree and time-resolved in BEAST.
A tight cluster of 105 sequences stood out in the ML phylogeny. All sequences originated from Glasgow and contained E138A and V179E. Mean genetic distance was <1% with multiple sets of identical sequences from different patients. Short branches in the BEAST phylogeny indicated rapid transmission (Figure 1). The outbreak subdivided into three subclusters, two of which displayed rapid and recent transmission events. The common ancestor of the outbreak dated back to 2004 and the oldest sequence represented a female PWID diagnosed in 2005. Five patients were diagnosed in 2008-2009 and all others between 2010 and 2016. We extracted node dates to estimate the timing of transmissions, demonstrating an acceleration of the transmission rate through time, culminating between 2013 and 2015 when 63 transmissions took place. All patients reported injecting drugs, and the majority were men (59/94, 63%), suggesting that infections have been transmitted primarily through injection rather than sexually. While disclosure of needle sharing was variable, the majority (88/90, 98%) were co-infected with Hepatitis C.
The strain is limited to Glasgow but transmission is ongoing. We are currently investigating associations between the outbreak and epidemiological parameters including homelessness.