Theme: Epidemiology & Public Health Research Year: 2023
Background:
Although reduced by harm reduction interventions, isolated and outbreak HIV transmission still occurs in PWID. Identification of clusters could foster public health measures to stop the chain of transmission.
Methods:
Available sequences from people living with HIV (PLWH) attending an outpatient clinic in Lombardy since 2015 were included in a phylogenetic analysis based on Maximum Likelihood (ML) method to confirm subtype and define transmission clusters (ref. HIV-1 subtype B HXB2, bootstrap >90%). Epidemiological investigation included interviews and consultation of medical records.
Results:
Among 794 PLWH followed up between 01/01/2015 and 31/12/2022, 167 had at least one pol sequence available while viraemic; ML tree based on these B-subtype sequences identified a single cluster of 20 subjects (bootstrap 98%), of whom 19 (95%) harboured the V106I mutation, versus 2/147 (1.36%) unlinked to the cluster (p=0.0001).
Of these 20 “cluster members”, 4 (20%) women, median (range) age 32 (21-57) years, 4 (20%) were diagnosed in prison, 3 (15%) in addiction centres, 6 (30%) as outpatients, 6 (30%) as inpatients, 1 (5%) in street mobile unit. All cases were HCVAb positive. All patients had a known history of injecting drug use and most had the same drug use network. The first case was diagnosed in 2006, the second, in 2015, had a datable primary HIV infection.
We hypothesize a founder effect of the first case during a period of low adherence to efavirenz-containing antiretroviral therapy, possibly selecting for V106I mutation. The subsequent spread of HIV over the following 7 years is likely due to sharing of injecting equipment in a close group of epidemiologically linked individuals.
Conclusion:
HIV transmission through injecting drug use includes the risk of spreading drug resistance. Phylogenetic analysis, by identifying transmission clusters, could serve as innovative strategy for real-time monitoring of HIV clustering, thereby favouring targeted outbreak response interventions.