CROI 2018 Abstract eBook

Abstract eBook

Poster Abstracts

support for migration (BF>10) between Rakai, Senyondo and Makungu FCs and Kampala along the Kampala-Masaka highway. Conclusion: Young adults (average age=35yrs) mainly associated with recent HIV-1 transmission and involved in fishing, farming, bar business and sex work were identified in transmission pairs. The viral dispersal patterns suggest that HIV-1 transmission in FCs along highways is not isolated from networks in the GP. Network-guided interventions targeted at potential HIV transmission hotspots with recurrent viral migration could be useful in preventing disease spread.

identify high rates of transmission. In this study we combine a phylogenetic measure with plasma viral load to develop and employ a newmetric, viral load- weighted diversification rate (VLWDR) to identify areas where viral load and transmission rates are simultaneously high among people living with HIV-1. Methods: We apply this method to 5,190 HIV-1 sequences from 2,853 anonymized patients living in British Columbia, Canada spanning 20 years (mean 2 sequences per patient, range 1-5). The data was split into five 4-year time intervals in order to build five approximate maximum likelihood phylogenetic trees fromwhich the diversification rates were calculated. VLWDR was calculated by combining this data with associated plasma viral loads. To maintain patient confidentiality, census tracts were merged with proximate neighbours until no fewer than five patients resided in that polygon in any time interval. Longitudinal summary statistics were generated for merged census tracts of patient residence and non-parametric Spearman rank correlation tests were used to evaluate associations. Results: Across British Columbia, the median VLWDR of people living with HIV connected to care decreased from 801 within 1996-1999 to 667 within 2012- 2015. Simultaneously, the estimated number of seroconversions decreased from 10.9 per 100,000 people per year within 1996-1999 to 1.26 per 100,000 people per year within 2012-2015. Spearman rank correlations support that the median and sum VLWDR, respectively, correlate with the estimated HIV seroconversion rate in geographic areas during the same time intervals (rho=0.207, p<0.001; rho=0.654, p<0.001). The distribution of median VLWDR and sum VLWDR in individual neighbourhoods in BC over time was mapped. Conclusion: Our data supports the hypothesis that areas that have simultaneously high viral load and HIV transmission rates as measured by a novel metric, VLWDR, tend to have high rates of seroconversion. Thus, by aggregating data by geographic area, studies of the temporal and spatial distribution of phylogenetic and clinical traits of HIV can identify areas at risk of ongoing transmission that merit additional public health resources.

952 PHYLOGENETIC AND GEOGRAPHIC SEPARATION IN HIV-INFECTED PEOPLE IN BRITISH COLUMBIA

David McVea 1 , Richard Liang 1 , Jeffrey Joy 1 , P. Richard Harrigan 1 , Art Poon 2 1 University of British Columbia, Vancouver, BC, Canada, 2 Western University, London, ON, Canada Background: Calculating phylogenetic distances between HIV infected individuals can reveal clusters of individuals who share risk factors that may be unknown and otherwise undetected. One clear shared risk factor for infectious diseases is geographic proximity, but the relationship between phylogenetic distance and geographic distance among people with HIV is not well understood. In this study, we describe the geographic distribution of phylogenetic clusters from British Columbia (BC), and compare the geographic and phylogenetic distances separating individuals with HIV. Methods: Using anonymized genotypes from the BC drug treatment database, the BC phylogenetic monitoring program calculates pairwise tip-to-tip distances between sequences in a phylogenetic tree. Clusters are defined when groups of >5 individuals are separated by short phylogenetic distances. We assigned each individual a geographic location using postal sortation areas centroids of point-of-care locations. We compared geographic and phylogenetic distances by calculating Spearman’s correlation with the Mantel test for significance. Results: Phylogenetic clusters are variably geographically distributed, having members in between 1 and 38 municipalities. The mean pairwise intra-cluster difference ranges from 1 to 440 km (median = 48.4 km, IQR = 19.5-88.6 km). There was no significant correlation between genetic and phylogenetic distances among the most recent 200 individuals added to the drug treatment database (r 2 = 0.002). In rapidly growing clusters, the association was variable and ranged from absent to moderate (r 2 = 0.35, p = 1.7 x 10 -8 ). Conclusion: There is no significant association between geographic and phylogenetic distances among recently identified individuals with HIV. This offers support for the use of phylogenetic clusters as an adjunct to traditional methods of outbreak detection, as the shared transmission risks among phylogenetically linked individuals would otherwise be missed. In rapidly growing clusters, there is a variable association among geographic and phylogenetic distances. This likely reflects the differing modes of transmission between clusters and the differently structured contact networks through which HIV infection spreads. Angela McLaughlin 1 , P. Richard Harrigan 2 , Jean A. Shoveller 1 , Jeffrey Joy 2 1 University of British Columbia, Vancouver, BC, Canada, 2 British Columbia Centre for Excellence in HIV/AIDS, Vancouver, BC, Canada Background: Identifying areas that are at a high risk for ongoing HIV transmission is critical for prioritizing targeted public health interventions. Despite advancements in testing and treating, foci of high transmission remain even in developed countries. Measures from phylogenetic trees can be used to

Poster Abstracts

954 PHYLOGEOGRAPHIC ANALYSIS SUGGESTS GRAVITY MODEL OF HIV TRANSMISSION IN MEXICO Antoine Chaillon 1 , Santiago Avila-Rios 2 , Ann M. Dennis 3 , Joel O. Wertheim 1 , Claudia García-Morales 2 , Daniela Tapia-Trejo 2 , Sanjay R. Mehta 1 , Gustavo Reyes- Terán 2 1 University of California San Diego, La Jolla, CA, USA, 2 National Institute of Respiratory Diseases, Mexico City, Mexico, 3 University of North Carolina Chapel Hill, Chapel Hill, NC, USA Background: Although Mexico has been highly successful in providing free ART for all HIV infected individuals, HIV detection and prevention efforts are lacking. Understanding the transmission dynamics of HIV across Mexico is key to improve identification of infected individuals and targeting of HIV prevention efforts. Methods: 4192 HIV-1 subtype B pol sequences sampled from unique individuals from 23 states across Mexico between 2001-2016 were analyzed. Phylogenetic and network analyses were performed to infer putative relationships between HIV sequences. We determined the spatial dispersal and growth rates among the identified clusters. The diffusion of the epidemic across Mexico was inferred using a Slatkin-Maddison approach on 1,000 iterations of random subsets of equal number of sequences per region. Results: 1389/4192 (33.1%) sequences had a putative linkage with at least one other sequence forming 510 clusters (range: 2-13 individuals). The median cluster growth rate (newly linked sequences) among the six largest clusters (size

953 PHYLODYNAMIC METHODS OF IDENTIFYING FOCI OF HIV-1 TRANSMISSION

CROI 2018 364