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O024 - PHYLOGENETIC INFERENCE OF THE TRANSMISSION DIRECTION OF PNEUMOCOCCAL INFECTIONS, A VALIDATION STUDY (ID 782)
Abstract
Background
Sustaining herd protection via reduced-dose schedules of pneumococcal vaccine may ameliorate some of the associated costs but necessitates a better understanding of Streptococcus pneumoniae (Sp) transmission. We ran a pilot study to explore a phylogenetic approach for detecting pneumococcal occurrence and direction of transmission.
Methods
Five putative transmission pairs and their same days’ nasopharyngeal swabs were selected from a longitudinal household study of asymptomatic carriage. Deep-sequencing of the infecting Sp populations was performed from culture sweeps and the direction of transmission was inferred using Phyloscanner. Transmission bottlenecks were assessed by comparing the frequency of single nucleotide polymorphism (SNPs) within transmission pairs.
Results
Phylogenetic clustering of all five transmission pairs was concordant with epidemiological information. The concordance of the direction of transmission inferred from phylogenies and from epidemiological criteria depended on the genome fragment size and the minimum number of SNPs included; with seemingly increasing concordance if phylogenetic inference is based on longer fragment sizes. In 4 of 5 instances, the putative source of transmission had higher number of unique SNPs than the recipient.
Conclusions
This study is one of the first to attempt inference of transmission directionality from bacteria using whole-genome NGS data. While our sample size was small, we show promise for detecting linked pneumococcal infection and their direction of transmission, particularly if read length is high.