Within-host diversity improves phylogenetic and transmission reconstruction of SARS-CoV-2 outbreaks (preprint)

Accurate inference of who infected whom in an infectious disease outbreak is critical for the delivery of effective infection prevention and control. The increased resolution of pathogen whole-genome sequencing has significantly improved our ability to infer transmission events. Despite this, transmission inference often remains limited by the lack of genomic variation between the source case and infected contacts. Although within-host genetic diversity is common among a wide variety of pathogens, conventional whole-genome sequencing phylogenetic approaches to reconstruct outbreaks exclusively use consensus sequences, which consider only the most prevalent nucleotide at each position and therefore fail to capture low frequency variation within samples. We hypothesized that including within-sample variation in a phylogenetic model would help to identify who infected whom in instances in which this was previously impossible. Using whole-genome sequences from SARS-CoV-2 multi-institutional outbreaks as an example, we show how within-sample diversity is stable among repeated serial samples from the same host, is transmitted between those cases with known epidemiological links, and how this improves phylogenetic inference and our understanding of who infected whom. Our technique is applicable to other infectious diseases and has immediate clinical utility in infection prevention and control.

Recurrent SARS-CoV-2 Mutations in Immunodeficient Patients (preprint)

Long-term SARS-CoV-2 infections in immunodeficient patients are an important source of variation for the virus but are understudied. Many case studies have been published which describe one or a small number of long-term infected individuals but no study has combined these sequences into a cohesive dataset. This work aims to rectify this and study the genomics of this patient group through a combination of literature searches as well as identifying new case series directly from the COG-UK dataset. The spike gene receptor binding domain (RBD) and N-terminal domains (NTD) were identified as mutation hotspots. Numerous mutations associated with variants of concern were observed to emerge recurrently. Additionally a mutation in the envelope gene, - T30I was determined to be the most recurrent frequently occurring mutation arising in persistent infections. A high proportion of recurrent mutations in immunodeficient individuals are associated with ACE2 affinity, immune escape, or viral packaging optimisation. There is an apparent selective pressure for mutations which aid intra-host transmission or persistence which are often different to mutations which aid inter-host transmission, although the fact that multiple recurrent de novo mutations are considered defining for variants of concern strongly indicates that this potential source of novel variants should not be discounted.

Generation of novel SARS-CoV-2 variants on B.1.1.7 lineage in three patients with advanced HIV disease (preprint)

The emergence of new SARS-COV-2 variants is of public health concern in case of vaccine escape. Described are three patients with advanced HIV-1 and chronic SARS-CoV-2 infection in whom there is evidence of selection and persistence of novel mutations which are associated with increased transmissibility and immune escape.

SARS-CoV-2 genomes recovered by long amplicon tiling multiplex approach using nanopore sequencing and applicable to other sequencing platforms (preprint)

Genomic surveillance has become a useful tool for better understanding virus pathogenicity, origin and spread. Obtaining accurately assembled, complete viral genomes directly from clinical samples is still a challenging. Here, we describe three protocols using a unique primer set designed to recover long reads of SARS-CoV-2 directly from total RNA extracted from clinical samples. This protocol is useful, accessible and adaptable to laboratories with varying resources and access to distinct sequencing methods: Nanopore, Illumina and/or Sanger.

Validation of an extraction-free RT-PCR protocol for detection of SARS-CoV2 RNA (preprint)

In light of supply chain failures for reagents and consumables needed for purification of nucleic acid for detection of SARS-CoV-2 RNA by RT-PCR, we aim to verify the performance and utility of a non-extraction protocol for RT-PCR ("direct RT-PCR"). We report improved sensitivity compared to earlier reports of direct RT-PCR testing of swab samples, in particular at the lower limit of detection (sensitivity 93% overall; 100% for specimens with high to moderate viral titre, Ct <34; 81% for specimens with a low viral titre, Ct [≥]34). Sensitivity is improved (from 90 to 93%) by testing in duplicate. We recommend swabs are re-suspended in water to minimise PCR inhibition. A cellular target is necessary to control for PCR inhibition and specimen quality. Direct RT-PCR is best suited to population level screening where results are not clinically actionable, however in the event of a critical supply chain failure direct RT-PCR is fit for purpose for the detection of SARS-CoV-2 infection. The results from our study offer front-line laboratories additional reagent options for performing extraction-free RT-PCR protocols.

Comparison of SARS-CoV2 N gene real-time RT-PCR targets and commercially available mastermixes (preprint)

We aim to test four one-step RT real-time mastermix options for use in SARS-CoV2 real-time PCR, with three primer/probe assays targeting the N gene. The lower limit of detection is determined using a SARS CoV2 N gene RNA transcript dilution series (to 1 copy/{micro}l) and verified using 74 nose and throat swabs. The N2 assay demonstrates the most sensitive detection of SARS-Cov-2 RNA. Three of the four mastermixes performed well, with the Takara One Step PrimeScript III RT-PCR Kit mastermix demonstrating improved performance at the lower limit of detection.