Key publications
RNA virus biology
Studies of specific viruses
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Locations and structures of influenza A virus packaging-associated signals and other functional elements via an in silico pipeline for predicting constrained features in RNA viruses
Emma Beniston, Jordan P. SkittrallAbstract
Influenza A virus contains regions of its segmented genome associated with ability to package the segments into virions, but many such regions are poorly characterised. We provide detailed predictions of the key locations within these packaging-associated regions, and their structures, by applying a recently-improved pipeline for delineating constrained regions in RNA viruses and applying structural prediction algorithms. We find and characterise other known constrained regions within influenza A genomes, including the region associated with the PA-X frameshift, regions associated with alternative splicing, and constraint around the initiation motif for a truncated PB1 protein, PB1-N92, associated with avian viruses. We further predict the presence of constrained regions that have not previously been described. The extra characterisation our work provides allows investigation of these key regions for drug target potential, and points towards determinants of packaging compatibility between segments.PLoS Computational Biology 2024;20(4):e1012009
Methods development
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A novel approach to finding conserved features in low-variability gene alignments characterises RNA motifs in SARS-CoV and SARS-CoV-2
Jordan P. Skittrall, Nerea Irigoyen, Ian Brierley, Julia R. GogAbstract
Collections of genetic sequences belonging to related organisms contain information on the evolutionary constraints to which the organisms have been subjected. Heavily constrained regions can be investigated to understand their roles in an organism’s life cycle, and drugs can be sought to disrupt these roles. In organisms with low genetic diversity, such as newly-emerged pathogens, it is key to obtain this information early to develop new treatments. Here, we present methods that ensure we can leverage all the information available in a low-signal, low-noise set of sequences, to find contiguous regions of relatively conserved nucleic acid. We demonstrate the application of these methods by analysing over 5 million genome sequences of the recently-emerged RNA virus SARS-CoV-2 and correlating these results with an analysis of 119 genome sequences of SARS-CoV. We propose the precise location of a previously described packaging signal, and discuss explanations for other regions of high conservation.
Use of clinical diagnostics
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Serology versus nucleic acid amplification to diagnose acute hepatitis E, United Kingdom, 2014–18
Jordan P. Skittrall, Hamid JalalAbstract
Objectives: Diagnosing hepatitis E infection usually involves specific IgM testing, but sensitivity/specificity concerns mean many guidelines and practices include confirmatory tests. We studied whether additional information confirmatory tests provide justifies their use.
Methods: We examined 9131 records of anti-hepatitis E IgM assays, 7615 of IgG assays, and 1726 of RT-PCR assays from our regional laboratory, spanning October 2014–October 2018. We paired 495 IgM assay results with a RT-PCR result. We examined whether IgM results predicted PCR results, reviewed discrepant pairs, and investigated the correlation between IgG and PCR results in patients with strongly reactive IgM assays.
Results: Anti-hepatitis E IgM titres are bimodal. A high cut-off value optimises prediction of RNA detectability. 7/404 low-IgM samples had detectable RNA, 6 from immunosuppressed patients. 26/91 high-IgM samples did not have detectable RNA. In high-IgM samples, RNA detectability was not associated with IgG titre (one-tailed Mann-Whitney U test, p = 0.14).
Conclusions: In immunocompetent patients, tests beyond IgM seldom add clinically useful information. In patients with immunocompromise, IgM and RNA could contribute information. Additional tests’ extra costs/intervention delays cannot be justified. IgM assay cut-offs should reflect titres’ bimodal distribution, with values standardised using international units. -
Diagnostic tool or screening programme? Asymptomatic testing for SARS-CoV-2 needs clear goals and protocols
Jordan P. Skittrall, Mary D. Fortune, Hamid Jalal, Hongyi Zhang, David A. Enoch, Nicholas M. Brown, Anne Swift
The Lancet Regional Health – Europe (2021) 1 100002 -
Specificity and positive predictive value of SARS-CoV-2 nucleic acid amplification testing in a low-prevalence setting
Jordan P. Skittrall, Michael Wilson, Anna A. Smielewska, Surendra Parmar, Mary D. Fortune, Dominic Sparkes, Martin D. Curran, Hongyi Zhang, Hamid JalalAbstract
Objectives: When the prevalence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is low, many positive test results are false positives. Confirmatory testing reduces overdiagnosis and nosocomial infection and enables real-world estimates of test specificity and positive predictive value. This study estimates these parameters to evaluate the impact of confirmatory testing and to improve clinical diagnosis, epidemiological estimation and interpretation of vaccine trials.
Methods: Over 1 month we took all respiratory samples from our laboratory with a patient’s first detection of SARS-CoV-2 RNA (Hologic Aptima SARS-CoV-2 assay or in-house RT-PCR platform), and repeated testing using two platforms. Samples were categorized by source, and by whether clinical details suggested COVID-19 or corroborative testing from another laboratory. We estimated specificity and positive predictive value using approaches based on maximum likelihood.
Results: Of 19 597 samples, SARS-CoV-2 RNA was detected in 107; 52 corresponded to first-time detection (0.27% of tests on samples without previous detection). Further testing detected SARS-CoV-2 RNA once or more (‘confirmed’) in 29 samples (56%), and failed to detect SARS-CoV-2 RNA (‘not confirmed’) in 23 (44%). Depending upon assumed parameters, point estimates for specificity and positive predictive value were 99.91–99.98% and 61.8–89.8% respectively using the Hologic Aptima SARS-CoV-2 assay, and 97.4–99.1% and 20.1–73.8% respectively using an in-house assay.
Conclusions: Nucleic acid amplification testing for SARS-CoV-2 is highly specific. Nevertheless, when prevalence is low a significant proportion of initially positive results fail to confirm, and confirmatory testing substantially reduces the detection of false positives. Omitting additional testing in samples with higher prior detection probabilities focuses testing where it is clinically impactful and minimizes delay.
Pandemic preparedness
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Preparing for the next pandemic: reserve laboratory staff are crucial
Jordan P. Skittrall, Neil Bentley, Tim Wreghitt, Paul Silverston, Huina Yang, Sani H. Aliyu, Anna A. SmielewskaAbstract
Lack of laboratory staff was an important obstacle in scaling up covid-19 testing. Jordan Skittrall and colleagues consider how we can be better prepared in future.
All publications
See Jordan’s Google Scholar profile for a full list of his publications.