Evaluation of Serological Tests for SARS-CoV-2: Implications for Serology Testing in a Low-Prevalence Setting.

BACKGROUND: Robust serological assays are essential for long-term control of the COVID-19 pandemic. Many recently released point-of-care (PoCT) serological assays have been distributed with little premarket validation. METHODS: Performance characteristics for 5 PoCT lateral flow devices approved for use in Australia were compared to a commercial enzyme immunoassay (ELISA) and a recently described novel surrogate virus neutralization test (sVNT). RESULTS: Sensitivities for PoCT ranged from 51.8% (95% confidence interval [CI], 43.1%-60.4%) to 67.9% (95% CI, 59.4%-75.6%), and specificities from 95.6% (95% CI, 89.2%-98.8%) to 100.0% (95% CI, 96.1%-100.0%). ELISA sensitivity for IgA or IgG detection was 67.9% (95% CI, 59.4%-75.6%), increasing to 93.8% (95% CI, 85.0%-98.3%) for samples >14 days post symptom onset. sVNT sensitivity was 60.9% (95% CI, 53.2%-68.4%), rising to 91.2% (95% CI, 81.8%-96.7%) for samples >14 days post symptom onset, with specificity 94.4% (95% CI, 89.2%-97.5%). CONCLUSIONS: Performance characteristics for COVID-19 serological assays were generally lower than those reported by manufacturers. Timing of specimen collection relative to onset of illness or infection is crucial in reporting of performance characteristics for COVID-19 serological assays. The optimal algorithm for implementing serological testing for COVID-19 remains to be determined, particularly in low-prevalence settings.

Characterisation of Treponema pallidum lineages within the contemporary syphilis outbreak in Australia: a genomic epidemiological analysis.

BACKGROUND: The incidence of syphilis has increased markedly in the past decade in high-income countries, including Australia. To date, however, genomic studies of Treponema pallidum have focused mainly on the northern hemisphere. Here, we aimed to characterise the lineages of T pallidum driving the current syphilis epidemic in Australia. METHODS: In this genomic epidemiological analysis, using phylogenomic and phylodynamic analyses, we analysed 456 high-quality T pallidum genomes collected from clinical samples in Australia between Oct 19, 2005, and Dec 31, 2020, and contextualised this information with publicly available sequence data. We also performed detailed genomic characterisation of putative antimicrobial resistance determinants, in addition to correlating single-locus typing of the TP0548 allele with the T pallidum phylogeny. FINDINGS: Phylogenomic analyses identified four major sublineages circulating in Australia and globally, two belonging to the SS14 lineage, and two belonging to the Nichols lineage. Australian sublineages were further delineated into twelve subgroups, with five of the six largest subgroups associated with men who have sex with men, and the sixth lineage was predominantly associated with heterosexual people. Most Australian T pallidum genomes (398 [87%] of 456) were genotypically macrolide resistant, and TP0548 typing correlated significantly with T pallidum genomic subgroups. INTERPRETATION: These findings show that the current syphilis epidemic in Australia is driven by multiple lineages of T pallidum, rather than one distinct outbreak. Major subgroups of T pallidum in Australia have emerged within the past 30 years, are closely related to global lineages, and circulate across different sexual networks. In conjunction with improved testing and treatment, these data could better inform the control of syphilis in Australia. FUNDING: National Health and Medical Research Council, Australian Research Council.

The characterization of mobile colistin resistance (mcr) genes among 33 000 Salmonella enterica genomes from routine public health surveillance in England.

To establish the prevalence of mobile colistin resistance (mcr) genes amongst Salmonella enterica isolates obtained through public health surveillance in England (April 2014 to September 2017), 33 205 S. enterica genome sequences obtained from human, food, animal and environmental isolates were screened for the presence of mcr variants 1 to 8. The mcr-positive genomes were assembled, annotated and characterized according to plasmid type. Nanopore sequencing was performed on six selected isolates with putative novel plasmids, and phylogenetic analysis was used to provide an evolutionary context for the most commonly isolated clones. Fifty-two mcr-positive isolates were identified, of which 32 were positive for mcr-1, 19 for mcr-3 and 1 for mcr-5. The combination of Illumina and Nanopore sequencing identified three novel mcr-3 plasmids and one novel mcr-5 plasmid, as well as the presence of chromosomally integrated mcr-1 and mcr-3. Monophasic S. enterica serovar Typhimurium accounted for 27/52 (52 %) of the mcr-positive isolates, with the majority clustering in clades associated with travel to Southeast Asia. Isolates in these clades were associated with a specific plasmid range and an additional extended-spectrum beta-lactamase genotype. Routine whole-genome sequencing for public health surveillance provides an effective screen for novel and emerging antimicrobial determinants, including mcr. Complementary long-read technologies elucidated the genomic context of resistance determinants, offering insights into plasmid dissemination and linkage to other resistance genes.