Evaluation of an automated platform for the detection of HEV RNA in plasma and stool.

INTRODUCTION: We evaluated the performance of the automated Altostar HEV RNA platform for detecting HEV RNA. METHODS AND RESULTS: Clinical performance was determined by testing 81 plasma samples and 10 fecal samples manually quantified previously with the Realstar RT-PCR assay using the Magnapure instrument for extraction. The assays were concordant for 79/81 plasma samples (97.5%) and 10/10 (100%) fecal samples. The two plasma samples that tested negative with the Altostar assay had a very low HEV RNA concentration (1.6 and 1.4 log10 IU/ml). Quantitative results obtained with the automated platform and the manual workflow were highly correlated (ρ= 0.98, p<0.01). The intra-run and inter-run standard deviation were 0.09 IU/ml and 0.13 IU/ml respectively. The assay was linear from 2 to 6 log IU/ml. The limit of detection determined by Probit analysis with the WHO HEV RNA standard was 7.6 [95% CI: 4.4-52.5] IU/ml. CONCLUSIONS: The Altostar platform enables highly accurate testing for the detection of HEV RNA in stool and the quantification of HEV RNA in plasma. This allowed us to shorten turnaround times and to save time for the technical staff.

Human papillomavirus testing using HPV APTIMA® assay and an external cellularity control in self-collected samples.

In cervical cancer screening programs, the detection of high-risk human papillomavirus (HR-HPV) is now widely implemented on physician-collected samples and has expanded to include self-collected samples. The use of a cellularity control (CC) is needed to reduce false-negative HPV results. An external mRNA CC for the HPV APTIMA® assay was assessed for its analytical performance and the results were compared with both cervix cytobrush samples taken by physicians and self-collected vaginal samples from 148 women. The performance of the CC was adjusted to control for the presence of cellular mRNA in the ThinPrep® and Multitest® transport media. This CC is user-friendly but implies to perform two independent assays on PANTHER® automate. Self-collected vaginal sampling gives a lower median CC results (13.2 vs. 16.9 min) but a higher risk of negative CC results (3.3 vs. 0%). The usefulness of the CC for the HR-HPV assay may be optimized by the definition of a threshold for a minimum cell number to be tested to increase confidence in HPV-negative results. The systematic use of an RNA CC increases confidence for HPV RNA assays on self-collected vaginal samples.

Influence of the Delta Variant and Vaccination on the SARS-CoV-2 Viral Load.

Studies comparing SARS-CoV-2 nasopharyngeal (NP) viral load (VL) according to virus variant and host vaccination status have yielded inconsistent results. We conducted a single center prospective study between July and September 2021 at the drive-through testing center of the Toulouse University Hospital. We compared the NP VL of 3775 patients infected by the Delta (n = 3637) and Alpha (n = 138) variants, respectively. Patient's symptoms and vaccination status (2619 unvaccinated, 636 one dose and 520 two doses) were recorded. SARS-CoV-2 RNA testing and variant screening were assessed by using Thermo Fisher® TaqPath™ COVID-19 and ID solutions® ID™ SARS-CoV-2/VOC evolution Pentaplex assays. Delta SARS-CoV-2 infections were associated with higher VL than Alpha (coef = 0.68; p ≤ 0.01) independently of patient's vaccination status, symptoms, age and sex. This difference was higher for patients diagnosed late after symptom onset (coef = 0.88; p = 0.01) than for those diagnosed early (coef = 0.43; p = 0.03). Infections in vaccinated patients were associated with lower VL (coef = -0.18; p ≤ 0.01) independently of virus variant, symptom, age and sex. Our results suggest that Delta infections could lead to higher VL and for a longer period compared to Alpha infections. By effectively reducing the NP VL, vaccination could allow for limiting viral spread, even with the Delta variant.

FRET from phase-separated vesicles: An analytical solution for a spherical geometry.

Förster resonance energy transfer (FRET) is a powerful tool for investigating heterogeneity in lipid bilayers. In model membrane studies, samples are frequently unilamellar vesicles with diameters of 20-200 nm. It is well-known that FRET efficiency is insensitive to vesicle curvature in uniformly mixed lipid bilayers, and consequently theoretical models for FRET typically assume a planar geometry. Here, we use a spherical harmonic expansion of the acceptor surface density to derive an analytical solution for FRET between donor and acceptor molecules distributed on the surface of a sphere. We find excellent agreement between FRET predicted from the model and FRET calculated from corresponding Monte Carlo simulations, thus validating the model. An extension of the model to the case of a non-uniform acceptor surface density (i.e., a phase-separated vesicle) reveals that FRET efficiency depends on vesicle size when acceptors partition between the coexisting phases, and approaches the efficiency of a uniformly mixed bilayer as the vesicle size decreases. We show that this is an indirect effect of constrained domain size, rather than an intrinsic effect of vesicle curvature. Surprisingly, the theoretical predictions were not borne out in experiments: we did not observe a statistically significant change in FRET efficiency in phase-separated vesicles as a function of vesicle size. We discuss factors that likely mask the vesicle size effect in extruded samples.