Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was first identified in Wuhan, China, in late 2019 and is the causative agent of the coronavirus disease 2019 (COVID-19) pandemic. Quantitative reverse-transcription polymerase chain reaction (qRT-PCR) represents the gold standard for diagnostic assays even if it cannot precisely quantify viral RNA copies. Thus, we decided to compare qRT-PCR with digital polymerase chain reaction (dPCR), which is able to give an accurate number of RNA copies that can be found in a specimen. However, the aforementioned methods are not capable to discriminate if the detected RNA is infectious or not. For this purpose, it is necessary to perform an endpoint titration on cell cultures, which is largely used in the research field and provides a tissue culture infecting dose per mL (TCID50/mL) value. Both research and diagnostics call for a model that allows the comparison between the results obtained employing different analytical methods. The aim of this study is to define a comparison among two qRT-PCR protocols (one with preliminary RNA extraction and purification and an extraction-free qRT-PCR), a dPCR and a titration on cell cultures. The resulting correlations yield a faithful estimation of the total number of RNA copies and of the infectious viral burden from a Ct value obtained with diagnostic routine tests. All these estimations take into consideration methodological errors linked to the qRT-PCR, dPCR and titration assays.

Due to the SARS-CoV-2 pandemic renewed attention has been directed towards viral neutralization assays and neutralizing antibodies quantification, for vaccine pre-clinical trials and determining vaccine efficacy over time. The gold standard to assess antibody titer is the plaque reduction neutralization test, an end-point assay which evaluates the highest serum antibody dilution that neutralizes viral replication, by inspecting the cytopathic effect induced on cell cultures. Here, we use planar, PEDOT:PSS-based organic electrochemical transistors for real-time, remote-controlled, reliable and fast electrical monitoring of the cytopathic effect induced by SARS29 CoV-2 on Vero E6 cell lines, allowing the quantification of serum neutralizing titer. Our low-cost and scalable device has the potential to speed-up large-scale viral neutralization screening without the need for cancerous staining or highly specialized operators. Finally, the technology could be easily transferred to assess neutralizing antibody response towards different viruses in their permissive cell substrates.

Nephropathic subjects with impaired immune responses show dramatically high infection rates of coronavirus disease 2019 (COVID-19). This work evaluated the ability to acquire and maintain protective antibodies over time in 26 hemodialysis patients and 21 kidney transplant recipients. The subjects were followed-up through quantitative determination of circulating SARS-CoV-2 S1/S2 IgG and neutralizing antibodies in the 6-month period after clinical and laboratory recovery. A group of 143 healthcare workers with no underlying chronic pathologies or renal diseases recovered from COVID was also evaluated. In both dialysis and transplanted patients, antibody titers reached a zenith around the 3rd month, and then a decline occurred on average between the 270th and 300th day. Immunocompromised patients who lost antibodies around the 6th month were more common than non-renal subjects, although the difference was not significant (38.5% vs 26.6%). Considering the decay of antibody levels below the positivity threshold (15 AU/mL) as “failure”, a progressive loss of immunisation was found in the overall population starting 6 months after recovery. A longer overall antibody persistence was observed in severe forms of COVID-19 (p = 0.0183), but within each group, given the small number of patients, the difference was not significant (dialysis: p = 0.0702; transplant: p = 0.1899). These data suggest that immunocompromised renal patients recovered from COVID-19 have weakened and heterogeneous humoral responses that tend to decay over time. Despite interindividual variability, an association emerged between antibody persistence and clinical severity, similar to the subjects with preserved immune function.

The incidence of total joint arthroplasty is increasing over time since the last decade and expected to be more than 4 million by 2030. As a consequence, the detection of infections associated with surgical interventions is increasing and prosthetic joint infections are representing both a clinically and economically challenging problem. Many pathogens, from bacteria to fungi, elicit the immune system response and produce a polymeric matrix, the biofilm, that serves as their protection. In the last years, the implementation of diagnostic methodologies reduced the error rate and the turn-around time: polymerase chain reaction, targeted or broad-spectrum, and next-generation sequencing have been introduced and they represent a robust approach nowadays that frees laboratories from the unique approach based on culture-based techniques.

Literature offers plenty of cases of immunocompromised patients, who develop chronic and severe SARS-CoV-2 infections. The aim of this study is to provide further insight into SARS-CoV-2 evolutionary dynamic taking into exam a subject suffering from follicular lymphoma, who developed a persistent infection for over 7 months. Eight nasopharyngeal swabs were obtained, and were analyses by qRT-PCR for diagnostic purposes. All of them were considered eligible (Ct < 30) for NGS sequencing. Sequence analysis showed that all sequences matched the B.1.617.2 AY.122 lineage, but they differed by few mutations identifying three genetically similar subpopulations, which evolved during the course of infection, demonstrating that prolonged replication is paralleled with intra-host virus evolution. These evidences support the hypothesis that SARS-CoV-2 adaptive capacities are able to shape a heterogeneous viral population in the context of immunocompromised patients. Spill-over of viral variants with enhanced transmissibility or immune escape capacities from these subjects is plausible.