Evaluation of the Roche antigen rapid test and a cell culture-based assay compared to rRT- PCR for the detection of SARS-CoV-2: A contribution to the discussion about SARS-CoV-2 diagnostic tests and contagiousness.

Background: The most sensitive method to detect SARS-CoV-2 relies on rRT-PCR; however, viral RNA can be detected weeks/months after clinical resolution. Since rRT-PCR cannot discern between non- and infectious virus, it is unclear whether the presence of viral RNA after recovery reflects infectious SARS-CoV-2. However, recent studies suggest a positive correlation between antigen rapid tests (Ag-RDT) and virus isolation that is more suited to assess contagiousness. Objectives: To assess the utility of SARS-CoV-2 diagnostic tests in different settings we evaluated the performance of Ag-RDT-based and a cell culture-based SARS-CoV-2 assay in comparison to rRT-PCR. Study design: A total of 61 Nasopharyngeal-Swabs tested positive by cobasⓇ SARS-CoV-2 rRT-PCR were in parallel evaluated with the Roche Ag-RDT and a cell culture-based assay to detect SARS-CoV-2. Results: SARS-CoV-2 was successfully isolated in 51/61 samples corresponding to 83.6%, which was 97.3% or 96.2% when considering samples with E-gene Ct-value <25 and <28, respectively. In comparison, the Ag-RDT showed an overall sensitivity of 85.2%, that increased to 100% and 96.2% using an E-gene Ct-value cut-off of <25 and <28, respectively. There was an overall good agreement between the commercial Ag-RDT and our in-house cell culture-based SARS-CoV-2 detection assay. However, SARS-CoV-2 could be isolated from two samples that tested negative by Ag-RDT. Conclusions: Our results support the use of the Roche Ag-RDT to detect SARS-CoV-2 exposure in large scale populations. However, it is recommended to use rRT-PCR, potentially in conjunction with cell culture-based SARS-CoV-2 assay, to support clinicians in making decisions regarding fragile patient groups.

Phenotypic testing of patient herpes simplex virus type 1 and 2 isolates for acyclovir resistance by a novel method based on real-time cell analysis.

BACKGROUND: Acyclovir (ACV) is the most commonly used drug for herpes simplex virus (HSV) infection therapy. Prolonged antiviral therapy or prophylaxis in immunocompromised patients may promote the development of drug-resistant strains. Due to the high polymorphism in genes involved in drug resistance, phenotypic methods, although work-intensive, are still required to test drug susceptibility. Real-time cell analysis (RTCA) based methods could offer a rapid and less labor-intensive alternative for phenotypic testing of ACV resistance. OBJECTIVE: To investigate the utility of a new RTCA based assay (RTCAA) to test acyclovir susceptibility of HSV clinical isolates. STUDY DESIGN: Four reference strains and 93 clinical isolates (60 HSV-1 and 33 HSV-2) were tested by RTCAA. In the presence of ACV concentrations from 2.2 to 140.8 µM, Vero cells were infected with different virus dilutions. IC50 values were calculated by dose-response curve (DRC) with area-under-curve (AUC) method. The reference strains and 22 clinical isolates were additionally tested by dye-uptake assay, and IC50 values of both methods were compared. RESULTS: IC50 values from RTCAA and dye-uptake assays were positively correlated (Spearman's rho = 0.897, p < 0.001) and quantitatively agreed (Bland-Altman plot). Based on a cut-off of 4 µM for HSV-1 and 13 µM for HSV-2, 87 isolates were classified as ACV-sensitive and 6 isolates as ACV-resistant. The reference strains showed the expected results of ACV susceptibility. CONCLUSION: RTCAA agrees well with the dye-uptake assay. Compared with other phenotypic methods, RTCAA requires less manipulation, reduces the workload and the turnaround time, and appears to be an objective and reliable method to test ACV susceptibility.

The sensitivity of an interferon-γ release assay in microbiologically confirmed pediatric tuberculosis.

UNLABELLED: This study aimed at determining the sensitivity of a whole blood interferon-γ release assay (IGRA) among children with microbiologically confirmed tuberculosis in a high-burden country. Children with a diagnosis of tuberculosis based on clinical and radiographic assessment were tested with an IGRA in addition to microbiologic examination of appropriate specimens for acid-fast bacilli, mycobacterial rRNA, and observation for growth of Mycobacterium tuberculosis on appropriate culture media. Of the 405 children with a clinical diagnosis of tuberculosis, 91 (22.5 %) had microbiologically confirmed tuberculosis, of whom 81 were tested with an IGRA. A positive result was obtained in 43 (sensitivity 53.1 %, 95 % confidence interval 42.3 to 63.6 %), uninfluenced by age, sex, or disease manifestation. CONCLUSIONS: The sensitivity of a whole blood interferon-γ release assay in microbiologically confirmed pediatric tuberculosis was low. An IGRA cannot, thus, be used as rule-in test, but it might be useful to rule in tuberculosis among children in whom tuberculosis is notoriously difficult to confirm microbiologically.