Molecular accuracy vs antigenic speed: SARS-CoV-2 testing strategies

Real-world usage of mass rapid antigen testing for COVID-19 in long-term care facilities and support programmes: results from long-term surveillance in North-Eastern Germany

BACKGROUND

From December 2020 to February 2023, the research project ZEPOCTS operated as a central surveillance centre for COVID-19 rapid antigen tests (RATs) in the German state Mecklenburg-Western Pomerania (M-W). Since mid-December 2020, long-term care facilities (LTCF) as well as support programmes in M-W had been obliged by ordinance to report on-site RATs to this surveillance project. However, most studies have measured RATs in cross-sectional studies or short-term comparisons with smaller samples, and only a few studies have followed the long-term development of COVID-19 testing, even though the pandemic lasted more than two years. The aim of this article is to present the surveillance methods and provide an overview of the outcome development of the results of RATs in LTCF and support programmes as well as a comparison with the infection development of the pandemic.

METHODS

The project was designed as a prospective longitudinal surveillance study. The analysis includes around 6,2 million RATs of 1,015 facilities for 120 weeks. For comparative analysis of the RATs' development in the LTCF and regional development of the pandemic, several inferential correlation tests and a nonparametric multiple changepoint detection analysis with pruned exact linear time (PELT) and changepoints over a range of penalties (CROPS) were performed.

RESULTS

The results indicate that the weekly positivity rates of RATs and polymerase chain reaction (PCR) tests correlated highly. The changepoint analysis revealed that changepoints of increase are primarily found earlier in the PCR distribution. Both the use of RATs by inpatient long-term care facilities and the distribution of the positivity rate of support programmes differed significantly from the other categories.

CONCLUSIONS

The study demonstrated a delayed increase in the RATs positivity rate in the participating facilities compared to PCR positivity rate of public health data. Still, it was observed that the positivity rate of RATs evidently follows the pandemic dynamics. We conclude that a frequent large-scale testing strategy was feasible but should consider reasonable adjustments to preserve existing resources. Further research is necessary to identify improvements for future applications.

Clinical and molecular fingerprint of SARS-CoV-2 among hospital employees in a period of Omicron BA.2 dominance

In the spring of 2022, SARS-CoV-2 Omicron BA.2 peaked in Germany. The main burden was staff shortage. To achieve effective identification and management of infected persons as well as early reintegration of recovered persons, an infection-control outpatient clinic was established at the Bundeswehr Central Hospital Koblenz. This article reports a secondary data analysis of 663 people with 1,174 visits to the outpatient clinic. For asymptomatic contacts, no correlation was observed between PCR result and testing time or frequency. Although no significant symptoms were documented, a high correlation was found between a positive antigen self-test and positive PCR. For clearance, a median time until a negative test was obtained was 8-11 days. The PCR gold standard was compared with ECLIA antigen testing for all indications. The results of this study challenge the rationale for testing asymptomatic contacts. Solely symptom-driven diagnostics by PCR also do not seem to be effective. However, contact persons or symptomatic persons with a positive rapid antigen test should be tested further. Whether this testing is done by ECLIA or PCR does not seem to matter. Clearance testing after recovery prior to day 8 is also not appropriate.

Comparison of Extraction-based and Elution-based Polymerase Chain Reaction Testing, and Automated and Rapid Antigen Testing for the Diagnosis of Severe Acute Respiratory Syndrome Coronavirus 2

We aimed to compare the differences in testing performance of extraction‐based polymerase chain reaction (PCR) assays, elution‐based direct PCR assay, and rapid antigen detection tests for severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2). We used nasopharyngeal swab samples of patients with coronavirus disease 2019 (COVID‐19). We used the MagNA Pure 24 System (Roche Diagnostics K.K.) or magLEAD 12gC (Precision System Science Co., Ltd.) for RNA extraction, mixed the concentrates with either the LightMix Modular SARS‐CoV PCR mixture (Roche Diagnostics K.K.) or Takara SARS‐CoV‐2 direct PCR detection kit (Takara Bio Inc.), and amplified it using COBAS® z480 (Roche Diagnostics K.K.). For elution‐based PCR, we directly applied clinical samples to the Takara SARS‐CoV‐2 direct PCR detection kit before the same amplification step. Additionally, we performed Espline SARS‐CoV‐2 (Fuji Rebio Co., Ltd.) for rapid diagnostic test (RDT), and used Lumipulse SARS‐CoV‐2 antigen (Fuji Rebio Co., Ltd.) and Elecsys SARS‐CoV‐2 antigen (Roche Diagnostics K.K.) for automated antigen tests (ATs). Extraction‐based and elution‐based PCR tests detected the virus up to 214–216 and 210 times dilution, respectively. ATs remained positive up to 24–26 times dilution, while RDT became negative after 22 dilutions. For 153 positive samples, positivity rates of the extraction‐based PCR assay were 85.6% to 98.0%, while that of the elution‐based PCR assay was 73.2%. Based on the RNA concentration process, extraction‐based PCR assays were superior to elution‐based direct PCR assays for detecting SARS‐CoV‐2.