Virus variant-specific clinical performance of SARS coronavirus two rapid antigen tests in point-of-care use, from November 2020 to January 2022

OBJECTIVES

Antigen rapid diagnostic tests (RDTs) for SARS coronavirus 2 (SARS-CoV-2) are quick, widely available, and inexpensive. Consequently, RDTs have been established as an alternative and additional diagnostic strategy to quantitative reverse transcription polymerase chain reaction (RT-qPCR). However, reliable clinical and large-scale performance data specific to a SARS-CoV-2 virus variant of concern (VOC) are limited, especially for the Omicron VOC. The aim of this study was to compare RDT performance among different VOCs.

METHODS

This single-centre prospective performance assessment compared RDTs from three manufacturers (NADAL, Panbio, MEDsan) with RT-qPCR including deduced standardized viral load from oropharyngeal swabs for detection of SARS-CoV-2 in a clinical point-of-care setting from November 2020 to January 2022.

RESULTS

Among 35 479 RDT/RT-qPCR tandems taken from 26 940 individuals, 164 of the 426 SARS-CoV-2 positive samples tested true positive with an RDT corresponding to an RDT sensitivity of 38.50% (95% CI, 34.00-43.20%), with an overall specificity of 99.67% (95% CI, 99.60-99.72%). RDT sensitivity depended on viral load, with decreasing sensitivity accompanied by descending viral load. VOC-dependent sensitivity assessment showed a sensitivity of 42.86% (95% CI, 32.82-53.52%) for the wild-type SARS-CoV-2, 43.42% (95% CI, 32.86-54.61%) for the Alpha VOC, 37.67% (95% CI, 30.22-45.75%) for the Delta VOC, and 33.67% (95% CI, 25.09-43.49%) for the Omicron VOC. Sensitivity in samples with high viral loads of ≥10⁶ SARS-CoV-2 RNA copies per mL was significantly lower in the Omicron VOC (50.00%; 95% CI, 36.12-63.88%) than in the wild-type SARS-CoV-2 (79.31%; 95% CI, 61.61-90.15%; p 0.015).

DISCUSSION

RDT sensitivity for detection of the Omicron VOC is reduced in individuals infected with a high viral load, which curtails the effectiveness of RDTs. This aspect furthert: limits the use of RDTs, although RDTs are still an irreplaceable diagnostic tool for rapid, economic point-of-care and extensive SARS-CoV-2 screening.

Surgical Fixation of Calcaneal Beak Fractures—Biomechanical Analysis of Different Osteosynthesis Techniques

The calcaneal beak fracture is a rare avulsion fracture of the tuber calcanei characterized by a solid bony fragment at the Achilles tendon insertion. Treatment usually requires osteosynthesis. However, lack of biomechanical understanding of the ideal fixation technique persists. A beak fracture was simulated in synthetic bones and assigned to five different groups of fixation: A) 6.5-mm partial threaded cannulated screws, B) 4.0-mm partial threaded cannulated screws, C) 5.0-mm headless cannulated compression screws, D) 2.3-mm locking plate, and E) 2.8-mm locking plate. Different traction force levels were applied through an Achilles tendon surrogate in a material-testing machine on all stabilized synthetic bones. Outcome measures were peak-to-peak displacement, total displacement, plastic deformation, stiffness, visual-fracture-line displacement, and mode of implant failure. The 2.3- and 2.8-mm plating groups showed a high drop-out rate at 100 N tension force and failed under higher tension levels of 200 N. The fracture fixation using 4.0-mm partial threaded screws showed a significantly higher repair strength and was able to withhold cyclic loading up to 300 N. The lowest peak-to-peak displacement and the highest load-to-failure and stiffness were provided by fracture fixation using 6.5-mm partial threaded cannulated screws or 5.0-mm headless cannulated compression screws. As anticipated, large 6.5-mm screw diameters provide the best biomechanical fixation. Surprisingly, the 5.0-mm headless cannulated compression screws yield reliable stability despite the absent screw head and washer. When such large screws cannot be applied, 4.0-mm screws also allow reasonable fixation strength. Plate fixation should be implemented with precaution and in combination with a restrictive postoperative motion protocol. Finally, clinical cases about the surgical application and recovery are included.

Clinical performance evaluation of SARS-CoV-2 rapid antigen testing in point of care usage in comparison to RT-qPCR

BACKGROUND

Antigen rapid diagnostic tests (RDT) for SARS-CoV-2 are fast, broadly available, and inexpensive. Despite this, reliable clinical performance data from large field studies is sparse.

METHODS

In a prospective performance evaluation study, RDT from three manufacturers (NADAL®, Panbio™, MEDsan®, conducted on different samples) were compared to quantitative reverse transcription polymerase chain reaction (RT-qPCR) in 5 068 oropharyngeal swabs for detection of SARS-CoV-2 in a hospital setting. Viral load was derived from standardised RT-qPCR Cycle threshold (Ct) values. The data collection period ranged from November 12, 2020 to February 28, 2021.

FINDINGS

The sensitivity of RDT compared to RT-qPCR was 42·57% (95% CI 33·38%-52·31%). The specificity was 99·68% (95% CI 99·48%-99·80%). Sensitivity declined with decreasing viral load from 100% in samples with a deduced viral load of ≥108 SARS-CoV-2 RNA copies per ml to 8·82% in samples with a viral load lower than 104 SARS-CoV-2 RNA copies per ml. No significant differences in sensitivity or specificity could be observed between samples with and without spike protein variant B.1.1.7. The NPV in the study cohort was 98·84%; the PPV in persons with typical COVID-19 symptoms was 97·37%, and 28·57% in persons without or with atypical symptoms.

INTERPRETATION

RDT are a reliable method to diagnose SARS-CoV-2 infection in persons with high viral load. RDT are a valuable addition to RT-qPCR testing, as they reliably detect infectious persons with high viral loads before RT-qPCR results are available.

FUNDING

German Federal Ministry for Education and Science (BMBF), Free State of Bavaria.

Cement-augmented screw fixation for calcaneal fracture treatment: a biomechanical study comparing two injectable bone substitutes

Background

The role of cement-augmented screw fixation for calcaneal fracture treatment remains unclear. Therefore, this study was performed to biomechanically analyze screw osteosynthesis by reinforcement with either a calcium phosphate (CP)-based or polymethylmethacrylate (PMMA)-based injectable bone cement.

Methods

A calcaneal fracture (Sanders type IIA) including a central cancellous bone defect was generated in 27 synthetic bones, and the specimens were assigned to 3 groups. The first group was fixed with four screws (3.5 mm and 6.5 mm), the second group with screws and CP-based cement (Graftys® QuickSet; Graftys, Aix-en-Provence, France), and the third group with screws and PMMA-based cement (Traumacem™ V+; DePuy Synthes, Warsaw, IN, USA). Biomechanical testing was conducted to analyze peak-to-peak displacement, total displacement, and stiffness in following a standardized protocol.

Results

The peak-to-peak displacement under a 200-N load was not significantly different among the groups; however, peak-to-peak displacement under a 600- and 1000-N load as well as total displacement exhibited better stability in PMMA-augmented screw osteosynthesis compared to screw fixation without augmentation. The stiffness of the construct was increased by both CP- and PMMA-based cements.

Conclusion

Addition of an injectable bone cement to screw osteosynthesis is able to increase fixation strength in a biomechanical calcaneal fracture model with synthetic bones. In such cases, PMMA-based cements are more effective than CP-based cements because of their inherently higher compressive strength. However, whether this high strength is required in the clinical setting for early weight-bearing remains controversial, and the non-degradable properties of PMMA might cause difficulties during subsequent interventions in younger patients.

The 'swing-door' technique for uncinectomy in endoscopic sinus surgery

Uncinectomy is an important step in endoscopic sinus surgery. The traditional method of performing uncinectomy has the risk of penetration of the lamina papyracea with orbital fat exposure. If the orbital penetration is not recognized, major complications may follow. In this study the authors used historical consecutive controls to compare the incidence of orbital penetration, identification of the natural ostium and lacrimal apparatus injury by the traditional surgical technique and a new technique of uncinectomy. Six hundred and thirty-six uncinectomies have been performed using the 'swing-door' technique. The 636 uncinectomies performed prior to changing techniques were used as historical controls. The incidence of orbital penetration (six compared to 0; p < 0.05) and ostium non-identification (42 not identified as compared to 0; p < 0.001) was significantly less with the new technique. One lacrimal injury occurred with the 'swing-door' technique compared to zero with the standard technique (p > 0.05). The techniques are described and the complications discussed. The authors recommend this technique as it is easy to learn, allows removal of the uncinate flush with the lateral nasal wall and allows easy identification of the natural ostium of the maxillary sinus.

'Bath-plug' technique for the endoscopic management of cerebrospinal fluid leaks

In the past cerebrospinal fluid (CSF) leaks were managed via a craniotomy with intradural repair. With the advent of endoscopic sinus surgery, transnasal repair has become more popular. The comparatively low morbidity and high success rate of endoscopic repair has made it the treatment of choice for CSF leak repair. As more surgeons practice endoscopic sinus surgery, the incidence of iatrogenic CSF leaks has increased. It is important that endoscopic sinus surgeons be aware of the techniques for closing such leaks. The aim of this study is to present a new technique for the endoscopic repair of CSF leaks. Since the technique was devised the authors have used the technique on six patients. All patients had lumbar drains inserted and five patients had intra-thecal fluorescein inserted for location of the leak. All repairs have been successful with an average follow-up of 13 months. The technique consists of introducing a fat plug with a specifically secured vicryl suture into the intradural space and placing traction on the suture to seal the defect much as a bath plug seals a bath. There were no complications in any of the patients either intra- or post-operatively. The difficulties and possible complications of the technique as well as the use of a lumbar drain and intra-thecal fluorescein are discussed.

Endoscopic transnasal dacryocystorhinostomy. Results in 21 patients

The transnasal endoscopic approach to the nasolacrimal sac was successfully applied in 20 out of 23 operations. The patients were followed up for 4-26 months, the first 21 operations having been performed in August 1988. Twenty-one nasolacrimal sacs had primary endoscopic transnasal surgery and 2 had previous failed external operations. Five operations were revised of which 3 were still unsuccessful.

Endoscopic transnasal dacryocystorhinostomy

The rigid Hopkins endoscope has been applied to simplify the operation of dacryocystorhinostomy, preventing unnecessary trauma to the medial orbital tissues. The success of the surgical technique is absolutely dependent on a thorough knowledge of the relevant surgical anatomy.

The middle ear transformer mechanism: man versus mouse

The anatomy and physiology of the middle ear transformer mechanism in man and a species of rodent, desmodillus auricularis, are compared. This rodent's middle ear mechanism has a transformer ratio of 147:1 as compared to 18,3:1 in man--some 8 times greater. The reasons for this difference are given and possible applications to middle ear surgery are suggested.