Is wet swab superior to dry swab as an intranasal screening test?

Nasopharyngeal Swabs vs. Nasal Aspirates for Respiratory Virus Detection: A Systematic Review

Nasal pathogen detection sensitivities can be as low as 70% despite advances in molecular diagnostics. This may be linked to the choice of sampling method. A diagnostic test accuracy review for sensitivity was undertaken to compare sensitivity of swabbing to the nasopharynx and extracting nasal aspirates, using the PRISMA protocol, Cochrane rapid review methodology, and QUADAS-2 risk of bias tools, with meta-analysis of included studies. Sensitivities were calculated by a consensus standard of positivity by either method as the ‘gold standard.’ Insufficient sampling methodology, cross sectional study designs, and studies pooling samples across anatomical sites were excluded. Of 13 subsequently eligible studies, 8 had ‘high’ risk of bias, and 5 had ‘high’ applicability concerns. There were no statistical differences in overall sensitivities between collection methods for eight different viruses, and this did not differ with use of PCR, immunofluorescence, or culture. In one study alone, Influenza H1N1(2009) favored nasopharyngeal swabs, with aspirates having 93.3% of the sensitivity of swabs (p > 0.001). Similarly equivocal sensitivities were noted in reports detecting bacteria. The chain of sampling, from anatomical site to laboratory results, features different potential foci along which sensitivity may be lost. A fair body of evidence exists that use of a different sampling method will not yield more respiratory pathogens.

Evaluation of Methods for Sampling of Staphylococcus aureus and Other Staphylococcus Species from Indoor Surfaces

Objectives

Methicillin-resistant Staphylococcus aureus (MRSA) is an increasing public and occupational health concern. As transmission of MRSA can occur via contact with fomites, it is crucial to have sensitive methods for sampling of bacteria. The overall aim of this study was to obtain knowledge about methods and strategies for quantitative sampling Staphylococcus species on surfaces.

Methods

The study was designed as a comparative sampling experiment with different samplers [dipslide (two agar types), swabs (three brands, used wet and dry, and elution from swabs or plate diluted)] on smooth stainless steel surfaces spiked with MRSA and methicillin-sensitive S. aureus (MSSA). Furthermore, bacteria sampled from indoor surfaces with frequent or infrequent contact with hands were quantified and identified using matrix-assisted laser desorption-ionization time-of-flight (MALDI-TOF) mass spectrometry (MS).

Results

Pre-moistened swabs in combination with dilution plating and dipslides were more sensitive than dry swabs. For recovery of MRSA and MSSA from surfaces with eSwabs, at least 0.3–100 CFU MRSA cm⁻² and 5.3–8.6 CFU MSSA cm⁻² should be present. The sensitivities of pre-moistened eSwabs were approximately 10-fold higher than those of dipslides and pre-moistened viscose and cotton swabs. The variation in concentrations of Staphylococcus species in replicate sampling of adjacent squares on indoor surfaces was higher for surfaces frequently touched by hands than for surfaces infrequently touched. In total 16 different Staphylococcus species were identified, and S. aureus was found only in 2 of 66 surface samples. A considerable overlap was found between species in replicate sampling within an environment and between the air and surfaces within an environment.

Conclusions

Pre-moistened eSwabs in combination with dilution plating were found to be the best method for surface sampling of MSSA and MRSA. The method can be used for assessing the risk of exposure and transmission of MRSA from environmental surfaces. To obtain a reliable measure of concentrations and the presence of Staphylococccus species a higher number of samples should be taken from surfaces with hand contact than from surfaces dominated by sedimented bacteria.

Rapid Large-Scale COVID-19 Testing During Shortages

The Coronavirus disease 2019 (COVID-19) pandemic caused by the Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) has resulted in economic and social lockdowns in most countries all over the globe. Early identification of infected individuals is regarded as one of the most important prerequisites for fighting the pandemic and for returning to a ‘New Normal’. Large-scale testing is therefore crucial, but is facing several challenges including shortage of sample collection tools and of molecular biological reagents, and the need for safe electronic communication of medical reports. We present the successful establishment of a holistic SARS-CoV-2 testing platform that covers proband registration, sample collection and shipment, sample testing, and report issuing. The RT-PCR-based virus detection, being central to the platform, was extensively validated: sensitivity and specificity were defined as 96.8% and 100%, respectively; intra-run and inter-run precision were <3%. A novel type of sample swab and an in-house-developed RNA extraction system were shown to perform as good as commercially available products. The resulting flexibility guarantees independence from the current bottlenecks in SARS-CoV-2 testing. Based on our technology, we offered testing at local, national, and global levels. In the present study, we report the results from approx. 18,000 SARS-CoV-2 tests in almost 10,000 individuals from a low-frequency SARS-CoV-2 pandemic area in a homogenous geographical region in north-eastern Germany for a period of 10 weeks (21 March to 31 May 2020). Among the probands, five SARS-CoV-2 positive cases were identified. Comparative analysis of corresponding virus genomes revealed a diverse origin from three of the five currently recognized SARS-CoV-2 phylogenetic clades. Our study exemplifies how preventive SARS-CoV-2 testing can be set up in a rapid and flexible manner. The application of our test has enabled a safe maintenance/resume of critical local infrastructure, e.g., nursing homes where more than 5000 elderlies and caretakers got tested. The strategy outlined by the present study may serve as a blueprint for the implementation of large-scale preventive SARS-CoV-2 testing elsewhere.

Utilizing Moist or Dry Swabs for the Sampling of Nasal MRSA Carriers? An In Vivo and In Vitro Study

This study investigates the quantitative bacterial recovery of Methicillin-resistant Staphylococcus aureus (MRSA) in nasal screenings by utilizing dry or moistened swabs within an in vivo and an in vitro experimental setting. 135 nasal MRSA carriers were each swabbed in one nostril with a dry and in the other one with a moistened rayon swab. Quantitative bacterial recovery was measured by standard viable count techniques. Furthermore, an anatomically correct artificial nose model was inoculated with a numerically defined suspension of MRSA and swabbed with dry and moistened rayon, polyurethane-foam and nylon-flocked swabs to test these different settings and swab-materials under identical laboratory conditions. In vivo, quantities of MRSA per nostril in carriers varied between <10¹ and >10⁷ colony forming units, with a median of 2.15x10⁴ CFU. However, no statistically significant differences could be detected for the recovery of MRSA quantities when swabbing nasal carriers with moist or dry rayon swabs. In vitro testing confirmed the in vivo data for swabs with rayon, polyurethane and nylon-flocked tips, since pre-moistening of swabs did not significantly affect the quantities of retrieved bacteria. Therefore, pre-moistening of swabs prior to nasal MRSA sampling provides no advantage in terms of recovering greater bacterial quantities and therefore can be omitted. In addition, this situation can be mimicked in an in vitro model, thereby providing a useful basis for future in vitro testings of new swab types or target organisms for screening approaches.