Swab. A seemingly innocuous word that softly fills your mouth when you articulate it. It has suddenly gained fame with the spread of COVID-19. Pre-pandemic, it wasn’t even on our radar. We would most likely associate the word with the humble Q-tip. Nowadays, the trending word is associated with the painful invasion of our nasal cavity. Google’s English Dictionary defines a swab as “an absorbent pad or piece of material used in surgery and medicine for cleaning wounds, applying medication, or taking specimens.” Swabs are in fact among the most routinely employed single-use medical devices in healthcare settings.
There, you have it: the swab is a multi-functional material. In view of its recently gained notoriousness, let’s explore the famous nasopharyngeal swab. You may already have had a close and or rather, a deep encounter with it, so you are probably aware that it is used to collect viral particles from the upper part of the pharynx, connecting the nasal cavity above the soft palate, that is the nasopharynx. In other words, the swab needs:
To be long enough to reach the depth of your nose
To be as comfortable and gentle as possible to minimize the unpleasantness of having a foreign object introduced into your schnozzle.
To capture the highest amount of viruses that may be present in the nasal cavity but also to release most of them in the transport medium.
To be sterile to avoid cross-contamination with environmental micro-organisms that could affect the subsequent steps involved in testing the virus.
You can already imagine that swabs are packed with innovative features despite their modest appearance. Take step 3 in the list above for example. There are plenty of absorbent materials available: Some will be better adapted to wound treatment than to specimen collection, others are designed to collect bacteria rather than viruses. To explore the range of swabs used for various medical needs, let’s follow one of the leading and oldest specialists, MWE (Medical Wire & Equipment). MWE, a company created in 1952 is a leader in the world of diagnostics with particular expertise in devices for specimen acquisition and transportation.
The Dryswab™ Range - Medical Wire includes cotton, rayon, and dacron swabs (Figure 1). For most clinical applications, rayon, polyester, or polyurethane swab buds are recommended. Calcium alginate, albumin coated and cotton bud swabs are useful for other applications.
Cotton fibers are very absorbent and soft. They are safe and economical. Hence, pharmaceutical-grade spun cotton fibers are ubiquitous in many applications for healthcare to forensics. However, the structure of cotton does not allow the efficient release of collected specimens. Cotton fiber is a natural material that contains fatty acids with anti-bacterial properties. It is very unsuitable for the recovery of fastidious bacteria with downstream applications used in microbiology or for PCR applications systems. Therefore, it is not recommended for specimen collection.
Rayon is a synthetic material made from wood pulp. The rayon bud is a spun fiber that like cotton is soft, absorbent, and relatively low cost. It is recommended for specimen collection and transport of live microorganisms.
Figure 1. Illustration of different types of Dryswab buds (illustration courtesy of MWE)
Dacron was the brand name coined by DuPont to describe a synthetic spun fiber made from polyester. Although no longer carried, the brand name Dacron is still used by some manufacturers. Swabs from Medical Wire with polyester buds (such as Dryswabs™) are particularly recommended for use in specimen collection in microbiology, rapid test diagnostics, and PCR analysis. The polyester buds are not as absorbent as cotton or rayon, but their release properties are first-rate which may explain their higher cost.
Polyurethane foam buds
The US FDA and CDC recommend polyurethane swabs for diagnostic testing. Medical Wire developed polyurethane foam buds adapted to various needs. A benefit of employing polyurethane buds is the ability to modify their sizes, shapes, and porosities. Reticulated (open-cell) polyurethane foam, used in the MWE Sigma range, enables reagents to flow through completely, allowing substantial access to sample materials. The expansive surface area permits the capture of a maximum quantity of target fluids, while not sticking to those fluids imparting the high recovery of sample material. The soft foam bud is more comfortable for patients and has significant advantages for both conventional and molecular methods.
Flocking is a procedure that applies short fibers called flock—cut from tow (a loose rope of thin continuous strands). A variety of flocked fibers, such as the conventional nylon or the more advanced polyester flock fibers may be used in the manufacturing of these specimen collection devices.
PurFlock® and Hydraflock® fibers are microscopic multifilament polymer fibers that are aligned electrostatically and bonded onto the surface of the end of the swab shaft. The result is a soft, fine velvety layer of individual fibers at the extremity of the shaft. This process creates a vast surface area, with practically the whole length of fiber being accessible for contact with the test surface. The individual fibers have various lengths which creates multiple outside layers for enhanced contact on irregular surfaces. Moreover, the hang of the outer ends, instead of being bound with a matrix, favors almost complete elution of the collected specimen from the bud into the transport or testing liquid. The sensitivity is highly enhanced. Both the PurFlock® and Hydraflock® fibers work in this way, but the effect is enhanced with Hydraflock® because the individual fibers radiate from the outer end to create an expansive architecture that supports rapid and extremely effective absorption and elution (Figure 2).
Figure 2. Illustration depicting the appearance of flocked swabs and enlarged details of Hydraflock (top) and Purflock (bottom) fibers structure (Illustration courtesy of MWE).
It becomes apparent that the buds from MWE swabs are diverse and varied. They are designed to serve many purposes. The shafts are also smartly designed. The material, the flexibility, diameter, and length of the shafts vary depending on the sample to be collected. As for nasopharyngeal swabs, MWE ensures that all clinical Transwab® products comply with the CLSI standard M40-A2 (for the Quality Control of Microbiology Specimen Transport Devices).
Solutions offered by MWE for the collection and transport of samples obtained from patients contain many other features. Take, for example, Sigma-MM. It combines all the elements for the new era of liquid preanalytical microbiology while remaining completely suitable for conventional methodologies.
The specimen is collected by swab into a tube containing a specially formulated liquid transport medium. Recommended ranges of products for SARS-CoV-2 collection and transport include Σ-VCM (Universal transport for Viruses, Chlamydia, Mycoplasma & Ureaplasmas), Σ-Virocult, Σ-MM. Some of the characteristics of the elements of the transport kit are summarized below:
New collection vial:
Screw cap-for sample integrity and security
Compatible with most automatic decapping systems
Integral swab capture-no further manual handling of swab shaft required
Colour code caps according to format and applications
Self-standing for convenience
Inner conical base-can be centrifuged
Soft polyurethane buds preferred by patients
High absorbency for optimum sample uptake
Open-cell for complete flow-through of medium and reagents
Maximum release of microorganisms
Entire specimen is released into liquid phase
Breakpoint for easy handling ensures exact fit of swab in tube and swab capture
Fine tip option for urethral and nasopharyngeal specimens
Treatment of shaft with antibiotic to avoid cross-contamination
As for the liquid medium, it inactivates highly infectious pathogens rendering specimens safe for transport and molecular analysis. For example, ∑-MM™ solution has the following features:
∑-MM™ solution rapidly kills microorganisms, including bacteria, mycobacteria, and viruses
Suitable for highly infectious clinical specimens
DNases and RNases immediately inactivated
DNA and RNA preserved for molecular testing
Can be used with any swab or liquid specimen
These features have a number of advantages:
Powerful reagents kill deadly pathogens immediately
Safe and stable for transport at ambient temperature
Suitable for all microorganisms
Effective for viruses, including Coronavirus
Effective for bacteria including mycobacteria
For further information do not hesitate to contact us at sales(at)alleight.com or visit MWE.
Please do not hesitate to comment or request any blogs for the future, we will gladly try to accommodate.
(PurFlock® and Hydraflock® are registered trademarks of Puritan Medical Products Co., LLC)