Nasopharyngeal Flocked Swabs: An Optimal Method for Respiratory Virus Detection

Female medical worker doctor taking corona virus sample from potentially infected smiling black girl

Respiratory viral infections are a major cause of morbidity and mortality worldwide, especially in children. Timely diagnosis of these infections is crucial for clinical management. Traditionally, nasopharyngeal washes or aspirates have been considered the gold standard for respiratory virus sampling. However, flocked nasopharyngeal swabs are being increasingly used as an alternative sampling method in recent years. Evidence from multiple studies has shown that nasopharyngeal flocked swabs may be comparable or even superior to traditional nasopharyngeal washes for respiratory virus detection.

In a study published in Journal of Clinical Microbiology in 2011, nasopharyngeal flocked swabs were compared with nasopharyngeal aspirates for detection of common respiratory viruses in pediatric outpatients using real-time multiplexed PCR. The results showed that flocked swabs had significantly higher overall detection rates than aspirates for RSV, rhinovirus, adenovirus and other viruses. For RSV, the most important cause of bronchiolitis and pneumonia in children, there was no significant difference between the two sampling methods. Flocked swabs were also much preferred by patients and parents over the uncomfortable nasopharyngeal aspirate procedure. The findings suggest that flocked swabs can replace aspirates for respiratory virus screening in pediatric outpatients.

Another study in Journal of Virological Methods in 2012 also arrived at similar conclusions. The sensitivity of flocked swabs versus nasal washes for detection of RSV, parainfluenza virus, metapneumovirus and influenza was analyzed in hospitalized children less than 3 years old using real-time PCR. The results showed comparable sensitivities between the two sampling methods for most viruses, especially when specimens were collected on the same day. Viral yields were higher in nasal washes, but this did not translate to significant differences in diagnostic sensitivity. Based on patient tolerance and ease of use, the authors concluded that flocked swabs are a reasonable alternative to nasal washes for respiratory virus detection in hospitalized children.

The superior performance of nasopharyngeal flocked swabs is attributable to their innovative design. Traditional rayon swabs have suboptimal collection efficiency and release of epithelial cells. In contrast, flocked swabs are made of nylon fibers attached to a plastic shaft, which enhances uptake and release of large amounts of epithelial cells. The improved sample quality leads to higher detection rates of viruses using PCR-based methods. Besides sample collection, flocked swabs also have benefits in sample storage and transportation. The swab tip can be cut off directly into a tube of transport medium, allowing viruses to remain stable at room temperature for prolonged periods.

Given the accuracy, ease of use and patient acceptability, nasopharyngeal flocked swabs should be considered the preferred sampling method for respiratory virus testing in both outpatient and inpatient settings. The sensitivity of nucleic acid amplification tests like PCR is highly dependent on specimen quality, and flocked swabs deliver optimal quality. As PCR-based diagnostic techniques become more widespread, flocked swabs will likely replace conventional sampling methods. Implementing flocked swabs can improve diagnosis, save costs and reduce patient discomfort during respiratory virus screening. More studies on the performance of flocked swabs in adults, immunocompromised patients and for emerging respiratory viruses would further consolidate their role as the new standard for respiratory virus detection in clinical practice.

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