Equivalence of self- and staff-collected nasal swabs for the detection of viral respiratory pathogens

Abstract

Background: The need for the timely collection of diagnostic biosamples during symptomatic episodes represents a major obstacle to large-scale studies on acute respiratory infection (ARI) epidemiology. This may be circumvented by having the participants collect their own nasal swabs. We compared self- and staff-collected swabs in terms of swabbing quality and detection of viral respiratory pathogens.

Methodology/principal findings: We conducted a prospective study among employees of our institution during the ARI season 2010/2011 (December-March). Weekly emails were sent to the participants (n = 84), reminding them to come to the study center in case of new symptoms. The participants self-collected an anterior nasal swab from one nostril, and trained study personnel collected one from the other nostril. The participants self-collected another two swabs (one from each nostril) on a subsequent day. Human β-actin DNA concentration was determined in the swabs as a quality control. Viral respiratory pathogens were detected by multiplex RT-PCR (Seeplex RV15 kit, Seegene, Eschborn, Germany). Of 84 participants, 56 (67%) reported at least one ARI episode, 18 participants two, and one participant three. Self-swabbing was highly accepted by the participants. The amount of β-actin DNA per swab was higher in the self- than in the staff-collected swabs (p = 0.008). β-actin concentration was lower in the self-swabs collected on day 1 than in those collected on a subsequent day (p<0.0001). A respiratory viral pathogen was detected in 31% (23/75) of staff- and in 35% (26/75) of self-collected swabs (p = 0.36). With both approaches, the most frequently identified pathogens were human rhinoviruses A/B/C (12/75 swabs, 16%) and human coronavirus OC43 (4/75 swabs, 5%). There was almost perfect agreement between self- and staff-collected swabs in terms of pathogen detection (agreement = 93%, kappa = 0.85, p<0.0001).

Conclusions/significance: Nasal self-swabbing for identification of viral ARI pathogens proved to be equivalent to staff-swabbing in this population in terms of acceptance and pathogen detection.

Figure 1. Timeline of staff-collected (interrupted line) and self-collected (solid line) swabs.

A staff-collected and a self-collected swab were obtained on day 1 from separate nostrils. The participants were instructed to collect a self-swab from each nostril the next day, but the actual day of self-swabbing ranged from day 2 to day 6, as indicated by the triangle.

Figure 2. Human β-actin DNA concentration in staff- and self-collected swabs.

A. Human β-actin DNA concentration in staff- and self-collected swabs obtained according to the time scheme shown in Fig. 1. β-actin DNA concentration was determined by real-time PCR and is plotted on the y-axis as the number of molecules per swab. Boxes: upper border, 75^th percentile; lower border, 25^th percentile; bold horizontal line, median; whiskers, minimum and maximum excluding outliers (circles); circles, outlying values exceeding the 75^th percentile by >1.5 times the height of the box. B. β-actin DNA concentration per swab in relation to time elapsed between onset of ARI symptoms and the day of swabbing (r² = 0.02, p = 0.32).

Figure 3. Agreement in pathogen detection between staff- and self-swabs collected on the same day.

Swabs were designated positive if any of 15 respiratory viral pathogens were detected by real-time PCR (Seeplex RV15 ACE Detection kit, Seegene Germany, Eschborn, Germany). Concordant scenarios are shown on the left, discordant scenarios on the right.

Figure 4. Relation between β-actin DNA concentration and viral positivity status in staff- and self-collected swabs collected on the same day.

Analysis based on the data set used for Figure 2, but stratified according to viral detection status (+ positive, − negative). Y-axis: human β-actin DNA molecules per swab. P values: p = 0.186 for comparison between negative and positive staff-swabs; p = 0.404 for comparison between negative and positive self-swabs (Wilcoxon rank sum test).