COMPARISON OF NASOPHARYNGEAL (NP) SWABS COLLECTED WITH PERNASAL FLOCKED SWABS VERSUS TO NP SWABS COLLECTED WITH TRADITIONAL TWISTED WIRE FIBER MINITIP FOR THE DETECTION OF RESPIRATORY VIRUSES USING SIMULFLUOR DFA

Introduction:  NP swabs and aspirates continue to be recommended as the specimen of choice for the detection of respiratory viruses in patients with symptoms compatible with a respiratory tract infection.  The yield of NP swabs depends on the quality and quantity of respiratory epithelial cells obtained.  The development of new flocked swabs capable of collecting more epithelial cells may thus result in improved sensitivity.

Objective:  The objective of this study was to compare the yield of respiratory epithelial cells using Copan flocked NP swabs placed in Starplex Multitrans S160 medium to that using traditional twisted wire fiber minitip swabs.

Methods:  Patients with a suspected viral respiratory tract infection had a NP swab collected using either the Copan flocked swab or the twisted wire swab and submitted to the microbiology lab for processing.  The type of swab collected was random and each patient had only one swab collected as per routine procedure.  In the lab, the swabs were used to make 2 cytospin direct smears for DFA (1 stained with Chemicon SimulFluor Respiratory virus Screen and one stained with SimulFluor Flu A/Flu B) and then, if sufficient material was available, inoculated into an R-Mix shell vial +/- an R-Mix TOO shell vial (Diagnostic Hybrids, USA) if the DFA was positive for Flu A/Flu B.  R-Mix shell vials were incubated for 48 hours before staining with Millipore (Chemicon) SimulFluor reagents.

Results:  A total of 269 flocked swabs and 159 wire swabs were collected between November 2007 and February 2008.  The yield of respiratory epithelial cells was substantially greater with the flocked swab vs the wire swab.  The detection of respiratory viruses was as follows:

Conclusions:  The Copan flocked swabs yielded more, as well as better quality respiratory epithelial cells which made the reading and interpretation of the DFA much easier.  The Millipore DFA reagent produced good clarity and well defined fluorescence even in the case of low positive samples. Those collecting swabs preferred the flocked swab because it was easier to break the shaft when placing it in the transport medium compared to the need to cut the shaft of the wire swab.  However, the yield of respiratory viruses did not differ between the two swabs.  This may be due to the fact that different patients were being tested (i.e. no patient had both swabs collected) and thus we could only determine the overall positivity rate using each swab.  As well, the number of swabs collected may have been too small to detect a difference.