Nylon Flocked Swabs Versus Rayon Swabs for Respiratory Viral Recovery of Pediatric Nasopharyngeal Specimens: Which Is Better?


Background: When diagnosing respiratory viral illness using nasopharyngeal swabs, specimen quality has always been a concern for the Clinical Virology laboratory and the clinician. The gold standard, the M4 swab, has been used as the universal collecting device. A new flocked swab designed to optimize both the collection and transport of respiratory samples appears to yield more virus. Increased viral recovery suggests we may be able to identify more patients with influenza and respiratory syncytial virus (RSV).

During the 2006-2007 influenza season we prospectively enrolled infants and children up to 18 years of age admitted to the Cleveland Clinic Children’s Hospital with respiratory symptoms. After informed consent each patient underwent nasopharyngeal swabbing with the rayon MicroTest M4 swab (placed in M4 transport medium) and the Flocked swab (in Copan universal transport medium). Clinical information was also collected at the time of enrollment such as age, sex, presence of cough, wheezing, nasal congestion, fever and rhinorrhea.

Objective: To evaluate the viral recovery from nasopharyngeal swabs for influenza A, influenza B, RSV, and human metapneumovirus (hMPV) comparing the new nylon flocked swab (COPAN Diagnostic Inc., Corona, CA) to the standard MicroTest M4 swab (Remel, Lenexa, KS) in symptomatic pediatric patients admitted to the hospital.

Materials and Methods: Sixty nasopharyngeal respiratory specimens were collected from 30 symptomatic children admitted to the hospital and extracted by Easy-Mag (NucliSENS®, BioMerieux Inc, Durham, NC) and tested by Real Time-PCR (RT-PCR) and direct fluorescence assay (DFA). ProFlu-1 and Pro hMPV assays (Prodesse, Inc., Waukesha, WI) are one-step RT-PCR assays based on: nucleic acid extraction, reverse transcription to generate complementary DNA (cDNA) from target RNA, and amplification and detection of target cDNA by using specific primers and probes. RT-PCR was performed using Rotor-Gene (Corbett Inc, San Francisco, CA) and DFA was performed using reagents from Diagnostic Hybrids per standard protocol.

Results:Fifty-six nasopharyngeal swabs (56 M4, 56 flocked) were tested by RTPCR and DFA. M4 and flocked swab results were compared. Preliminary results of RT-PCR and DFA showed 18 out of 56 patients (32.0 %) were positive for respiratory viruses (5 RSV, 3 influenza A, 5 influenza B, and 5 hMPV). RT-PCR appears to be more sensitive than DFA as DFA only detected 13 of 56 positive samples. M4 and flocked swabs showed comparable results.

Conclusion: Although our preliminary numbers are small, at this point we are unable to show increased viral recovery with the flocked swab. Additional study enrollment is currently ongoing. However, M4 and flocked swabs both detected the same number of positive symptomatic patients from the nasopharyngeal samples.