Comparison of nasopharyngeal flocked swabs and aspirates for rapid diagnosis of respiratory viruses in children

https://doi.org/10.1016/j.jcv.2007.12.003Get rights and content

Abstract

Background

The quality of clinical specimens is a crucial determinant for virological diagnosis.

Objectives

We compared the viral diagnostic yield for influenza A and respiratory syncytial virus (RSV) from the recently developed nasopharyngeal flocked swabs (NPFS) with nasopharyngeal aspirates (NPA) collected in parallel from 196 hospitalized children with acute respiratory infection during the peak period of influenza A and RSV activity in Hong Kong. Specimens were tested by RT-PCR for influenza A and RSV and viral load determined. They were also tested by direct immunofluorescence (DIF) for influenza A and B, RSV, parainfluenza types 1–3 and adenovirus.

Results

Both NPA and NPFS had excellent sensitivity (100%) for detecting influenza A by RT-PCR but NPA was slightly more sensitive than NPFS for detecting RSV by both RT-PCR (100% vs. 92.3%) and DIF (87.2% vs. 84.6%) and for detecting influenza A by DIF (90.2% vs. 82.9%). Viral load for influenza A in NPA and NPFS was not significantly different but that for RSV was higher in NPA.

Conclusion

NPA remains the optimal specimen for diagnosis of respiratory infections by RT-PCR and DIF. However, collection of NPFS is easier to perform in an out-patient setting, was more acceptable to parents and less likely to generate aerosols than NPA engendering potentially less infection control hazard.

Introduction

Acute respiratory infections are the most common illnesses of otherwise healthy adults and children and most of these infections are caused by viruses (Treanor, 2002). Furthermore, novel emerging viral respiratory infections (e.g. SARS) have the potential to cause explosive disease outbreaks with huge impact on economies and society in general (Peiris et al., 2004). Rapid viral diagnosis leads to optimized clinical care, reduced antibiotic use, helps infection control and is cost effective (Woo et al., 1997). Antigen detection methods have been commonly used for rapid respiratory viral diagnosis but PCR-based methods are now becoming more widely used. In all these methods the type and quality of the clinical specimen is of utmost importance. Nasopharyngeal aspirates (NPA) are generally considered the best specimens for rapid detection of respiratory viruses (Ahluwalia et al., 1987, Zambon, 1998, Macfarlane et al., 2005). However, obtaining a NPA is unpleasant to the patient, requires specialized equipment and a skilled operator for specimen collection and therefore difficult to obtain in an out-patient or field setting. Nasal swab specimens have been found to be less productive than NPA in some studies (Macfarlane et al., 2005) but not in others (Heikkinen et al., 2002). Nasopharyngeal swabs (NPS) have been reported by some to have comparable positivity rates to NPA (Frayha et al., 1989) although this is still controversial (Ahluwalia et al., 1987). Compared to NPA, conventional NPS swabs usually yield fewer epithelial cells for direct antigen detection by IF assay (Ahluwalia et al., 1987).

Recently a flocked-nasopharyngeal swab was designed with the aim of improving the yield of nasopharyngeal epithelial cells and enhancing diagnostic yield (Copan Diagnostics, Corona, CA). A study showed that flocked swabs yielded more cells and provided better clinical specimen when compared with nasal swab (Daley et al., 2006, Chernesky et al., 2006). However, there are still no direct comparisons between nasopharyngeal flocked swabs (NPFS) and NPA for the rapid diagnosis of respiratory viruses by direct immunofluorescence assay and PCR. We conducted a prospective study in children with acute respiratory disease comparing NPFS with NPA for the detection of influenza A and respiratory syncytial virus (RSV) by PCR and direct immunofluorescence (DIF) assays. We also compared the viral nucleic acid load in parallel NPA and NPFS specimens using quantitative real time PCR.

Section snippets

Patients and specimens

One hundred ninety-six hospitalized children under 18 years of age with acute respiratory tract infections at Queen Mary hospital from February to May 2007 were recruited. The study protocol was approved by the ethics committee of Queen Mary Hospital and written informed consent was obtained prior to recruitment. NPA and NPFS were collected in parallel from each patient. The NPA specimen was collected from one nostril and the NPS specimen from the other. Initially, children were randomized to

Diagnostic yield by NPA and NPFS specimens

Paired NPA and NPFS were collected from one hundred ninety-six pediatric patients recruited during February to May 2007 which is the peak influenza A and RSV season in Hong Kong. There were 113 males and 83 females with the mean age 6.3 months, range 1–89 months. RT-PCR was done on all specimens for influenza A and RSV. DIF was done on all specimens for influenza A and B, RSV, parainfluenza type 1, 2, 3 and adenovirus. Virus culture was done for all NPA specimens. RT-PCR or PCR was done for

Discussion

We compared the NPFS and NPA collected in parallel from 196 hospitalized pediatric patients for diagnosis of respiratory infections by DFA tests and for diagnosis of influenza A and RSV by RT-PCR. The reason for focusing on influenza A and RSV for the RT-PCR study was that these viruses were known to be the predominant respiratory virus infections occurring during the period of the study.

Specimens from either method yielded epithelial cells of good morphology and in adequate numbers for

Acknowledgements

We thank C.M. Pang, K.M. Chan and S.Y. Lam for technical assistance. We acknowledge research grants from the Research Grants Council of Hong Kong (HKU 7396/03M), Special Research Achievement Award from The University of Hong Kong to J.S.M.P. (10205969) and Research Fund for the Control of Infectious Diseases of Hong Kong Grant 04050492.

References (16)

  • S. Mitchell et al.

    Clinical assessment of a generic DNA amplification assay for the identification of respiratory adenovirus infections

    J Clin Virol

    (2003)
  • G. Ahluwalia et al.

    Comparison of nasopharyngeal aspirate and nasopharyngeal swab specimens for respiratory syncytial virus diagnosis by cell culture, indirect immunofluorescence assay, and enzyme-linked immunosorbent assay

    J Clin Microbiol

    (1987)
  • K.H. Chan et al.

    Evaluation of the Directigen FluA + B test for rapid diagnosis of influenza virus type A and B infections

    J Clin Microbiol

    (2002)
  • M. Chernesky et al.

    Use of flocked swabs and a universal transport medium to enhance molecular detection of Chlamydia trachomatis and Neisseria gonorrhoeae

    J Clin Microbial

    (2006)
  • P. Daley et al.

    Comparison of flocked and rayon swabs for collection of respiratory epithelial cells from uninfected volunteers and symptomatic patients

    J Clin Microbiol

    (2006)
  • H. Frayha et al.

    Nasopharyngeal swabs and nasopharyngeal aspirates equally effective for the diagnosis of viral respiratory disease in hospitalized children

    J Clin Microbiol

    (1989)
  • P. Gruteke et al.

    Practical implementation of a multiplex PCR for acute respiratory tract infections in children

    J Clin Microbiol

    (2004)
  • T. Heikkinen et al.

    Nasal swab versus nasopharyngeal aspirate for isolation of respiratory viruses

    J Clin Microbiol

    (2002)
There are more references available in the full text version of this article.

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