PARTICIPANTS, METHODS, AND RESULTS

The study was conducted between November 1999 and March 2000 in a paediatric community based office practice and at the Hospital for Sick Children, Toronto, Canada. Paired lower nasal swabs (LNS) and high nasopharyngeal swabs (NPS) were obtained from each of 199 children with a median age of 1.5 years (range 11 days to 13.8 years), presenting with acute ARI. For LNS a cotton tipped swab was placed 1.0–1.5 cm into the nostril and rotated three or four times. For NPS, the swab was inserted 5.0–6.0 cm in the opposite nostril and the rotation procedure repeated. Swabs were submitted in transport medium for rapid diagnosis of influenza and respiratory syncytial virus (RSV) by direct immunofluorescence microscopy (DFA)³ using monoclonal antibodies (Light Diagnostics, Temecula, California), and by an influenza specific enzyme immunoassay (EIA; Directigen, Becton, Dickinson & Co.).³ Discomfort with each procedure was assessed in a subset of children. For those less than 3 years of age, cry duration was measured. In older children, a standard Oucher pain scale⁴ (score 0–100) and a validated Child Facial Coding System⁵ (score 1–100), using videotape recordings of 13 facial expressions was measured by a trained coder unaware of the study design. The study was approved by the Hospital for Sick Children Research Ethics Board and informed consent was obtained.

Of the 308 swabs analysed, influenza virus was detected in 27% (54 of 199) of LNS and 29% (57 of 199) of NPS using DFA (table 1). Influenza virus was detected in 26% (52 of 199) of LNS and 28% (55 of 199) of NPS using EIA. For RSV, the detection from LNS and NPS was identical at 20% (39 of 199) using DFA (table 1).

The sensitivity of LNS compared with NPS for influenza virus detection using DFA and EIA was 86% (95% CI: 81% to 91%) and 87% (95% CI: 83% to 92%) respectively, with identical specificities of 97% (95% CI: 95% to 99%). Positive predictive values were 91% (95% CI: 87% to 95%) and 92% (95% CI: 88% to 96%) using DFA and EIA respectively, and negative predictive values were identical at 95% (95% CI: 92% to 98%). The detection of RSV was comparable to that of influenza virus (table 1). Significantly less pain was experienced with LNS compared with NPS on all three outcomes measured. In two of the assessments, the measured pain was fourfold lower with LNS (table 2).

COMMENT

In this study nasal swabs were shown to be as effective as nasopharyngeal swabs in identifying respiratory viruses (influenza, RSV), consistent with a recent report showing a similar result for influenza when compared with nasopharyngeal aspirates.² Nasal swabs were also shown to be significantly less painful. Although the measurement of pain in this study was limited by the small sample size of convenience, the results were nevertheless both clinically and statistically significant. We conclude that nasal swabs should be considered the procedure of choice for the detection of respiratory viruses in children presenting with ARI.