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

Abstract

Paired nasopharyngeal aspirate (NPA) and nasopharyngeal swab (NPS) specimens obtained from each of 32 hospitalized infants with X-ray-confirmed pneumonia (91%) or bronchiolitis were tested for respiratory syncytial virus (RSV) infection by virus culture, the indirect immunofluorescent-antibody (IFA) technique, enzyme-linked immunosorbent assay (ELISA; Ortho Diagnostic Systems, Inc.), and spot hybridization with a human genomic probe to quantitate cellular DNA. RSV was isolated in cell cultures from 72% (23 of 32) of patients by using NPA specimens compared with 47% (15 of 32) by using NPS specimens. With tissue culture positivity as the reference test, the sensitivities of the ELISA on NPA and NPS specimens were found to be 69% (16 of 23) and 61% (14 of 23), respectively, with a specificity and a positive predictive value from both sites of 100%. The sensitivities of the IFA technique compared with the cell culture on NPA and NPS specimens were 61% (14 of 23) and 52% (12 of 23) with specificities of 89 and 78% and positive predictive values of 96 and 92%, respectively. Despite the recovery of significantly more cells (as shown by detection of more cellular DNA by using NPA specimens), virus was detected by the IFA technique or ELISA at similar frequencies in paired specimens. However, virus was recovered more often from NPA than NPS specimens by cell culture, and ELISA optical density readings and the number of RSV-positive fluorescing cells were greater for NPA specimens. NPA specimen collection was less traumatic for the patient, was an easier procedure for the physician to perform, and provided a superior laboratory specimen for RSV diagnosis than the NPS technique.

Swabbing for respiratory viral infections in older patients: a comparison of rayon and nylon flocked swabs

“…We believe that there is a lot to be gained from an increased awareness of proper sampling techniques and sampling tools. For semi-quantitative assessments of respiratory pathogens in children, immunofluorescent assays or viral culture have been widely applied [14,[17][18][19], whereas in the current study, CT values were obtained for this purpose. Most studies applying real-time PCR for the detection of respiratory agents simply determine whether there is an infection or not.…”

Comparison of four nasal sampling methods for the detection of viral pathogens by RT-PCR—A GA2LEN project

“…However, few studies have compared the viral yields from samples taken by two or more sampling methods. Among these, some found nasal aspirates and washes superior to nasal or nasopharyngeal swabs for the detection of respiratory pathogens (Ahluwalia et al, 1987;Covalciuc et al, 1999;Frayha et al, 1989;Heikkinen et al, 2001Heikkinen et al, , 2002. In contrast, other comparative studies obtained adequate viral yields from nasopharyngeal swabs and nasal brushes, for the detection of viruses using immunofluorescent assays and cultures (Barnes et al, 1989;Frayha et al, 1989).…”

“…Confirmation of a viral aetiology for respiratory infections is important both for clinical diagnosis as antiviral treatments are becoming available, and for studying respiratory viruses and their interaction with the respiratory tract (Hayden, 2004). Successful detection of a respiratory virus depends on many variables, including sampling for nasal secretions, which may considerably influence the detection rates (Ahluwalia et al, 1987;Barnes et al, 1989;Covalciuc et al, 1999;Frayha et al, 1989;Heikkinen et al, 2001Heikkinen et al, , 2002Xiang et al, 2002). Several recent studies have attempted to compare different nasal sampling methods (usually no more than two), using mainly detection methods other than PCR, without reaching a clear conclusion (Ahluwalia et al, 1987;Barnes et al, 1989;Covalciuc et al, 1999;Frayha et al, 1989;Heikkinen et al, 2001Heikkinen et al, , 2002Xiang et al, 2002).…”

Molecular Testing for Respiratory Viruses

“…Respiratory viruses are no different and since site of replication for these viruses is primarily the URT, in particular the NP region, it is best to sample that region for diagnostic testing. Of the URT samples, NP aspirates have traditionally been considered the most sensitive specimen for the detection of respiratory viruses [96,97]. However, a recent review by Jartti et al [98] indicates that at least in children all NP samples, aspirates, washes, swabs, or brushings, have statistically equal sensitivity for NAAT, particularly when flocked swabs are used [99].…”