[Concordance of nasal swabs and nasopharyngeal swabs in the detection of respiratory viruses by direct immunofluorescence].

BACKGROUND

The most used test for the diagnosis of viral respiratory infection is the detection of viral antigens by direct immunofluorescence (DFA), in samples taken by nasopharyngeal swab (NPS) or aspirate (NPA). It would be desirable to have a less uncomfortable technique to obtain a sample from the patient, but of equal performance.

AIM: To evaluate the diagnostic agreement between nasal swab (NS) and nasopharyngeal swab (NPS) in the detection of respiratory viruses by DFA and compare the degree of discomfort of both techniques in pediatric patients.

METHODOLOGY: Cross-sectional study in children who consulted to a pediatric emergency service with respiratory symptoms. Two samples (NPS and NS) per child were collected. The concordance between the two was determined by Kappa (K) coefficient and the degree of discomfort by a visual pain scale.

RESULTS

We obtained 112 samples from 56 children, one by each technique. 82.1% were concordant, K = 0.61 (CI 95%, 0.39-0.83) for the detection of any virus, and K = 0.69 (CI 95%, 0.46-0.92) and K = 0.76 (CI 95%, 0.51-1) for syncytial respiratory virus and influenza A detection, respectively. The degree of discomfort was significantly lower for the NS.

CONCLUSION

There is considerable agreement in the detection of respiratory viruses by DFA between samples obtained by NS and NPS, but not enough to recommend a change in the sampling method in this population.