Comparison of influenza viral load in nasopharyngeal and midturbinate swabs.

Different specimen types are used for influenza diagnosis but comparative data for viral loads from different swab types are limited. We compared influenza viral loads (determined by quantitative reverse transcription polymerase chain reaction [RT-PCR]) in 93 paired midturbinate and nasopharyngeal swab aliquots from influenza infected patients enrolled in a phase 3 randomized-controlled study with the objective of maximizing the number of swabs available for sequence analysis. Midturbinate swabs yielded a 53% lower viral load versus nasopharyngeal swabs, and this difference was similar for influenza A and B. These data suggest that nasopharyngeal swabs might be preferred in diagnostic settings when obtaining higher viral load is important.