Evaluating addition of self-collected throat swabs to nasal swabs for respiratory virus detection

BACKGROUND: Early and accurate detection of respiratory viruses (RV) is important for patient management. We have previously shown that self-collected nasal swabs (NS) are feasible and as sensitive as clinician-collected nasal washes for detection of RV, but the additive benefit of self-collected throat swabs is unknown. OBJECTIVES: To evaluate the added yield of self-collected nasal to throat swabs for detection of RV by PCR in patients with upper respiratory tract infection (URTI) symptoms. STUDY DESIGN: Patients with URTI symptoms self-collected paired polyurethane foam NS and nylon flocked throat swabs and completed a symptom survey. Swabs were tested for 12 RV by real-time reverse transcription (RT)-PCR. Descriptive, McNemar's, and Wilcoxon signed rank statistical tests were used. RESULTS: 115 paired nasal and throat swabs were collected from 63 individuals, with 71/115 (62%) positive for a RV by at least one specimen, including 51 positive by both, 17 positive by NS only, and 3 positive by throat swab only. The sensitivity of NS was 96% (95%CI: 88-99) versus 76% (95% CI: 65-85) in throat swabs, p<0.001. The median PCR cycle threshold (Ct) in 51 concordant samples was lower (indicating higher viral concentration) in NS (25.1) versus throat swabs (32.0). The three samples positive only by throat swab had high Ct values (33.8, 36.2, and 38.8, all rhinovirus). CONCLUSION: Self-collection of NS was significantly more sensitive than self collection of throat swabs for detection of RV by RT-PCR. The addition of throat sampling does not appear to increase the diagnostic load in the self-testing setting.