Viral Titer of Respiratory Syncytial Virus in the Nasal Cavity in Different Sites in Children and Adults.

Analysis of the viral load in respiratory syncytial virus (RSV) infection has focused on the nasopharyngeal site (NPS) near the lower respiratory tract, which is the primary lesion site, and the viral load in the anterior nasal site (ANS) near the nostrils has not been clarified in adults or children. The study evaluated the nasal distribution of RSV. A total of 49 patients, with 0 months to 71 years of age, participated in the study. A total of 774 specimens were collected from the ANS and NPS. In the pediatric group, the highest viral load in the NPS was 1.1 × 10¹⁰ copies/mL on day 1 of onset, and the highest in the ANS was 4.1 × 10⁹ copies/mL on day 2. Thereafter, the viral load at both sites decreased gradually over time. The adult group showed a peak viral load on the onset day, with 1.5 × 10¹⁰ copies/mL in the NPS and 8.4 × 10⁹ copies/mL in the ANS. By day 7 of onset, the viral load was 3.9 × 10⁸ copies/mL in the NPS and 1.3 × 10⁸ copies/mL in the ANS, indicating that the viral load at both sites remained parallel. We demonstrated that the RSV load was present in the ANS and NPS of children and adults from the date of onset. The ANS is closer to the nostrils and is a more promising specimen collection site than the NPS at all ages but has a lower viral load than the NPS.