RSV Molecular Epidemiology Pre- and Post-COVID-19 Pandemic Periods in Seattle, Washington, USA

Globally, RSV declined to historically low levels following stay-at-home orders in 2020 and re-emerged as restrictions lifted, with large inter-seasonal outbreaks and other shifts in epidemiology. The effect of the pandemic restrictions on genomic diversity has not been well studied.

Individuals with respiratory symptoms were enrolled into community-based surveillance studies and provided nasal swabs over three respiratory virus seasons from 2019 to 2022 in the Seattle metropolitan area in Washington State, USA. Samples were tested for RSV by RT-qPCR, with whole genome sequencing performed for a subset.

Among children and adults, respectively, 1.8% (232/13,014) and 0.2% (86/46,042) of samples tested positive for RSV-A and 1.1% (139/13016) and 0.3% (119/46043) for RSV-B. Positive cases were observed in childcare (n = 39), clinic (n = 270), university (n = 20), workplace (n = 32) or nursing facility (n = 1) sites and through at-home self-administered testing (n = 253). Median age for all participants was 33 years (IQR: 23, 48) and 3 years (IQR: 3, 33) for those who tested positive. Cough (≥ 85%) and rhinorrhea (≥ 85%) were the most common symptoms for RSV cases. During 2019-2020, six RSV-A and three RSV-B lineages circulated (majority lineages A.D.1 and B.D.4.1.1). Almost no RSV was detected during 2020-2021. During 2021-2022, RSV-B lineage B.D.E.1 was dominant.

In a community surveillance study spanning several years, RSV was commonly detected in young children across several sites. Circulation of RSV was disrupted by pandemic mitigation measures, with shifts in genomic diversity detected after lifting of pandemic restrictions.