716. Molecular Epidemiology of Respiratory Syncytial Virus in Children and Adults in Seattle, WA

BACKGROUND: Respiratory syncytial virus (RSV) is the most important cause of pneumonia in children <5 years worldwide and may cause severe disease in elderly and high-risk adults. Multiple RSV strains co-circulate and evolve over seasons. We seek to describe the evolution of RSV over five seasons in Seattle, WA, USA with two seasons reported here. METHODS: From 2014 to 2016, subjects 6 months and older seeking outpatient care for acute respiratory illness at Kaiser Permanente Washington were enrolled in the Influenza Vaccine Efficacy Network (Flu VE Network) and a respiratory swab was collected. Real-time polymerase chain reaction (RT-PCR) was performed to test and quantify RSV and subtype positive samples. A subset of RSV samples with cycle threshold (CT) value <30 will be sequenced using a metagenomic next-generation sequencing (NGS) approach. Specific RSV genotypes will be associated with severe disease, defined as requiring emergency department care or hospitalization, or chest radiographic findings. RESULTS: A total of 8,730 patients were enrolled in the Flu VE Network and PCR testing of seasons 2014/2015 and 2015/2016 resulted in 562 of 4,137 (13.6%) RSV-positive specimens. Of patients with RSV-positive specimens, 204 (36.5%) were adults 18–64 years and 112 (20.0%) were 65+ years. RSV-B predominated in the 2014/2015 season (n = 298; 83.7%), whereas RSV-A was more common in the 2015/2016 season (n = 154; 79.8%) (Figure 1). The median (IQR) CT value for RSV-A specimens was 26.7 (23.3–29.9) compared with 27.9 (25.2–31.3) for RSV-B. CONCLUSION: One RSV subtype predominated within each season. Similar RSV subtype distributions were seen across age categories. With multiple RSV vaccine candidates in development, understanding the genetic diversity and circulation of RSV various viruses within a population is important for analyzing the effects of a vaccine on the evolution of RSV. [Image: see text] Figure 1, Total counts (A) and proportions (B) of RSV-A and RSV-B specimens collected from study patients in Seattle, WA during 2014/2015 and 2015/2016 seasons, by age category. DISCLOSURES: M. L. Jackson, sanofi pasteur: Grant Investigator, Research support. H. Chu, Sanofi-Pasteur: Grant Investigator, Grant recipient.