Abstract
BACKGROUND: Respiratory syncytial virus (RSV) typically causes winter outbreaks in temperate climates. During summer 2017, the Minnesota Department of Health received a report of increased cases of severe RSV-B infection. METHODS: We compared characteristics of summer 2017 cases with those of 2014-2018 summers. To understand the genetic relatedness among viruses, we performed high-throughput sequencing of RSV from patients with a spectrum of illness from sites in Minnesota and Wisconsin. RESULTS: From May to September 2017, 58 RSV cases (43 RSV-B) were reported compared to 20-29 cases (3-7 RSV-B) during these months in other years. Median age and frequency of comorbidities were similar, but 55% (24/43) were admitted to the ICU in 2017 compared to 12% in preceding 3 years (odds ratio, 4.84, P < .01). Sequencing was performed on 137 specimens from March 2016 to March 2018. Outbreak cases formed a unique clade sharing a single conserved nonsynonymous change in the SH gene. We observed increased cases during the following winter season, when the new lineage was the predominant strain. CONCLUSIONS: We identified an outbreak of severe RSV-B disease associated with a new genetic lineage among urban Minnesota children during a time of expected low RSV circulation.