Summer outbreak of severe RSV-B disease, Minnesota, 2017 associated with emergence of a genetically distinct viral lineage

BACKGROUND: Respiratory syncytial virus (RSV) typically causes winter outbreaks in temperate climates. During summer 2017, the Minnesota Department of Health (MDH) received a report of an increased cases of severe RSV-B infection.

METHODS: We compared characteristics of summer 2017 cases with those from the surrounding 4 summers (2014-2018). To understand the genetic relatedness among viruses, we performed high-throughput sequencing of RSV from patients with a spectrum of illness from multiple clinical sites in Minnesota and Wisconsin.

RESULTS: From May-Sept. 2017, 58 cases of RSV (43 RSV-B) were reported compared to 20-29 cases (3-7 RSV-B) during the same time frame in other years. The median age and frequency of co-morbidities was similar, but 55% (24/43) were admitted to the ICU in 2017 compared to 12% in preceding 3 years (OR: 4.84, p<0.01). Sequencing was performed on 137 specimens from March 2016-March 2018. Outbreak cases formed a unique clade sharing a single conserved non-synonymous change in the SH gene. We observed increased cases during the following winter season, during which time the new lineage was the predominant circulating 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.