Cluster of Norovirus Genogroup IX Outbreaks in Long-Term Care Facilities, Utah, USA, 2021

Abstract

We report 5 clustered acute gastroenteritis outbreaks in long-term care facilities in Utah, USA, that were linked to healthcare employees working at multiple facilities. Four outbreaks were caused by norovirus genotype GIX. We recommend continued norovirus surveillance and genotyping to determine contributions of this genotype to norovirus outbreaks.

Keywords: Norovirus; United States; Utah; acute gastroenteritis; enteric infections; food safety; long-term care facilities; viruses.

Figure 1

Onset dates for reported cases of acute gastroenteritis among 5 long-term care facilities during March 28–April 24, 2021, in study of cluster of norovirus genogroup IX outbreaks in long-term care facilities, Utah, USA, 2021. Of 290 total reported cases of acute gastroenteritis, we were able to obtain onset dates for 247 cases. Each colored box represents 1 case of acute gastroenteritis.

Figure 2

Phylogenetic comparisons of norovirus genes in study of cluster of norovirus genogroup IX outbreaks in long-term care facilities, Utah, USA, 2021. We generated phylogenetic trees by using the maximum-likelihood method and Tamura-Nei distance model (15). We compared nucleotide sequences of the RdRp gene (1,430 nt) (A) and major capsid gene (1,668 nt) (B) from the 12 sequences obtained from the 4 LTCF outbreaks with 33 GIX strains obtained from GenBank. The bootstrap percentages are shown next to the branches. We generated initial trees automatically by applying neighbor-joining algorithms to a matrix of pairwise distances estimated by using the maximum composite-likelihood approach and then selecting the topology with the superior log-likelihood value. We conducted evolutionary analyses by using MEGA11 software (15). Scale bars indicate nucleotide substitutions per site.