Molecular Characterization of Noroviruses Causing Acute Gastroenteritis Outbreaks among US Military Recruits, 2013-2023

Abstract

Norovirus is the leading cause of acute gastroenteritis (AGE) worldwide. Norovirus outbreaks at military facilities can cause loss of training and working days and increased healthcare utilization, affecting force readiness. During 2013-2023, we enrolled 2,304 US military recruits from 4 basic training facilities to investigate AGE outbreaks among this population. Among enrollees, we detected norovirus in 433 (18.8%) AGE cases, and norovirus caused 49 AGE outbreaks during our longitudinal study. On average, each norovirus case-patient missed 1.2 training days due to illness, and 6.2% required infusion care. Whole-genome sequencing of selected samples from each outbreak produced full-length genomes (6,989-7,787 bp) for 39 samples. Norovirus GII.4 Sydney was the most (12/39, 30.8%) identified genotype over the study period. Phylogenetic and comparative genomic analyses revealed that several outbreak strains were responsible for causing >1 outbreak, even across different training sites. Our findings can inform infection control practices at military installations and overall norovirus vaccine development.

Keywords: AGE; Norovirus; US military; United States; WGS; acute gastroenteritis; enteric infections; recruit training; viruses; whole-genome sequencing.

Figure 1

Maximum-likelihood phylogram in a study of molecular characterization of noroviruses causing acute gastroenteritis outbreaks among US military recruits at 4 basic training facilities, 2013–2023. Phylogram reveals genetic relatedness of whole-genome sequences (+7,500 bp) for 39 of the 49 selected outbreak virus study strains characterized by whole-genome analysis. Outbreak study strains are labeled from left to right as follows: sample identification/location sample was collected/year sample was collected/genogroup and P-type/outbreak number. The 4 facilities were Marine Corps centers in California and South Carolina, a Navy center in Illinois, and an Army center in Missouri. Bootstrap values >70% are indicated at branch nodes where applicable. Scale bar indicates nucleotide substitutions per site.

Figure 3

Maximum-likelihood phylogram of GII ORF2 (VP1) in a study of molecular characterization of noroviruses causing acute gastroenteritis outbreaks among US military recruits at 4 basic training facilities, 2013–2023. Phylogram reveals genetic relatedness GII ORF2 (VP1) deduced amino acid sequences (+580 bp) for 26 of the 39 norovirus outbreak strains. Outbreak study strains are labeled from left to right as follows: sample identification/location sample was collected/year sample was collected/genogroup and P-type/outbreak number. The 4 facilities, identified by color, were Marine Corps centers in California and South Carolina, a Navy center in Illinois, and an Army center in Missouri. Bootstrap values >70% are indicated at branch nodes where applicable. Scale bar indicates nucleotide substitutions per site. ORF, open reading frame; VP, virus capsid protein.

Figure 2

Maximum-likelihood phylogram of GI ORF2 (VP1) in a study of molecular characterization of noroviruses causing acute gastroenteritis outbreaks among US military recruits at 4 basic training facilities, 2013–2023. Phylogram reveals genetic relatedness of GI ORF2 (VP1) deduced amino acid sequences (+550 bp) for 13 of the 39 norovirus outbreak strains. Outbreak study strains are labeled from left to right as follows: sample identification/location sample was collected/year sample was collected/genogroup and P-type/outbreak number. The 4 facilities, identified by color, were Marine Corps centers in California and South Carolina, a Navy center in Illinois, and an Army center in Missouri. Bootstrap values >70% are indicated at branch nodes where applicable. Scale bar indicates nucleotide substitutions per site. ORF, open reading frame; VP, virus capsid protein.