Data from: Vomiting as a symptom and transmission risk in norovirus illness: evidence from human challenge studies

Background: In the US, noroviruses are estimated to cause 21 million cases
annually with economic losses reaching $2 billion. Outbreak investigations
frequently implicate vomiting as a major transmission risk. However,
little is known about the characteristics of vomiting as a symptom or the
amount of virus present in emesis. Methodology and Principal Findings:
Emesis samples and symptomology data were obtained from previous norovirus
human challenge studies with GI.1 Norwalk virus, GII.2 Snow Mountain
virus, and a pilot study with GII.1 Hawaii virus. Viral titers in emesis
were determined using strain-specific quantitative RT-PCR. In all four
studies, vomiting was common with 40–100% of infected subjects vomiting at
least once. However, only 45% of subjects with vomiting also had diarrhea.
Most of the emesis samples had detectable virus and the mean viral titers
were 8.0 x 105 and 3.9 x 104 genomic equivalent copies (GEC)/ml for GI and
GII viruses, respectively (p = 0.02). Sample pH was correlated with GII.2
Snow Mountain virus detection. Conclusions and Significance: Half of all
subjects with symptomatic infection experienced vomiting and the average
subject shed 1.7 x 108 GEC in emesis. Unlike shedding through stool,
vomiting is more likely to result in significant environmental
contamination, leading to transmission through fomites and airborne
droplets. This quantitative data will be critical for risk assessment
studies to further understand norovirus transmission and develop effective
control measures. The correlation between sample pH and virus detection is
consistent with a single site of virus replication in the small intestine
and stomach contents becoming contaminated by intestinal reflux.
Additionally, the frequency of vomiting without concurrent diarrhea
suggests that epidemiology studies that enroll subjects based on the
presence of diarrhea may be significantly underestimating the true burden
of norovirus disease.