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.

背景：据估算，美国每年因诺如病毒（norovirus）感染导致的病例达2100万例，经济损失高达20亿美元。暴发调查常将呕吐列为主要的传播风险因素，但目前对于呕吐这一症状的特征，以及呕吐物中携带的病毒载量，相关认知仍较为匮乏。
研究方法与主要结果：本研究从既往三项诺如病毒人体挑战试验（分别针对GI.1型诺沃克病毒、GII.2型雪山病毒）以及一项针对GII.1型夏威夷病毒的先导试验中，获取了呕吐物样本与症状学数据。采用毒株特异性定量逆转录聚合酶链反应（quantitative RT-PCR）测定呕吐物中的病毒载量。四项试验均显示呕吐症状普遍：40%~100%的感染受试者至少出现过一次呕吐，但仅45%伴有呕吐症状的受试者同时出现腹泻。多数呕吐物样本可检测到病毒，GI型与GII型病毒的平均病毒载量分别为8.0×10^5 基因组等价拷贝数（GEC）/ml与3.9×10^4 GEC/ml（p=0.02）。样本pH值与GII.2型雪山病毒的检测结果存在相关性。
结论与意义：在出现症状的诺如病毒感染者中，有半数曾出现呕吐症状，每名受试者平均经呕吐物排出1.7×10^8 GEC的病毒。与经粪便排毒不同，呕吐更易造成严重的环境污染，进而通过物体表面污染物（fomites）与空气飞沫实现传播。本研究获得的定量数据，对于进一步阐明诺如病毒传播机制、制定有效防控策略的风险评估研究至关重要。呕吐物样本pH值与病毒检测结果的相关性，与病毒在小肠内单一部位复制、随后肠液反流污染胃内容物的机制相符。此外，无伴随腹泻的呕吐症状发生率，提示仅以腹泻症状招募受试者的流行病学研究，可能大幅低估了诺如病毒感染的真实疾病负担。