SUMMARY The purpose of this study was to examine global epidemiological trends in human norovirus (NoV) outbreaks by transmission route and setting, and describe relationships between these characteristics, viral attack rates, and the occurrence of genogroup I (GI) or genogroup II (GII) strains in outbreaks. We analysed data from 902 RT-PCR-confirmed, human NoV outbreaks extracted from a systematic review of articles published from 1993 to 2011 and indexed under the terms “norovirus” and “outbreak.” Multivariate regression analyses demonstrated that foodservice and winter outbreaks were significantly associated with higher attack rates. Food- and waterborne outbreaks were associated with multiple strains (GI+GII). Waterborne outbreaks were significantly associated with GI strains, while healthcare-related and winter outbreaks were associated with GII strains. These results identify important trends for epidemic NoV detection, prevention, and control.

Contamination of oysters with human noroviruses (HuNoV) constitutes a human health risk and may lead to severe economic losses in the shellfish industry. There is a need to identify a technology that can inactivate HuNoV in oysters. In this study, we conducted a randomized, double-blinded clinical trial to assess the effect of high hydrostatic pressure processing (HPP) on Norwalk virus (HuNoV genogroup I.1) inactivation in virus-seeded oysters ingested by subjects. Forty-four healthy, positive-secretor adults were divided into three study phases. Subjects in each phase were randomized into control and intervention groups. Subjects received Norwalk virus (8FIIb, 1.0 ؋ 10 4 genomic equivalent copies) in artificially seeded oysters with or without HPP treatment (400 MPa at 25°C, 600 MPa at 6°C, or 400 MPa at 6°C for 5 min). HPP at 600 MPa, but not 400 MPa (at 6°or 25°C), completely inactivated HuNoV in seeded oysters and resulted in no HuNoV infection among these subjects, as determined by reverse transcription-PCR detection of HuNoV RNA in subjects' stool or vomitus samples. Interestingly, a white blood cell (granulocyte) shift was identified in 92% of the infected subjects and was significantly associated with infection (P ‫؍‬ 0.0014). In summary, these data suggest that HPP is effective at inactivating HuNoV in contaminated whole oysters and suggest a potential intervention to inactivate infectious HuNoV in oysters for the commercial shellfish industry.

Norovirus is the most common cause of acute infectious gastroenteritis, causing approximately 21 million cases annually in the USA. The virus is highly contagious and resistant to decontamination, making outbreaks difficult to control. To facilitate the development of better control methods, this study characterized the viral shedding patterns in stools from subjects experimentally infected with genogroup I or II norovirus. Viral stool titers were determined by quantitative real-time RT-PCR for all stools produced in the first 7 days post-challenge and representative stools through day 35 post-challenge. The shedding titers and disease course were analyzed with respect to virus type, illness, and subject demographics. Infection with GII.2 Snow Mountain (SMV) resulted in more symptoms and a higher frequency of painful symptoms compared to GI.1 Norwalk (NV) infection. However, NV infection produced stool viral titers approximately 2 logs higher than those seen in SMV infections. Both NV and SMV were shed in stools for up to 3 weeks after the resolution of symptoms, but long shedding durations were more common in NV infections. For each challenge virus, shedding titers and patterns were not correlated with subject demographics or clinical course. This is the first study to report shedding dynamics in experimental GII norovirus infection.

cHuman norovirus (NoV) outbreak investigations suggest that the hands of infected individuals play an important role in NoV transmission. However, there is no experimental evidence documenting the likelihood and degree of NoV contamination on hands. As part of a clinical trial designed to evaluate the efficacy of high-pressure processing for Norwalk virus (NV) inactivation in oysters, 159 hand rinse samples were collected from 6 infected and 6 uninfected subjects. NV was concentrated from the samples by polyethylene glycol precipitation, followed by RNA extraction using an automated guanidinium isothiocyanate-silica method. NV RNA was detected and quantified using multiple NV-specific reverse transcription-quantitative PCR (RT-qPCR) assays. A total of 25.4% (18/71) of the hand rinse samples collected from 6 infected volunteers were presumptively positive for NV, with an average of 3.86 log 10 genomic equivalent copies (GEC) per hand. Dot blot hybridization of PCR products obtained using a different primer set, and DNA sequencing of selected amplicons, provided further confirmation of the presence of NV in the hand rinses. NV contamination was also detected in two hand rinse samples obtained from one uninfected subject. These findings provide definitive evidence of NV contamination on the hands of infected subjects observed under controlled clinical research conditions. Such data support the need for better hand hygiene strategies to prevent NoV transmission. Human noroviruses (NoVs) are the most common cause of acute viral gastroenteritis worldwide (1) and a leading cause of food-borne disease (2, 3). They are spread primarily by the fecal-oral route but are also shed in vomitus. As such, NoV can be transmitted via consumption of fecally contaminated food or water or by contact with contaminated fomites and hands. The relative importance of each of these transmission routes is not well studied, but the potential for human hands to facilitate NoV transmission is widely recognized.A recent epidemiological study by the CDC (4) identified NoV as the predominant etiology of food-borne disease outbreaks, and the largest proportion of these outbreaks were associated with food handlers implicated as the source of contamination. Food handlers are of particular concern (5) because they may shed NoV at extremely high titers for days or weeks during a symptomatic or asymptomatic NoV infection and subsequently transfer viruses from their hands to food. Furthermore, both laboratory and epidemiological data (6-8) provide evidence that NoV may persist on hands and fomites for extended periods of time. For example, Malek et al. (9) described an outbreak of NoV infection in which the index case was an infected food handler who worked for a delicatessen meat supplier company and handled sliced delicatessen meat with bare hands 1 day after recovering from gastroenteritis symptoms. This investigation documented a clear association between the contaminated hands of the food handler and the subsequent NoV outbreak. Because of NoV-cont...

Norovirus (NoV) is a leading cause of acute viral gastroenteritis among children, yet its burden of disease among immunocompromised hosts and its role in hospital acquired infections (HAI) is not well characterized. To determine the prevalence, genotypes, and NoV loads among immunocompromised children and children with HAI, residual stool samples, and clinical data were collected at two major pediatric hospitals in metropolitan Atlanta from 92 children that were immunocompromised and/or had a hospital acquired acute gastroenteritis. NoV was identified in 16.3% (15/92) of all stool specimens; 23.4% (11/47) in immunocompromised only children, and 13.3% (4/30) in children with HAI. All NoV positive cases were genogroup II (GII), and GII.4 was the predominant strain followed by GII.3, GII.12, and GII.13. The average NoV load for immunocompromised patients was 6.3 ± 1.4 log genome equivalent copies (GEC) per gram of stool compared to 5.8 ± 1.1 log GEC among patients with HAI. NoV infections are common among immunocompromised children and children with hospital-acquired gastroenteritis, underscoring the urgent need for rapid NoV detection system, and highlighting the importance of strict hospital hygiene practices.