Fecal Viral Load and Norovirus-associated Gastroenteritis

Chan, Martin C.W.; Sung, Joseph J.Y.; Lam, Robert F.; Chan, Paul K.S.; Lee, Nelson; Lai, Robin Kit-Ho; Leung, Wai Keung

doi:10.3201/eid1708.060081

Cited by 37 publications

(35 citation statements)

References 6 publications

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“…In a recent study in which the number of norovirus cDNA copies per gram of stool specimen was analyzed, a discrepancy was found between the different norovirus genogroups. Chan et al found median viral loads of 8.4 ϫ 10 5 and 3.0 ϫ 10 8 copies/g of stool specimen for norovirus GI and GII, respectively, and speculated that the higher viral loads of GII strains were due to their higher transmissibility (5). Of note, our results showed that GII/4 strains had the highest mean viral load overall (7.96 ϫ 10 9 copies/g of stool), further increasing the clinical importance of this dominating genotype.…”

Section: Discussionmentioning

confidence: 99%

Norovirus Infections in Symptomatic and Asymptomatic Food Handlers in Japan

Ozawa¹,

et al. 2007

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Noroviruses are the leading cause of outbreaks of gastroenteritis in the world. At present, norovirus genogroup II, genotype 4 (GII/4), strains are the most prevalent in many countries. In this study we investigated 55 outbreaks and 35 sporadic cases of norovirus-associated gastroenteritis in food handlers in foodcatering settings between 10 November 2005 and 9 December 2006 in Japan. Stool specimens were collected from both symptomatic and asymptomatic individuals and were examined for norovirus by real-time reverse transcription-PCR; the results were then confirmed by sequence analysis. Norovirus was detected in 449 of 2,376 (19%) specimens. Four genogroup I (GI) genotypes and 12 GII genotypes, including one new GII genotype, were detected. The GII/4 sequences were predominant, accounting for 19 of 55 (35%) outbreaks and 16 of 35 (46%) sporadic cases. Our results also showed that a large number of asymptomatic food handlers were infected with norovirus GII/4 strains. Norovirus GII had a slightly higher mean viral load (1 log unit higher) than norovirus GI, i.e., 3.81 ؋ 10 8 versus 2.79 ؋ 10 7 copies/g of stool. Among norovirus GI strains, GI/4 had the highest mean viral load, whereas among GII strains, GII/4 had the highest mean viral load (2.02 ؋ 10 8 and 7.96 ؋ 10 9 copies/g of stool, respectively). Importantly, we found that asymptomatic individuals had mean viral loads similar to those of symptomatic individuals, which may account for the increased number of infections and the predominance of an asymptomatic transmission route.The positive-sense polyadenylated single-stranded RNA virus family Caliciviridae contains four genera: Norovirus, Sapovirus, Lagovirus, and Vesivirus (1). The prototype strain of human norovirus is the Norwalk virus (NV/Human/US/1968), which was first discovered in an outbreak of gastroenteritis in an elementary school in Norwalk, OH, in 1968 (15). Noroviruses are the leading cause of outbreaks of gastroenteritis in the world; they cause outbreaks in various settings, including hospitals, cruise ships, schools, and restaurants (2,9,12,15,23,24,29). In addition, noroviruses have been detected in environmental samples (e.g., treated and untreated sewage) as well as in contaminated foods such as oysters, shellfish, sandwiches, salads, raspberries, and even ice (7,18,19,26). Numerous molecular epidemiological studies have revealed a global distribution of these viruses (25,27,31).The most widely used method of detecting noroviruses is reverse transcription-PCR (RT-PCR), which has high sensitivity; also, the products can be used for further genetic analysis. Real-time RT-PCR assays have also been developed; they are sensitive, broadly reactive, and rapid for the detection of human noroviruses in clinical stool specimens and environmental samples (13,14,21).As the detection methods become more and more sensitive, the numbers of genogroups and genotypes are expected to increase. One emerging characteristic is that strains have been found to persist in one geographical region, only to disapp...

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Section: Discussionmentioning

confidence: 99%

Norovirus Infections in Symptomatic and Asymptomatic Food Handlers in Japan

Ozawa¹,

et al. 2007

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“…GII.4 strains have been reported to cause more severe illness [20,27] and a higher viral load in infected persons than other strains [28], which may lead to more frequent disease transmission. A higher environmental stability has also been discussed [26].…”

Section: Discussionmentioning

confidence: 99%

Epidemiology of norovirus gastroenteritis in Germany 2001–2009: eight seasons of routine surveillance

et al. 2013

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SUMMARYWe analysed data on laboratory or epidemiologically confirmed cases (n = 856 539) and on outbreaks (n = 31 644) notified during week 31 (2001) to week 30 (2009), and performed molecular typing of specimens from 665 outbreaks. We aimed at identifying demographic and molecular characteristics to inform on potential additional approaches to prevent disease spread in the population. The mean incidence by norovirus season (week 31 in one year to week 30 in the following year) was 130 (range 19-300) cases/100 000 population and was highest in persons aged <5 years (430/100 000) and 575 years (593/100 000). The proportion hospitalized in community-acquired cases was 8-19% per season. The mean norovirus-associated mortality was 0·05/100 000 per season and 0·5/100 000 in the 575 years age group. Most outbreaks with known setting (75%) occurred in hospitals (32%), nursing homes (28%), households (24%) and childcare facilities (10%). GII strains dominated in the outbreak specimens. GII.4 strains were found in 82% of nursing home outbreaks, 85% of hospital outbreaks, and 33% of childcare facility and school outbreaks. Cases in younger individuals were notified earlier during the season than adult cases, and outbreaks in childcare facilities and schools preceded those in nursing/residential homes, hospitals and private households. We suggest future studies to investigate more closely potential transmission patterns between children and adults.

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“…From genotyping data of 7 cases of the norovirus outbreak during the jamboree, we know that 3 different norovirus genotypes circulated during this outbreak from genogroup I and II. Recent work (32) showed fi rst signs of a different viral load, which could indicate different transmissibility and different generation times between genogroup I and genogroup II. However, all genotyped strains were found during days 7-9 of the outbreak; although we cannot rule out the possibility that genotype replacement occurred, the most transmissible type is highly unlikely to have dominated during the fi rst 3 days before giving way to less transmissible types.…”

Section: Discussionmentioning

confidence: 99%

Enhanced Hygiene Measures and Norovirus Transmission during an Outbreak

Heijne¹,

Teunis²,

Morroy³

et al. 2009

Emerg. Infect. Dis.

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Control of norovirus outbreaks relies on enhanced hygiene measures, such as handwashing, surface cleaning, using disposable paper towels, and using separate toilets for sick and well persons. However, little is known about their effectiveness in limiting further spread of norovirus infections. We analyzed norovirus outbreaks in 7 camps at an international scouting jamboree in the Netherlands during 2004. Implementation of hygiene measures coincided with an 84.8% (95% predictive interval 81.2%-86.6%) reduction in reproduction number. This reduction was unexpectedly large but still below the reduction needed to contain a norovirus outbreak. Even more stringent control measures are required to break the chain of transmission of norovirus. G astroenteritis is one of the most common causes of illness (1). Recent fi ndings indicate norovirus is the most common cause of gastroenteritis (2,3). Of all gastroenteritis outbreaks reported in the Netherlands during 2002, 54% were caused by norovirus (4). Norovirus is predominantly transmitted through the fecal-oral route, either indirectly through contaminated food or surfaces or directly from person to person (5). It can be transmitted through small infectious droplets (aerosols) after a vomiting episode (6,7) and can survive for a very long time in the environment (5,8). Most norovirus outbreaks are seen in settings where clusters of vulnerable, susceptible persons live closely together, such as nursing homes, hospitals, and daycare centers (4), and in settings in which turnover of susceptible persons is high, such as hotels and cruise ships (9,10).Norovirus infection can cause serious medical complications, such as dehydration, in persons with underlying illness (11). No antiviral treatment exists for norovirus infection, and although norovirus vaccines are in development (12), none are available yet. Early studies suggested that norovirus outbreaks could be contained by rapid implementation of enhanced hygiene measures, such as washing hands, thoroughly cleaning contaminated surfaces, avoiding contact between sick and healthy persons, and requesting caretakers and cleaning staff to wear gloves and aprons (13-16). However, in nursing homes or on cruise ships, norovirus can cause consecutive outbreaks, even after implementation of strict hygiene protocols (9,17,18). No quantitative estimates exist of the results of such enhanced hygiene measures on reducing further transmission of norovirus. To our knowledge, the effect of enhanced hygiene measures has not been investigated in randomized controlled trials or in statistical analyses of outbreaks.We investigated the effect of enhanced hygiene measures on reducing norovirus transmission during an outbreak. We measured the effectiveness of enhanced hygiene measures as the relative reduction in the reproduction number-defi ned as the average number of secondary cases caused by 1 typical case-in the absence of and after enhanced hygiene measures. The value of this reproduction number provides crucial information about transmissi...

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Fecal Viral Load and Norovirus-associated Gastroenteritis

Cited by 37 publications

References 6 publications

Norovirus Infections in Symptomatic and Asymptomatic Food Handlers in Japan

Norovirus Infections in Symptomatic and Asymptomatic Food Handlers in Japan

Epidemiology of norovirus gastroenteritis in Germany 2001–2009: eight seasons of routine surveillance

Enhanced Hygiene Measures and Norovirus Transmission during an Outbreak

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