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      Gastroenteritis outbreaks on cruise ships: contributing factors and thresholds for early outbreak detection

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          When an increased number of acute gastroenteritis (AG) cases is detected among tourists staying at the same accommodation, outbreak management plans must be activated in a timely manner to prevent large outbreaks. Syndromic surveillance data collected between 1 January 2010 and 31 December 2013 by five seagoing cruise ships were analysed to identify attack rate thresholds for early outbreak detection. The overall incidence rate of AG was 2.81 cases per 10,000 traveller-days (95% confidence interval (CI): 0.00–17.60), while the attack rate was 19.37 cases per 10,000 travellers (95% CI: 0.00–127.69). The probability of an outbreak occurring was 11% if 4 per 1,000 passengers reported symptoms within the first 2 days of the voyage, and this increased to 23 % if 5 per 1,000 passengers reported such within the first 3 days. The risk ratio (RR) for outbreak occurrence was 2.35, 5.66 and 8.63 for 1, 2 and 3 days’ delay of symptoms reporting respectively, suggesting a dose–response relationship. Shipping companies’ policies and health authorities’ efforts may consider these thresholds for initiating outbreak response measures based on the number of cases according to day of cruise. Efforts should focus on ensuring travellers report symptoms immediately and comply with isolation measures.

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          Most cited references 17

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          Norovirus Disease in the United States

          Although recognized as the leading cause of epidemic acute gastroenteritis across all age groups, norovirus has remained poorly characterized with respect to its endemic disease incidence. Use of different methods, including attributable proportion extrapolation, population-based surveillance, and indirect modeling, in several recent studies has considerably improved norovirus disease incidence estimates for the United States. Norovirus causes an average of 570–800 deaths, 56,000–71,000 hospitalizations, 400,000 emergency department visits, 1.7–1.9 million outpatient visits, and 19–21 million total illnesses per year. Persons >65 years of age are at greatest risk for norovirus-associated death, and children <5 years of age have the highest rates of norovirus-associated medical care visits. Endemic norovirus disease occurs year round but exhibits a pronounced winter peak and increases by ≤50% during years in which pandemic strains emerge. These findings support continued development and targeting of appropriate interventions, including vaccines, for norovirus disease.
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            The Vast and Varied Global Burden of Norovirus: Prospects for Prevention and Control

            Globally, norovirus is associated with approximately one-fifth of all diarrhea cases, with similar prevalence in both children and adults, and is estimated to cause over 200,000 deaths annually in developing countries. Norovirus is an important pathogen in a number of high-priority domains: it is the most common cause of diarrheal episodes globally, the principal cause of foodborne disease outbreaks in the United States, a key health care–acquired infection, a common cause of travel-associated diarrhea, and a bane for deployed military troops. Partly as a result of this ubiquity and burden across a range of different populations, identifying target groups and strategies for intervention has been challenging. And, on top of the breadth of this public health problem, there remain important gaps in scientific knowledge regarding norovirus, especially with respect to disease in low-income settings. Many pathogens can cause acute gastroenteritis. Historically, rotavirus was the most common cause of severe disease in young children globally. Now, vaccines are available for rotavirus and are universally recommended by the World Health Organization. In countries with effective rotavirus vaccination programs, disease due to that pathogen has decreased markedly, but norovirus persists and is now the most common cause of pediatric gastroenteritis requiring medical attention. However, the data supporting the precise role of norovirus in low- and middle-income settings are sparse. With vaccines in the pipeline, addressing these and other important knowledge gaps is increasingly pressing. We assembled an expert group to assess the evidence for the global burden of norovirus and to consider the prospects for norovirus vaccine development. The group assessed the evidence in the areas of burden of disease, epidemiology, diagnostics, disease attribution, acquired immunity, and innate susceptibility, and the group considered how to bring norovirus vaccines from their current state of development to a viable product that will benefit global health.
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              The frequency of a Norwalk-like pattern of illness in outbreaks of acute gastroenteritis.

              Records of 642 outbreaks of acute gastroenteritis were reviewed to determine the proportion of outbreaks that were clinically and epidemiologically consistent with Norwalk-like virus infection. Using as our criteria stool cultures negative for bacterial pathogens, mean (or median) duration of illness 12-60 hours, vomiting in greater than or equal to 50 per cent of cases, and, if known, mean (or median) incubation period of 24-48 hours, we found that 23 per cent of waterborne outbreaks, 4 per cent of foodborne outbreaks, and 67 per cent, 60 per cent, and 28 per cent of outbreaks in nursing homes, in summer camps, and on cruise ships, respectively, satisfied the criteria for Norwalk-like pattern. Of 54 outbreaks that satisfied the criteria for Norwalk-like pattern, 14 were investigated for virus etiology. Ten of these (71 per cent) yielded serologic evidence of Norwalk-like virus infection. Norwalk-like viruses are probably an important cause of outbreaks of acute gastroenteritis. Investigation for Norwalk virus antibody in outbreaks that are clinically and epidemiologically consistent with Norwalk-like virus infection is likely to yield diagnostically useful results.

                Author and article information

                Euro Surveill
                Euro Surveill
                European Centre for Disease Prevention and Control (ECDC)
                09 November 2017
                : 22
                : 45
                [1 ]Department of Hygiene and Epidemiology, Faculty of Medicine, University of Thessaly, Larissa, Greece
                [2 ]Celestyal Cruises, Piraeus, Greece
                [3 ]Robert Koch Institute, Berlin, Germany
                [4 ]The members of the group are listed at the end of the article
                Author notes

                Correspondence: Christos Hadjichristodoulou ( xhatzi@ )

                16-00576 16-00576
                This article is copyright of The Authors, 2017.

                This is an open-access article distributed under the terms of the Creative Commons Attribution (CC BY 4.0) Licence. You may share and adapt the material, but must give appropriate credit to the source, provide a link to the licence, and indicate if changes were made.

                Surveillance and Outbreak Report
                Custom metadata

                maritime, ship, travel, health, gastroenteritis, threshold, norovirus, cruise


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