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  • CLINICAL MICROBIOLOGY REVIEWS, July 1993, p. 199-210 Vol. 6, No. 30893-8512/93/030199-12$02.00/0Copyright 1993, American Society for Microbiology

    Outbreaks of Food-Borne and WaterborneViral Gastroenteritis

    CRAIG W. HEDBERG* AND MICHAEL T. OSTERHOLMAcute Disease Epidemiology Section, Minnesota Department of Health, Minneapolis, Minnesota 55440

    INTRODUCTION ........................................................................ 199AGENTS OF VIRAL GASTROENTERITIS ASSOCIATED WITH OUTBREAKS OF

    FOOD-BORNE AND WATERBORNE DISEASE ..................................................................199LABORATORY AND EPIDEMIOLOGIC METHODS USED TO CONFIRM OUTBREAKS

    OF VIRAL GASTROENTERITIS ........................................................................ 200Norwalk Virus IEM........................................................................ 200Norwalk Virus RIA and Biotin-Avidin Immunoassay .................................................................201Norwalk Virus EIA and Polymerase Chain Reaction..................................................................201Methods for Norwalk-Like Viruses ........................................................................ 201Methods for Rotavirus ........................................................................ 202Virus Isolation ........................................................................ 202Epidemiologic Methods ........................................................................ 202

    CLINICAL AND EPIDEMIOLOGIC FEATURES OF OUTBREAKS OFVIRAL GASTROENTERITIS ........................................................................ 202

    Clinical Features ......................................................................... 202Epidemiologic Features ........................................................................ 203

    MODES OF TRANSMISSION, PREVENTION, AND CONTROL ..................................................203Contaminated Shellfish ........................................................................ 204Infected Food Handlers ........................................................................ 204Waterborne Transmission ........................................................................ 205Airborne Transmission ........................................................................ 205Outbreak Control ........................................................................ 205

    RELATIVE IMPORTANCE OF VIRAL GASTROENTERITIS TO ALL OUTBREAKSOF FOOD-BORNE AND WATERBORNE DISEASE .............................................................206

    SUMMARY ......................................................................... 206ACKNOWLEDGMENTS ........................................................................207REFERENCES ........................................................................ 207

    INTRODUCTION

    A viral etiology for outbreaks of acute infectious nonbac-terial gastroenteritis (AING) was confirmed in 1972 (67).Norwalk virus was subsequently shown to be a frequentcause of outbreaks of food-borne and waterborne AING inthe United States (20, 40, 69, 76). From 1978 through 1982,the clinical and epidemiologic features of outbreaks of food-borne and waterborne Norwalk virus infection were charac-terized (4, 43, 44, 47, 48, 70-72, 74, 108, 115); also, duringthe 1980s, an increasing variety of viral agents were impli-cated as causing outbreaks of food-borne or waterborneillness (8, 9, 26, 36, 45, 46, 60, 61, 73, 86, 105, 110). Theclinical aspects of these illnesses and the epidemiologicaspects of the outbreaks resembled those caused by Nor-walk virus. Transmission by food or water has been docu-mented for astroviruses, caliciviruses, rotaviruses, and agroup of small round structured viruses (SRSVs) known asNorwalk-like viruses (20).Laboratory confirmation of viruses as the causes of food-

    borne and waterborne illness is based on demonstration ofvirus particles or antigen in stool or demonstration of a risein specific antibody to the virus. These laboratory methodscontinue to be developed and refined. However, serologic or

    * Corresponding author.

    antigen testing is not widely available, and laboratory con-firmation of the etiology remains the exception in mostpublic health investigations of viral gastroenteritis outbreaks(19, 20). Thus, national surveillance data on food-borne andwaterborne illness in the United States and elsewhere un-derestimate the public health significance of these viruses.The use of epidemiologic criteria to classify outbreaks offood-borne and waterborne illness caused by Norwalk-likeviruses was promoted in 1982 but has not been widelyadopted by the public health community (5, 68). In theabsence of specific laboratory confirmation, epidemiologicclassification of these outbreaks may provide a more accu-rate assessment of their public health significance.

    AGENTS OF VIRAL GASTROENTERITIS ASSOCIATEDWITH OUTBREAKS OF FOOD-BORNE AND

    WATERBORNE DISEASE

    Several reviews of the clinical and epidemiologic featuresof viral gastroenteritis have been published recently (7, 20,21, 29). Outbreaks of food-borne or waterborne illness haveprimarily been associated with the small RNA viruses suchas Norwalk virus (69). Several Norwalk-like viruses havenot been well characterized with respect to their nucleic acidtype. It is possible that some small viruses, such as Ditchling

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  • 200 HEDBERG AND OSTERHOLM

    TABLE 1. Instructions for collecting specimens to evaluate outbreaks of viral gastroenteritisa

    Instructions for:Parameter

    Stool Serum

    Source 10 ill persons; 10 controls for comparison Same persons from whom stool was collected(optional) (controls optional)

    Specimen At least 10 mi/person in clean dry containers 15-ml (adults) and 3-ml (children) bloodspecimens collected in tubes containing noanticoagulants

    Time Within 48-72 h after onset of illness Collect acute-phase specimens at same time asstool; collect convalescent-phase specimens3-4 wk after onset of illness.

    Storage and shipping Immediately refrigerate at 4C. Place bagged Refrigerate tubes of serum until shipped withand sealed specimens with frozen refrigerant frozen refrigerant packs in insulated box.packs in insulated box. Send by overnight Keep specimens frozen by shipping on drymail. DO NOT FREEZE. ice. Send by overnight mail.

    a Adapted from the CDC (19).

    and Cockle agents, may be DNA parvoviruses (11). SmallRNA calciviruses and astroviruses and the larger double-stranded RNA rotaviruses are infrequently associated withoutbreaks of food-borne or waterborne disease (25, 55, 60).

    Classification of the Norwalk-like viruses has been basedlargely on morphology, mainly because of our inability tocultivate many of these viruses in vitro and the relativelysmall numbers of virus particles that can be recovered fromstool (12, 21, 29). Recently, findings from biochemical andimmunologic studies have resulted in a reevaluation of therelationship between Norwalk virus and the caliciviruses(25).Norwalk virus and Norwalk-like viruses are the most

    widely recognized agents of outbreaks of food-borne andwaterborne viral gastroenteritis (20). Norwalk virus was thefirst of these viruses to be characterized and serves as theepidemiologic prototype for the group. Norwalk-like virusesare small, round, morphologically similar viruses 25 to 30 nmin diameter (3, 12, 67, 93). Individual viruses (Norwalk,Hawaii, Snow Mountain, and Otofuke viruses) have beennamed for the locations of outbreaks from which the viruswas first isolated. The viruses are visually distinguishable byimmune electron microscopy (IEM) (25, 52, 90). Theseviruses have surface structures that are more amorphousthan those of calciviruses and astroviruses and that havebeen used as the basis for classifying the latter viruses (12).Norwalk virus and several Norwalk-like viruses possess asingle major structural polypeptide with molecular weightsthat range from 59,000 (Norwalk virus) to 63,000 (SRSV-9)(38, 52). Some Norwalk-like viruses exhibit antigenic cross-reactivity, as demonstrated by serologic responses of pa-tients (52, 90).

    Caliciviruses are similar in size to Norwalk-like viruses. Inaddition, cross-reacting antibody responses to infectionswith Norwalk virus and caliciviruses have been demon-strated by serology (25). However, caliciviruses are distin-guishable from Norwalk virus by characteristic cup-shapeddepressions on their outer surfaces. Astroviruses are char-acterized by having star-shaped configurations on smoothouter surfaces (12). These features can be distinguished byelectron microscopy (EM).

    Rotaviruses are approximately 70 nm in diameter andpossess a double-stranded segmented RNA core. Five dis-tinct antigenic groups of rotavirus have been recognized.

    Group A rotaviruses comprise the primary human patho-gens, while groups B through E have been associatedprimarily with animals (21). Group B and C rotaviruses havebeen primarily associated with infections in swine, and bothhave been implicated as causing outbreaks of food-borne orwaterborne viral gastroenteritis in humans in China (groupB) and Japan (group C) (86, 105). The diversity of rotavirusesis great. In addition to group specificity, a rotavirus can beclassified by serotype specificity, subgroup specificity, andstrain specificity (21, 116). These markers have potentialepidemiologic utility in the investigation of rotavirus out-breaks.

    Other viruses that are known or suspected to causegastroenteritis in humans but have not been implicated ascausing outbreaks of food-borne or waterborne illness in-clude adenoviruses, coronaviruses, enteroviruses, pestivi-ruses, picobirnaviruses, and toro