Human noroviruses: Challenges in Prevention and Control

Human noroviruses: Challenges in Prevention and ControlDr. Kristen GibsonAssistant Professor, Department of Food ScienceUniversity of Arkansas

AFDO Conference

Norovirus Transmission

Fecal contaminated water (irrigation, washing, etc.) can lead to contamination of minimally processed foodstuffs (oysters, raw produce). Food can also become contaminated by food handlers during preparationFlooding eventsSome historyDiscovered in 1972 by EMInfectious stool filtrate derived from outbreak in an elementary school in Norwalk, OH (1968)

Originally called Norwalk virusPrototype strain of the noroviruses

Common Misnomers for NorovirusStomach Flu

24-hour Flu

Winter Vomiting Disease

Cruise Ship VirusNorovirus is commonly referred to as the flu: seasonal component rapid onset4

Over 90% of diarrheal illness outbreaks on cruise ships are due to norovirus.Norovirus: 2012-2013

Virus Structure and FunctionViruses are small, intracellular parasites that cannot reproduce by themselves.

An infectious virus particle is referred to as a virion.

A virion consists of the nucleic acid and an outer shell of protein, referred to as a capsid.

A virion may be enveloped or non-enveloped.

Most viral host ranges are narrow.

7Viruses also often express proteins that modify host-cell processes so as to maximize viral replication.Envelope is basically a phospholipid bilayer or an outer membrane that prevents the breakdown of protein capsid and nuleic acids

Foodborne viruses of human health concern are:Non-enveloped

Small (25-100 nm)

Resistant to environmental degradation8How small is small?

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18NorovirusSingle-stranded RNA, non-enveloped viruses5 genogroups (GI, GII, GIII, GIV, GV) and 31 genetic clustersHuman = GI, GII, and GIVCDC, 2006. Norovirus: Technical Fact Sheet; Hutson et al. 2004

GII are more common followed by GI strainsGenetic clusters indicate similarity

Glass et al., 200980%Differ by 60% based on capsid sequenceGenotypes differ by 40%20NorovirusSingle-stranded RNA, non-enveloped viruses5 genogroups (GI, GII, GIII, GIV, GV) and 31 genetic clustersHuman = GI, GII, and GIV

Clinical Symptoms24-48 hr incubation Vomiting, watery diarrhea, stomach cramps, nausea, and general malaiseSelf-limiting (24-60 hrs)No known chronic sequelaeComplications include volume depletion and dehydrationPotential for chronic infections in immunocompromised and physically stressed individualsCDC, 2006. Norovirus: Technical Fact Sheet; Hutson et al. 2004

GII are more common followed by GI strainsGenetic clusters indicate similarityNorovirusRoutesFecal-oral route (food, water, person-person)

Environmental and fomite contamination

Aerosolization of vomitus (hotel carpet, reusable grocery bags)

Ease of transmissionID = 19 to 100 virions

High rate of secondary transmission

ImmunityStrain-specific, lasting only a few months

Population immunity plays role in formation of novel variantsCDC, 2006. Norovirus:Technical Fact Sheet

Virus particles can be shed up to 3 weeks after exposureFecal shedding of GII is 100-fold higher than GI therefore possibly explaining its dominance within outbreaks and the environment

U.S. Foodborne Outbreaks 2009-2010Norovirus caused 49% (233) of lab confirmed single etiology outbreaks reported.34% due to an unknown etiologyMost common food commodity associated with NoV outbreaks are leafy vegetables.NoV caused the most outbreaks from 1998 to 2008

www.cdc.gov

Source: www.foodqualitynews.com

Food safety issue?

Highly contagiousProlific sheddingConstantly evolvingLimited immunityModerately virulent

Large pool of susceptible hosts24Leading cause of endemic diarrheal disease across all age groupsPersistence and Environmental Stability

Resistant to common chemical disinfectants

Thermo-tolerant

Survives for weeks on surfaces and for months in waterFood safety issue?Numerous NoV outbreaks each year are due totransmission via contaminated surfaces.

25Food as a Vehicle for Norovirus TransmissionPrimary transmissionContamination of foods in the raw material stage before harvestBivalve mollusks such as oystersApplication of contaminated water and sewage sludge to fruit and vegetable cropsLeafy vegetables, green onions, etc.

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Oysters and Norovirus

Slide courtesy Michael T Osterholm University of Minnesota 28

Slide courtesy Michael T Osterholm University of Minnesota 29

Slide courtesy Michael T Osterholm University of Minnesota 30Food as a Vehicle for Norovirus TransmissionPrimary transmissionContamination of foods in the raw material stage before harvestBivalve mollusks such as oystersApplication of contaminated water and sewage sludge to fruit and vegetable cropsLeafy vegetables, green onions, etc.

Secondary transmissionOccurs during processing, storage, distribution, and final preparationField workersInfected food handlersContaminated surfaces or equipment

31Retail Food EnvironmentsCritical Control PointsHand hygieneHand sanitizers (NOT a replacement for)Hand washing

Appropriate sanitizers and disinfectantsConcentrationContact time

Tools for application and cleaningSpray, foam, impregnated wipesReusable or disposable cloths

33Cleaning Cloth Study

34Interestingly most studies of cleaning cloths have concentrated on bacteriaand usually in hospital settings as opposed to food service settings.Cleaning Cloths?

Cellulose CottonCellulose CottonMicrofiberNonwoven ClothCotton Terry Towel35Primary QuestionsWhat is the virus removal efficiency of each cloth?

Do the cloths transfer virus back to the surface? If so, what level of virus is transferred?36Cleaning Cloth StudyTwo surfacesStainless steelSolid surface (e.g., formica)

5 cleaning clothsCotton-cellulose blend (2)MicrofiberNon-wovenTerry bar towel

4 NoV surrogates and NoV GI.137Cleaning Cloth StudyVirus Removal100,000 to 1,000,000 viruses on surface700 viruses from solid surface across all cloths1,400 viruses from stainless steel across all cloths

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Two log difference in virus transfer between cellulose/cotton and terry towel cloths.Cleaning Cloth Study: Virus Transfer39Cleaning Cloth StudyUse of appropriate cleaning tools is a CRITICAL step in controlling transmission

Reusable cloths may be reservoirs for transmission of pathogens

First study to look at virus removal and transfer by cleaning clothsWHY?

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Outbreaks associated with food or restaurant settings have significantlyhigher attack rates (>50%) than outbreaks in other settings.How to Address Food Safety and NorovirusShift the approach used for monitoring and control strategiesProactive vs. ReactiveUnderstand the characteristics of norovirus

Optimization of methods for the detection of norovirus in foodstuffs

Hazard Analysis and Critical Control Points (HACCP)Better characterize risk posed by individual microbial contaminantsInvestigate priority contaminants (i.e., norovirus)Selection of appropriate treatment technology

Outbreak SurveillancePassive vs. Active42No virological criteria exists for water used in the production/processing of fresh produceWASH YOUR HANDS