Human noroviruses challenges in prevention and control
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Human noroviruses : Challenges in Prevention and Control. Dr. Kristen Gibson Assistant Professor, Department of Food Science University of Arkansas AFDO Conference. Norovirus Transmission. Some history…. Discovered in 1972 by EM

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Human noroviruses: Challenges in Prevention and Control

Dr. Kristen Gibson

Assistant Professor, Department of Food Science

University of Arkansas

AFDO Conference


NorovirusTransmission


Some history…

  • Discovered in 1972 by EM

    • Infectious stool filtrate derived from outbreak in an elementary school in Norwalk, OH (1968)

  • Originally called “Norwalk virus”

    • Prototype strain of the noroviruses


Common Misnomers for Norovirus

  • Stomach Flu

  • “24-hour” Flu

  • Winter Vomiting Disease

  • Cruise Ship Virus

  • Norovirus is commonly

  • referred to as the “flu”:

    • seasonal component

    • rapid onset


Over 90% of diarrheal illness outbreaks on cruise ships are due to norovirus.


Norovirus: 2012-2013


Virus Structure and Function

  • Viruses 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.


Foodborne viruses of human health concern are:

  • Non-enveloped

  • Small (25-100 nm)

  • Resistant to environmental degradation


How small is “small”?


How small is “small”?


How small is “small”?


How small is “small”?


How small is “small”?


How small is “small”?


How small is “small”?


How small is “small”?


How small is “small”?


How small is “small”?


Norovirus

  • Single-stranded RNA, non-enveloped viruses

    • 5 genogroups (GI, GII, GIII, GIV, GV) and 31 genetic clusters

    • Human = GI, GII, and GIV

CDC, 2006. Norovirus: Technical Fact Sheet; Hutsonet al. 2004


80%

Glass et al., 2009


Norovirus

  • Single-stranded RNA, non-enveloped viruses

    • 5 genogroups (GI, GII, GIII, GIV, GV) and 31 genetic clusters

    • Human = GI, GII, and GIV

  • Clinical Symptoms

    • 24-48 hr incubation

    • Vomiting, watery diarrhea, stomach cramps, nausea, and general malaise

    • Self-limiting (24-60 hrs)

    • No known chronic sequelae

    • Complications include volume depletion and dehydration

    • Potential for chronic infections in immunocompromised and physically stressed individuals

CDC, 2006. Norovirus: Technical Fact Sheet; Hutsonet al. 2004


Norovirus

  • Routes

    • Fecal-oral route (food, water, person-person)

    • Environmental and fomite contamination

    • Aerosolization of vomitus (hotel carpet, reusable grocery bags)

  • Ease of transmission

    • ID = 19 to 100 virions

    • High rate of secondary transmission

  • Immunity

    • Strain-specific, lasting only a few months

    • Population immunity plays role in formation of novel variants

CDC, 2006. Norovirus:Technical Fact Sheet


U.S. Foodborne Outbreaks 2009-2010

  • Norovirus caused 49% (233) of lab confirmed single etiology outbreaks reported.

    • 34% due to an unknown etiology

  • Most common food commodity associated with NoV outbreaks are leafy vegetables.

  • NoV caused the most outbreaks from 1998 to 2008

Source: www.foodqualitynews.com

www.cdc.gov


Food safety issue?

  • Highly contagious

  • Prolific shedding

  • Constantly evolving

  • Limited immunity

  • Moderately virulent

Large pool of

susceptible hosts


Food safety issue?

  • Persistence and Environmental Stability

    • Resistant to common chemical disinfectants

    • Thermo-tolerant

    • Survives for weeks on surfaces and for months in water

Numerous NoV outbreaks each year are due to

transmission via contaminated surfaces.


Food as a Vehicle for Norovirus Transmission

  • Primary transmission

    • Contamination of foods in the “raw” material stage before harvest

      • Bivalve mollusks such as oysters

    • Application of contaminated water and sewage sludge to fruit and vegetable crops

      • Leafy vegetables, green onions, etc.


Oysters and Norovirus


Slide courtesy Michael T Osterholm University of Minnesota


Slide courtesy Michael T Osterholm University of Minnesota


Slide courtesy Michael T Osterholm University of Minnesota


Food as a Vehicle for Norovirus Transmission

  • Primary transmission

    • Contamination of foods in the “raw” material stage before harvest

      • Bivalve mollusks such as oysters

    • Application of contaminated water and sewage sludge to fruit and vegetable crops

      • Leafy vegetables, green onions, etc.

  • Secondary transmission

    • Occurs during processing, storage, distribution, and final preparation

      • Field workers

      • Infected food handlers

      • Contaminated surfaces or equipment


Retail Food Environments


Critical Control Points

  • Hand hygiene

    • Hand sanitizers (NOT a replacement for…)

    • Hand washing

  • Appropriate sanitizers and disinfectants

    • Concentration

    • Contact time

  • Tools for application and cleaning

    • Spray, foam, impregnated wipes

    • Reusable or disposable cloths


Cleaning Cloth Study


Cleaning Cloths?

Cellulose Cotton

Cellulose Cotton

Microfiber

Nonwoven Cloth

Cotton Terry Towel


Primary Questions

  • What 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?


Cleaning Cloth Study

  • Two surfaces

    • Stainless steel

    • Solid surface (e.g., formica)

  • 5 cleaning cloths

    • Cotton-cellulose blend (2)

    • Microfiber

    • Non-woven

    • Terry bar towel

  • 4 NoV surrogates and NoV GI.1


Cleaning Cloth Study

  • Virus Removal

    • 100,000 to 1,000,000 viruses on surface

      • 700 viruses from solid surface across all cloths

      • 1,400 viruses from stainless steel across all cloths


Cleaning Cloth Study: Virus Transfer

Two log difference in virus transfer between cellulose/cotton

and terry towel cloths.


Cleaning Cloth Study

  • Use 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 cloths…WHY?


Outbreaks associated with food or restaurant settings have significantly

higher attack rates (>50%) than outbreaks in other settings.


How to Address Food Safety and Norovirus

  • Shift the approach used for monitoring and control strategies

    • Proactive vs. Reactive

    • Understand 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 contaminants

    • Investigate priority contaminants (i.e., norovirus)

    • Selection of appropriate treatment technology

  • Outbreak Surveillance

    • Passive vs. Active


WASH YOUR HANDS


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