Transcript Kristen E. Gibson, Assistant Professor of Molecular Food

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
– 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; Hutson et 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
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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; Hutson et 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
Source: www.foodqualitynews.com
• 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
www.cdc.gov
Food safety issue?
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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
Nonwoven Cloth
Microfiber
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
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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