noroviruses and gastroenteritis
TRANSCRIPT
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Investigating Noroviruses:Investigating Noroviruses:
A Case StudyA Case Study
David Bergmire-Sweat, MPHDavid Bergmire-Sweat, MPH
North Carolina Department of HealthNorth Carolina Department of Healthand Human Servicesand Human Services
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Norovirus FactsNorovirus Facts
Small, round-structured viruses fromSmall, round-structured viruses from
CaliciviridaeCaliciviridae familyfamily
First recognized as pathogenic cause ofFirst recognized as pathogenic cause of
gastroenteritis in 1968, Norwalk, Ohiogastroenteritis in 1968, Norwalk, Ohio
Transmitted via fecal-oral routeTransmitted via fecal-oral route
Highly contagiousas few as 10 viralHighly contagiousas few as 10 viral
particles can cause infectionparticles can cause infection
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SymptomsSymptoms
Incubation period ~ 24-48 hours, can be lessIncubation period ~ 24-48 hours, can be less
VomitingVomiting
Watery non-bloody diarrheaWatery non-bloody diarrhea Abdominal crampsAbdominal cramps
NauseaNausea
Low-grade feverLow-grade fever
Symptoms typically resolve ~ 24-60 hours (1-3 days)Symptoms typically resolve ~ 24-60 hours (1-3 days)
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Documented Modes ofDocumented Modes of
TransmissionTransmission Foodhandler contamination of items inFoodhandler contamination of items in
restaurantrestaurant
Daycare centersDaycare centers
Secondary person-to-personSecondary person-to-person
Aerosolized (vomiting and diarrhea)Aerosolized (vomiting and diarrhea)
Cleaning up after ill person in a bathroomCleaning up after ill person in a bathroom
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Immunity & EpidemiologyImmunity & Epidemiology
Seems to be strain-specific and temporarySeems to be strain-specific and temporary
(few months)(few months)
CDC estimates 23 million cases of acuteCDC estimates 23 million cases of acutegastroenteritis annually in U.S. due togastroenteritis annually in U.S. due to
norovirusesnoroviruses
CDC estimates noroviruses cause ~50% ofCDC estimates noroviruses cause ~50% ofall foodborne disease outbreaksall foodborne disease outbreaks
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DetectionDetection Best method is via reverse transcriptaseBest method is via reverse transcriptase
polymerase chain reaction (RT-PCR)polymerase chain reaction (RT-PCR)
Viral RNAViral RNA
Adults can shed viral particles for up to 2Adults can shed viral particles for up to 2
weeks after symptoms resolveweeks after symptoms resolve
Infants and toddlers may shed longerInfants and toddlers may shed longer
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Case StudyCase Study
Small state university northSmall state university north
of Houston, TXof Houston, TX
Student body ~ 10,000Student body ~ 10,000
studentsstudents
2,054 students owned meal2,054 students owned meal
plansplans
125 students present to125 students present to
student health center andstudent health center andlocal hospital withlocal hospital with
gastrointenteritis in 24 hrgastrointenteritis in 24 hr
periodperiod
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SymptomsSymptoms
125 ill students on March 10-11 1998125 ill students on March 10-11 1998
23 admitted to hospital23 admitted to hospital
91% reported vomiting91% reported vomiting
85% reported diarrhea (3+ loose stools in85% reported diarrhea (3+ loose stools in
24 hours)24 hours)
68% reported abdominal cramps68% reported abdominal cramps
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Epidemic CurveEpidemic Curve
0
5
10
15
20
25
30
35
Date 5-
Mar
6-
Mar
7-
Mar
8-
Mar
9-
Mar
10-
Mar
11-
Mar
12-
Mar
13-
Mar
14-
Mar
15-
Mar
Cases by Onset Date
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Laboratory InvestigationLaboratory Investigation
62 stool samples sent to Texas Department62 stool samples sent to Texas Department
of Health Lab in Austinof Health Lab in Austin
All negative forAll negative forSalmonella, Shigella,Salmonella, Shigella,
Campylobacter, Yersinia, E. coliCampylobacter, Yersinia, E. coli O157:H7,O157:H7,
Bacillus cereus,Bacillus cereus, andand Staphylococcus aureusStaphylococcus aureus
18 samples tested for Norovirus by RT-18 samples tested for Norovirus by RT-PCR; 9 were positivePCR; 9 were positive
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Challenges of CafeteriaChallenges of Cafeteria
OutbreaksOutbreaks Verifying ExposuresVerifying Exposures
Identifying potentialIdentifying potential
healthy controlshealthy controls Finding people toFinding people to
interview theminterview them
Hundreds of foodHundreds of food
itemsitems
Rule in/out otherRule in/out other
exposuresexposures
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Rapid ActionRapid Action
Outbreak occurred toward end of week,Outbreak occurred toward end of week,
right before Spring Breakright before Spring Break
Sanitarians from local health departmentSanitarians from local health department
investigated, realized cafeteria was about toinvestigated, realized cafeteria was about to
close for week and perform massiveclose for week and perform massive
cleaning/maintenancecleaning/maintenance Locked down all present food items,Locked down all present food items,
instructed staff not to throw anything outinstructed staff not to throw anything out
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Epidemiologic InvestigationEpidemiologic Investigation
Unmatched Case-Unmatched Case-
control study bycontrol study by
Texas Dept. of HealthTexas Dept. of Health 36 ill subjects36 ill subjects
136 well controls136 well controls
Matched Case-controlMatched Case-control
study by CDCstudy by CDC
29 ill subjects29 ill subjects 29 well controls29 well controls
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Findings Matched StudyFindings Matched Study
Exposure Odds Ratio ConfidenceIntervals
Pvalue
Deli sandwich
3/9 lunch
11.0 1.6-473 < 0.01
Deli sandwich3/9 supper
6.0 0.7-276 0.06
Deli sandwich3/10 lunch
8.0 1.1-355 0.02
Deli sandwich3/10 supper
1.0 0.01-79 .75
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Findings Unmatched StudyFindings Unmatched Study
Exposure Odds Ratio ConfidenceIntervals
Pvalue
Deli sandwich 3/9lunch
11.1 3.9-32 < 0.001
Deli sandwich 3/9supper
7.1 1.6-33
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InterpretationInterpretation
Both studies implicated deli sandwichesBoth studies implicated deli sandwiches
on 3/9 and 3/10on 3/9 and 3/10
The more controls in a study, the betterThe more controls in a study, the better
statistical power you havestatistical power you have
No other restaurants or food items showedNo other restaurants or food items showed
any associationany association
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Cafeteria Staff InvestigationCafeteria Staff Investigation
Sanitarians and epidemiologists interviewedSanitarians and epidemiologists interviewed
foodhandlersfoodhandlers
All denied illnessAll denied illness All except one submitted stool samples forAll except one submitted stool samples for
testingtesting
One refused; cafeteria manager fired herOne refused; cafeteria manager fired her She was responsible for slicing deli meats andShe was responsible for slicing deli meats and
making deli sandwichesmaking deli sandwiches
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DiscussionDiscussion
CDC and TDH epidemiologists wereCDC and TDH epidemiologists weredisappointed with cafeteria manager decisiondisappointed with cafeteria manager decision
to fire the one employeeto fire the one employee Much more difficult to get cooperationMuch more difficult to get cooperation
Eventually did interview herEventually did interview her
She denied illness, but had infant with diarrheaShe denied illness, but had infant with diarrhea
Stool sample from infant was PCR positive forStool sample from infant was PCR positive forNorovirusNorovirus
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Chance to Learn SomethingChance to Learn Something
Researchers at BaylorResearchers at Baylor
College of MedicineCollege of Medicine
agreed to try to findagreed to try to findvirus RNA on delivirus RNA on deli
meatmeat
Never been doneNever been done
beforebefore
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Success!Success!
Lab successful inLab successful indesigning protocol fordesigning protocol forrecovering virus RNArecovering virus RNA
from deli meatfrom deli meat Pulsed-Field GelPulsed-Field Gel
analysis of PCR resultsanalysis of PCR resultsshowed identicalshowed identical
pattern between infant,pattern between infant,ill students, and deliill students, and delimeatsmeats
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Take Home PointsTake Home Points
Viral gastroenteritis is easy to spreadViral gastroenteritis is easy to spread
Foodhandlers must be extremely careful, evenFoodhandlers must be extremely careful, even
when they are not sick, with hygienewhen they are not sick, with hygiene It is possible to recover Norovirus from foodIt is possible to recover Norovirus from food
Quick reaction by local health departmentQuick reaction by local health departmentsanitarians preserved food samplessanitarians preserved food samples
Collaboration with research lab advancedCollaboration with research lab advancedscience of food safety researchscience of food safety research