Noroviruses and Gastroenteritis

8/14/2019 Noroviruses and Gastroenteritis

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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


2/21

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

Documents

Noroviruses and Gastroenteritis