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Interpretive Summary:

Quantitative Risk Assessment on thePublic Health Impact of PathogenicVibrio parahaemolyticusIn Raw Oysters

Center for Food Safety and Applied NutritionFood and Drug AdministrationU.S. Department of Health and Human Services

July 2!

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Quantitative Risk Assessment on the Public Health Impact of PathogenicVibrio parahaemolyticusin Raw Oysters

PR!A"

#his "nterpretive Summary provides an overvie* of the 2+ Food and DrugAdministration ,FDA- Vibrio parahaemolyticusris assessment. "ts purpose is to /rieflydescri/e0 in non1technical language0 the material covered in the complete ris assessment.#his includes /acground information on Vibrio parahaemolyticus0 the techniues anddata used to develop the ris assessment0 the results of the ris assessment0 and theinterpretation0 implications and limitations of those findings. A full understanding of theris assessment reuires the reader to consider the complete ris assessment. #hecomplete ris assessment may /e o/tained on the "nternet at TU***.cfsan.fda.govUT. Aprinted copy *ill /e provided upon reuest. %euests may /e fa3ed to the CFSAN4utreach and "nformation Center at 51677189918822.

I#$RO%&"$IO#

Vibrio parahaemolyticusis a /acterium that occurs naturally in coastal marine *aters andestuaries ,*here rivers flo* into the sea-. "t is recogni:ed *orld1*ide as a significantcause of /acterial seafood1/orne illness. #he United States Centers for Disease Controland &revention ,CDC- estimates that of the appro3imately 7066 Vibrioillnesses each yearin the United States0 appro3imately 206 are estimated to /e associated *ith Vibrioparahaemolyticusand ra* oyster consumption. Vibrio parahaemolyticusis normallypresent in many types of ra* seafood0 including fish0 crustaceans0 and molluscan shellfish."t multiplies and coloni:es in the gut of filter1feeding shellfish such as oysters0 clams0 and

mussels. Not all strains of Vibrio parahaemolyticuscause illness; on the contrary0pathogenic strains represent a small percentage of the total Vibrio parahaemolyticuspresent in the environment or seafood.

FDA conducted this 7 and5>>6 in the United States involving more than 7 cases of Vibrio parahaemolyticusillness. #hese out/reas rene*ed concern for this pathogen as a serious food/orne threatto pu/lic health and raised concerns a/out the effectiveness of the ris managementguidance availa/le at that time.

2Vibrio parahaemolyticus %is Assessment
http://www.cfsan.fda.gov/http://www.cfsan.fda.gov/http://www.cfsan.fda.gov/http://www.cfsan.fda.gov/http://www.cfsan.fda.gov/

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#his ris assessment is /ased on a uantitative simulation model. #he focus is on ra*oysters0 /ecause that is the food in the United States predominately lined to out/reas ofillness associated *ith this pathogen since 5>>7. #he ris assessment e3amines eventsoccurring from oyster harvest to consumption that influence the levels of Vibrioparahaemolyticus liely to /e present in ra* oysters at the time of consumption. #helevels of Vibrio parahaemolyticusin oysters at the time of consumption are influenced /ythe harvest methods and environmental conditions0 as *ell as the handling of oysters afterharvest. #hese practices and conditions vary considera/ly among different geographicareas and at different times of the year. #herefore0 the model *as constructed to predictillnesses for each harvest region and season in the United States. #he lielihood andseverity of illness follo*ing e3posure to pathogenic Vibrio parahaemolyticusfromconsumption of ra* oysters *as estimated. 4nce developed0 the /aseline model *as usedto develop

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specified su/population. For this ris assessment the lielihood and severity of illnessfrom the consumption of ra* oysters containing pathogenic Vibrio parahaemolyticus*ere predicted. An important part of this step is determining the uncertaintiesassociated *ith these predicted ris estimates distinguishing0 to the e3tent possi/le0uncertainty from the inherent variation that occurs in any /iological and environmentalsystem.

Summary Figure 5 depicts a schematic representation of the components of the Vibrioparahaemolyticusris assessment model. #he $3posure Assessment model *as separatedinto three modules? harvest0 post1harvest0 and consumption. #he model outputs from the$3posure Assessment *ere then com/ined *ith the Dose1%esponse model to relate thesee3posures to pu/lic health outcomes. #he model inputs are e3pressed as distri/utionsinstead of single point estimates ,such as a mean-. Using a distri/ution allo*s a range ofvalues0 each *ith a specific freuency of occurrence0 to /e included in the model.Distri/utions are commonly used in simulation modeling to account for the inherent/iological varia/ility in nature and our uncertainty of the

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Summary !igure )* Schematic Representation of the 1ibrio parahaemolyticusRisk

Assessment +o,el E#he light grey /o3es *ith /lac lettering sho* the Harvest (odule0 the gray/o3es *ith /lac lettering sho* the &ost1Harvest (odule0 the dar grey /o3es *ith *hite lettering sho*the Consumption (odule0 the *hite /o3es *ith /lac lettering sho* the Dose1%esponse model0 and the*hite /o3es *ith dar /lac outline sho* the %is Characteri:ation. 'p Vibrio parahaemolyticusG


Cold Storage TimeDie-off Rate

Relationship between TotalVpin Oysters and Water

TemperatureTotal Vp/g Oyster

at Harvest

Water Temperature[regional/seasonal

variation]

Ratio of athogeni! to Total Vp/gin Oysters

Duration of HarvestTime-to-Refrigeration"ir Temperature#rowth Rate

Cooldown Time#rowth RateCooldown Time

#rams per Oyster$umber of Oystersper Serving

athogeni!Vp/g in Oysters

at Harvest

athogeni! Vp/gOysters at Time of

%nitial Refrigeration

athogeni! Vp/gOysters at Retail

Ris& of %llness'per year(

Dose-ResponseRelationship

Ris& of %llness'per serving(

athogeni!Vp/g Oysters at

Refrigeration

athogeni! Vp per

serving atConsumption

Human Clini!alStudies

Surveillan!e Data

)re*uen!y ofServings

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HA2AR% I%#$I!I"A$IO#

Vibrio parahaemolyticusis a salt tolerant /acterium and a normal inha/itant of the marineenvironment. #his /acterium is found in many types of seafood0 including fish0crustaceans0 and molluscan shellfish. "t *as first isolated in 5>! and implicated in anout/rea of food poisoning in Japan. "n the United States0 the first confirmed out/rea ofVibrio parahaemolyticusillness occurred in (aryland in 5>75. Since 5>>70 several largeout/reas0 associated *ith the consumption of ra* oysters0 have /een reported in theUnited States. #hese out/reas are sho*n in Summary #a/le 2.

Summary $able -* Outbreaks of Illnesses from Vibrio parahaemolyticus

Associate, with "onsumption of Raw Oysters in the &nite, States

3ear (ocation #umber of "ases

5>>7 &acific North*esta 2>5>>65>>65>>6

&acific North*esta

#e3asNortheast Atlantic

+6+59/

522 Ne* )or 722 Ne* Jersey 552+ Alasa +9

a #he &acific North*est includes California0 4regon0 Bashington State0 and ritish Colum/ia./ 2>9 cases in #e3as and52 cases in other states that *ere traced /ac to oysters harvested from #e3as.

Human illnesses from ingestion of Vibrio parahaemolyticushave /een *ell documented.Any e3posed individual can /ecome infected *ith Vibrio parahaemolyticusand developillness. #he most common clinical manifestation of Vibrio parahaemolyticusinfection isgastroenteritis0 an inflammation of the gastrointestinal tract. @astroenteritis is usually an

illness of short duration and moderate severity that is characteri:ed /y diarrhea0 vomiting0and a/dominal cramps. Vibrio parahaemolyticusinfections can also lead to septicemia0 asevere0 life1threatening disease caused /y the multiplication of pathogenic microorganismsandor the presence and persistence of their to3ins in circulating /lood. "ndividuals *ithunderlying chronic medical conditions ,such as dia/etes0 alcoholic liver disease0 hepatitis0and those receiving immunosuppressive treatments for cancer or A"DS- do not appear to/e at a higher ris of acuiring the initial infection than other*ise healthy people.Ho*ever0 individuals *ith underlying chronic conditions do appear to have a higher ris ofthe initial infection developing into septicemia.

#he CDC estimates that of the total Vibrioillnesses in the United States ,average 7066per year-0 there are appro3imately +0! Vibrio parahaemolyticusillnesses and of thoseappro3imately 206 are estimated to /e associated *ith ra* oyster consumption. #herehave /een reports of Vibrio parahaemolyticusillness associated *ith various types ofcooed and ra* seafood including crayfish0 lo/ster0 shrimp0 cra/0 oysters0 and clams.Vibrioillnesses associated *ith cooed seafood are liely due to inadeuate heating orrecontamination after cooing. Although thorough cooing destroys Vibrio0 oysters areoften eaten ra*0 *hich may e3plain *hy it is the most common seafood associated *ithVibrioinfection in the United States. $pidemiological data indicate that consumers of ra*oysters are 2.6 times more liely to e3perience Vibrio parahaemolyticusillness compared


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to non1ra* oyster eaters. Food intae surveys indicate that ra* shellfish is not acommonly consumed food in the United States? only 5 to 2I of the populationconsumes ra* shellfish at least once a year. Among oyster consumers0 ra* oysters aretypically eaten appro3imately once every 9 *ees and the typical serving si:e ranges from9 to 2+ oysters0 *ith 52 /eing the most freuent.

Not all strains of Vibrio parahaemolyticuscause illness; on the contrary0 pathogenicstrains generally represent a small percentage of the total Vibrio parahaemolyticuspresentin the environment or seafood. &athogenic Vibrio parahaemolyticusstrains are moreliely to produce symptomatic infections and have one or more distinctive traits that aregenerally a/sent in non1pathogenic strains. #*o important virulence indicators are thea/ility to produce thermosta/le direct hemolysin ,#DH- and the a/ility to produce arelated to3in0 thermosta/le related hemolysin ,#%H-. Hemolysin is an en:yme that /reasdo*n red /lood cells on a /lood agar plate0 *hich is referred to as the anaga*aphenomenon. #he vast maority of Vibrio parahaemolyticusstrains isolated from thestools of patients *ith Vibrio parahaemolyticusgastroenteritis are #DH1positive ,#DHK-.#he role of traits other than #DH has not yet /een determined. #herefore0 for the

purposes of this ris assessment0 pathogenic Vibrio parahaemolyticusis defined as strainsthat are #DHK.

Vibrio parahaemolyticusinfections occur throughout the year0 peaing in spring andsummer. Cases are most often associated *ith the regions of the country *ithin closepro3imity to marine environments. #he geographical distri/ution of cases attri/uted tooysters from specific harvest areas liely reflects the propensity for individuals in closepro3imity to coastal areas to consume ra* shellfish. ie*ise0 the volume of oystersharvested in the U.S. each year varies /y season. Appro3imately 99I of the annual oysterharvest occurs in the *inter and fall *ith the remainder in spring and summer. #here arealso regional differences in the oyster harvest volume; the @ulf Coast accounts for

appro3imately one1half of the oyster harvest0 the &acific North*est a/out a fourth0 andless than a tenth from the (id1Altantic region. "n addition0 regional climatic differences,e.g.0 *ater temperatures- and post1harvest handling practices influence the levels ofVibrio parahaemolyticusin shellfish and conseuently the potential for illness.

HA2AR% "HARA"$RI2A$IO#

"n a uantitative ris assessment0 the Ha:ard Characteri:ation typically entails thedetermination of a dose1response relationship for a specified population0 relating theincidence of an identified adverse effect *ith the level of e3posure to a particularmicroorganism ,or su/stance-. #his dose1response relationship is often e3pressed as arelation /et*een different levels of e3posure and the lielihood ,or pro/a/ilities- that suche3posures *ill result in illness. For this ris assessment0 a uantitative relationship *asdeveloped to predict the num/er and severity of illnesses resulting from ingestion ofpathogenic Vibrio parahaemolyticus.

A uantitative dose1response model for Vibrio parahaemolyticus*as developed /ased onhuman clinical feeding studies. #he model e3trapolates the o/served illness rates from thestudies to doses and illness rates that are more liely to /e encountered *ith contaminated


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oysters. Ne3t0 the dose1response curve *as adusted to account for the estimates of theannual illness /urden ,206 cases per year- as determined /y CDC. #his approach istypically referred to as Vibrio parahaemolyticus %is Assessment

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Summary !igure -. $he %ose4Response +o,el for Vibrio parahaemolyticus (Vp)E#he solid line is the /est estimate of the model fit to pooled human feeding studies. #he dashed linesho*s the shift adustment so that the model predictions agree *ith epidemiological surveillance data.($ denotes the ma3imum lielihood estimate. "D!is the dose corresponding to a !I pro/a/ility ofgastroenteritis.G

5POS&R ASSSS+#$

#he purpose of the $3posure Assessment is to determine the lielihood of ingestingpathogenic Vibrio parahaemolyticusfrom consumption of ra* oysters0 and the liely levelof e3posure. "nsufficient data are availa/le on the levels of pathogenic Vibrioparahaemolyticusin ra* oysters at the moment of consumption. #herefore0 the modelpredicts these levels using availa/le data on the factors that influence the levels of thepathogen present in oysters at harvest. #hese factors include the environmental conditionsthat contri/ute to the liely presence of Vibrio parahaemolyticusin oysters at harvest andthe impact of post1harvest handling and processing practices on the gro*th or decline of

Vibrio parahaemolyticusin oysters prior to consumption. "n addition0 the freuency ofoyster meals and the amount of oysters consumed per serving *ere considered.

#he $3posure Assessment *as divided into three modules that reflect the chain of eventsfrom oyster harvest to consumption? Harvest0 &ost1Harvest0 and Consumption. #he levelsof total and pathogenic Vibrio parahaemolyticusin oysters *ere estimated for eachhandling or processing event. #he predicted levels of Vibrio parahaemolyticusfrom eachmodule *ere used as inputs for the su/seuent module ,e.g.0 results from the Harvest


0%

25%

50%

75%

100%

100,000

1,000,000

10,000,000

100,000,000

1,000,000,000

+ean Dose ',p !ells per serving(

Ris&of%llness

%nferredDose-

ResponsewithOyster)ood+atri

+. of Dose-ResponseObserved in

,olunteer)eeding Trialswith0i!arbonate

%nferred %D12withOyster )ood

+atri

stimated

%D12in )eedingTrials

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Summary #a/le 8 provides the predicted mean levels of Vibrio parahaemolyticusatharvest for each of the 2+ regionseason com/inations. Across all regions0 the predictedlevels are much higher in the *armer months compared to the cooler months. #hepredicted levels for the @ulf Coast region are considera/ly higher than the other regionsdue to the *armer *ater temperatures. During the summer0 the levels of Vibrioparahaemolyticusin the mid1Atlantic and Northeast Atlantic are higher than those of the&acific North*est ,*hen harvest occurs /y dredging-. $ven during the summer0 airtemperatures in the &acific North*est are cooler0 on average0 than in the @ulf and Atlanticregions. Ho*ever0 e3posure to higher temperatures for longer time periods0 such asoccurs during intertidal harvest in some &acific North*est areas0 allo*s for additionalgro*th0 resulting in an increase of total and pathogenic Vibrio parahaemolyticusto levelshigher than that of the Northeast Atlantic region.

Summary $able 6* Pre,icte, +ean (evels of Vibrio parahaemolyticus per gram inOysters At4Harvest

Region (evel Summera !alla 0intera Springa

@ulf Coast #otal 205 22 !2 >+

,ouisiana-/ &athogenic + L5 L5 2@ulf Coast,Non1ouisiana-/

#otal 205 22 !2 >+&athogenic + L5 L5 2

(id1Atlantic #otal 76 !5 8 2&athogenic 5 L5 L5 L5

Northeast Atlantic #otal 28 88 + +2&athogenic L5 L5 L5 L5

&acific North*est,Dredged-c

#otal ! L5 L5 L5&athogenic L5 L5 L5 L5

&acific North*est,"ntertidal-d

#otal 9! 2 L5 95&athogenic 5! L5 L5 5

a&redicted mean levels of total and pathogenic Vibrio parahaemolyticusper gram of ra* oysters. 'alues

rounded to 2 significant digits./

Note? the values for ouisiana and non1ouisiana areas are the same/ecause the *ater temperature is similar for these regions. Differences in the @ulf Coast states occur inthe post1harvest portion of the model ,See Summary #a/le +-. c&redicted mean levels *hen oyster reefsare su/merged. d&redicted mean levels after intertidal e3posure.

Post4Harvest +o,ule* #he &ost1Harvest (odule of the $3posure Assessment modelpredicts the effects of typical industry practices on Vibrio parahaemolyticus densities inoysters during transportation0 distri/ution0 and storage from harvest through retail. Afteroysters are harvested0 levels of Vibrio parahaemolyticuscan increase or decline in oystersduring handling and storage /efore consumption. After harvesting0 oysters are typicallystored unrefrigerated on the oyster /oat for a period of time ranging from a fe* hours to

more than half a day. #he potential gro*th of Vibrio parahaemolyticusin the oystersduring this period of unrefrigerated holding is a function of the air temperature at the timeof harvest and the length of time oysters are unrefrigerated. 4nce the oysters are placedunder refrigeration ,e.g.0 during transport or after arrival at *holesalers-0 the rate ofgro*th slo*s until oysters reach a

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Summary $able 8* Pre,icte, +ean (evelsof $otal an, Pathogenic Vibrioparahaemolyticusper Serving of Oysters at "onsumption

Region (evel Summera !alla 0intera Springa

@ulf Coast ,ouisiana- #otal 5200 5020 !60 +090&athogenic 250 20 >6 70>

@ulf Coast ,Non1ouisiana- #otal 60!0 !0 270 8020&athogenic 5!0 66 +7 !09

(id1Atlantic #otal 20!0 920 26 6!0&athogenic +08 55 L5 50!

Northeast Atlantic #otal !0 550 8 50&athogenic 69 57 L5 56

&acific North*est,Dredged-/

#otal 250 +9 2 50>&athogenic +9 5 L5 +8

&acific North*est ,"ntertidal-c

#otal 880 6 8 80&athogenic 70! 57 L5 7+

a&redicted mean levels of total and pathogenic Vibrio parahaemolyticusper serving of ra* oysters.'alues rounded to 2 significant digits. /&redicted mean levels *hen oyster reefs are su/merged. c&redicted mean levels after intertidal e3posure.

RIS/ "HARA"$RI2A$IO#

#he %is Characteri:ation com/ines the results of the $3posure Assessment model *iththe Dose1%esponse model to predict the num/er of illnesses and the severity of illnessassociated *ith different regions and seasons. $stimates of the uncertainty associated *iththese predictions of ris and illness /urden ,i.e.0 upper and lo*er /ounds- are alsodetermined. For simplicity0 the results of these regional and seasonal predictions of illnessare presented /elo* as the mean of the distri/ution ,i.e.0 the mean num/er of predictedillnesses-. A detailed description of the uncertainty distri/utions can /e found in the

complete ris assessment. Sensitivity analyses *ere conducted to evaluate the importanceof the various input factors on the model results. #he model *as validated /y comparingthe results to a retail study and epidemiological data.

Pre,icte, Illness 9ur,en

%is per Serving. #he

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Summary $able * Pre,icte, +ean Risk per Serving Associate, with the"onsumption of Pathogenic Vibrio parahaemolyticusin Raw Oysters

Region +ean Risk Per Servinga

Summer !all 0inter Spring $otal

@ulf Coast ,ouisiana- +.+ 3 51+ +.8 3 51! 2.5 3 519 5.7 3 51+ 9.9 3 51+

@ulf Coast ,Non1ouisiana-/ 8.5 3 51+ 5.> 3 51! 5.5 3 519 5.2 3 51+ +.! 3 51+

(id1Atlantic >.2 3 51! 2.2 3 519 5.5 3 516 8.5 3 51! 5.8 3 51+

Northeast Atlantic 5.6 3 51! +. 3 517 5.5 3 516 8.9 3 519 2.2 3 51!

&acific North*est ,Dredged- 5. 3 51! 2.9 3 516 6.5 3 515 6.7 3 517 5.5 3 51!

&acific North*est ,"ntertidal-c 5.+ 3 51+ 8.> 3 517 5.7 3 51> 5.8 3 51! 5.! 3 51+a %is per serving refers to the predicted ris of an individual /ecoming ill ,gastroenteritis alone orgastroenteritis follo*ed /y septicemia- *hen he or she consumes a single serving of ra* oysters.

/"ncludes oysters harvested from Florida0 (ississippi0 #e3as0 and Ala/ama. #he time from harvest torefrigeration in these states is typically shorter than for ouisiana.c4ysters harvested using intertidal methods are typically e3posed to higher temperature for longer times

/efore refrigeration compared *ith dredged methods.

%is per Annum* #he 2I are attri/uted to oysters harvested from the @ulf Coast,ouisiana and non1ouisiana states- region in the spring0 summer and fall and from the&acific North*est ,intertidal- region in the summer. #he lo*er num/ers of illnessespredicted for the Northeast Atlantic and (id1Atlantic oyster harvests are attri/uta/le /othto the colder *ater temperatures and the smaller harvest from these regions. #heharvesting practice also has an impact on the illness rate. "ntertidal harvesting in the&acific North*est poses a much greater ris than dredging in this region ,5>2 vs. +illnesses per year-. #his is liely attri/uta/le to elevation of oyster temperatures duringintertidal e3posure leading to Vibrio parahaemolyticusgro*th.Summary $able ;* Pre,icte, +ean Annual #umber of Illnesses Associate, with the"onsumption of Vibrio parahaemolyticusin Raw Oysters

Region +ean Annual Illnessesa

Summer !all 0inter Spring $otal

@ulf Coast ,ouisiana- 50+9 582 7 !! 20!@ulf Coast ,Non1ouisiana-/ 2>> !5 8 5>8 !+9

(id1Atlantic 7 + L5 + 5!

Northeast Atlantic 5+ 2 L5 8 5>

&acific North*est ,Dredged- + L5 L5 L5 +

&acific North*est ,"ntertidal-c

578 5 L5 56 5>2$O$A( 50>8 5> 5 728 20629

a (ean annual illnesses refers to the predicted num/er of illnesses ,gastroenteritis alone or gastroenteritisfollo*ed /y septicemia- in the United States each year./ "ncludes oysters harvested from Florida0 (ississippi0 #e3as0 and Ala/ama. #he time from harvest torefrigeration in these states is typically shorter than for ouisiana. c 4ysters harvested using intertidalmethods are typically e3posed to higher temperature for longer times /efore refrigeration compared *ithdredged methods.

5!Vibrio parahaemolyticus %is Assessment

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Severity of "llness. #he predicted num/er of cases of septicemia *as determined for thetotal United States population as sho*n in Summary #a/le 6. #he num/er of predictedcases of septicemia *as calculated /y multiplying the mean num/er of predicted illnesses,Summary #a/le 7- /y the pro/a/ility of gastroenteritis progressing to septicemia,.28-. #he calculation of the pro/a/ility of gastroenteritis progressing to septicemia isdescri/ed in the complete ris assessment. Since most of the cases of illness are predictedto /e associated *ith the @ulf Coast ,ouisiana- harvest0 this is also the harvest that*ould /e e3pected to /e associated *ith the highest num/er of cases of septicemia.

Anyone e3posed to Vibrio parahaemolyticuscan /ecome infected and developgastroenteritis. Ho*ever0 compared to the healthy population0 there is a/out a +1foldhigher pro/a/ility of an infected individual *ith a concurrent underlying chronic medicalcondition developing septicemia. #he model predicts a/out 7 cases of septicemia eachyear for the total population0 of *hich 2 *ould /e e3pected to occur in healthy individualsand ! *ould /e e3pected to occur among the immunocompromised population.


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Summary $able

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Summary !igure 6* $orna,o Plot of Influential 1ariability !actors of Vibrioparahaemolyticus=1p> Illness per Serving of Raw Oysters in the 'ulf "oast=(ouisiana> Summer Harvest

+o,el 1ali,ation

$3posure predictions *ere validated /y comparing predicted Vibrio parahaemolyticuslevels in oysters at the time of consumption to data from a 5>>615>>> survey of Vibrioparahaemolyticuslevels in oysters at retail conducted colla/oratively /y the "nterstateShellfish Sanitation Conference ,"SSC- and the FDA ,Summary Figure +-. #hese data*ere not used in the development of the ris assessment model. "n general0 the meanVibrio parahaemolyticuslevels predicted /y the model compared *ell *ith the meanlevels from the "SSCFDA survey0 particularly for the @ulf and (id1Atlantic summer *henthe ris of illness is highest. For the &acific North*est0 the model predictions are higherthan the "SSCFDA estimates0 /ut there is su/stantial uncertainty associated *ith the"SSCFDA data for this region due to the relatively small num/er of samples. ased onthe generally good agreement /et*een model1predicted V. parahaemolyticusdensities and

o/served densities at retail0 the e3posure assessment portion of the model is considered to/e validated.


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Summary !igure 7* Observe, log).%ensity of $otal Vibrio parahaemolyticusat Retail"ompare, to +o,el Pre,ictions for the 'ulf "oast =(ouisiana an, non4(ouisianastates> E#he error /ars indicate one standard deviation a/ove and /elo* either the model predictions,suare /o3- or o/served values ,filled circle-.G

#he corresponding validation of the ris estimates /ased on a comparison of the risassessment predictions and availa/le epidemiological data sho*ed a higher degree of

uncertainty. #he surveillance data reported to CDC are the only data availa/le to validatethe model predictions of illness for each region and season. #emporally0 the modelpredictions and CDC data /oth indicate that the ris of illness is higher in the spring andsummer than in the *inter and fall. Ho*ever0 agreement /et*een the surveillance dataand the regional predictions of ris *ere less clear cut0 though /oth sho*ing similar trends,e.g.0 the highest num/er of illnesses are associated *ith @ulf Coast oysters follo*ed /y&acific North*est oysters-. "n part0 this uncertainty reflects the fact that the surveillancedata indicate *here ,location- the illness occurred and the model predicts illnessesattri/uted to *here ,region- oysters *ere harvested. "t is difficult to trace the oysters thatcaused an illness /ac to the harvest region. ecause of the intrinsic difference in *hat thet*o systems measure ,location of illness occurrence vs. harvest region of oysters thatcause illness-0 full validation of the regional model predictions of illness /ased on regional

surveillance data *ill reuire additional research and targeted surveillance initiatives *ithmore thorough trace/ac data.

0HA$4I! S"#ARIOS

5>Vibrio parahaemolyticus %is Assessment

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model predi!tions

Summer )allSpringWinter

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#he ris assessment model can /e used to estimate the liely impact of interventionstrategies on the predicted num/er of illnesses. #he impact of different harvestingmethods0 seasons ,i.e.0 *ater and air temperatures-0 time until refrigeration0 and length ofstorage /efore consumption *ere parameters considered in the /aseline model. ychanging one or more of the input parameters and measuring the resulting change in themodel outputs0 the liely impact of ne* or different processing procedures or regulatoryactions can /e evaluated. #hese changes to the /aseline model are commonly referred toas -. #reatmentsuch as immediate refrigeration decreased the num/er of predicted illnesses /yappro3imately 51fold. #he effect of immediate refrigeration is less pronounced in thecooler regions than in the *armer @ulf Coast. #reatment causing a 21log decrease in the

levels of Vibrio parahaemolyticusin oysters reduces the pro/a/ility of illness /yappro3imately 51fold. #reatment causing a +.!1log decrease in the num/er of Vibrioparahaemolyticus/acteria reduces predicted illness to an e3tent that maes it unliely thatillnesses *ould /e o/served.


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Summary $able ?* Pre,icte, +ean #umber of Illnesses per Annum from Re,uctionof (evels of Pathogenic Vibrio parahaemolyticusin Oysters

RegionPre,icte, +ean #umber of Illnesses per Annum

9aseline Imme,iateRefrigerationa

-4logRe,uctionb

7*84logRe,uctionc

@ulf Coast ,ouisiana- 20! 22 22 L5

@ulf Coast ,Non1ouisiana- !+9 6 9 L5(id1Atlantic 5! 2 L5 L5Northeast Atlantic 5> 8 L5 L5&acific North*est ,Dredged- + L5 L5 L5&acific North*est ,"ntertidal- 5>2 59 2 L5

$O$A( 20629 8>5 8 L5a%epresents refrigeration immediately after harvest; the effectiveness of *hich varies /oth regionally andseasonally and is typically appro3imately 51log reduction.

/ %epresents any process *hich reduces levels of Vibrio parahaemolyticusin oysters 21log0 e.g.0 free:ing.c %epresents any process *hich reduces levels of Vibrio parahaemolyticusin oysters +.!1log0 e.g.0 mildheat treatment0 irradiation0 or ultra high hydrostatic pressure.

Re,ucing the $ime4to4Refrigeration

For this scenario0 the impact of

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Summary !igure 8* Pre,icte, ffectiveness of $wo %ifferent +etho,s of "ooling onVibrio parahaemolyticusRisk for the 'ulf "oast Region =(ouisiana an, non4(ouisiana> Summer Harvest E$rrors /ars denote central >!I of uncertainty distri/utiona/out the mean I reduction.G

Re4submersion of Interti,ally Harveste, Oysters


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ooling wit nor"al re&rigeration !#p to 10 rs

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As an e3ample of a harvest practice scenario0 the impact of overnight su/mersion ofoysters *as evaluated. #he model predicts the levels of Vibrio parahaemolyticus inintertidally1harvested oysters0 e.g.0 oysters are placed into /asets and removed after thetide rises0 a typical practice in the &acific North*est. Vibrioparahaemolyticuslevels canincrease in oysters during intertidal e3posure /ut overnight su/mersion of the oysters in*ater has /een sho*n to reduce these levels. Delaying harvest until near the end of thetidal cycle0 ust /efore oysters are e3posed again0 *as predicted to reduce the ris ofillness /y appro3imately >I. %esearch is needed to determine *hether the predictedlevel of reduction can /e achieved *hen oysters are staced in /asets.


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Sample49ase, "ontrol Plans

#he FDA"SSC recommends that the levels of Vibrio parahaemolyticusin oysters note3ceed 50 cellsgram and the "SSC interim control plan ,"C&- recommendsmonitoring of oyster meats for the presence of Vibrio parahaemolyticus. &rior to 250"SSC recommended that shellfish harvest *aters /e re1sampled for pathogenic Vibrioparahaemolyticusif the levels of total Vibrio parahaemolyticusin oyster meats at harveste3ceed 50 cellsgram. "n 250 the "C& *as revised to recommend that shellfishharvest *aters /e re1sampled for pathogenic Vibrio parahaemolyticusif the levels of totalVibrio parahaemolyticusin oyster meats at harvest are a/ove !0 cellsgram.

#he incidence of illness *as evaluated assuming that it *as possi/le to identify ande3clude oysters from the ra* maret *hich contained various specified levels of Vibrioparahaemolyticuseither at harvest or at retail. #he @ulf Coast region ,ouisiana-Summer harvest is presented here as an e3ample. As sho*n in Summary Figures 9 and 70restricting the levels of Vibrio parahaemolyticusin oysters either at1harvest or at1retailreduces the num/er of predicted illnesses0 /ut reuires diversion of oysters from the ra*

maret ,or modification of handling practices to reduce post1harvest Vibrioparahaemolyticusgro*th-. For the @ulf Coast region ,ouisiana- summer harvest0 in thea/sence of su/seuent post1harvest mitigation0 e3cluding oysters containing M50Vibrio parahaemolyticusg at the time of harvest is predicted to prevent appro3imately59I of illnesses *ith an impact of appro3imately 8I of the oyster harvest,SummaryFigure 9-. Ho*ever0 e3cluding oysters containing M50 Vibrio parahaemolyticusat1retail reduced predicted illness /y >>I /ut *ould reuire appro3imately +8I of the oysterharvest to /e diverted from the ra* maret consumption ,or su/ected to preventivecontrols-. #he impact of compliance *ith different

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Summary !igure * Potential ffect of "ontrol of $otal Vibrio parahaemolyticus9acterium per gram At4Harvest for the 'ulf "oast Region =(ouisiana> SummerHarvest

Summary !igure ;* Potential ffect of "ontrol of $otal Vibrio parahaemolyticuspergram At4Retail for the 'ulf "oast Region =(ouisiana> Summer Harvest

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2!Vibrio parahaemolyticus %is Assessment

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#his ris assessment included an analysis of the availa/le scientific information and data inthe development of a model to predict the pu/lic health impact of pathogenic Vibrioparahaemolyticus in ra* oysters. #he assessment focuses on comparing the relative risamong different geographic regions0 seasons0 and harvest practices. #he scientific dataand the mathematical models developed during the ris assessment facilitate a systematicevaluation of strategies to reduce the pu/lic health impact of pathogenicVibrioparahaemolyticusassociated *ith the consumption of ra* oysters.

Although the ris assessment modeled sporadic Vibrio parahaemolyticusillnesses0 stepstaen to reduce sporadic cases *ould /e e3pected to reduce the si:e and freuency ofout/reas. #he proportional reduction *ould depend on the virulence of the out/reastrain and on the surviva/ility and gro*th of the strain follo*ing post1harvest treatments.(itigation or control measures aimed at decreasing levels of Vibrio parahaemolyticusinoysters *ill also liely decrease levels of other species in theVibriogenus ,or family-0 suchas Vibrio vulnificus.elo* are the responses to the uestions that the ris assessment team *as charged *ith

ans*ering.

0hat is known about the ,ose4response relationship between consumption of Vibrioparahaemolyticusan, illnesses@

Although an individual may /ecome ill from consumption of lo* levels of Vibrio

parahaemolyticus0 it is much more liely that he or she *ill /ecome ill if the level ishigh. #he pro/a/ility of illness is relatively lo* ,L.5I- for consumption of 50Vibrio parahaemolyticuscellsserving ,euivalent to a/out ! cellsgram oysters-.Consumption of a/out 5 million Vibrio parahaemolyticuscellsserving ,!thousand cellsgram oysters- increases the pro/a/ility of illness to a/out !I.

Anyone e3posed to Vibrio parahaemolyticuscan /ecome infected and develop

gastroenteritis. Ho*ever there is a greater pro/a/ility of gastroenteritis developinginto septicemia ,and possi/ly death- among the su/population *ith concurrentunderlying chronic medical conditions.

#he model predicts a/out 206 Vibrio parahaemolyticusillnesses from oyster

consumption each year. 4f infected individuals0 appro3imately 7 cases ofgastroenteritis *ill progress to septicemia each year for the total population0 of *hich2 individuals *ould /e from the healthy su/population and ! *ould /e from theimmunocompromised su/population.

#his ris assessment assumed that pathogenic strains of Vibrio parahaemolyticusare

#DHKand that all strains possessing this characteristic are eually virulent.(odifications can /e made to the ris assessment if data /ecome availa/le for ne*

virulence determinants. For e3ample0 data from out/reas suggest that fe*ermicroorganisms of Vibrio parahaemolyticus48?9 are reuired to cause illnesscompared to other strains.

0hat is the freuency an, eBtent of pathogenic strains of Vibrio parahaemolyticusinshellfish waters an, in oysters@

evels of pathogenic Vibrio parahaemolyticususually occur at lo* levels in shellfish

*aters.


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evels of pathogenic Vibrio parahaemolyticusin oysters at the time of harvest are

only a small fraction of the total Vibrio parahaemolyticuslevels.

0hat environmental parameters =e*g*C water temperatureC salinity> can be use, topre,ict the presence of Vibrio parahaemolyticusin oysters@

#he primary driving factor to predict the presence of Vibrio parahaemolyticusinoysters is *ater temperature. Salinity *as a factor evaluated /ut not incorporated intothe model. Salinity is not a strong determinant of Vibrio parahaemolyticuslevels inthe regions that account for essentially all the commercial harvest. 4ther factors suchas oyster physiology and disease status may also /e important /ut no uantifia/le data*ere availa/le to include these factors in the model.

#here are large differences in the predicted levels of Vibrio parahaemolyticusin

oysters at harvest among regions and seasons. For all regions0 the highest levels ofVibrio parahaemolyticus*ere predicted in the *armer months of summer and springand the lo*est levels in the fall and *inter.

4verall0 the highest levels of total and pathogenic Vibrio parahaemolyticus*ere

predicted for the @ulf Coast ,ouisiana- and the lo*est levels in the &acific North*est,Dredged- harvested oysters.

After harvest0 air temperature is also an important determinant of the levels of Vibrio

parahaemolyticusin oysters. Vibrio parahaemolyticuscan continue to gro* andmultiply in oysters until they are adeuately chilled.

evels of Vibrio parahaemolyticusare lo*er in oysters after harvest in the cooler vs.

*armer months. #his means that reducing the time /et*een harvest and cooling *ill/e more important in the summer and spring than in the fall and *inter.

How ,o levels of Vibrio parahaemolyticusin oysters at harvest compare to levels atconsumption@

Bith no mitigation treatments0 levels of Vibrio parahaemolyticusare higher in oystersat consumption than at harvest. #he difference /et*een Vibrio parahaemolyticusdensities at1harvest versus at1consumption is largely attri/uta/le to the e3tent ofgro*th that occurs /efore the oysters are cooled to no1gro*th temperatures.

evels of Vibrio parahaemolyticusin oysters vary /y region and season and are

highest during the summer.

During intertidal harvest0 oysters are e3posed to higher temperatures for longer times0

allo*ing additional gro*th of Vibrio parahaemolyticusin oysters and leading tohigher predicted ris of illness.

&reventing gro*th of Vibrio parahaemolyticusin oysters after harvest ,particularly in

the summer- *ill lo*er the levels of Vibrio parahaemolyticusin oysters and0 as a

conseuence0 lo*er the num/er of illnesses associated *ith the consumption of ra*oysters.

0hat is the role of post4harvest han,ling on the level of Vibrio parahaemolyticusinoysters@

&ost1harvest measures aimed at reducing the Vibrio parahaemolyticuslevels in oysters

reduced the model1predicted ris of illness associated *ith this pathogen.


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%educing the time /et*een harvest and chilling has a large impact on reducing levels

of Vibrio parahaemolyticusin oysters and the num/er of illnesses. &redictedreductions *ere greater for shorter times to refrigeration using ice ,oysters reach no1gro*th temperature in 5 hour- compared to cooling under conventional refrigeration,*hich may tae up to 5 hours until oysters reach a no1gro*th temperature-.

0hat re,uctions in risk can be anticipate, with ,ifferent potential intervention

strategies@

4verall. #he most influential factor affecting predicted ris of illness is the level of

total Vibrio parahaemolyticus in oysters at the time of harvest. "ntervention strategiesshould /e aimed at reducing levels of Vibrio parahaemolyticus andor preventing itsgro*th in oysters after harvest. #hese strategies0 either at1harvest or post1harvest0may need to consider regionalseasonal differences. For e3ample0 the use of ice onharvest /oats to cool oysters to the no1gro*th temperature of Vibrioparahaemolyticus *ill have a larger impact on reducing illnesses in the summer than inthe *inter *hen air temperatures are cooler and Vibrio parahaemolyticuslevels arelo*er.

%egionalSeasonal Differences. #he ris of Vibrio parahaemolyticusillness is

increased during the *armer months of the year0 *ith the magnitude of this increase afunction of the e3tent to *hich the gro*ing *aters ,and air temperature- are attemperatures that support the gro*th of the pathogen ,e.g.0 temperatures a/ove5C-. For each region0 the predicted num/ers of illnesses are much higher for the

summer compared to the *inter months. "ntervention measures that depend oncooling oysters to no1gro*th temperatures for Vibrio parahaemolyticusmay /e moreimportant in *armer seasons and regions.

#he ris of Vibrio parahaemolyticusillness is su/stantial in the @ulf Coast region*here *ater temperatures are *arm over a large part of the year as compared to theNortheast Atlantic region *here *ater temperatures support the gro*th of Vibrioparahaemolyticusonly during a relatively small portion of the year. A difference isseen among the regions due to different harvesting methods. Bithin the @ulf Coast0the predicted num/er of illnesses is much higher in ouisiana compared to other statesin this region /ecause the harvest /oats in ouisiana are typically on the *ater longer0i.e.0 leading to a longer time from harvest to refrigeration. Harvest volume is also adetermining factor; in the summer0 ouisiana accounts for appro3imately 77I of the@ulf Coast harvest. #his is also seen in the &acific North*est /y comparing intertidalversus dredged harvesting. "ntertidal harvesting accounts for 7!I of the &acificNorth*est harvest and e3poses oysters to higher temperatures longer0 allo*ing greater

gro*th of Vibrio parahaemolyticus. 4vernight su/mersion for a single tidal cycle0reduces levels of Vibrio parahaemolyticusin oysters and the ris of illness.

&ost1Harvest #reatments. &ost1harvest treatments that reduce levels of Vibrio

parahaemolyticus/y 2 to +.!1logs *ere found to /e effective for all seasons andregions0 *ith the most pronounced effects seen for regions and seasons *ith higher/aseline ris. #he model sho*s that any treatment that causes at least a +.!1logdecrease in the num/er of Vibrio parahaemolyticus/acteria reduces the pro/a/ility of


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illness to such an e3tent that fe* illnesses *ould /e identified /y epidemiologicalsurveillance. Ho*ever0 some out/rea strains ,e.g.0 48?9- are more resistant tomitigations than endemic pathogenic Vibrio parahaemolyticusstrains0 and the durationor e3tent of treatment may need to /e more stringent to achieve an euivalent degreeof reduction. Studies have sho*n that /oth Vibrio parahaemolyticusand Vibriovulnificusrespond similarly to control measures such as ultra high pressure0 mild heattreatment0 and free:ing. #herefore0 mitigations aimed at decreasing levels of Vibrioparahaemolyticus*ill also liely decrease levels of Vibrio vulnificus.

#he model also demonstrated that if oysters are not refrigerated soon after harvest0Vibrio parahaemolyticusrapidlymultiply resulting in higher levels. For e3ample0 themodel indicates that for the @ulf Coast there is a significant reduction ,51fold- in thepro/a/ility of illness *hen the oysters are placed in a refrigerator immediately afterharvest. ess pronounced reductions are predicted for the other regions. &redictedreduction in illness is less in colder seasons /ecause oysters harvested in cooler*eather are already at or /elo* the temperature threshold for Vibrioparahaemolyticusgro*th and as such refrigeration has little additional impact on

levels of Vibrio parahaemolyticus.

At1Harvest and At1%etail Controls. Controlling the levels of Vibrio parahaemolyticus

in oysters at1harvest or at1retail ,after refrigeration and storage- drastically reduces thenum/er of predicted illnesses /ut *ould reuire diversion of oysters from the ra*maret or modification of handling practices to reduce post1harvest Vibrioparahaemolyticusgro*th. For the @ulf Coast ,ouisiana- region in the summer0e3cluding all oysters *ith at least 50 Vibrio parahaemolyticusg at1harvest *ouldreduce illness /y appro3imately 59I at a loss of appro3imately 8I of the total harvestfrom the ra* consumption maret; and this same control level at1retail *ould reduceillness /y a/out >>I *ith a +8I loss from the ra* oyster maret ,or su/ected to

preventive controls-. #he effectiveness of the control level either at1harvest or at1retailto reduce illnesses depends on the e3tent of compliance *ith that control level.

"n a sample1/ased control strategy0 a reasona/le surrogate for pathogenic Vibrioparahaemolyticusmay /e total levels of this microorganism. Criteria for reection ofoysters /ased on the levels of this surrogate might have to vary /y region. Fore3ample0 an at1harvest control criterion /ased on total Vibrio parahaemolyticuslevelsin the &acific North*est might need to /e more stringent than in the @ulf Coast/ecause the incidence of pathogenic strains appears to /e higher in the &acificNorth*est. Ho*ever0 in an out/rea0 the ratio of pathogenic to total Vibrioparahaemolyticus may not /e the same or consistent0 and the model does not evaluate

ho* *ell total Vibrio parahaemolyticus*ould serve as a surrogate for pathogenicVibrio parahaemolyticusin an out/rea situation.

"n conclusion0 the ris assessment illustrates that the levels of Vibrio parahaemolyticusatthe time of harvest play an important role in causing human illness. Ho*ever0 otherfactors that either reduce or allo* gro*th of Vibrio parahaemolyticusin oysters are alsoimportant in determining the num/er of illnesses. For e3ample0 shortening the time1to1

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refrigeration of oysters in the summer controls gro*th of Vibrio parahaemolyticusinoysters and su/seuently reduces illnesses associated *ith this microorganism.

#he results of this ris assessment are influenced /y the assumptions and data sets that*ere used to develop the $3posure Assessment and Dose1%esponse models. #hepredicted ris of illness among consumers of ra* oysters could change as a result of futuredata o/tained from continuing surveillance studies. "t is anticipated that periodic updatesto the model *ill continue to reduce the degree of uncertainty associated *ith the factorsthat influence the ris. #his ris assessment provides an understanding of the relativeimportance of and interactions among the factors influencing ris. "t can /e used tofacilitate the formulation of effective guidance and reuirements for the industry and in theevaluations of ris mitigation strategies. #his "nterpretive Summary provides a /rief0 non1technical description of the materials covered0 /ut a full understanding reuires the readerto consider the complete ris assessment.

99n-1075-bkg0004-01-ra-01 (1)

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