The Versatile Salmonella: Contaminating Cantaloupes, Peanut

Butter, Chocolate and Sprouts

Michael Doyle

The Versatile Salmonella

● Incidence and trends of salmonellosis in United States

● Risk factors for acquiring salmonellosis

● Prevalence and trends of Salmonella in meat and poultry

● Survival characteristics of Salmonella

● Infectious dose

● Food-assisted outbreaks of salmonellosis (other than meat or poultry)

● Salmonella contamination of imported foods

Incidence of cases of Campylobacter, Salmonella, and Escherichia coli O157 infections under surveillance in the Foodborne Diseases Active Surveillance Network (Food Net), 2000 - 2006

National HealthPathogen Year No. of cases/100,000 persons Objective for 2010

Campylobacter 2000 15.72001 13.82002 13.42003 12.62004 12.92005 12.92006 12.7 12.3

Salmonella 2000 14.42001 15.12002 16.12003 14.52004 14.72005 14.6 2006 14.8 6.8

U.S. Centers for Disease Control and Prevention

Risk Factors for Sporadic Salmonella Enteritidis Infections in the United States (2002 – 2003)

Risk Factors Identified Population Attributable Fraction

Eating chicken outside the home 35%

International travel 30%

Eating undercooked eggs inside the home

15%

Lizard in the home 7%

Bird in the home 5%

Eating eggs outside the home 5%

R. Marcus et al. Epidemiol. Infect. 2006

Selected case-control studies demonstrating risk of acquiring salmonellosis from food prepared outside the home

Salmonella Serotype Risk factor Population Attributable Risk

MDR Typhimurium Eating scrambled eggs prepared outside the home

13%

Heidelberg Eating eggs prepared outside the home

39%

Serogroup B or C Eating eggs prepared in a restaurant

9%

T. F. Jones and F. J. Angulo, Clin. Infect. Dis. 43:1324 (2006)

Prevalence of Salmonella in Meat and Poultry Determined by USDA-FSIS Pathogen Reduction/HACCP Verification Testing Program

Calendar Year

Broiler Carcasses

Ground Chicken

Ground Turkey

Steer & Heifer Carcasses

Bull & Cow Carcasses

Ground Beef

Hog Carcasse

s

(% Positive)

Baseline

(Pre-1998) 20 44.6 49.9 1.0 2.7 7.5 8.7

1998 10.8 4.2 36.5 0 1.1 6.4 5.8

1999 11.4 16.2 31.6 0.3 2.2 4.3 9.8

2000 9.1 13.8 25.7 0.4 2.2 3.3 6.2

2001 11.9 19.5 26.2 0.6 2.4 2.8 3.8

2002 11.5 29.1 17.9 0.3 1.7 2.6 3.2

2003 12.8 35.5 25.4 0.4 1.5 1.7 2.5

2004 13.5 25.5 19.9 0.3 0.8 1.6 3.1

2005 16.3 32.4 23.2 0.6 1.3 1.1 3.7

2006 11.4 45.0 20.3 0.3 0.8 2.0 4.0

USDA-FSIS (http://www.fsis.usda.gov/OPHS/haccp/salm6year.htm)

Some Salmonella strains have unusual resilience to extreme environmental conditions

● Preexposure to adverse environmental conditions can precondition salmonellae to tolerate extreme conditions▲ Preexposure to sodium chloride in acidic environment can

increase tolerance of salmonellae to low concentrations of organic acids

● Anaerobic conditions can potentiate greater salt tolerance

● Brief exposure of S. Typhimurium cells to mild acidic environments (pH 5.5 - 6.0) followed by exposure of adapted cells to pH < 4.5 (acid shock) triggers acid tolerance response▲ Cells can survive in extreme acidic environments (pH 3 - 4)

Acid stress can trigger enhanced resistance of salmonellae to other adverse

environmental conditions

● Growth of S. Typhimurium at pH 5.8 engendered: ▲ increased thermal tolerance at 50ºC;▲ enhanced thermal tolerance to high osmotic stress

(2.5 M NaCl)▲ increased resistance to the antibacterial lactoperoxidase

system and surface active agents such as polymyxin B

Salmonella can persist in hostile environments

● Heat resistance increases with decreased moisture content/water activity

● Acquires greater heat resistance following exposure to sublethal temperatures▲ Synthesizes heat shock proteins

● S. infantis can grow in tomatoes at pH 4.0

Infectious dose of Salmonella

● Newborns, infants, the elderly and immunocompromised individuals are more susceptible to Salmonella infections than healthy adults▲ Incompletely developed immune system in newborns or

infants▲ Weak or delayed immune response in the elderly and

debilitated persons▲ Low gastric acid production in infants and seniors

Human infectious dose of SalmonellaFood Serovar Infectious Dose (CFU)

Eggnog Meleagridis 104 – 107

Anatum 105 – 107

Imitation Ice Cream Typhimurium 104

Chocolate Eastbourne 102

Hamburger Newport 101 – 102

Cheddar Cheese Heidelberg 102

Chocolate Napoli 101 – 102

Cheddar Cheese Typhimurium 100 – 101

Chocolate Typhimurium ≤ 101

Alfalfa Sprouts Newport < 4.6 X 102

Ice Cream Enteritidis < 2.8 X 101

High fat content of food influences infectious dose

● High fat content of chocolate (cocoa butter), cheese (milk fat), and meat (animal fat) is common factor among foods associated with low infectious dose

● Suggested that entrapment of salmonellae within hydrophobic lipid micelles affords protection against the bactericidal action of gastric acidity

● Rapid emptying of gastric contents could also provide alternate mechanism

Examples of Major Outbreaks of Salmonellosis Associated with Chocolate-based Products

Year Country Salmonella serovar No. of Cases

1973 Canada and USA Eastbourne 217

1982 England and Wales Napoli 245

1987 Norway and Finland Typhimurium 361

2000-2001 Germany & International Oranienburg >439

2006 United Kingdom Montevideo > 50

Contributing factor to Chocolate-associated outbreaks of salmonellosis

● Contamination of chocolate during processing via leaking pipe/contaminated water

Salmonella Survival in a Chocolate Confectionary Product

● Thermal inactivation of salmonellae in molten chocolate is not practically possible because the time-temperature conditions required to kill the pathogen in this high sucrose-containing product of low water activity would result in organoleptically unacceptable product

● Salmonellae can survive for many years in finished chocolate products when stored at ambient temperature

● Effective decontamination of raw cocoa beans and stringent in-plant control measures to prevent cross-contamination of products are critical

Salmonella Tennessee Outbreak Associated with Peanut Butter

● From August 2006 – May 2007, 628 persons in 47 states were infected with S. Tennessee▲ Vehicle was two brands of peanut butter made by

same manufacturer at same processing facility▲ Source of contamination was a leaky roof over

area after peanut roasting

Centers for Disease Control and Prevention, June 1,

2007

Salmonellosis from Raw Almonds

● In 2003 – 2004, 29 cases of Salmonella Enteritidis infections in 12 states and Canada from California-grown raw almonds▲ 13 million pounds of raw almonds recalled

● In 2001, outbreak of S. Enteritidis infections, mostly in Canada, during 6-month period▲ Traced to 3 CA orchards

MMWR 53(22):484-487 (June 11, 2004)

Salmonellosis from Raw Almonds

● Almonds are California’s largest agricultural crop ($1.5 billion annually)▲ 1 billion pounds produced in 2003

● 5% of almonds consumed in US are raw● Harvesting, drying and hulling-shelling practices

enable cross contamination▲ Salmonella isolated for many months from soil of

almond orchards; almonds that contact soil can be contaminated

● Almonds can be pasteurized with heat, steam or propylene oxide to reduce risk of contamination

Examples of Outbreaks of Salmonellosis Associated with Tomatoes

● Two multistate (midwest) outbreaks of salmonellosis identified by laboratory-based surveillance▲ In 1990, 176 cases of S. Javiana▲ In 1993, 100 cases of S. Montevideo

● Source: Tomatoes from a single South Carolina tomato packer▲ Contamination likely occurred at packing shed

♦Field-grown tomatoes dumped into common water bath► Tomatoes placed in water cooler then tomato pulp

absorb water and salmonellae into core tissues through stem scar

C. W. Hedberg et al. Epidemiol. Infect. 122:385 (1999)

Examples of Outbreaks of Salmonellosis Associated with Tomatoes

Date Pathogen Location

No. of Cases

Likely Source of Contamination

1990 S. Javiana Multistate 176 Packinghouse

1993 S. Montevideo Multistate 100 Packinghouse

1998-99 S. Bailden Multistate 85 Field Contamination

2002 S. Newport 24 States 512 Packinghouse

2004 Multiserotypes Salmonella

Multistate 564 Packinghouse

2005 S. Newport Multistate 72 Field Contamination (Irrigation Pond)

2005 S. Braenderup Multistate 82 Field Contamination

2006 S. Newport Multistate 115 Not Determined

2006 S. Typhimurium Multistate 190 Packinghouse

Salmonellosis Outbreak Associated with Cantaloupes

● More than 400 cases of Salmonella Poona infection in 23 states and Canada during June-July 1991

● Vehicle – cantaloupe▲ Likely source of cantaloupe was Rio Grande region of

Texas▲ Implicated cantaloupe associated with fruit salads from

salad bars● FDA survey of imported cantaloupes and watermelons at

U.S. border in 1990 and 1991 isolated Salmonella spp. from about 1% of rinds

Morbid. Mortal. Weekly Rep. 40:549, 1991

Examples of Salmonellosis Outbreaks Associated with Cantaloupes

Year Type of Melon Pathogen Location No. of Cases

1989-90 Cantaloupe S. Chester Multistate 245

1991 Cantaloupe S. Poona Multistate > 400

1997 Cantaloupe S. Saphra California 24

1998 Cantaloupe S. Oranienburg Canada 22

2000 Cantaloupe S. Poona Multistate 47

2001 Cantaloupe S. Poona Multistate 50

2002 Cantaloupe S. Poona Multistate, Canada 58

2006 Fruit salad; cantaloupe; honeydew

S. Oranienburg 10 States, Canada 41

Salmonella Contamination during Cantaloupe Production

● 6 cantaloupe farms and packing plants in South Texas and 3 farms in Colima State, Mexico were sampled to evaluate Salmonella contamination of cantaloupe during production and processing▲ Sampled cantaloupe surface and irrigation water▲ E. coli detected on 3.9% of melons from

Texas and 25.7% from Mexico

A. Castillo et al. J. Food Protect. 67:713-720 (2004)

Salmonella Contamination during Cantaloupe Production

● Salmonella isolated from:

Texas Mexico

– Cantaloupes at melon farm

Field 1/400 (0.2%) 0/75

Before wash 1/150 (0.6%) 0/75

After wash 1/150 (0.6%) 1/75 (1.3%)

In cooler 2/250 (0.8%) 0/75

– Irrigation water (at source) 9/70 (13%) 4/15 (27%)

After filtration 0/5 5/15 (33%)

As delivered to field 2/25 (8%) 1/15 (7%)

Salmonella Associated with Cantaloupes

● Reported outbreaks have been associated both with whole melons contaminated in growing fields and with precut melons

▲ Disinfection of irregular surface of cantaloupes is difficult

▲ Cut fruit can be contaminated when rind is removed and fruit is sliced

▲ Inner flesh of melons contains nutrients that support microbial growth; improper refrigeration of cut melon can cause Salmonella growth

What Food Is Considered by Many Food Safety Experts to be the Most

Hazardous?

Examples of Salmonellosis Outbreaks Associated with Sprout Consumption

Sprout No. of

Date Type Pathogen Location Cases

1988 Bean Salmonella Saint-Paul UK 143

1994 Alfalfa S. Bovismordificans Sweden 282

Finland 210

1995 Alfalfa S. Newport Oregon 58

British Columbia 70

1995 Alfalfa S. Newport Denmark 154

1995 Alfalfa S. Stanley Multistate, Finland 242

1996 Alfalfa S. Montevideo, S. Meleagridis California >500

1997 Alfalfa S. Infantis, S. Anatum Kansas, Missouri 109

1998 Alfalfa S. Havana, S. Cubana, S. Tennessee California 34

1999 Sprouts Salmonella Colorado 79

1999 Alfalfa S. Paratyphi B Canada 51

2000 Mung Bean S. Enteritidis California 45

2001 Mung Bean S. Enteritidis Canada 85

2001 Alfalfa S. Kottbus Washington 23

2003 Alfalfa Salmonella Oregon > 9

2007 Alfalfa S. Weltevreden Norway 10

FDA Warning Regarding Sprout Consumption

● July 9, 1999 consumer advisory by U.S. Food and Drug Administration▲ All consumers (not just those at highest risk of

foodborne illness) can reduce the risk of foodborne illness by cooking sprouts or completely avoiding consumption of sprouts♦FDA believes that all sprouts (not only alfalfa

or clover sprouts) may pose a risk

Microbiological Safety Issues Associated with Imported Foods

● Sanitation practices for food production and preparation are not universally equivalent throughout the world

Chicken/Shrimp Farming in Thailand

● Chicken/shrimp farming is only means of income for many small stakeholders▲ Chicken coops (e.g., 20,000 birds/farm) sit in

rows suspended over ponds that hold shrimp and fish♦Livestock below feeds on waste from above

BBC News, January 27, 2004

Food Safety Issues with Imported Fishery/Seafood Products

● Salmonella is the most common contaminant of fish and fishery products resulting in detention by FDA▲ In 2001, of 6,405 violations 28.6% were for

adulteration by Salmonella♦More than half of violations for Salmonella

were for contaminated shrimp and prawns

J. Allhouse et al., USDA, ERS, International Trade and Seafood Safety, AER-828, p. 109-124, Nov 2003

Examples of FDA Food Import Refusals for Salmonella Contamination for August 2007

Country Product

China Shrimp Harvested in India then sent to ChinaChina ChivesChina Whole Black PeppercornsChina Dog Chicken StripsEgypt BasilEgypt FennelIndia Frozen GingerIndia Frozen Fish Chunks in TrayIndia Black PepperIndia Cumin

(Continued)

Examples of FDA Food Import Refusals for Salmonella Contamination for August 2007 (Continued)

Country Product

Indonesia CinnamonIndonesia Frozen Grouper FilletsMalaysia Frozen ShrimpMexico Dry Hard CheesePakistan Coriander PowderPhilippines Frozen OctopusPhilippines Dried Taro LeavesThailand Shrimp & PrawnsVietnam Frozen GrouperVietnam Ground Black Pepper

FDA Import Program (www.fda.gov/ora/import/ora_import_program.html)

Conclusions

● Salmonella spp. is the leading cause of foodborne bacterial disease in the United States

● There has been minimal progress in reducing the incidence of salmonellosis during the past decade

Conclusions

● Substantial progress has been made in reducing Salmonella contamination of meat products but not ground poultry products

Conclusions

● Eggs and poultry are major vehicles of Salmonella infections, however, many other foods, including fresh produce and occasionally some RTE products are also important contributors

● Many imported foods are vehicles of Salmonella because they are produced or processed under unsanitary conditions

Conclusions

● Many strains of Salmonella are unusually resilient to extreme environmental conditions▲ Preexposure to sodium chloride or acid

increase tolerance to acid

● Heat resistance increases with decreased moisture content

● Salmonella can persist for months to years in soil and in dry locations in food processing facilities

Conclusions

● Need for renewed emphasis by food industry to prevent and control Salmonella contamination from farm to plate