Food- and Waterborne diseases

CausesRoles of microbes

Contributing factors

Three overlapping groups of GI disorders

• Pathogenic microbes and toxins that they form (most common)

• Algae and parasites• Other

– Toxins formed from breakdown of food– Toxic chemicals– Allergens– Digestive or nutritional disorders

Investigating foodborne disease

• Regulatory agencies (USDA, FDA, CDC)• Outbreak: two or more people get sick from

eating the same food (with the same symptoms)

• Chemical poisoning, highly fatal disease: one case is enough

Major pathogens (in terms of cost)

• Campylobacter jejuni• Clostridium perfringens• E. coli O157:H7• Listeria monocytogenes• Salmonella• Staphylococcus aureus• Toxoplasma gondii

Categories of microbial infection

• Intoxication (toxin is preformed)• Infection (microbes can grow in body)• Toxicoinfection (organisms ingested, die, and

release toxins)• Opportunistic pathogens

Major pathogens associated with foodborne diseases

• Intoxication– C. botulinum highest mortality– S. aureus most cases

• Pathogens– Salmonella, Listeria monocytogenes

• Toxicoinfection– C. perfringens, followed by B. cereus

• Viral diseases– Hepatitis, Norwalk-type viruses

Why certain foods?

• Raw vs finished foods• Food environment favors the growth of a

pathogen• Quality control is lacking• More handling

Predominant food types

• Meats- Salmonella S. aureus• Egg products- Salmonella• Fish- Salmonella, C. botulinum• Fruits and vegetables- C. botulinum• Processed meats, unpasteurized milk- L.

monocytogenes• Salmonella is ubiquitous

Incidence of foodborne illness

• Restaurants, fast-food, cafeterias, schools– High volume, much handling

• Homes– Improper cooling and storage, cross-

contamination• Outings (picnics, etc.)

– Mishandling, “temperature abuse”• Commercial preparation- outbreaks rare, but

can affect large numbers of people

Factors contributing to outbreaks from pathogenic bacteria and viruses

• Improper refrigeration most common factor (according to data from 1980s)

• Poor personal hygiene• Survival of pathogens due to improper

cooking• Cross-contamination• Unsafe food sources

‘Tis the season…

• Foodborne outbreaks more common during the summer months

• Why do you think so?• Regional conditions• Migration patterns• Different susceptibilities to disease (age,

general health, immune status)• Innate virulence of pathogen

FoodNet established 1996

• Objectives:– Determine frequency and severity of foodborne

diseases– Trace foodborne diseases to specific foods– Determine the epidemiology of new bacterial,

viral, parasitic pathogens– Use epidemiological studies and surveillance of

outbreaks to reduce foodborne illnesses (are initiatives working?)

Nine pathogens evaluated over 10-year period (1996-2005, > 25 million persons)

• Campylobacter ssp.- declined 30%• Salmonella- decreased, then increased• Shigella ssp.- decreased 43%• E. coli O157:H7 -decreased 29%• Listeria monocytogenes- decreased 32%• Yersinia enterocolitica – decreased 43%• Vibrio spp. increased 41%• Cryptosporidia –much fluctuation; unchanged overall• Cyclospora- unchanged• Highest incidence (Salmonella) ca 14 per 100,000 populaiton

Is foodborne illness underreported?

• Studied surveillance and reporting systems like FoodNet (Mead et al., Emerg. Infect Dis, 1999)

• Total number of foodborne illness from known and unknown causes: 76 million– Known pathogens accounted for about 25% of all foodborne illnesses– 75% of deaths caused by Salmonella, Listeria, and Toxoplasma

• Not all outbreaks can be documented accurately• Some cases are sporadic, some outbreak• Some pathogens are transmitted by food, but also other

sources• Answer: yes

Foodborne intoxications: features

• Can be produced while pathogen is growing in food or preformed (presence of viable microbes not always necessary)

• May be heat sensitive or heat stable• Onset of symptoms may be very rapid (30 minutes)• Fever not usually produced• Toxins tend to affect body systems (enterotoxins,

neurotoxins)

Staphylococcus aureus

Citizendick.org

Microbiologyinpictures.org

Gram-positive coccusTransmitted from skin and hair (by handling)Multiplies in foods held at room temperature

Toxin does not affect food qualityMore than 17 enterotoxinsHeat stableStimulates vagus nerve, induces vomiting

Grows in a wide variety of foods

Neurotoxins: Clo. botulinum (Gram-positive anaerobe)

• Foodborne– Preformed; spreads from intestines to peripheral

nerves• Infant- ingestion of spores• Hidden- in feces but food source unknown• Wound- anaerobes can grow in deep wounds• Inadvertent- BoTox gone awry

Air.ky.gov

Mycotoxicosis

Secondary metabolites, not toxins

Can be carcinogenic,Hallucinogenic (ergot)

AflatoxinAspergillus speciesliver damage

Foodborne infections

• Live cells are consumed and penetrate gut lining

• Produce toxins and/or cause cell damage• Does levels vary greatly• Symptoms usually occur after 24 hours• Some can spread out of the digestive system

Salmonellosis

• Most common cause of foodborne illness- and most persistent

• Carrier state persists after recovery• Inflammation leads to loss of fluid and

diarrhea• Associated with wide variety of foods• Gram-negative rod, non-lactose fermenting

Listeriosis

• Recently recognized as foodborne pathogen- oppotunistic?

• Psychrotroph- can grow in refrigerators, so low-level contamination can increase

• Highly fatal to young, old, pregnant, immune compromised

• Zero tolerance because of high fatality rate

Listeriosis forms of disease

• Febrile gastroenteritis– High infectious dose– Flu-like symptoms– Bacteria shed for weeks or months in feces

• Invasive systemic disease– Infectious dose of 100-1000– Passes through intestines into body; can affect

liver, brain, placenta

Listeriosis is usually sporadic

• Strict controls in place for ca 20 years• High-risk people told to avoid soft cheeses and

ready-to-eat foods without heating• Rapid testing possible with serological

methods

Pathogenic E. coli• Most E. coli are harmless and at very high levels in intestines• Six groups can cause disease

– Enterotoxigenic (ETEC)• Traveler’s diarrhea; toxin; no inflammation; high dose required

– Enteropathogenic (EPEC)- infant diarrhea– Enteroinvasive (EIEC)-dysentery (bloody diarrhea)– Enterohemorrhagic(EHEC)- bloody diarrhea and HUS

(hemorrhagic uremic syndrome)• Shiga-like toxin kills cells

– Enteroaggregative (EAEC)– Diffuse-adhering (DAEC)

Toxicoinfections

• Spore formers: cells do not multiply but form spores and release toxins– Clostridium perfringens (meats) – Bacillus cereus (variety of foods)

• Gram-negative cells multiply, or die and release toxins– Vibrio cholerae- contaminated food and water– ETEC- fecally contaminated food and water

Opportunistic pathogens or toxins

• Don’t normally cause disease• Breakdown products of proteins• Algal toxins (Gonyaulax catenella)• Parasites (worms and protozoans)

New and emerging food borne pathogens

• Are they really new, or newly confirmed?• Pathogens can increase or decrease as

causative agents for illness– Food consumption patterns– Changes in food processing and marketing– Changes in agricultural practices– Migration of food and people– Health of individuals

More knowledge of pathogens

• Many are discovered in large outbreaks– Campylobacter jejuni– EHEC O157:H7– Listeria monocytogenes, among others

• More data• New testing technology• Regulatory practices, education

Food habits• More seafood, more vibrio and hepatitis• More low-heat-processed foods stored longer• More consumption of raw foods

– Fruits, vegetables, and juices: organisms modified to low-pH and low temperature environments

• New pathogens– Hepatitis E– H. pylori– BSE– Aeromonas

Summary

• Foodborne illness has been recognized for centuries• New pathogens are regularly “added to the list”- and

this will continue• Illness may be sporadic or due to an outbreak• Much is known about many organisms, their

symptoms, and the onset of disease• Not everyone reacts to exposure the same way