Foodborne Disease Outbreak Investigation

FOODBORNE DISEASE OUTBREAK INVESTIGATION

Food for Thought

The majority of outbreaks are foodborne

Why investigate?

The single most important reason to investigate an alleged foodborne disease outbreak is to identify the contaminated food and remove it from the market place to prevent the occurrence of further illness.

Foodborne Disease

• Food poisoning is an incorrect term
• Foodborne illnesses/diseases are usually either infectious (foodborne infections) or toxic (foodborne intoxications) in nature, caused by agents that enter the body through the ingestion of food.

VIRUSES, BACTERIA, and PARASITES

Viruses

• Viruses can only reproduce within living cells in the body of the host and cannot multiply in foods
• Some viruses remain infectious in the environment and thus can be transported through food (eg., ROTAVIRUS, HEPATITIS A)
• Foodborne viruses can cause infection and not intoxication

Bacteria

• Able to multiply in or on food
• Under optimum conditions, large numbers can easily be achieved
• Pathogenic bacteria can cause foodborne infections or intoxications
• B.CEREUS, C.BOTULINUM, S.AUREUS

BACTERIAL REQUIREMENTS

1. Food: Most bacteria require what is known as potentially hazardous food

• Milk or milk products, eggs, meat, poultry, fish, shellfish, crustaceans, raw seed sprouts, heat treated vegetables and vegetable products.

• Generally high protein, moist foods

1. Water: Bacteria require moisture to thrive

• The water activity (Aw) is the amount of water available in food
• The lowest Aw at which bacteria will grow is 0.85

• Most potentially hazardous foods have a water activity at 0.97 to 0.99

1. pH: Best growth a neutral or slightly acidic pH

• Potentially hazardous foods have a pH of 4.6-7.0

1. Temperature: The danger zone for potentially hazardous foods is 45 to 140F (7 to 60C)

• This is the zone where most bacterial growth occurs

1. Time: Potentially hazardous foods must not be allowed to remain in the danger zone for more than 4 hours

Parasites

• Cause infection, but not intoxication
• Do not multiply in foods but can survive in the environment and hus be transported through food
• E.HISTOLYTICA, T.GONDII, G.LAMBLIA

Summary:

CLASSIFICATION OF FOODBORNE DISEASES

FOODBORNE INFECTION

• Diarrhea, abdominal cramps, (+) fever, (+) (-) vomiting
• This is caused by ingestion of food contaminated by either viruses, bacteria or parasites, and occurs in one of two ways:

1. Invade and multiply in the intestinal tract mucosa and/or other tissues
2. Bacteria in ingested food invade and multiply in the intestinal tract and then release toxin or toxins that damage tissues or interfere with normal organ or tissue function (toxin-mediated infection)

*Viruses and parasites are not able to cause a toxin-mediated infection*

FOODBORNE INTOXICATION

• Diarrhea, abdominal cramps, (-) fever, (+) vomiting
• This is caused of food already contaminated by a toxin. Sources of toxin are:

1. Certain bacteria
2. Poisonous chemicals
3. Toxin found naturally or formed in animals, plants or fungie (eg., certain fish, shellfish, certain wild mushrooms)

*Viruses and parasites are unable to cause intoxications*

TRANSMISSION OF PATHOGENS:

1. Most foodborne dieases: fecal-oral route
2. Raw food contaminated with a pathogen is not cooked long enough to kill the pathogen or is consumed raw
3. Cooking utensils are used on a raw food contaminated with a pathogen, and then the same utensils are used to another uncooked food.

RECOGNIZING FOODBORNE DISEASE

• Symptoms – may indicate likely cause ad permit a more efficient investigation
• Single cases are difficult to associate with a particular food or establishment unless there is a distinctive clinical syndrome (eg., FISHBORNE CIGUATERA POISOING)
• Investigators’ usual problem: to implement control measures before an etiologic agent has been identified
• Outbreaks of food borne disease are usually recognized by the occurrence of illness among people who eat one or more foods in common AND the time illness occurs within a short period of time from each other
• The incubation period in relation with the clinical symptoms is useful in determining an etiologic agent.

RULE OF THUMB but not LAW

• Intoxicants have rapid onset – no fever
• Toxins in the stomach – vomiting
• Toxins in the intestines  - diarrhea
• Infections – fever

FOOD BORNE INFECTION

• The incubation period generally rather long – days
• Usual symptoms are diarrhea, nausea, vomiting, abdominal cramps and fever.
• Organisms possess colonization or adherence factors, allowing them to attach and to multiply in specific parts of the intestine.

FOOD BORNE INTOXICATION

• Illness form an intoxication manifests more rapidly because the body is affected quickly by the toxin or wants to expel it
• Time for growth and invasion of the intestinal lining, is in an infection, is not required
• The incubation for an intoxication is often measured in minutes or hours (eg., S.AUREUS toxin-related illness, 1-6hrs)
• Vomiting- most common or sometimes the only symptom
• Nausea, diarrhea, interference with sensory and motor functions (double vision, weakness, numbness, etc.)
• Fever- rarely present
• Absence of fever is important when trying to determine cause of illness