Overview
* CDC estimates that 9.4 million of the illnesses are caused by 31 known foodborne pathogens
* 90% of all illnesses due to known pathogens are caused by seven pathogens:
norovirus,
* is a virus
* aka stomach flu
* present in feces
Salmonella
* is a bacteria
* present in eggs, poultry, meat, vegetables, fruits
Campylobacter
* is a bacteria
* present in chicken feces
Toxoplasma
* is a parasite
* present in uncooked meats, cat feces
E. coli O157:H7
* is a bacteria
* present mostly in cows
* produces Shiga toxin
Listeria
* is a bacteria
* present in raw foods
Clostridium perfringens
* is a bacteria
* present everywhere, especially undercooked meat
Causes of Food Borne Illnesses
* Bacteria (Salmonella, campylobacter, E coli, listeria, clostridium perfringen)
* Viruses (norovirus)
* Parasites
– Protozoan(toxoplasma)
– Worms (tapeworm)
* natural toxins (alfatoxin from mold peanuts, tetradotoxin from puff fish, mushroom toxins)
* Others such as prions (human mad cow or vCJD)
Outbreak Investigation: Ten Steps
Step 1: Prepare for Field Work
* Research the disease/situation
* Gather needed supplies/equipment
* Make official and personal travel arrangements
* Follow protocol to make local contacts
Step 2: Establish existence of an outbreak
* Expected number of cases
– health records, surveys
*Other factors
– better reporting
Step 3: Verify the diagnosis
* Verify diagnostic procedures are correct
* Verify no lab errors
* Interview patients for
– cause
– source
– spread
Step 4: Define and identify cases
Define cases
* Case definition (4 components)
– clinical information
– patient demography
– location
– time sequence
* Case definition example for influenza-like illness
– clinical information: fever of 100F orally or 101F rectally, plus coughing
– patient demography
– location
– time sequence: Oct1 to May 31
Identify cases
* Case types
– confirmed
– probable
– possible
* Line listing
– ID or case number
– clinical info
– time
– personal info
– place
– risk factors and possible causes
Step 5: Describe TPP (Time, Place, Person) Triad
* Time
– Epidemic curve or epi curve
* Place
– spot map
* Person
– affected population
Types of descriptive studies
* Case report: for single patient
* Case series: for multiple patients
* Correlative studies
– Time series analysis
– Ecologic relations
* Cross sectional
Step 6: Develop Hypothesis or AHE (Agent, Host, Envionment) Triad
* Agent: virus, bacteria, protozoa, fungi, worms
* Hypothesis must be testable
* Should be based on current knowledge and updated
Step 7: Evaluate Hypothesis
* Past cases
* Observational studies
* Cohort
– retrospective or history: past to present
– prospective: now to future
* Case control
* Must have lab verification to validate hypothesis
Calculation
* Cohort table
* Attack rate: sick / total
* Relative risk: exposed attack rate / un-exposed attack rate
>1.0: positive association
= 1.0: no association
(need more study on this)
Step 8: Refine Hypothesis and do Additional Studies
Implement Control and Preventative measures
* Break chain of transmission: any or all within AHE
* Interrupt transmission or exposure: quarantine
* Reduce susceptibility: immunization, education
Criteria to draw conclusions
* Temporality
* Consistency
* Coherence, 1 to 1 relationship
* Strength of association
* Biological plausibility
* Dose/response
Step 10: Communicate Findings
* Oracle briefing
* Written report