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FDSC 408 Exam 3 Study Guide
Terms in this set (34)
Be able to walk through the steps of investigating a foodborne outbreak
-Detecting a possible outbreak
-Defining and finding cases
-Generating hypotheses (Hypothesis generating interviews)
-Testing the hypothesis
(Analytic studies and lab testing of samples)
-Finding the point of contamination and sources of the food
-Controlling an outbreak (Recall products, remove source of contamination, and revise production process)
-Deciding an outbreak is over (When the number of cases returns to baseline)
Curve used to identify clusters. A visual display of the onset of illness among cases associated with an outbreak. X-axis= months, bar= weeks, y axis= # of cases reported. Based on certain strain of microorganisms.
an incident in which two or more persons experience a similar illness resulting from the ingestion of a common food. A group of illnesses in a cluster of people who have something in common that caused the illness
isolated cases where we can rarely home in on which of the foods they consumed are the source of their illness. Individuals who became ill but you cannot link them. For example: improper preparation of food at home which led to foodborne illness
A larger number of people than expected with the same illness in a given time period and area
Nationally Notifiable Disease
diseases defined as notifiable by the Council of State and Territorial Epidemiologists.Formal reporting of cases is done when a physician identifies a case and contacts the health department. Example: E. coli.
foods that tend to be consumed together
pulse field gel electrophoresis. "Fingerprinting of isolates". Restriction enzymes/restriction endonucleases digest DNA at specific sequences. DNA from isolates cut using the same "rare cutting" restriction enzyme.
Advantages and Disadvantages of PFGE
Advantages: Can distinguish isolates to the strain level, each pattern given unique identifier, analyze barcodes through database which assigns them a name.
Disadvantages: sometimes isn't discriminatory enough, difficulty comparing patterns between labs, patterns can change slightly during an outbreak, highly technical procedure to perform.
Case Control Study
A case-control study is designed to help determine if an exposure is associated with an outcome (i.e., disease or condition of interest).
What kinds of information can a case control study give you?
Generate questionnaires to people that are sick/meet case definition and people who are healthy/never showed signs of disease, ask them if they ate any of the foods on the list within a particular time frame. Calculate the number of cases that report exposure to food or indicate that they did not consume that type of food. Used to calculate odds ratio. Can tell you if the illness is linked to a food or not.
What are some challenges to a case control study?
Challenges: food recall (asking sick people what foods that they might have eaten weeks or months ago), and co-linear foods (ex: tomatoes commonly eaten with hot peppers, difficult to tweak apart when they are in combinations like this)
Why is it important to have a matched case control study?
It is important to have a matched case control study because you interview ill patients and try to construct control group that matches them as best as possible in terms of sex, ethnicity, and/or where they live. If these variables are overlooked you could be led to the wrong conclusions.
What is an odds ratio (OR) and how is it calculated? What OR value would a food have if it was associated with an illness? If it wasn't associated with an illness?
-Odds ratio= odds of exposure in cases/odds of exposure in controls
-OR greater than 1 means that there is a suspected link to disease/illness
-OR less than or equal to 1 means that it is not associated with illnesses.
-An Odds ratio of 1 means that the consumption of food yielded no difference between people who got sick and people who did not
What three pieces of data do investigators hope to collect in order to solvean outbreak investigation (the "three-legged stool")?
1. Have to have the food survey info that clearly shows that the food or event have a high odds ratio
2. Need to be able to isolate specific microorganisms from this product
3. Use whole genome sequencing to show that the isolated microorganism and the microorganism affecting the patients are the same
Understand the reasons that investigators may find multiple PFGE patterns
Multiple PFGE patterns could be due to isolates with one band differences (insertions and deletions). Can get small changes in genome, loss of a plasmid can cause loss of band, which shows a change in the PFGE pattern.
Why isn't data perfectly accurate for OR all of the time?
OR data isn't perfectly accurate all of the time due to food recall, co-linear foods, matched case control study issues
What is WGS?
-WGS allows for more outbreaks solved and fewer cases per outbreak.
-WGS: researchers collect a DNA sample and then determine the identity of the 3 billion nucleotides that compose the human genome. Used to sequence food borne pathogens which are then uploaded to the "Genometrackr" database
Compare WGS to PFGE
-WGS: can be too discriminatory, analysis still not routine for most labs, initial equipment purchase expensive, infrastructure changes
-PFGE: sometimes isn't discriminatory enough, difficulty comparing patterns between labs, patterns can change slightly during an outbreak, highly technical procedure to perform.
What types of DNA differences can WGS detect?
-SNPs: single nucleotide polymorphisms
-Deletions: can be few to hundreds of thousands of nucleotides
-Insertions: can be few to hundreds of thousands of nucleotides
Name advantages and disadvantages to using the WGS detection method in determining the cause of an outbreak.
Disadvantages: can be too discriminatory, analysis still not routine for most labs, initial equipment purchase expensive, infrastructure changes
Advantages: more outbreaks solved, fewer cases per outbreak. Improves our ability to identify outbreaks and link isolates from patients and food to outbreak
What are the "Big Six" and why are they important?
-They are considered adulterants
-When grouped together they are twice as common as E. coli O157:H7
-Serogroups of E. Coli (Non O157 Shiga toxin E. coli)
-O26, O45, O111, O103, O121, O145
Compare and contrast E. coli and Shigella. How can you tell the difference between outbreaks related to each?
-Shigella is a fancy name for E. coli
-Similarities: pH, aw optimum, temp range
-S. dysenteriae produce shiga toxin
-However, Shigella is non-motile and lactose negative and humans are the only known reservoir for it
-For E. coli, it is motile and ferments lactose to gas, and its most common reservoirs are cattle which can transfer it to humans
One of the patients still has some leftovers that you think may have contained the pathogen. What tests might you run on this food to further identify the pathogen responsible?
Run molecular sequencing (PFGE and whole genome sequencing) in order to identify "fingerprint" the pathogen and see if the pathogen of interest matches the microorganism that is affecting the sick patient
Which organism is often linked to raw milk consumption?
Are outbreaks from pasteurized milk as frequent as those linked to raw milk?
-More outbreaks are due to raw milk than pasteurized mil when normalized by quantity sold
-More foodborne illness cases from raw milk consumption occur in children
-Most foodborne illnesses from the consumption of raw milk occur in states that raw milk sales are legal.
What are the different laws states set up for themselves concerning raw milk sales, and where does Pennsylvania fall?
Laws of other states: in some states you can buy raw milk on farms but not in a retail situation, in other states herd-shares are legal, in other states there are no laws on herd-sharing (not allowed but not enforced to anyone who has one), other states raw milk cannot be sold for human consumption but it can be sold in pet food stores, in New Jersey states raw milk sales are illegal
Laws of PA: raw milk sales are legal
Hypothesis generating interview
Health officials interview people to find out what and where the ill person ate and went in the days or weeks before they got sick.
Open-ended hypothesis generating interview
Open-ended questions are less constrained, which allows interviewees to express themselves freely, but they are more difficult to code and analyse. By administering an open-ended hypothesis-generating questionnaire to some of the first case-patients the investigator(s) will attempt to learn about potential exposures to known risk factors.
designed to help determine if an exposure is associated with an outcome (i.e., disease or condition of interest).
PulseNet is a national laboratory network that connects foodborne illness cases to detect outbreaks. PulseNet uses DNA fingerprinting of bacteria making people sick, to detect thousands of local and multistate outbreaks.
the establishment of organizational or system standards, targets, and goals to improve public health practices.
A bacteria that will have the disease resolve itself (salmonella, campylobacter, etc)
Using a battery of phenotypic tests as a way to classify individual members of a species. Practical use: human illness only associated with 1-2 biotypes
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