Investigating an Outbreak Flashcards
what is an outbreak?
outbreak/epidemic exists when there are more cases of a particular disease than expected in a given area or among a specific group of people over a particular period of time
why do we investigate an outbreak? (6)
- to control and prevent disease
- to determine the severity and risk to others
- for research opportunities and to gain additional knowledge
- training opportunities
- program considerations (training and prevention)
- public, political, or legal concerns
what are the 7 steps of investigating an outbreak?
- prepare for field work
- verify outbreak
- plot epidemic curve
- calculate attack rates
- determine source of epidemic
- recommend control measures
- follow up
what are the 5 things that happen in step 1 of investigating an outbreak (preparing for field work)?
- research what is known about the disease or symptoms
- learn about demographics and customs of local population
- make admin and travel arrangements
- build your team with clear delineation of responsibilities and assignments
what are the 4 things that happen in step 2 of investigating an outbreak (verifying outbreak)?
- establish a case definition that is non-ambiguous with clinical/diagnostic verification if possible with person/place/time descriptions
- identify and count cases of illness
- determine if disease is above endemic levels or if looking at a different disease with similar symptom
- develop and administer a questionnaire to determine demographics, behaviors, and exposures
how is an epidemic curve plotted?
number of cases on the y axis by their date or time of onset (x axis)
what does the overall pattern of an epidemic curve tell you?
the increase, peak, and decrease can tell type of epidemic and incubation period
what can outliers of an epidemic curve tell you?
if a case is unrelated, early or late exposures, index case, secondary cases
describe the epidemic curve of a vector borne disease (3)
- starts slowly (climate effects can modify)
- the time between the 1st case and peak is comprable to incubation period
- slow tail, will rise again or repeat until run out of susceptible people
describe the epidemic curve of a point source epidemic
large population exposed over a short period of time so high peak at beginning and then tapers off; most common form of transmission for food-borne disease
describe the epidemic curve of a continuing common source or intermittent exposure epidemic
several peaks, cannot isolate incubation period
give an example of a point source epidemic
legionnaire’s disease
give an example of continuing common source or intermittent exposure epidemic
cholera
describe the 3 steps in step 4 of investigating an outbreak (calculate attack rates)
- calculate attack rate for each possible risk factor
- if there is an obvious commonality for the outbreak, calculate attack rates based on exposure status (a community picnic, then later you can calculate this to individual items at the picnic)
- if there is no obvious commonality for the outbreak, calculate attack rates based on specific demographic variables
describe step 5 of investigating an outbreak (determining source of epidemic)
attack rates can point statistically to the factor most closely associated with becoming a case, but it may require more than one risk factor to become a case, so ask if there are case that are NOT associated with your source (like malaria not from a mosquito)
describe 3 things that happen in step 6 of investigating an outbreak (recommending control measures)
- recommend measures that would serve to reduce transmission (toss potato salad)
- these recs will be considered by public health personnel
- then long-term measures will be provided to prevent future outbreaks (here is how to store the potato salad)
describe 4 things that happen in step 7 of investigating an outbreak (following up)
- follow up to determine the effects of the intervention measures incorporated
- meet with your team to critique and refine your response
- identify what works well and what did not
- communicate the specifics on the outbreal for study and educational applications
define a foodborne disease outbreak
an incident in which two or more persons experience a similar illness after ingestion of a common food and epidemiologic analysis implicated the food as the source of the illness
define intoxication as related to foodborne illness
ingestion of foods with toxicants of certain plants and animals, metabolic products formed and excreted by microbes while they multiply, or poisonous substances introduced during production, processing, transportation, or storage of food
define infections as related to foodborne illness
caused by the entrance of pathogenic microbes into the body and the reaction of the body tissues to their presence or to the toxins they generate within the body
give 4 rules of thumb, but not laws, related to foodborne illnesses
- intoxicants are rapid onset, no fever
- toxins in the stomach produce vomiting
- toxins in the intestines produce diarrhea
- infections produce fever
what are the 3 types of foodborne contamination? give examples of each
- physical: glass, metal fragments, dirt, bone
- chemical: pesticides, cleaning compounds, poisonous metals (lead), additives and preservatives
- biological: bacteria, virus, fungi, protists, yeast, mold, parasites, insects, rodents, poisonous fish and plants
what are the 6 bacterial requirements?
- food
- water
- pH
- temperature
- time
- oxygen
what kind of food do most bacteria require?
what we consider to be potentially hazardous food such as milk or milk products, eggs, meat, poulty, fish, shellfish (anything high protein and moist)
describe bacterial water requirement
most bacteria require moisture to thrive
what is Aw?
water activity: the amount of water available in food
what is the lowest Aw where bacteria can grow?
0.85
what is the Aw range of most potentially hazardous foods?
0.97-0.99
at what pH range do most bacteria grow best?
neutral or slightly acidic (4.6-7.0)
what is the danger zone of temperature for foods (where most bacterial growth occurs)?
45-145 degrees F
describe how time relates to temperature for bacterial growth in foods
do not let food stay in the danger zone of temperature for more than 4 hours!!!
do all bacteria require the same amount of oxygen?
no; can be aerobic, anaerobic, or facultative anaerobes
what are the 6 major causes of foodborne disease?
- improper cooling
- improper cooking
- improper reheating
- improper holding temperature
- cross contamination
- infected food handlers, poor employee hygiene
