Field and outbreak epidemiology

Question 1

What causes disease?

what are the three factors of disease?

Answer 1

1. Agent
   what caused the disease?
   - Ex. Microbes, toxins, etc.
2. Host
   Who has the disease?
   -Ex. Genetic or personal characteristics
3. Environment
   Where was the disease transmitted?

-Ex. Air pollution, weather, climate, social situations.

Question 2

What is the epidemiological triangle?

Answer 2

The triangle with the host on top of the peak, environment to the right, and agent to the left .

Question 3

Direct disease transmission

Answer 3

Direct Transmission
- Direct and usually immediate transfer of infectious agents to portal of entry.

ex. person to person

Question 4

Indirect Disease Transmission

Answer 4

1. Vehicle- Borne infections
   - Infection results from contact with vehicles, contaminated non-moving objects.
2. Airborne infections
   - Spread of droplet particles present in the air such as classrooms or airplanes.
3. Vector- borne infections
   - infection results from vector which is animal or insect.

Question 5

Field epidemiology

Answer 5

The problem is unexpected

A timely response may be demanded

Intervention of epidemiologists and presence in field required to solve problem

Investigation time likely to be limited because of need for timely intervention

Question 6

disease surveillance

Answer 6

~ States must report cases of certain diseases to the CDC.
ex. list of diseases updated annually

~ Contains especially dangerous of outbreak prone diseases such as smallpox, anthrax, and plague.

Question 7

What are some uses of Disease Surveillance?

Answer 7

1. Estimate magnitude of the problem.
2. Determine geographic distribution of illness
3. Portray the natural history of a disease.
4. Detect epidemics/ define a problem.
5. Generate hypotheses/stimulate research.
6. Evaluate control measures.
7. Monitor changes in infectious agents.

Question 8

1. How to prepare for the Fieldwork?

Answer 8

1. Research the disease
   - what will you need in the field?
   ex. personal protective equipment, culture medium, shipping supplies.
2. Establish team structure
   - know how big of a team is needed
   - define the roles for whose involved
3. Make arrangements
   - this could involve traveling and communication.

Question 9

what are the four plans ?

Answer 9

1. Prepare for fieldwork
2. Establish the Existence of an Outbreak
3. Confirm the Diagnosis
4. Establish a case

Question 10

2. How to establish the existence of an outbreak?

Answer 10

First define outbreak: “An epidemic limited to localized increase in incidence of a disease, e.g, in a village, town, or closed institution”

ask how can we know if the incidence is in excess or normal?
Even if the incidence is clearly in excess of normal, it may not represent an outbreak? why?

Question 11

3. How to confirm the Diagnosis ?

Answer 11

For infectious diseases, know how how to do about it ,for instance what about environmental exposure/toxins?

If specialized lab tests are needed, obtain samples early.

Visit patients, review history, include a proper clinician qualified to make diagnosis.

Question 12

4. Establish criteria for case identification

Answer 12

Establish case definition
- A set of criteria that clearly states what a “case” is in this outbreak.

list the 4 components of establishing criteria:

1. Clinical information about the disease
2. Characteristics of the people affected
3. information about the location/ place
4. Specific time frame
5. Describe and Orient Data
6. Formulate Hypotheses
7. Evaluate (Test) Hypotheses
8. Renfine Hypotheses/ Additional Studies
9. Implement Control and Prevention Measures
10. Communicate Findings

Question 13

Define and Identify Cases

Answer 13

Examples of a case definition of Listeria:
Symptoms :
Fever, headache, confusion, loss of balance, miscarriage, muscle aches.

A confirmed case:

• Presence of Listeria Monocytogenes in blood, spinal fluid, amniotic fluid, or placenta.
• Symptoms appear within 2 months of consuming contaminated food.

Question 14

Define and Identify Cases

Answer 14

1. Identify and count cases
   - ideally, we need to identify 100% of cases
2. Search for missing cases
3. in a closed population, this process if more straightforward:
   ex.
   - how would you approach this with an outbreak at UT, how about a city-wide outbreak in Austin or even potentially nation-wide outbreaks with contaminated food?
4. Data collection :
   ID, address, demographics, clinical info, possible risk factor exposures, and line listing.

Question 15

5. How to describe and Orient Data?

Answer 15

1. Conduct descriptive epidemiology: person, place, time
2. “person” factors include:
   - sex, age, demographics, occupation, high-risk behaviors
3. “place” factors include”
   - places of residence/occupation, county, zip code
4. “Time” factors include:
   - Data of onset, diagnosis, duration of illness, duration of exposure ( construct an epi curve).

Question 16

what is an epi curve?

Answer 16

A visual display of the onset of illness among cases associated with an outbreak.
It would tell you the month or year of onset and the number of cases.

Question 17

How to classify the Epidemic?

Answer 17

Make sure mode of transmission is assessed:

1. common source epidemic
   - starting at specific point through intermittent or continuous exposures to source over days, weeks, years.
2. Propagated epidemic
   - spread gradually from person to person
   - or as result of common source of exposure that is then spread secondarily from person to person.
3. Mixed epidemic
   - involved combination of both types
   - Typically begin with common source and then propagated person to person.

Question 18

what are some questions to ask to clarify an epidemic?

Answer 18

• is outbreak from single source, or single-point exposures.
• is disease spread from person to person?
• is outbreak airborne; behaviorally or chemically caused; and does the outbreak involve multiple events or exposures.
• is there sources of infection from unapparent sources?
• is there a vector involved in transmission?

Question 19

Determine who is at risk of Becoming case

Answer 19

• Determine who is ill and who is well exposed group
• classify by individual disease and exposure histories.
• clinical, medical, lab findings confirmed.
• Use 2x2 for classifying cases by exposure status

Question 20

6. How to formulate the hypotheses ?

part i

Answer 20

Once you have describe data, you can begin to formulate hypotheses about the disease origin and transmission
- truly an on-going process

Your hypotheses should take into account person, place, time information.

• why would a disease affect mostly elderly people?
• why might a disease be limited to a particular neighborhood or members of a church?

Question 21

6. Formulate hypotheses

(Part ii)

Answer 21

After analyzing data, you see that most of the affected people are older or pregnant. Also, many of them ate cantaloupe.

Possibility: Contaminated cantaloupe are leading to an increase in Listeria infections in people with compromised immune systems.

Question 22

Evaluate ( Test ) Hypotheses

Answer 22

1. Sometimes, clear evidence negates the need for evaluation.
   - outbreak of botulism in 100 kids who all ate meatloaf at the school cafeteria on one particular day.
2. if it is less clear, a formal hypothesis test is needed.
   - cohort or case-control study.

Question 23

7. Evaluate ( Test ) Hypotheses

Answer 23

A. Cohort study

• used when the population is small and well-defined. Ex;
  1. cruise ship
  2. event

B. Survey all people at risk for potential exposures ;

1. calculate an “ attack rate” (incidence) for each exposure.
2. compare attack rates for those that were exposed to those that were not exposed.

C. Case-control study

1. used when the population is larger or less well defined.
   - entire city, county, or state

D. Identify non-cases (aka controls) to compare to the cases.
- Determine the rates of exposures among the cases and controls and compute the odds ratio.

Question 24

8. Refine Hypotheses/ Additional Studies

Answer 24

if the tests of the hypotheses prove inconclusive, it is necessary to revisit them.

additional case-control studies of re-doing a cohort study with broader questions on exposures can uncover true agents and vectors of disease.

Question 25

9. How to implement control and prevention measures?

Answer 25

This is doe throughout the investigation;
- as soon as a possible agent or vector is suspected, eliminate the source if possible.
- recall of cantaloupe from
Jensen Farms in Colorado.

It could be that the outbreak is ending by the time you arrive.
- These become preventive steps for future outbreaks.

Question 26

10. How to communicate findings

Answer 26

A. often 2 components:

1. oral briefing for local health authorities
2. written report

B. Oral Briefing 
    1. Summarize your finding 
     and control/ prevention 
     measures
     2. keeps necessary people 
      informed 

C. Written report
1. Standard scientific write-up, contributes to the body of knowledge of the disease of question and highlights successful and problematic components of outbreak investigations.