7. Outbreak investigation

Question 1

Why do we use Epidemiological curves?

Answer 1

Used to determine the mode of spread, determine the most likely period of exposure (time trend), and determine the magnitude of an outbreak.

Question 2

Give Examples of Epidemiological curves:

Answer 2

• Point-source outbreak curve
• Continuous common sourceoutbreak curve
• Propagated outbreak curve

Question 3

What is Point-source outbreak curve?

Answer 3

• People are exposed over a brief time
  to the same source, such as a single meal or an event.
• The number of cases rises rapidly to a
  peak and falls gradually.
• The majority of cases occur within
  one incubation period of the disease.

Question 4

What is Continuous common source outbreak?

Answer 4

• People are exposed to the same source, but exposure is prolonged over a period of days, weeks, or longer.
• The curve rises gradually and might
  plateau.

Question 5

What is Propagated outbreak?

Answer 5

• No common source.
• The outbreak spreads from personto-person.
• The curve will assume progressively taller peaks, each being one incubation period apart.

Question 6

What you need to determine the most likely period of exposure for an outbreak?

Answer 6

you need to know the average incubation period for the disease and the range of incubation periods, which are the min & max reported incubation periods.

Question 7

What is the Epidemiologic steps of an outbreak investigation?

Answer 7

1. Establish the existance of an outbreak
2. Verify the diagnosis, rule out laboratory errors
3. Construct a working ‘case definition’
4. Find cases systematically and record information
5. Perform descriptive epidemiology (epi-curves, geographic distribution, personal characteristics)
6. Develop hypotheses, evaluate hypotheses epidemiologically (analytic studies)
7. Compare and reconcile with laboratory and environmental studies
8. Implement control and preventive measures
9. Initiate and maintain surveillance
10. Communicate findings

Question 8

What is Case definition?

Answer 8

• must not include the exposure or risk facis a standard set of criteria for deciding whether an individual should be classified as having the health condition of interest (it is not a diagnostic criteria).
• must not inc;ude the exposure/risk factor your intrested in evaluating

Question 9

What are the classes of Outbreak Investigation?

Answer 9

Sporadic disease
Endemic disease
Epidemic disease
Outbreak
Cluster
Pandemic

Question 10

Definition of Sporadic disease?

Answer 10

disease that occurs infreuqently and irregularly.

Question 11

Definition of Endemic disease?

Answer 11

refers to the constant presence and/or usual prevalence of a disease or infectious agent in a population within a geographic area. (ex. malaria in africa)

Question 12

Definition of Epidemic?

Answer 12

increase, often sudden, in the number of cases of a disease above what is normally expected in that population in that area.

Question 13

Definition of Outbreak?

Answer 13

carries the same definition as epidemic, often used for a more limited geographic area.

Question 14

Definition of Cluster?

Answer 14

refers to an aggregation of cases grouped in place and time that are suspected to be greater than the number expected, even though the expected number may not be known.

Question 15

Definition of Pandemic?

Answer 15

refers to an epidemic that has spread over several countries or continents, usually affecting a large number of people

Question 16

What are the primary contributing factors in Epidemic?

Answer 16

• Source of infection
• Mode of transmission
• Susceptible population

Question 17

What are the secondary contributing factors in Epidemic?

Answer 17

• Socioeconomic factors
• War
• Weather
• Education

Question 18

What are the categories of case definition?

Answer 18

Suspected: a case that meets the clinical case definition

Probable: a suspected case with borderline laboratory findings and/or epidemiological link to
confirmed case

Confirmed: suspected or probable case with definitive laboratory confirmation

Question 19

What is the definition of Clinical case definition?

Answer 19

An illness with sudden onset of fever (>38.5°C rectal or >38.0°C axillary) and one or more of the
following: neck stiffness, altered consciousness, other meningeal sign or petechial or puerperal rash.

Question 20

What is the definition Laboratory criteria for diagnosis?

Answer 20

Positive cerebrospinal fluid (CSF) antigen detection or positive culture.

Question 21

What is the definition of Incubation period?

Answer 21

the time elapsed between exposure and the appearance of first symptoms.

Question 22

What is the definition of Latency period?

Answer 22

the time elapsed between exposure and infectiousness.

Question 23

What is the definition of Basic reproduction number (R0)?

Answer 23

• mathematical model of an outbreak
• The expected number of cases directly generated by one case in a population where all individuals are susceptible to infection. The definition assumes that no other individuals are infected or immunized (naturally or through vaccination).

Question 24

what is the effective reproduction number (Re or Rt)?

Answer 24

representing the average number of new infections caused by a single infected individual at time t in the partially susceptible population.

Question 25

whar is the definition of Herd immunity?

Answer 25

occurs when a significant proportion of the population (or the herd) have been vaccinated (or are immune by some other mechanism), resulting in protection for susceptible (unvaccinated) individual.

Question 26

what is herd immunity threshold?

Answer 26

it is the proportion of a population that need to
be immune in order for an infectious disease to become stable in that community.

*The higher the R value, the higher the herd immunity threshold is.

Question 27

How can you find the effective reproduction number (Re or Rt)?

Answer 27

It can be found by multiplying R0 by the fraction of the population that is susceptible (Re = R0 * x)