Disease outbreak

Question 1

Define endemic

Answer 1

• Constant presence of disease or infectious agent in a given geographical area, population or subgroup
• The usual rate of disease

Question 2

What is an outbreak?

Answer 2

• Occurrence of new cases of disease clearly in excess of the baseline frequency for that population over a given period of time
• Synonymous with epidemic (although generally considered to be a more localized epidemic)

Question 3

Define epidemic?

Answer 3

• Any disease occurring at a greater frequency in a defined comminity or institutional population over a given period of time
• An excessive rate of disease

Question 4

What is a pandemic?

Answer 4

• A pandemic is an epidemic occurring over a wide area, crossing international boundaries and affecting a large number of people

Question 5

What is an attack rate?

Answer 5

• Measure of the number of persons affected by a disease outbreak among persons at risk
• The total number of people who develop disease in population divided by the number in the population at risk

Question 6

What is a secondary attack rate?

Answer 6

• The probability that infection occurs among susceptible persons within a reasonable incubation period following a known contact with an infectious person or infectious source
• This person must have been directly exposed to disease vs. primary where they just need to be in population at risk

Question 7

Define virulence

Answer 7

• The severity of disease produced by the organism in a given host
• It is expressed as the number of cases of severe and fatal infection divided by the total number clinically infected

Question 8

Define case-fatality, how is it calculated?

Answer 8

• The PROPORTION of people contracting a disease who will die of that disease
• DIFFERENT THAN MORTALITY RATE
  CF = #deaths / #diagnosed patients
• Can be thought of as the ‘risk’ of death

Question 9

• What is the mortality rate?

Answer 9

• AKA Crude death rate

- Estimation of the portion of the population that dies during a specific period from all causes of death

Question 10

What is a point-source epidemic?

Answer 10

• Exposure is brief and essentially simultaneous.
• Cases rise to peak rapidly to peak and falls gradually
• Most cases occur within one incubation period
• Ex: Restaurant with contaminated food

Question 11

What is an extended source epidemic?

Answer 11

• Exposure period lasts for a period of days to weeks

Question 12

What is a propagated epidemic?

Answer 12

• An epidemic that begins with only a few exposed persons but is then maintained by person to person transmission
• Ex: Influenza

Question 13

How does Risk differ from case fatality?

Answer 13

Risk: new cases/persons at risk
- refers to initial development of condition

CF: #deaths / # of diagnosed patients
- refers to risk of death among those with condition