Epidemiology 3 Disease surveillance and measure morbidity

Question 1

What are some ways we can get information for a patient about his past medical issues ?

Answer 1

Data sources

•Sources of data can be used to obtain information about the person’s illness

–Hospitalization (medical and hospital records)

•Information about the illness even before medical care was sought, we may have to obtain information from the patient

–Questionnaire or interview

Question 2

.What is morbidity ? What is rate in terms of disease ? What is proportion ?

Answer 2

Morbidity

-measures

• Occurrence of disease can be measured using rates or proportions.
• Rates:

–Tell us how fast the disease is occurring in a population

•Proportions: Infected/non infected

–Tell us what the fraction of the population is affected

Do not get confuse with prevalence !

Question 3

.What is incidence rate ? What is the formula ?

Answer 3

Incidence rate

•Incidence rate:

–Number of new cases of a disease that occur during a specified period of time in a population at risk for developing the disease.

•Incidence rate per 1,000=

–No. of new cases of a disease occurring in the population during a specified period of time/ No. of persons who are at risk of developing the disease during that period of time.

Question 4

What is incidence rate ? How can it be looked at ?

Answer 4

Incidence rate

•Incidence rate is a risk measure

–This risk can be looked at in any population group, such as a particular age group, males or females, an occupational group, or a group that has been exposed to a certain environmental agent

Question 5

What is a time period, and does it matter ? How long are people in the incidence rate followed ?Wha is Cumulative incidence ?

Answer 5

Time period

• Time period is arbitrary
• Incidence rate-individuals in the group have been followed up for that entire period

–week, month, year, 5 years

•Cumulative incidence-incidence rate calculated using a period of time

Question 6

What is prevalence ? Formula

Answer 6

Prevalence

• Number of affected persons present in the population at a specific time/ number of persons in the population at that time
• Prevalence per 1,000=

–Number of cases of a disease present in the

population at a specified time x 1,000

Number of persons in the population at that specified time

•Prevalence=Persons with Diabetes in San Juan (2011)/ San Juan population (2011) x 1,000

Question 7

What does prevalance measure ? Does it determined when the disease developed ? Why yes or no ?

Answer 7

Differences between incidence & prevalence

•Prevalence-determines who has the disease and who does not.

–It is not determining when the disease developed.

•The numerator of prevalence includes a mix of people with different durations of disease, and as a result we do not have a measure of risk.

Question 8

What does incidence include that prevalence does not ?

Answer 8

Incidence includes only new cases or events.

Question 9

What is point prevelance ?Period prevalance ?

Answer 9

Prevalence

• Point prevalence-prevalence of the disease at a certain point in time.
• Period prevalence-how many people have had the disease at any point during a certain time period.

–time period is arbitrary

(month, a single calendar year, 5-year period)

Question 10

What happens to incidence and prevelance when new cases are presented of a diease ? Death ? cure ?

Why is prevalance needed for a commmunity.

Answer 10

Prevalence

• Addition of new cases (incidence) is increasing the prevalence, while death and/or cure is decreasing the prevalence.
• Prevalence is an important and useful measure of the burden of disease in a community.

–How many clinics are needed, types of rehabilitation services are needed

Question 11

Is Prevelance a measure of risk ?

Answer 11

Prevalence is not a measure of risk

Gordis,

Question 12

What is the formula for attack rate ?

Answer 12

Attack rate

•Attack rate

–Number of people at risk in whom a certain illness develops/ Total number of people at risk

•Example:

–Number of people who ate a certain product and became ill/ Total number of people who ate that product

Gordis,

Question 13

What is correlation ? Whats is the unit ? What does ranges from 1+ to -1 mean ?

Answer 13

Correlation

• Measure of association: Correlation coefficient (r)
• Coefficient ranges between +1 and -1, represents the extent to which there is a linear relationship between exposure and disease

Question 14

What does +1 correlation mean ? -1, and 0 correlation ?

Answer 14

•+ 1 perfect positive correlation

–Weight and blood pressure

•-1 perfect negative correlation

–Physical activity (hours) and blood pressure

•0 no correlation

Question 15

Why might surveillance be carried out ?

Answer 15

Surveillance

• Surveillance may be carried out to monitor changes in disease frequency or to monitor changes in prevalence of risk factors.
• Surveillance is also to monitor for completeness of vaccination coverage.

Question 16

What is passive surveillance ?

Answer 16

Passive surveillance-either available data on reportable diseases are used or reporting is mandated or requested with the responsibility for the reporting often failing on the health care provider or district health officer.

Gordis,

Question 17

What is active surveillance ?

Answer 17

Active surveillance-denotes a system in which a project staff make periodic field visits to health care facilities to identify new cases of a disease.

Question 19

What does risk mean in epi

Answer 19

it means chances it it will happen.

Question 20

what is the difference between morbidity and mortality ?

Answer 20

morbidity: the degree of sickness
mortality: The measure of death!