describing the health of the population and occurrence.ppt

7/27/2019 Describing the Health of the Population and Occurrence.ppt

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Describing the Health of thePopulation and Occurrence of

Diseases

Haripurnomo Kushadiwijaya


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Characterizing a population in time andplace,

Identifying prioritized medical and healthproblems,

Identifying risk factors of the problems,

Identifying prioritized, appropriate interventionto control the problems.

Why Describing the Health of the Population

and Occurrence of Diseases is Important

Assignment: Try to find what science or branch of science

that is instrumental to reach above aims.


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Despite the understanding of continuum ofprepathogenesis and pathogenesis that

would bring us to nuances or stages of

disease, a dichotomy of diseased and non-

diseased states is often used as an outcomeof exposure and non-exposure.

An appropriate definition of case (diseased),

non-case (non-diseased), and any magnitude

of exposure will be needed.


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Ability to quantify occurrence of disease is

required for any epidemiologic investigation. The following is an example (Hennekens).

Disease Frequency

Location: New cases ofhepatitis:

Reporting period: Population:

City A 58 1985 25,000

City B 35 1984 - 1985 7,000

Annual rate ofoccurrence ofhepatitis:

City A:58/ 25,000/ 1 yr =232/ 100,000/year

City B:35/ 7,000/ 2 yrs =250/ 100,000/year

Hypothetical data on frequency of hepatitis in two cities

Note: For ease of comparing rates directly, the same unit of population in the

denominator of each rate is used.


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Prevalence quantifies the proportion of individualsin a population who have the disease at a

specific instant and provides an estimate of theprobability (risk) that an individual will be ill at a

point of timeor in a period oftime:

Prevalence

P = number of existing cases of a disease / total population, at a given

point in time


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Examples of Prevalence

- On July 31, 2004 the number of blind persons in the district ofK (population 255,000) is 51. The prevalence is 51/ 255,000 =

20 per 100,000. (example of a point prevalence)

- In 2005 the number of all tuberculosis cases in the district of

H (population 225,000) is 225. The prevalence is 225/225,000

= 100 per 100,000. (example of a period prevalence)


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Incidence quantifies the number of new events orcases of disease that develop in a population ofindividuals at risk during a specified time interval.There are two specific types of incidencemeasures: cumulative incidence and incidence rateor density.

Incidence

I = number of new cases of a disease during a given period of time/total population at risk.


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Examples of Incidence

Cumulative incidence gives an estimateof the probability, or risk, that anindividual will develop a disease duringa specified period of time:

A total of 2390 women aged 1649 years were studied. Ofthese, 482 were OC (oral contraceptive) users at the 1973 initialsurvey. At a second survey in 1976, 27 of the OC users haddeveloped bacteriuria. This results in a cumulative incidence ofbacteriuria among OC users of 27 per 482 or 5.6 percent duringthis 3-year period.

This incidence could be viewed differently if it referred to a 6-month period, a 1-year period, a 5-year period, or a 10-yearperiod.


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Notes on Incidence

Incidence rate, force of morbidity ormortality, or incidence density providesa more precise estimate of impact ofexposure in a population:

ID = number of new cases of a disease during giventime period / total person-time of observation, at risk.

Time period at risk of a new case observed maydiffer. Person-time for incidence density should becalculated specifically.


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Yr1

Yr2

Yr3

Yr4

Yr5

Yr6

Yr7

Yr8

Yr9

Yr10

Yr11

Total timeat risk:

Subject A 2.0

Subject B 3.0

Subject C 11.0

Subject D 7.0

Subject E 4.5

Total years atrisk:

27.5

Calculation of person-years for incidence density

Initiation of follow-up, time followed, occurrence of disease

ID = 2 cases / 27.5 person-years = 7.2 / 100 person-years of observation


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- For any measure of disease frequency,

precise definition of the denominator is

essential for both accuracy and clarity.The denominator of a measure of

incidence should include only those at

risk of developing the disease

- Occurrence of a disease can be broken

down by characteristics of human hosts:

sex, age group, occupation

Notes:


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Special types of incidence and prevalence measures:

Rate Type Numerator Denominator

Morbidity rate Incidence New cases of nonfatal disease Total population atrisk

Mortality rate Incidence Number of deaths from adisease (or all causes)

Total population

Case-Fatality rate Incidence Number of deaths from a

disease

Number of cases of

that disease

Attack rate Incidence Number of cases of a disease Total population atrisk, for a limitedperiod ofobservation

Disease rate atautopsy

Prevalence Number of cases of a disease Number of personsautopsied

Birth defect rate Prevalence Number of babies with a givenabnormality

Number of livebirths

Period prevalence Prevalence Number of existing cases plus

new cases diagnosed during agiven time period

Total population


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Examples of data sources:

- Yearly health profile of a district (example ofHealth Profile Book)

- Electronic data base of selected health centres

(BERBAHPKM.xls)

- Ministry of Health website

- Local health services websites
http://localhost/var/www/apps/conversion/tmp/scratch_1/BERBAHPKM.xlshttp://localhost/var/www/apps/conversion/tmp/scratch_1/BERBAHPKM.xls

describing the health of the population and occurrence.ppt

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