distribution of disease2

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Distribution

of Disease


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Distribution of disease

Distribution is an essential component in

descriptive epidemiology and refers to thestudy or summary of the frequencies of

disease or values of ameasurement

according to groups definedby factors such as age, time and place.


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measurement values ofdistribution of disease

Concept of rate and ratio

Incidence measurement

Mortality measurement


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1. The concept of rate andratio

Ratio, is also called relativeratio, it is the quotient of two

values, which reflects the relativelevel of two values and oftenexpressed by multiple or percent.

Rate AB

10 0


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proportion

Proportion reflects the proportionor distribution of parts of certain

entirety and often expressed bypercent.

proportionthe number of part

the number of entirety

100


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E P I D E M I O L O G Y A N D

H E A L T H S T A T I S T I C S

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(1) incidence rate

Within a certain time and a certain population

and estimated by counting the number of new

cases of disease.

k=100% 1000

IR number of new cases in a certain population /

number at risk in the same timek


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To descript the distribution of disease

To explore the pathogenesis

To put forward the hypothesis of pathogenesis

To evaluate the effect of the prevention and curemeasures.

Application of incidence rate


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(2) attack rate

k=

riskatpeopleofnumbertotal

developsillnesscertainaAR

The proportion of persons within a

population who develop a particular outcome

within a specified period of time

k=100% 1000


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(3) prevalence rate

The proportion of person in a given

population that has a particular disease at a

point or interval of time

k=100%, 1000,

PR number of new or old cases /

persons at risk in the same time k


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The factors influence on prevalence rate

incidence rate and course of disease

(3) prevalence rate

DIP =


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(3) prevalence rate

Application prevalence rate often

represents occurence or epidemicsituation of chronic disease.


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(4) infection rate

Is the proportion affected by a disease of a

investigated and often expressed by present.

Application IR can research affectedsituation of some infectious disease or

parasitic disease and effect of prevention

and curation.

IR number of affected cases /investigated persons

100%


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(5)secondary attack rate SAR

Application SAR can represent theintensity of infectious power, analyze

epidemic factor and evaluate the effect of

prevention measurements.

SAR number of second-affected cases

/susceptible persons 100%


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2.mortality measurement

(1)mortality rate

The proportion of persons within a given

population die from a particular disease.

k 1000MR death number /average population k


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Application Crude mortality rate represents

total death level, which is synthetical reflection

of culture and health level of country or area.

(1)mortality rate


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(2)fatality rate

Is the proportion of persons within a

population affected by a particular disease that

dies from the disease within a specified periodof time.

FR number of deaths /number of diagnosed

patients 100%


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(4)potential years of life lost, PYLL

=

=e

i

iidaPYLL

1


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outbreak

A sudden ,unexpected increase in the

occurrence of a disease within a

relatively limited geographic area

The affected patients have the same route of

transmission and source of infection


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three primary Distribution of

disease

place distribution

time distribution

persons distribution


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Time distribution 1 rapid fluctuation 2 seasonally 3 periodicity 4 secular trend

(secular change)


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Person distribution of disease

age

sex

occupation

race

Social class

Marriage and family

behave


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(1) age

Age is perhaps the most important factor

because there is greater variation in age-

specific disease rates than in rates defined by

almost any other personal attribute. for

example, measles, mumps tend to occur

most commonly in childhood.


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(3) occupation

Different occupation have different influence

on incidence rate mortality rate of disease

because different physical factor, medicalfactor, biological factor and spirit factor can

lead to different diseases.


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(4) race and ethnicity

Persons with different race and ethnicity

have different genetic factor, custom,natural

condition and religion, which can lead todifferent diseases.


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