EPIDEMIOLOGY What is Epidemiology?

Distribution of Disease

WHEN Time

WHERE Place

WHO Person

EPIDEMIOLOGY

Distribution of Disease

EPIDEMIOLOGY

Distribution of Disease

Place• Geographic

-Restricted/Wide spread

-Coastal/inland

• Weather(temp. , humidity , rainfall)

• Altitude/latitude/longitude

• Urban/rural

EPIDEMIOLOGY

Distribution of Disease

Person• Age• Sex• Race• Education• Occupation• behavior

EPIDEMIOLOGY

Distribution of Diseasemorbidity rates

The numerator is new cases The denominator may change over time as people

develop disease However, in practice in large studies, the denominator is often the mid-

year population in small studies, the denominator includes persons at risk of the disease

Incidence rate

EPIDEMIOLOGY

Distribution of Diseasemorbidity ratesAttack rate عليه

مسائل

Population at risk/ period

Attack rate =

Number of episodes during specified period

x 10n

Acute recurrent diseases , e.g. URTI, food poisoning. A person may catch the disease

more than once.

EPIDEMIOLOGY

Distribution of Diseasemorbidity rates

Attack rate

Example:

In a village of 600 persons, 120 visits to the PHCC were due to food poisoning.

What is the attack rate of food poisoning in the village ?

EPIDEMIOLOGY

Distribution of Diseasemorbidity rates

Attack rate

Example:

In a village of 600 persons, 120 visits to the PHCC were due to flu.

What is the attack rate of flu in the village ?

0

EPIDEMIOLOGY

Distribution of Diseasemorbidity ratesIncidence

rateFactors affecting incidence:

1- New risk factor Contraceptive pills & thromboembolism.

2- Changing virulence H1N1virus & influenza pandemic

3- Changing pattern of interventionChemoprophylaxis & meningitis

EPIDEMIOLOGY

Distribution of Diseasemorbidity ratesIncidence

rateFactors affecting incidence:

4-Population patternAging & degenerative diseases & cancer

5- ReportingIncrease in reporting &

Early stage of surveillance &

EPIDEMIOLOGY

Distribution of Diseasemorbidity ratesIncidence

rateFactors affecting incidence:

6-Screening 7-New diagnostics

New diagnostic

early detection of cases detection of cases

EPIDEMIOLOGY

Distribution of Diseasemorbidity ratesIncidence

rateFactors affecting incidence:8- Changing classification

Blood pressure

140/80 mmhg Vs 160/90 mmhg

incidence

Fasting blood sugar

126 mg/100ml Vs 140 mg/100ml

incidence

EPIDEMIOLOGY

Distribution of Diseasemorbidity ratesPrevalence rate وتفهمي مسائل

يعني ايش Point prevalence

Period prevalence

It involves old and new cases It measures the disease status in the

population.It measures the disease burden.

( All Cases)

EPIDEMIOLOGY

Distribution of Diseasemorbidity rates

= 1OnX

Prevalence rate

Point prevalence:

Total cases (old + new) at fixed point of time at fixed point of time

in a place

total population in that place

EPIDEMIOLOGY

Distribution of Diseasemorbidity rates

= 1OnX

Prevalence rate

Period prevalence:

Total cases (old + new) during a period of timeduring a period of time

in a place

total population in that place

EPIDEMIOLOGY

Distribution of Diseasemorbidity rates

prevalence rate

example

MOH conducted a survey for RVF among workers in slaughterhouses in Makkah . 224 seropositive workers were identified among 6000 workers.

Calculate the prevalence of RVF.

EPIDEMIOLOGY

Distribution of Diseasemorbidity rates

prevalence rateFactors affecting prevalence :

1- Incidence rate

Incidence rate

Prevalence rate

averageduration of

disease

& 2- Disease duration

= X

Incidence

Longer duration