Slide 1: 6/24/2011 1 Dr. Irfan Momin Community Medicine Department,
Government medical college, Surat Descriptive epidemiology Objectives: : 6/24/2011 2 Objectives: Describe Person, Place and Time distribution of disease occurrence.
List the uses of descriptive epidemiology Epidemiology : 6/24/2011 3 Epidemiology Epidemiology is the study of
health-related events and application of this study
to prevent and control health problems. Components of Epidemiology : 6/24/2011 4 Measuring Disease Frequency
Quantify disease using rates and ratios
Describe Distribution of disease
Who is getting the disease? Person
when is the disease occurring? Time
where is the disease occurring? Place
Uses: Formulation of hypotheses concerning causal and preventive factors Components of Epidemiology Components of Epidemiology : 6/24/2011 5 Analytic epidemiology
Uses: Identify determinants of disease
Hypotheses are tested
(why and how the disease is occurring.) Components of Epidemiology Slide 6: 6/24/2011 6 Descriptive epidemiology describes the distribution of health-related events by time, place, and personal characteristics in order to answer
who (person). Slide 7: 6/24/2011 7 I- Time Variation of disease occurrence include:
Annual occurrence, seasonal occurrence, and daily or even hourly occurrence during an epidemic.
Knowing time trend of a disease will help health professionals establish control measures.
Time trends include:- Secular (long-term) trends: Graphing the annual cases or rate of a disease over a period of years (Decades or centuries) shows long-term or secular trends in the occurrence of the disease.We commonly use these trends to suggest or predict the future incidence of a disease. : 6/24/2011 8 Secular (long-term) trends: Graphing the annual cases or rate of a disease over a period of years (Decades or centuries) shows long-term or secular trends in the occurrence of the disease.We commonly use these trends to suggest or predict the future incidence of a disease. Slide 9: 6/24/2011 9 Secular (Long-term trends) is influenced by population features e.g.
Change of degree of susceptibility e.g. by immunization
Environmental sanitation and
Nutritional status of a population. Slide 10: 6/24/2011 10 Death rate for Tuberculosis, 1860-1960, United States, Source: US Bureau of the Census, Historical Statistics of the United States; Colonial Times to 1970 (Washington, D.C: Government Printing Office, 1975), Part 1 pp58,63. Note: Data between 1860 and 1900 for Massachusetts only. Periodic (cyclic variation) : 6/24/2011 11 Periodic (cyclic variation) Where disease occurrence for a period then increase again in cyclic pattern e.g. measles in pre vaccination era occur every 2 – 3 years Seasonality:By graphing the occurrence of a disease by week or month over the course of a year or more we can show its seasonal patternExample:Cases of influenza increases in winter. Food poisoning and diarrhea increase in summer. : 6/24/2011 12 Seasonality:By graphing the occurrence of a disease by week or month over the course of a year or more we can show its seasonal patternExample:Cases of influenza increases in winter. Food poisoning and diarrhea increase in summer. Seasonality:Seasonal patterns may suggest hypotheses about:- how the infection is transmitted- what behavioral factors increase risk- other possible contributors to disease occurrence. : 6/24/2011 13 Seasonality:Seasonal patterns may suggest hypotheses about:- how the infection is transmitted- what behavioral factors increase risk- other possible contributors to disease occurrence. Slide 14: 6/24/2011 14 Rapid fluctuation : 6/24/2011 15 Rapid fluctuation Usually occur in the form of epidemics that appear abruptly and ends abruptly either natural or due to intervention Slide 16: 6/24/2011 16 Day of week and time of day:
Analysis at these shorter time periods is especially important for :
Conditions that are potentially related to occupational or environmental exposures, which may occur at regularly scheduled intervals. Slide 17: 6/24/2011 17 II- Place characteristics
We describe a health event by place.
Disease may vary by:
place of residence,
place of employment,
hospital unit, etc.
depending on which may be related to the occurrence of the health event. Slide 18: 6/24/2011 18 Place characteristics
Analyzing data by place can give an idea of
where the agent that causes a disease lives and multiplies,
what may carry or transmit it, and
how it spreads.
Use spot map to locate the possible source or risk factors. Geography : 6/24/2011 19 Geography The location of certain place determine its climatic conditions e.g. temperature, humidity, wind,… which favour certain agents and vectors. Disease variation by Place may be due to: Geology : 6/24/2011 20 Geology The structure of soil affects disease occurrence e.g.
Hardness of water ----- CVD Chemical and physical environment : 6/24/2011 21 Chemical and physical environment Iodine deficiency in the soil (oasis) ---goiter Environmental sanitation : 6/24/2011 22 Environmental sanitation Good sanitation decrease diarrhoeal diseases. Availability of Health Services : 6/24/2011 23 Availability of Health Services Vaccination ---prevent infectious diseases
Health Education ---- healthy behaviour
Detection and treatment of infectious diseases ------- limit spread. Slide 24: 6/24/2011 24 III- Person characteristics:
In descriptive epidemiology, we also organize or analyze data by “person” characteristics such as:
age, race, sex, marital status, socioeconomic status, as well as behaviors and environmental exposures. Slide 25: 6/24/2011 25 Age:
Age is probably the single most important “person” attribute, because almost every health-related event or state varies with age.
Type of disease: e.g.
Neonates ----- congenital anomalies and birth trauma
Elderly ------ Degenerative diseases, CVD Slide 26: 6/24/2011 26 Severity of disease:
Whooping cough is severe under one year
Pneumonia is fatal in early 2 months
Fracture is severe in old age Slide 27: 6/24/2011 27 Clinical form of disease:
Thyroxine deficiency ---- cretinism in young
----Myxodema in adults
T.B. ------ Miliary in children
----- Pulmonary in adults
Explanation of disease variation by age may be explained by
exposure to risk factors or
degree of immunity or susceptibility
response to a causative agent. Slide 28: 6/24/2011 28 Sex:
Some diseases are sex-linked due to:
anatomic differences e.g. cancer cervix , cancer prostate or,
genetic differences between the sexes e.g. Haemophilia.
Other diseases are related to occupations and environmental exposure which differ in both sexes. e.g. accidents and lung diseases Slide 29: 6/24/2011 29 Ethnic and racial groups:
Ethnic group: any group of people who have lived together long enough to acquire common characteristics, either biologically or socially.
Some races are susceptible to specific diseases e.g. sickle cell anaemia in Negros due to genetic predisposition
Some races got immunity due to long exposure Familial tendency : 6/24/2011 30 Familial tendency Clustering of some diseases within certain families may be due to:
Genetic factors, or
common exposure, or
life style Religion : 6/24/2011 31 Religion Religion usually determine the behaviour of its followers
Prohibition of alcohol ----- liver disease
Male circumcision------ cancer penis Slide 32: 6/24/2011 32 Socioeconomic status:
Socioeconomic status is measured by:
Education ---- health behaviour
Occupation ----- income
Family income ---- environmental condition, housing conditions, access to health facilities Occupation : 6/24/2011 33 Occupation Determine the occupational exposure to certain risk factors in work place.
Occupation is also one of the determinant of socioeconomic class which affects the disease occurrence (nutritional diseases,…) Marital Status : 6/24/2011 34 Marital Status Some diseases are common among single others among married due to:
Differences in habits
Nature of work
People in dangerous work usually remain single The End : 6/24/2011 35 The End Thank You firstname.lastname@example.org