1. Descriptive Epidemiology Dr. Salwa Tayel
Comunicación y Gerencia
بسم الله الرحمن الرحيم
3/10/2010
Descriptive Epidemiology Dr. Salwa Tayel

2. Descriptive epidemiology Family & Community Medicine Department
Dr. Salwa Tayel
Associate Professor
Family & Community Medicine Department
King Saud University
Descriptive Epidemiology Dr. Salwa Tayel
3/10/2010

3. Descriptive Epidemiology Dr. Salwa Tayel
Learning Objectives:
By the end of this lecture students will be able to:
Describe Person, Place and Time characteristics of disease occurrence.
Identify the uses of descriptive epidemiology
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Descriptive Epidemiology Dr. Salwa Tayel

4. Descriptive Epidemiology Dr. Salwa Tayel
Descriptive epidemiology describes the distribution of health-related events by time, place, and personal characteristics in order to answer:
when (time),
where (place),
who (person).
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Descriptive Epidemiology Dr. Salwa Tayel

5. Descriptive Epidemiology Dr. Salwa Tayel
I- Time Variation of disease occurrence
Annual occurrence, seasonal occurrence, and daily or even hourly occurrence of disease may occur.
Knowing time trend of a disease will help health professionals establish control measures.
Time trend include:
Secular trend (long-term)
Periodic (cyclic variation)
Rapid fluctuation (short time)
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Descriptive Epidemiology Dr. Salwa Tayel

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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.
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Descriptive Epidemiology Dr. Salwa Tayel

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Secular (Long-term trend) is influenced by population features e.g.
Change of degree of susceptibility e.g. by immunization
Socioeconomic
Environmental sanitation and
Nutritional status of a population.
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Descriptive Epidemiology Dr. Salwa Tayel

8. Death rate for Tuberculosis, , 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.
Author: John Last, Canada
Death rate for Tuberculosis, , United States, Source: US Bureau of the Census, Historical Statictics 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. Ecological Determinants of Disease
The 19th century change in the pattern of disease was more than a direct cause-effect relationship of improved sanitation to reduced death rates from infections, it was aided by a change in values and behavior. The death rate from tuberculosis began to fall in the early 19th century and continued to fall steadily long before the discovery of effective chemoprophylactic regimens virtually wiped out the disease in the rich nations in the 1950s.
Prosperity led to improved housing conditions and better nutrition. Literacy increased. It became less common for several children in the family to share the same bed. Being well-fed, better housed, well-informed, and separated from others by enough space to reduce the probability of person-to-person transmission of infection, all helped to reduce the burden of premature death. Perhaps there was also a rise in the natural (maternal to infant) level of immunity to some of the infections that had previously carried off huge numbers of infants and children, and a decline in the virulence of some of the most lethal pathogens.
Descriptive Epidemiology Dr. Salwa Tayel
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9. Descriptive Epidemiology Dr. Salwa Tayel
Changing TB mortality
In the last century, decline in TB mortality was due to:
better housing, ventilation
improved nutrition
medical care (streptomycin reduced deaths in UK by 51% ).
However, it is not all good news. TB is on the increase among the growing numbers of homeless peoples in Europe and America, among the poorest living in economies under transition, such as in E. Europe. Also, those countries experiencing war or other politically-determined privations where disease surveillance and treatment have been disrupted, such as, currently, Afghanistan and Iraq, are probably seeing an increase in TB infections and deaths.
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Descriptive Epidemiology Dr. Salwa Tayel

10. Recently, TB rates are increasing. why?
Environmental: (poor nutrition, housing, hygiene, sociopolitical; wars).
Host changes: increased susceptibility (e.g. HIV/AIDS infection), travel, migration,..
Agent changes: Development of drug resistant strains of TB.
A real change in disease incidence or mortality can occur due to changes in the environment, in the host or in the agent.
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Descriptive Epidemiology Dr. Salwa Tayel

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
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Descriptive Epidemiology Dr. Salwa Tayel

12. Descriptive Epidemiology Dr. Salwa Tayel
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 pattern Example: Cases of influenza increases in winter. Food poisoning and diarrhea increase in summer.
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Descriptive Epidemiology Dr. Salwa Tayel

13. Descriptive Epidemiology Dr. Salwa Tayel
Seasonality: Seasonal patterns may suggest hypotheses about: - how the infection is transmitted - what behavioral factors increase risk - environmental and other possible contributors to disease occurrence.
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Descriptive Epidemiology Dr. Salwa Tayel

15. Rapid fluctuation (short time)
Usually occur in the form of point source epidemics that appear abruptly and ends abruptly either natural or due to intervention.
e.g. food poisoning
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Day of week and time of day:
Analysis at shorter time periods is especially important for :
Conditions that are potentially related to occupational or environmental exposures, which may occur at regularly scheduled intervals.
Lifestyle Factors In the first half of the last century people were too busy trying to survive to worry about health as much we do today, much less about how we might practice healthier habits in order to prevent disease. Progress that did occur was brought about through the organization of unions in the workplace, legislatures, and public health ordinances. Toward the end of the century, in 1990, the Healthy People 2000 report made a call to work toward a culture that actively promotes responsible behavior and the "adoption of life-styles that are maximally conducive to good health■ (USDHHS, 1990). Since that time, there is more and more concrete evidence indicating that practicing healthy habits can significantly decrease our chances of developing chronic disease. Therefore, of all the health determinants that we have discussed, lifestyle factors are among the most controllable and influential factors influencing our health.
Author: Diane Wilson, USA
From “Lifestyle Factors and the Prevention Movement”
Additionally, prevention of injuries with safer products, use of seat belts and child seats, awareness of safety in the home, smoke detectors, etc. have saved many lives and much injury over the course of the 20th century.
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Descriptive Epidemiology Dr. Salwa Tayel

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II- Place characteristics
Disease may vary by:
place of residence,
birth place,
place of employment,
School district,
hospital unit, etc.
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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.
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Descriptive Epidemiology Dr. Salwa Tayel

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Disease variation by Place may be due to:
Geography
The location of certain place determine its climatic conditions e.g. temperature, humidity, wind,… which favour certain agents and vectors.
e.g. malaria, Yellow fever,..
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Descriptive Epidemiology Dr. Salwa Tayel

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Geology
The structure of soil affects disease occurrence e.g.
Hardness of water CVD
Radioactive materials leukemia
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Descriptive Epidemiology Dr. Salwa Tayel

22. Chemical and physical environment
Iodine deficiency in the soil (oasis) ---goiter
Sulpher dioxide chronic bronchitis
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Descriptive Epidemiology Dr. Salwa Tayel

23. Environmental sanitation
Filth diseases in poor sanitation
Good sanitation decrease diarrhoeal diseases
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Descriptive Epidemiology Dr. Salwa Tayel

24. Availability of Health Services
Vaccination ---prevent infectious diseases
Health Education healthy behaviour
Detection and treatment of infectious diseases limit spread.
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Descriptive Epidemiology Dr. Salwa Tayel

25. Descriptive Epidemiology Dr. Salwa Tayel
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.
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Descriptive Epidemiology Dr. Salwa Tayel

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Age:
Age is probably the single most important “person” attribute, because almost every health-related event or state varies with age.
Age affects:
Type of disease: e.g.
Neonates congenital anomalies and birth trauma
Elderly Degenerative diseases, CVD
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Descriptive Epidemiology Dr. Salwa Tayel

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Severity of disease:
Whooping cough is severe under one year
Pneumonia is fatal in early 2 months
Fracture is severe in old age
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Descriptive Epidemiology Dr. Salwa Tayel

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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.
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Descriptive Epidemiology Dr. Salwa Tayel

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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
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Descriptive Epidemiology Dr. Salwa Tayel

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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
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Descriptive Epidemiology Dr. Salwa Tayel

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Familial tendency
Clustering of some diseases within certain families may be due to:
Genetic factors, or
common exposure to the same dietetic, social, psychological and environmental influences.
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Religion
Religion usually determine the behaviour of its followers
Prohibition of alcohol liver disease
Male circumcision cancer cervix
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Descriptive Epidemiology Dr. Salwa Tayel

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Socioeconomic status:
Socioeconomic status is measured by:
Education health behaviour
Occupation income
Family income ---- environmental condition, housing conditions, access to health facilities
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Descriptive Epidemiology Dr. Salwa Tayel

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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, filth diseases,…)
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Descriptive Epidemiology Dr. Salwa Tayel

35. Descriptive Epidemiology Dr. Salwa Tayel
Marital Status
Study of disease frequency with marital status indicates that:
Mental illnesses are more likely to affect single individuals.
Breast cancer affects more females who remain single or marry late,
Cancer cervix is more common among early married females.
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Descriptive Epidemiology Dr. Salwa Tayel

36. Descriptive Epidemiology Dr. Salwa Tayel
Marital Status
Death rates are lower for married than for single. This may be due to:
Persons who live dangerously tend to live single.
Persons in poor health tend to remain single.
There are differences in habits and way of life of single and married people; feeding outdoor,…
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Descriptive Epidemiology Dr. Salwa Tayel

37. Descriptive Epidemiology Dr. Salwa Tayel
The End
Thank You
Website
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Descriptive Epidemiology Dr. Salwa Tayel