Presentation on theme: "Presenter – Anil Koparkar Moderator –Dr. Chetna Maliye."— Presentation transcript:
Presenter – Anil Koparkar Moderator –Dr. Chetna Maliye
Introduction Definition of Descriptive epidemiology Descriptive and analytical epidemiology Types of Descriptive Studies Case Reports and Case Series Cross Sectional and Longitudinal Descriptive Studies Epidemiological Descriptions according Person Time Place References
Epidemiology Greek words epi = people Logos = the study of “Epidemiology is the study of the distribution and determinants of health-related states or events in specified populations, and the application of this study to the control of health problems”.
Type of study Alternate name Unit of study A. Observational studies Descriptive studies Analytical studies Ecological Correlational Populations Cross-sectional Prevalence Individuals Case -Control Case -Reference Individuals Cohort Follow Follow-up/ Longitudinal Individuals B. Experimental/ intervention Studies Randomized Controlled Studies Clinical Trial Patients Field Trial Healthy person Community Trial Community intervention studies Communities
Definition A study in which only one group, i.e. subjects having the outcome (disease or any other health related phenomena of interest) are studied, without any comparison group, for describing the outcome or health - related phenomena according to its frequency or such other summary figures (as mean), and its distribution according to selected variables related to person, place and time.
DescriptiveAnalytical 1 group is studiedAt least 2 groups are studied At the start – no hypothesis At the start - definite hypothesis At the end - possible hypotheses At the end - confirms or rejects the hypothesis.
Case Reports and Case SeriesCase Series based on reports of a single, or else a series of cases - treated or untreated - without any specific comparison (control) group describing signs, symptoms or patho-physiological parameters in the series of patients do not indicate risk.
Cross Sectional Descriptive Studies mainly directed to work out the: Prevalence Mean Pattern surrogate for longitudinal descriptive studies
Longitudinal Descriptive Studies follows up single group of subjects over a defined period objectives: To see the incidence To describe the ‘natural history of a disease’ To describe a health related natural phenomena To study the ‘trend’ of a disease & ‘health - related phenomena
Cross sectional studyLongitudinal study To know prevalence, mean, pattern of disease, etc. To know incidence, natural history of a disease, health related natural phenomena, trend of a disease or health - related phenomena researcher examines only oncesubject examined at least twice gives us the “prevalence”gives us the “incidence”. Less time consuming & easyShould be preferred when possible, but often a difficult way.
AgeAge: Distribution of the disease according to “age - specific” rates. Death rates Highest during infant, preschool age & extreme old age, Lowest during years group Measles in childhood, cancer in middle age, atherosclerosis in old age is common non - communicable (chronic) diseases - rising trend during middle age. Bimodality
Sex: Some diseases more common in females- gall bladder and thyroid; CHD, AIDS,IHD, peptic ulcer, inguinal hernia, accidents and lung cancer is less common. The sex related differences may be due to hormonal or other biological differences or due to differences in attitude towards life.
Ethnic Group group of persons who have a greater degree of homogeneity than the population at large in respect of biologic inheritance and present day customs categories of variables Race - e.g. Mongoloid, Caucasian & Negroid. Nativity - e.g. European, Indian, Chinese etc. Religion Local reproductive and social units(Cast)
4. Social Class : independent risk factor for the disease or it may be indirectly associated. Commonly used scales Prasad’s scale based on per capita per month income & Kuppuswamy scale which takes an ordinally scaled combination of education, occupation and income. 5. Occupation : The stress of occupation and exposure to various physical, chemical and biological disease agents therein, may be associated with high occurrence of such diseases. On the other hand, entry into occupation is itself likely to be related to particular physical (e.g. soldiers) and mental (e.g. Doctors) capabilities
6. Education : Education - improved level of knowledge - reduced risk of disease. level of formal education illiterate, just literate (upto 5th standard), upto matriculation, upto college, graduate, and post - graduate or Doctoral level. 7. Marital Status : In general, mortality rates - married < single < widowed < divorced. 8. Family Variables : Depending on the scope of the epidemiological investigations at hand, various family variables as family size, birth order, maternal age, parental deprivation during childhood, familial aggregation of disease, and so on, are studied.
9. Twin Studies : Very powerful methods for evaluating the genetic background of a disease. Working premise - monozygotic twins carry identical genes, while dizygotic twins are simply like two different siblings from genetic point of view. Concordance between monozygotic & dizygotic twins - genetic background. discordance in monozygotic twins - environmental etiology. 10. Other Variables: Various Socio - Demographic, Physiological, Biochemical, Immunological characteristics.
A. Common Source (Vehicle) Epidemics - 1. Common Source (Vehicle), Single (Point) Exposure: 2. Common Source, Continued exposure 3. Common Source, interrupted exposure B. Propagated Source C. Seasonal fluctuations D. Cyclical Changes E. Secular trends
A. Common Vehicle Epidemics - 1. Common Source (Vehicle), Single (Point) Exposure:Common Source (Vehicle), Single (Point) Exposure The infective material remains present in the vehicle for a brief period of time Has certain characteristic features All cases occur within one known incubation period of the disease. The epidemic curve has a sharp onset and an equally abrupt decline. The peak of the epidemic is sharp and coincides with the median incubation period of the disease.
A. Common Vehicle Epidemics - 2. Common Source, Continued exposureCommon Source, Continued exposure when an infectious agent persists in the common vehicle for some amount of time The final decline of the epidemic occurs due to contamination is removed or all possible “susceptible” have become infected. Has certain characteristic features epidemic curve rises slowly, falls gradually; peak is not sharp but rather plateau - like and duration of epidemic is stretched out.
A. Common Vehicle Epidemics - 3. Common Source, interrupted exposure source introduces the infection into the vehicle only interruptedly
B. Propagated Source: In such an epidemic, the source itself propagates, i.e. multipliesPropagated Source The fall of the epidemic occurs due to development of enough herd immunity The epidemic curve rises slowly, in waves Reaches a flat plateau and then declines slowly.
C. Seasonal fluctuations Malaria and JE - immediate post monsoon season; Airborne / droplet - winters when people tend to congregate and overcrowd. Asthma spring and autumn suggesting specific environmental factors in causation. Seasonal fluctuations are usually demonstrated by line diagrams. They may help differentiating two similar – appearing illnesses like JE and meningococcal meningitis - the former having a peak during post monsoon and the latter manifesting a peak during peak winters.
D. Cyclical Changes: These are periodic peaks in disease frequencies occurring every years. Ex. Measles- epidemics tend to occur in cycles of 2 – 3 years. E. Secular trends : These are time trends occurring over a period of decades. Ex. Cancers of various sitesSecular trends stomach and uterus - declining trend in death rate cancers of lung and pancreas - rising trend breast cancer mortality rate - no change.
Many diseases have typical spatial relationships; goiter - foothill regions, Anthrax and brucellosis - rural areas CHD - affluent countries Differences in the distribution of a disease political boundaries - international comparison, regional comparison within countries natural boundaries - rural - urban differences, altitude, or local distribution of disease
Japan has very low CHD mortality rates but high rates for cerebro - vascular accidents, Hypertension and gastric CA; UK has high lung CA rates while USA has high CHD rates. “Migrant Studies” is good method of dissecting this fact out.
Countries - X Y Disease(D)pattern- x y Now let ‘m’ be the disease pattern of the Group of people A in country Y, then If disease D is due to genetic factor, then ‘m’ will approximate to ‘x’. And If disease D is due to environmental factor, then ‘m’ will approximate to ‘y’. International Comparisons (…cont.)
Regional Variations within countries : e.g. goiter -in the foot hill areas in India. Rural - Urban differences : point out towards possible environmental factors; e.g. IHD, STDs, Hypertension etc. are more common in the urban areas while oro - faecal infections are more common in rural areas.
Local distributions : The finding may finally be due to one of the two reasons: 1. The inhabitants of that place, OR 2. Some etiologic factors, characteristic in the place are present. If this is the reason, then : (i) High rates of disease will be observed in all ethnic groups in that area. (ii) High rates are not observed in persons of similar ethnic groups living in other areas. (iii) Healthy persons entering that area become ill with a frequency similar to the indigenous inhabitants. (iv) Inhabitants who have left that area do not show high rates. (v) Some evidence of the disease may also be found in animals in the same area.
common methods used: Spot Mapping : simplest, yet a very productive method of displaying the place - related distribution of a disease Map - on - map: we combine two maps to bring disease frequencies, plotted as colored dots, into visual approximation with other variables like roads, rivers, indices of poverty etc. This technique may also be used for studying “movement” of a disease in both time and place.
Spot map of deaths from cholera in Golden Square area, London, 1854 This pump was later suspected and proved to be a source of infection
1. Centers for Disease Control and Prevention. Principles of Epidemiology an Introduction to Applied Epidemiology & Biostatistics. 2 nd Ed Bhalwar R. Textbook of Public Health and Community Medicine.1 st ed Park K. Park’s textbook of preventive and social medicine. 20 th edition, Banarsidas Bhanot publishers, Jabalpur, India Beaglehole R, Bonita R, Kjellstrom T. Basic Epidemiology.2 nd edition. World Health Organization , 6-11, Last JM, ed. Dictionary of Epidemiology, Second edition. New York: Oxford U. Press, 1988: MacMahon B, Trichopoulos D. Epidemiology Principles and Methods. Second ed.Little, Brown and company. 1996: