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Prof. Saman Wimalasundera

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1 Prof. Saman Wimalasundera
MBBS DO PhD Professor in Community Medicine Former Head, Department of Community Medicine In charge Ophthalmologist Community Ophthalmology center Faculty of Medicine University of Ruhuna Galle Sri Lanka

2 Epidemiology and its application

3 The concepts of epidemiology were first
suggested by Hippocrates in the fifth century B.C. that the development of human disease might be related to external and personnel environment of an individual.

4 The word epidemiology is derived from
Greek and means “Studies upon people” Epi – Upon, Demos – People, Logia – Study In contrast to clinical medicine epidemiology involves the study of group of people rather than individuals.

5 Epidemiologist vs. clinician
A clinician identifies the ailment in his patients using certain scientifically developed tools to ascertain history of illness, clinical examination and investigations. Epidemiologist addresses the understanding of the distribution and determinants of a disease in a community (not an individual) using standard parameters.

6 What constitute epidemiology
Epidemiology includes:- 1. The methods for measuring the health of groups and determining the attributes and exposures that influence health. 2. The study of the occurrence of disease in its natural habitat rather than in the controlled environment of the laboratory.

7 3. The methods for the quantitative study of
the distribution, variation, and determinants of health related outcomes in specific groups (sub populations) of individuals, and the application of this study to the diagnosis, treatment, and prevention of disease status or events.

8 Evolution of epidemiology
The evolution of medical sciences in its earlier phase was based on curative medicine. The primary objective was to cure a patient of his illness. Doctors in historical times looked at their patients as ill people who needed some treatment.

9 Thus medical science was individual
oriented. But gradually it became evident that better human health could be achieved by prevention of diseases rather than by cure.

10 A Historical Sketch A Long sketch of time ran for more than 2
millennia from Hippocrates ( B.C.) to the first third of 19th century. Hippocrates developed the medical approach by providing concise, accurate and complete description of actual clinical cases.

11 An Italian clinician called Bernardino
Ramazzini in 1700 moved from observation of clinical cases to the consideration of ‘work circumstances’ in similar cases. He is now regarded as the founder of occupational medicine. (Explained in his book. “De Morbis Artificum Diatriba”).

12 The major step forward in epidemiology occurred in 1662
The major step forward in epidemiology occurred in John Graunt analyzed the weekly reports of births and deaths in London. For the first time in the history, a quantified pattern of disease, deaths and births was Found. John Graunt is regarded as the founder of demography now. His observations were published in his book. Named “ the nature and political observations made upon the bills of Mortality”.

13 After two centuries William Farr (1839) a
physician was given the responsibility for medical statistics in England and Wales. He set up a system for routine compilation of vital statistics and application of data for evaluation of deaths.

14 Hippocrates, Ramzinni, Graunt and Farr
contributed to the understanding of disease frequency and distribution. Another British physician John Snow formulated and tested a hypothesis concerning the origins of an epidemic of cholera in London on the basis of available descriptive data.

15 Snow postulated that cholera was
transmitted by contaminated water. (then unknown mechanism) He observed that death rates from Cholera were particularly high in certain areas of London. Those areas were supplied with water by two water companies namely “Lambeth” and “Southwark & Vauxhall” in Both the companies that time drew water from river Themes at a point heavily polluted with sewage.

16 The Lambeth company then changed its
source to an area of Themes where the water was quite free from sewage of London. The rate of cholera deaths then declined in those areas suppied by Lambeth company.

17 Death rates from cholera According to water company supplying sub districts of London
Population in 1851 Cholera deaths in Deaths per 100,000 living Southwark and Vauxhall Both companies Lambeth 167, 654 301, 149 14, 632 192 182 00 114 60

18 Concepts of epidemiology
Definitions “Epidemiology is defined as the study of the distribution and determinants of health related status or events in specified populations and the application of this study to control the health problems” (Last 1988)

19 Applications of epidemiology
The epidemiology is useful in: 1. Search of cause/causes of disease/diseases. 2. Helps to describe the health status of population or groups. 3. Helps to discover and bridge gaps in natural history of diseases.

20 4. Helps in controlling the diseases. To break
the weakest link in chain of transmission of communicable diseases and reducing non communicable diseases. 5. Helps in planning of health programs on evidence basis and setting up of health priorities. 6. Helps to evaluate health programs and interventions.

21 7. Helps to determine the chances or
probability of occurrence of disease/ deaths and disability 8. Helps in better management of health services and hospital services. 9. Helps to set-up cut-off levels between normal and abnormal population and establish trigger levels for action or intervention.

22 Sources of epidemiological Measurements
1. Cross sectional surveys 2. Medical records 3. Death certificate 4. Census 5. Organizational data

23 Domains of epidemiology
Descriptive epidemiology Descriptive epidemiology is the most Basic form of epidemiology. It is concerned with the description of the patterns of occurrence of health-related status or events in groups. The determination of frequency and distribution of disease, incidence, prevalence, and mortality rates are included in descriptive epidemiology.

24 Analytical epidemiology
Analytical epidemiology is based on the observations made in the descriptive epidemiology. The design, execution and analysis of subjects between groups helps evaluate potential association between risk factors and health outcomes to answer the question “why?”.

25 Analytical epidemiology consists of two types of research processes
1. Observational process 2. Experimental studies

26 Basic triads of descriptive and analytical epidemiology
There are two different triads (3 essential components) considered in studying different sections

27 Descriptive epidemiology
Analytical epidemiology Time (when) Host Place (where) Agent Person (who) Environment

28 Triad of descriptive epidemiology
Time Changing or stable Seasonal variations Secular trends (long-term study of incidence) Point source or propagated Cyclical variations (spikes of incidences at regular intervals)

29 Triad of descriptive epidemiology
Place Geographically restricted or wide spread Relation to water and food supply Multiple cluster involvement or one Rural/Urban distribution

30 Triad of descriptive epidemiology
Person Age Socio economic status Gender Ethnicity / Race Behavior

31 Triad of analytical epidemiology
Agent Nutrients Poisons Allergens Radiation Physical trauma Microbes Psychological factors

32 Triad of analytical epidemiology
Host factors Genetic factors Immunologic state Age Personal behavior

33 Triad of analytical epidemiology
Environment Overcrowding Atmospheric changes Modes of transmission Vector Vehicle Reservoir

34 This forms the basis of clinical epidemiology.
When periodic observations are made over a long period of time in patients with a wide spectrum of clinical manifestations of the disease, a complete profile of the natural history of the disease may be obtained. This forms the basis of clinical epidemiology.

35 Epidemiology of diseases
Sri Lanka is said to be facing a double disease burden due to communicable and non communicable diseases (NCD) today. What is triple burden???

36 The diseases burden in the country is given in
terms of (apart from basic measures) 1.Years of potential life lost 2.Life expectancy free from disability 3. Disability adjusted life years lost – DALYs 4.Quality adjusted life years lost - QUALYs loss per 1000 population. Country has to fight to control communicable and non communicable diseases.

37 Epidemiology of communicable diseases (CCD)
Definition :- Communicable disease A communicable or infectious disease is an illness caused by transmission of a specific infectious agent or its toxic products from an infected person or animal to a susceptible host, either directly or indirectly through an intermediate animal host, vector or inanimate environment (Last 1995)

38 Disease Transmission Man to man Animal to man

39 What is an Epidemic? It is the occurrence of cases of illness,
specific health related behavior or other health related events clearly in excess of normal expectancy in a community or region.

40 An Endemic disease A disease that usually present in a
population or given area at a relatively high prevalence and incidence rates in compared to other areas. E.g. Malaria is an endemic disease in Polonnaruwa

41 Major emerging and re-emerging infectious diseases
1. HIV/AIDS 2. Hepatitis B and Hepatitis C 3. Tuberculosis 4. Dengue 5. Malaria 6. Japanese encephalitis 7. Plague 8. Cholera

42 Major reasons for emergence of infectious diseases
High population growth, uncontrolled and unplanned urbanization, Poor environmental sanitation, Migration of population, Natural disasters, Growing international trade, tourism and rapid travel, Alterations in microorganisms, Resistance to antimicrobials, Insecticide resistance, Weak public health system. Illiteracy and ignorance.

43 Chain of infection or chain of transmission
Infectious agent Transmission process Host ENVIRONMENTS

44 Infectious agent Pathogenicity Virulence Infectivity

45 Transmission process This is the second important link in the
chain of infection. Transmission is defined as “Spread of infectious agent through the environment or to another person, from the reservoir and source”.

46 Methods of transmission
Direct and Indirect

47 Direct methods of transmission
Touching Kissing Sexual intercourse Child birth Breast-feeding Air borne, short distance via droplets (by coughing, Laughing, sneezing, spitting). Transfusion of blood Transplacental from mother to fetus

48 Indirect transmission
Vehicle borne transmission (by contaminated food and water) Vector borne transmission Parenteral by unsafe injection Fomite transmission Unclean hands

49 Control of communicable diseases (CCD)-discuss under 5 headings
1. Control of infectious agents in the environments 2. Control of infectious agent in host 3. Control of outbreaks of CCD 4. Other measures 5. Specific measures for control of HIV epidemic

50 (1) Control of infectious agents in the environments
Controlling sources of infection 1. Supply of safe drinking water by treatment and chlorination of water, pasteurization of milk. Safe disposal of human excreta and animal excreta by sewerage system and sanitary latrines, compost pits/manure pits. 3. Control vectors of diseases – by source reduction and anti-larval and anti-adult measures. 4. Animals – vaccinate dogs against rabies and eliminate street dogs. 5. Rodent control measures-trapping and killing 6. Hospital waste management 7. Disinfections

51 (2) Control of infectious agent in host
1. Reservoir control 2. Practice of chemoprophylaxis 3. Surveillance 4. Notification 5. Quarantine 1. Complete quarantine 2. Modified quarantine 6. Isolation 7. Education and behavior

52 Control of outbreaks of CCD-different steps will be discussed later
Communicable diseases like Malaria, JE, DHF , Hepatitis E & A, Hepatitis B and Diarrhoeal diseases quite often occur in epidemic proportion. Many local and focal outbreaks are being reported quite frequently; Hence, control of outbreaks of these diseases is an essential requirement.

53 (4) Other measures 1. Legislation Epidemic disease control act. And
notification helps control of CCD. 2. Observe international health regulations

54 Notifiable diseases Group A Cholera Plague Yellow fever

55 Group B Rubella Diphtheria Enteric fever Food poisoning Leptospirosis Measles Tuberculosis

56 Whooping cough Acute anterior poliomyelitis Simple continued fever of over seven days Dengue Dysentery Encephalitis Human rabies Malaria Tetanus Typhus fever Viral Hepatitis




60 Epidemiology of non-communicable diseases (NCD)
Non communicable diseases cover wide range of heterogeneous conditions affecting different organs and systems of different socioeconomic groups. Over the last two decades morbidity and mortality due to cardiovascular diseases, mental disorders, cancer and trauma have been rising due to following causes.

61 Causes 1. Rise in life expectancy and increasing
number of senior citizens. 2. Changing life styles: Faulty diet, use of alcohol, sedentary life-physical inactivity and rising stress-leading to obesity and stress related problems.

62 3. Exposure to environmental risk factors-air
pollution. 4. Use of tobacco 5. Increasing population and rise in automobiles and trauma incidence.

63 Implications In view of the chronic morbidity and high
cost involve in the management of non- communicable diseases attention need to be focused on prevention, early detection and appropriate management. Further, these diseases cause lot of disability and dependency and disease burden.

64 Multi - factorial origin
Causes of NCD are multi-factorial. Range of life styles: risk taking behavior, changing dietary pattern, physical inactivity, use of alcohol and tobacco and stress in life have been incriminated.

65 Future For non-communicable diseases throughout
the all levels of care so as to reduce morbidity and mortality.

66 1. Well-structured information education and
communication for primary and secondary prevention of NCD. 2. Reorientation and skill up gradation of health care providers

67 3. Establishment of Referral linkages between
primary secondary and tertiary institution. 4. Production and provision of drugs for NCD. 5. Development of institution for rehabilitation of disabled persons due to NCD, teaching persons to live with their disability.

68 6. Development of hospices for terminally ill
people who cannot have home based care. 7. Creation of epidemiological database on NCD especially, CVD’s, strokes and diabetes.

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