This document provides an overview of epidemiology and epidemiological studies. It defines epidemiology as the study of disease distribution, determinants, and frequencies in populations. It describes different epidemiological study designs including descriptive, analytical, and interventional studies. It also covers topics such as infectious disease epidemiology, chronic disease epidemiology, disease prevention and control, and investigating and controlling epidemics.

1. Epidemiology
1Dr. RS Mehta, MSND, BPKIHS

2. Introduction
Contents of the course:
1. Definition
2. Epidemiological Studies
3. Uses of Epidemiology
4. Epidemiology of infectious Diseases
5. Control of epidemics
6. Epidemiology of NCD
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3. Dr. RS Mehta, MSND, BPKIHS 3

4. Definition of Epidemiology
It is the study of distribution, determinants and
frequencies of diseases
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5. Distribution of Disease
• Diseases are distributed according to:
– Place
– Person
– Time
• Study of distribution of diseases is essential in
descriptive studies
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6. Place Distribution
(Geographical distribution)
• Geography of diseases can identify the role of
the following factors in disease causation:
– Genes,
– Environment,
– Culture,
– Nutrition,
– Socio-economic and
– Cultural factors
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7. Person Distribution
• In descriptive studies persons should be
defined by:
– Age
– Ethnicity
– Sex
– Occupation
– Marital status
– Behaviour
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8. Distribution of diseases according to age
• Age is strongly related to disease:
– Certain diseases are frequent in specific age
(measles in childhood, cancer in middle age,
atherosclerosis in old age)
– Bimodality: some diseases affect 2 age groups
(Hodgkin's disease) – 20 and 80 years
– Some diseases are more serious and progressive
in specific age groups
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9. Distribution of diseases according to sex
• Biological differences (e.g. Hormonal
disorders)
• Cultural behavior (e.g. 4:1 male to female lung
cancers due to smoking, and so alcohol car
accidents . .)
• Some diseases are more frequent in male:
duodenal ulcer, CHD ..
• Some diseases are more severe in females
(CVA)
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10. Distribution of diseases according to
ethnicity
• Some diseases are more frequent among
specific racial groups:
– Essential hypertension
– CHD
– Cancers
– Sickle cell anaemia
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11. Distribution of diseases according to
marital status
• Mortality rates is lower for married males may
be due to:
– Healthy persons are more likely to get married
• Married persons had healthy lifestyle
• STDs are more frequent among unmarried
• Ca cervix is more common among married
women
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12. Distribution of diseases according to
occupation
• Occupation may alter the habit pattern of
employees e.g. (night shifts may alter sleep ..)
• Occupational hazards may affect health
(biological, chemical, physical, psychosocial,
mechanical)
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13. Distribution of disease according to
behaviour
• Behaviour factors (smoking, alcohol,
sedentary life, overeating, drug abuse, stress
..)
• Behaviour is a strong risk factor in modern-day
diseases:
– CHD
– Cancers
– CHD
– Accidents
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14. Time distribution
1. Short-term fluctuations (epidemics)
2. Periodic fluctuations (seasonal trend)
3. Long term fluctuations (e.g. diabetes show a
consistent upward trend in the developed
countries during the last 50 years
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15. Determinants of Diseases
• Biological factors (Bacteria, viruses etc)
• Chemical factors (pesticides, lead etc)
• Physical factors (radiation, heat ..)
• Mechanical factors (accidents)
• Psychosocial factors (stress, alcohol etc)
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16. Frequencies of Diseases
• Fertility Rates
• Morbidity Rates
• Mortality Rates
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17. Fertility Rates
Crude Birth Rate (1000):
Number of live births during the year
Population
General fertility Rate (1000):
No of live births in an area during a year
Female 15 -49
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18. Morbidity Rates
• Incidence (1000):
Number of new cases of a specific disease
during a given period
Population at risk
• Prevalence (100):
Number of new and old cases of a specific
disease during a given period
Population at risk
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19. Mortality Rates
• Crude death rate (1000)
No of deaths during a year
Population
• Specific death rate
• Case fatality rate (100):
Deaths due to a particular disease
Total no of cases due to the same diseae
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20. Survival Rate
Survival rate (100)
Total patients alive after 5 years
Total patients diagnosed or treated
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21. Standardize Mortality Rate
SMR (100)
Observed deaths
Expected deaths
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22. Years of potential life lost (YPLL)
• Is an estimate of the average years a person
would have lived if he or she had not died
prematurely
• The reference age should correspond roughly
to the life expectancy of the population under
study
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23. Person-years of potential life lost in the United States
in 2006
• Cancer 8,628,000
• Heart disease and strokes 8,760,000
• Accidents and other injuries 5,873,000
• All other causes 13,649,000 person-years
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24. The disability-adjusted life year (DALY)
1. It is a measure of overall disease burden
2. Expressed as the number of years lost due to ill-
health, disability or early death.
3. Originally developed by Harvard University for the
World Bank in 1990,
4. The WHO adopted the method in 2000
5. The DALY is becoming increasingly common in the
field of public health and health impact assessment
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25. DALYs in Millions
• HIV/AIDS 46.7
• Lower respiratory infections 42.2
• Diarrhoeal diseases 32.2
• Malaria 30.9 8.2 4
• Neonatal infections and others - 13.4 3.
• Prematurity and low birth weight 11.3
• Tuberculosis 10.8
• Road traffic accidents
• COPD 3.1
• Protein-energy malnutrition 7.1
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26. Dr. RS Mehta, MSND, BPKIHS 26

27. Epidemiological studies
Main Types of epidemiological Studies:
1. Descriptive Studies
2. Analytical (Comparative Studies
3. Interventional studies (experimental)
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28. Nomination
• Case control study (retrospective) e.g. Ca lung ---
smoking
• Cohort study (prospective) e.g. smoking -- Ca lung
• Cross-sectional Study: a study in a known short
period of time (Picture)
• Longitudinal Study: observation is repeated in the
same population over a long period of time (film)
• Facility-Based Study
• Community-Based study
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29. Uses of Epidemiological Studies
• Descriptive studies: To develop hypothesizes
• Analytical Studies: To test hypothesis
• Experimental studies: To confirm hypotheisi
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30. Dr. RS Mehta, MSND, BPKIHS 30

31. Uses of Epidemiology
1. Community diagnosis
2. Control of epidemics
3. Prevention and control of diseases
4. Evaluation of curative and preventive measures
5. Study of natural history of diseases
6. Planning for Health Services
7. Implementation of H. Services
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32. Dr. RS Mehta, MSND, BPKIHS 32

33. Epidemiology of Infectious disease
• Definitions
• Agent
• Concepts of causation
• Disease Transmission
• Susceptible Host
• Prevention
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34. Definitions
• Infectious disease = Clinically manifested
disease resulting from an infection
• Contagious disease = diseases transmitted
through contact (scabies, trachoma, leprosy)
• Communicable disease = infectious illness
transmitted directly or indirectly
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35. cont. definitions
• Endemic = constant presence of a disease in
an area
• Nosocomial = hospital acquired infection
• Iatrogenic = physician induced disease
• Exotic = disease transported in a country
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36. Concepts of causation
• Supernatural theory
• Germ theory
• Multifactorial Theory
• Web causation Theory
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37. Epidemiological Triangle
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Agent
HostEnvironment

38. Agent of infectious disease
It is a biological agent:
• Viruses (HIV ,,)
• Ricketsiae (Typhus ..)
• Fungi (Candida ..)
• Bacteria (Streptococcus)
• Protozoa (Plasmodium ..)
• Metazoa (tapeworms)
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39. Nominations`
• Infectivity: ability of infectious agent to invade
and multiply in human being
• Pathogenicity: ability to induce clinical disease
• Virulence: Power of killing
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40. Susceptible Host
Host factors:
1. Demographic (age, sex, ethnicity ..)
2. Genetics
3. Immunity
4. Social and economical
5. Life style
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41. Environmental Factor
Environmental factors related to the:
1. Host
2. Agent
3. Vector
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42. Infectious Agent
• Bacteria
• Virus
• Fungi
• Protozoa
• …………
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43. Chain of infection
• Infectious agent
• Reservoir
• Portal of Exit
• Means of transmission
• Portal of entry
• Susceptible Host
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44. Reservoir
• People
• Equipment
• Water
• ……………….
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45. Portal of Exit
• Excretions
• Droplet
• Skin
• ……………
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46. Dr. RS Mehta, MSND, BPKIHS 46

47. 1. Droplet contact
• coughs or sneezes coughing or sneezing
include (at least):
– Bacterial Meningitis
– Common cold
– Influenza
– Streptococcal throat
– Tuberculosis
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48. 2. Fecal-Oral Transmission
• Direct contact is rare in this route
• Indirect through water, food is common
• Examples:
– Cholera
– Hepatitis A
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49. 3. Sexual Transmission
• Direct Transmission (contact during
intercourse)
• Indirect from secretions (semen or fluid
secreted by female) examples:
– HIV
– Gonorrhea
– Hepatitis B
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50. 4. Oral Transmission
• direct oral contact such as Kissing
• indirect by sharing a drinking glass or a
cigarette.
• Most of diseases that transmitted by oral
contact are forms of herpes
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51. 5. Transmission by direct contact
• They are called contagious
• Examples:
– Impetigo
– Syphilis
– Leprosy
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52. 6. Vertical Transmission
• From mother to child (in-utero or during
childbirth),
• Examples:
– HIV
– Hepatitis B
– Syphilis
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53. 7. Iatrogenic Transmission
Transmission due to medical procedures
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54. 8. Vector borne transmission
• A vector is an organism that transmits
infection
• Examples:
– Flies – Gastroenteritis
– Mosquitoes: Malaria, Trypansomiasis,
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55. Portal of Entry
• Broken skin
• Mucus membranes
• Gastrointestinal/respiratory/urinary tract
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56. Susceptible Host
• Neonates
• Diabetes
• Immunosuppressant
• Cardiopulmonary disease
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57. Dr. RS Mehta, MSND, BPKIHS 57

58. Definition of an epidemic
• Abnormal increase of incidence of a disease (≥
2 SD) or
• Doubling of cases during a week
• Appearance of unknown disease in an area
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59. Investigation of an epidemic
1. Verification of diagnosis
2. Confirmation of an epidemic
3. Defining population at risk
4. Search for other cases
5. Data analysis
6. Formulation of hypothesis
7. Testing hypothesis
8. Evaluation of ecological factors
9. Further investigation of population at risk
10. Writing report
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60. Control of epidemic
• Treatment
• Control
• Notification
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61. Dr. RS Mehta, MSND, BPKIHS 61

62. Definition
Chronic diseases which have one or more of the
following characteristics:
• permanent
• have residual disability
• non-reversible
• require special training of the patient for
rehabilitation
• require a long period of supervision,
observation or care
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63. Examples of Non-communicable Diseases
• Cardiovascular diseases
• CHD
• Ca
• Hypertension
• diabetes
• Accident
• Blindness
• Obesity
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64. The Problem
• 32 million people die due to non-
communicable diseases every year
• Affects adults
• Affects the quality of life
• It is increasing, mainly in developing countries
– Life expectancy is increasing
– Change of life style
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65. Impact of Non-communicable diseases on
the lives of people
• Disabilities
• Family hardship
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66. Risk factors of Non-communicable diseases
• Smoking, Alcohol
• Inability to obtain preventive health services
• Life style changes
• Stress
• Environmental risk factors: (Occupational hazards,
Pollution (air, water)
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67. Dr. RS Mehta, MSND, BPKIHS 67

68. Definition of Disease Prevention
Any activity which reduces morbidity and
mortality of diseases
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69. Primordial Level
(Health Promotion)
• Definition: Helping people to improve Health
• Interventions of Health Promotion:
– Health Education promoting healthy lifestyle
– Environmental modification
– Nutritional Interventions
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70. Levels of Prevention
• Primary Level
• Secondary Level
• Tertiary Level
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71. Primary Level of Prevention
• Actions taken before the onset of a specific
disease
• Examples:
– Bed nets
– Vaccines
– ….
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72. Secondary Level of Prevention
Early diagnosis and adequate treatment
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73. Tertiary Level of Prevention
• Tertiary level of Prevention (Rehabilitation)
– Medical rehabilitation
– Occupational rehabilitation
– Social rehabilitation
– Psychological rehabilitation
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74. Disease Control
• An ongoing operations aimed at reducing:
– The incidence of disease
– The duration of disease
– Complication of the disease
– The financial burden to the community
• It concentrates on primary and secondary
prevention
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75. Thank You
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