Epidemology

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1. UNIT-III EPIDE M IOLOGY MD. DANISH RIZVI Msc (N) Community

2. introduction The term epidemiology is derived from the Greek word epidemic. – Epi means-Among, upon, – Demos means study population or people and – Logos means scientific study. So – it is the scientific study of the disease pattern in human population. – In broad sense, it is the study of effects of multiple factors on human health. – It is multidisciplinary subject involving those of the physician, Biologists, Public Health experts, Health educators etc.

3. Definitions Epidemiology as, study of the distribution and determinants of diseases frequency in man. (Mac Mohan and Pugh) The study of the disease, any diseases, as a mass phenomenon. (Greenwood 1935) " The study of the distribution and determinants of health related states or events in specified population and the application of the study to of health problems“ (J.M. Last 1988)

4. Objectives of epidemiology Study of frequency and distribution of health and health related problems in community at large. Identification of determinants i.e. etiological factors causing health and health related problems. Need based planning and administration of comprehensive health care programmes with the available resources to deal with health and health related problems • Evaluating the effectiveness of the programmes to provide feedback.

5. USES OF EPIDEMIOLOGY To study the rise and fall of disease in the population community diagnosis Planning and evaluation Evaluation of Individual's risk and chances Syndrome identification Completing the natural history of disease Searching for cause and risk factors.

6. Determination of the origin of a disease whose cause is known Investigation and control of a disease whose cause is either unknown or poorly understood. Acquisition of information on the ecology and natural history of a disease. Planning and monitoring of disease control programmes. Assessment of the economic effects of a disease and analysis of the costs and economics benefits of alternative control programmes.

7. Determine the usefulness and effectiveness of new/innovative techniques, measures and programmes Complete the clinical picture of chronic diseases & slow growing diseases Identify syndromes by describing the distribution and association of clinical phenomena in the population. Forecast the likely occurrence of diseases on the basis of epidemiological principles

8. purposes To prevent, control and eradicate health and health related problems. To reduce/minimize the impact of the problems. To promote health and quality of life of people at large.

9. T erminology Endemic When an infectious disease more or less prevailing on a locality or community called as endemic • E.g.. Chickenpox Pandemic When an epidemic spread from one country to another or even whole world infecting most of the population then the conditions called as pandemic• E.g .. Covid 19.

10. Epidemic Sudden out break of Infectious disease that spreads rapidly through Population affecting a large number of population in short period of time is called as epidemic • E.g.. AIDS in Africa DISEASE: A pattern of response by a living organism to some form of invasion by a foreign substance or injury which causes an alteration of the organisms normal functioning also – an abnormal state in which the body is not capable of responding to or carrying on its normally required functions PATHOGENS: organisms or substances such as bacteria, viruses, or parasites that are capable of producing diseases PATHOGENISES: the development, production, or process of generating a disease

11. PATHOGENIC: means disease causing or producing agent PATHOGENICITY: describes the potential ability and strength of a pathogenic substance to cause disease INFECTIVE: diseases are those which the pathogen or agent has the capability to enter, survive, and multiply in the host VIRULENCE: The ability of an agent of infection to produce disease. The virulence of a microorganism is a measure of the severity of the disease it causes. INVASSIVNESS: the ability of microorganisms to enter the body and spread in the tissues. 2. the ability to infiltrate and actively destroy surrounding tissue, a property of malignant tumors.

12. HYPER ENDEMIC: Diseases that affect a high proportion of population at risk. HOLO ENDEMIC: Disease that is highly prevalent in a population & is commonly acquired early in life, in most all of the children of the population MESO ENDEMIC: Diseases that affect a moderate proportion of population at risk. HYPO ENDEMIC: Diseases that affect a small proportion of population at risk. SPORADIC: sporadic is something that happens occasionally or at irregular intervals. INCIDENCE: ( NEW CASES) measure of the probability of occurrence of a given medical condition in a population within a specified period of time. Although sometimes loosely expressed simply as the number of new cases during some time period, it is better expressed as a proportion or a rate with a denominator.

13. PREVALENCE : ( old +new) The number of people within a population who have a certain disease at a given point in time POINT PREVALENCE: How many cases of a disease exist in a group of people at that moment. AGENT: is the cause of the disease Can be bacteria, virus, parasite, fungus, mould Chemicals (solvents), Radiation, heat, natural toxins (snake or spider venom) HOST: is an organism, usually human or animal, that harbours the disease ENVIRONMENT: is the favourable surroundings and conditions external to the human or animal that cause or allow the disease or allow disease transmission

14. VECTOR: Any living non-human carrier of disease that transports and serves the process of disease transmission Insects: fly, flea, mosquito; rodents; deer RESERVOIRS: humans, animals, plants, soils or inanimate organic matter (feces or food) in which infectious organisms live and multiply Humans often serve as reservoir and host ZOONOSIS: When a animal transmits a disease to a human INFECTION: The entry & development or multiplication of disease producing agent in or on body of man/animal Is called infection. INCUBATION PERIOD: Time interval b/w the entry of diseased agent into the body of host appearances of first sign & symptoms of disease.

15. INFECTIOUS AGENT: Any agent which is capable of producing an infection is called infectious agent. INFESTATION: An infestation is the presence of animal parasite either externally or internally. CONTACT: Any person who has remain in association with the infected person or the infected particles can also develop the disease. CONTAGIOUS DISEASE: A disease which is transmitted by contact. LATENT PERIOD: The period between exposure and the onset of the period of communicability, which may be shorter or longer than incubation period .

16. Concept of epidemiology Epidemiology is a strategy for the study of factors relating to the etiology, prevention, and control of disease; to promote health; and to efficiently allocate efforts and resources for health promotion,maintenance and medical care in human populations. Epidemiology is that field of medical science which is concerned with the relationship of various factors and conditions which determine the frequencies and distributions of an infectious process, a disease, or a physiologic state in a human community.

17. Dynamics of disease transmission The Reservoir. Mode of Transmission. Susceptible Host.

18. RESERVOIR A reservoir is defined as “any person, animal, arthropod, plant, soil or substance in which an infectious agent lives and multiplies , on which it depends primarily for survival, and where it reproduces itself in such manner that it can be transmitted to a susceptible host”.

19. Reservoir of infectious agent Eg:- In hookworm infection, the reservoir is man and the source of infection is soil contaminated with infective larvae. In typhoid fever the reservoir is a case or carrier is man and the source of infection is faeces or urine of patient or contaminated food and water. Types of reservoirs: Human reservoir Animal reservoir Reservoir in non living things

20. Human reservoir The most important source or reservoir of infection for human is man himself. Human may be Case Carrier

21. Human reservoirs are 2 types 1. Cases : A case is defined as “ a person in the population having the particular disease, health disorder or condition under investigation”. The cases are of following types: Clinical cases Sub clinical cases Latent cases

22. 1. clinical illness:- Clinical illness may be mild or moderate, typical or atypical, severe or fatal. Mild cases may be more important source of infection than severe cases. ii. Sub clinical cases Sub clinical cases are also known as in apparent, missed or abortive cases. The disease agent may multiply in the host but does not manifest itself by signs and symptoms. Sub clinical infection may be detected only by laboratory tests. iii. Latent infection When a virus is present in the body but exists in a resting (latent) state without producing more virus. A latent viral infection usually does not cause any noticeable symptoms and can last a long period of time before becoming active and causing symptoms.

23. 2. CARRIERS In some diseases, either due to inadequate treatment or immune response, the disease agent is not completely eliminated, leading to a carrier state. A carrier is defined as an infected person or animal that harbours a specific infectious agent and serves as a potential source of infection for others. The elements in a carrier state are:- The presence of disease agent in the body. The absence of recognizable signs and symptoms Spread of disease agent in the discharges or excretions.

24. Classification of carriers

25. A. TYPE (a) Incubatory carriers: Carriers which spread the infectious agent during the incubation period of disease. This usually occurs during the last few days of incubation period. Eg:- measles, mumps, polio, influenza, hepatitis B ( b) Convalescent carriers:- Carriers which continue to spread disease during the period of convalescence. Eg ;-Typhoid, Dysentery, Cholera, Diptheria (c) Healthy carriers:- An asymptomatic carrier ( healthy carrier or just carrier ) is a person or other organism that has become infected with a pathogen, but that displays no signs or symptoms. Although unaffected by the pathogen, carriers can transmit it to others or develop symptoms in later stages of the disease.

26. B. DURATION (a) Temporary carriers:- Carriers which spread infectious agent for short period of time (b) Chronic carriers:- Carriers which spread infectious agent for indefinite period C. PORTAL OF EXIT Urinary Intestinal Respiratory Others –(skin eruptions, open wounds,blood)

27. 2. ANIMAL RESERVOIR The source of infection may sometimes be animals and birds. The diseases and infections which are transmissible to man from vertebrate are called zoonoses. Eg :- Rabies, Yellow Fever, Influenza 3. RESERVOIR IN NON LIVING THINGS: Soil and inanimate matter can also act as reservoir of infection

28. Mode of trasmission DIRECT TRANSMISSION • Direct contact • Droplet infection • Contact with soil • Inoculation into skin or mucosa • Trans placental or vertical transmission

29. Indirect Transmission 5 ‘F’ food, flies, fomite, finger, fluid INDIRECT TRANSMISSION Vehicle borne Vector borne Air borne Fomite borne Unclean hands & fingers

30. 1. Direct contact Infection may be transmitted by direct contact from skin to skin, mucosa to mucosa, or mucosa to skin. Eg :- STD, AIDS, leprosy, leptospirosis, skin and eye infections 2. Droplet infection This is direct projection of spray of droplets of saliva and nasopharyngeal secretions during coughing, sneezing, talking or spitting. The droplet spread is usually limited to a distance of 30- 60 cm between source and host Eg :-Respiratory Infections, Common Cold, Tuberculosis, Diphtheria.

31. 3. Contact with soil:- The disease agent may be acquired by direct exposure to the disease agent in the soil Eg :- hook worm, tetanus, mycosis 4. Inoculation into skin:- Disease agent may be inoculated directly into the skin or mucosa Eg:-rabies virus by dog bite, Hepatitis B by contaminated needles 5. Transplacental transmissin:- Disease agents can be transmitted transplacentally. S-Syphilis T-Toxoplasma O-Other infections(AIDS, varicella, Hepatitis B) R-Rubella virus C-Cytomegalo virus H-Herpes virus

32. Indirect transmission 1. VEHICLE BORNE Vehicle borne transmission implies transmission of the infectious agent through the agency of water, food, raw vegetables, fruits, milk, blood etc . Classification of vector borne disease:- 1. By vector Invertebrate Eg-arthropods( flies, mosquitoes, cockroach, ticks, mites, bugs) Vertebrate Eg-mice, rodents 2. By transmission chain Man and a non vertebrate host (man-mosquitoe- man in malaria) Man , another vertebrate host and a non vertebrate host (bird- arthropod-man) Man and 2 intermediate host (man-cyclops-fish-man)

33. FOMITE BORNE Fomites are inanimate articles or substances other than water or food contaminated by infectious agents. Eg- soiled clothes, syringes, instruments etc. 5. UNCLEAN HANDS Lack of personal hygiene favour person to person transmission of infection.

34. SUSCEPTIBLE HOST: FOUR STAGES: PORTAL OF ENTRY SITE OF ELECTION PORTAL OF EXIT LOW GRADE IMMUNITY

35. DISEASE CYCLE: INCUBATION PERIOD PRODROMAL PERIOD FASTIGIUM DEFERVESCENCE CONVALESCENCE DEFECTION

36. INTUBATION PERIOD : the period between exposure to an infection and the appearance of the first symptoms of disease Prodromal period: This period is of short duration, which ranges from one to four days.The pathogenic agent multiply in human host and the vague system appear . Fastigium: The symptoms are clear cut and are related to particular disease. Disease can be identified by clinical diagnosis. the most severe point in the course of an illness DEFERVESCENCE The body's defence begin to respond and there is decline of infection. The clients condition starts improving and feels better. CONVALESCENCE: Convalescence is the gradual recovery of health and strength after illness or injury. It refers to the later stage of an infectious disease or illness DEFECTION: The patient's condition is improved and comes to his pre illness stage i.e is free from illness as the recovery has occured.

37. THEORIES AND MODELS OF DISEASE CAUSATION 1. Germ theory Epidemiological traid theory Multifactorial causation theory Web causation theory

38. It states that microorganisms known as pathogens or "germs" can lead to disease. These small organisms, too small to see without magnification, invade humans, other animals, and other living hosts. Their growth and reproduction within their hosts can cause disease "Germ" may refer to not just a bacterium but to any type of microorganism or even non-living pathogen that can cause disease, such as , fungi , viruses , prions (misfolded proteins), or viroids ( plant pathogens) Diseases caused by pathogens are called infectious diseases .

39. EPIDEMILOGICAL TRAID MODEL The germ theory of disease has many limitations This model showing the interaction and interdependence of agent , host, environment

40. The Analytical Epidemiologic Triad This model comprises a susceptible host (the person at risk for the disease), a disease agent (the proximate cause), and an environmental context for the interaction between host and agent. Thus, development of disease is a combination of events: A harmful agent A susceptible host An appropriate environment September 8, 2014 Epidemiological Triads 45

41. Agents Biological (micro-organisms) Physical (temperature, radiation, trauma, others) Chemical (acids, alkalis, poisons, tobacco, medications / drugs, others) Environmental (nutrients in diet, allergens, others) Nutritional (under- or over-nutrition) Psychological experiences September 8, 2014 Epidemiological Triads 46

42. Host Factors Host factors are intrinsic factors that influence an individual’s exposure, susceptibility, or response to a causative agent. These include: Genetic endowment Immunologic state Personal behavior (life-style factors): diet, tobacco use, exercise, etc Personal characteristics (described before, under “person”), including: age, gender, socio-economic status, etc. September 8, 2014 Epidemiological Triads 47

43. Environmental factors are extrinsic factors which affect the agent and the opportunity for exposure. These include: Physical factors: e.g. geology, climate (temperature, humidity, rain, etc) Biological factors: e.g. insects that transmit an agent Socioeconomic factors: e.g. crowding, sanitation, and the availability of health services Phenomena which bring the host and agent together: vector, vehicle, reservoir, etc Environment

44. Agent factors include infectious microorganisms, e.g. virus, bacterium, parasite, or other agents. They may be necessary but not always sufficient alone to cause disease. Host factors are intrinsic factors that influence an individual’s exposure, susceptibility, or response to a causative agent Environmental factors are extrinsic factors which affect the agent and the opportunity for exposure. Summary of Analytical Triad

45. WEB OF CAUSATION According to this disease never depends upon single isolated cause rather it develops from a chain of causation in which each link itself is a result of complex interaction of preceding events these chain of causation which may be the fraction of the whole complex is known as web of causation.

46. ICEBERG OF DISEASE Disease in a community is compared to an iceberg.

47. The floating tip of ice berg represents clinical cases Submerge portion shows undiagnosed cases or hidden mass of disease Undiagnosed reservoir of disease is a challenge to modern techniques in preventive medicine

48. CONCEPTS OF DISEASE CONTROL The term disease control refers ongoing operation aimed at reducing: The incidence of disease. The duration of disease and the consequently the risk of transmission. The effect of infection including physical and psychological complication. The financial burden to the community. DISEASE MONITORING: Defined as “the performance and analysis of routine measurement aimed at detecting changes in the environment or health status of population.” e.g. growth monitoring of child, Monitoring of air pollution, monitoring of water quality etc. DISEASE SURVEILLANCE: Defined as “the continuous scrutiny of the factors that determine the occurrence and distribution of disease and other conditions of ill health.” E.g. Poliomyelitis surveillance programme of WHO.

49. CONCEPTS OF PREVENTION The goals of medicine are to Promote health, To preserve health, To restore health when it is impaired And to minimize suffering and distress. These goals are embodied in the word " prevention"

50. Actions aimed at eradicating, eliminating or minimizing the impact of disease and disability, or if none of these are feasible, retarding the progress of the disease. The concept of prevention is best defined in the context of levels, traditionally called primary, secondary and tertiary prevention. A fourth Level, called primordial prevention, was later added.

51. 1. PRIMORDIAL PREVENTION DEFINITION “It is the prevention of the emergence or development of risk factors in countries or population groups in which they have not yet appeared.” INTERVENTION The main intervention in primordial prevention is through individual and mass health education.

52. Health promotion Health education Environmental modifications Nutritional interventions Lifestyle and behavioural changes. Health education to improve healthy habits and health consciousness in the community. Improvement in nutritional standards of the community. Healthful physical environment (Housing, water supply, excreta disposal, etc.,) Good working condition Marriage Counselling Periodic Selective examination of risk population.

53. Specific protection Use of Specific immunization (BCG, DPT,MMR vaccines) Chemoprophylaxis (tetracycline for Cholera, dapsone for Leprosy, Chloroquine for malaria,etc.,) Use of specific nutrients (vitamin A for Children, ironfolic acid tablets for Pregnant mothers) Protection against accidents (Use of helmet, seatbelt,etc.,) Protection against occupational hazards. Avoidance of allergens. Protection from air pollution.

54. PRIMARY PREVENTION

55. SECONDARY PREVENTION Definition: The action which halts the progress of a disease at its incipient stage and prevents complications”. INTERVENTIONS: Individual and mass case-finding measures. Screening surveys(urine examination for diabetes,etc.,) Selective examination

56. SECONDARY PREVENTION

57. TERTIARY PREVENTION Tertiary prevention can be defined as all measures available to reduce or limit impairments and disabilities, minimize suffering caused by existing departures from good health and to promote the patient adjustment to irritable conditions MODES OF INTERVENTION: Disability limitation Rehabilitation

58. TERTIARY PREVENTION

59. REHABILITATION: Medical rehabilitation: (restoration o Bodily Function). the capacity to earn a and social of personal dignity and Vocational rehabilitation:( restoration of livelihood) Social rehabilitation: (restoration of family relationship). Psychological rehabilitation: (Restoration confidence) EXAMPLES FOR REHABILITATION : Establishing schools for the blind. Prevention of aids for the crippled. Reconstructive surgery in Leprosy. Change of profession for a more suitable one and modification of life in general in the case of TB, etc.,

60. REHABILI T A TION

61. mortality & morbidity Measurements

62. RATE RATIO PRAPORTION

63. A f r acti o n i s m a d e u p o f 2 nu m b ers . The top number is called the NUMERATOR and the bottom number is called the DENOMINATOR. In the fraction ¾ the 3 is the numerator and the 4 is the denominator.

64. No of death in one year Death rate= - - - - - - - - - - - - - - - - - - - - X 1000 Total mid year population Numerator D e nomin at o r . Time specification Multiplier (Numerator is part of denominator )

65. The value obtained by dividing one quantity by another- X/Y. Male to female ratio. A ratio often compares two rates, death rates for women and men at a given age.

66. R a t i o al s o e x p r esse s r elatio n o f s i z e between the two quantities. Numerator is not part of Denominator. Expressed as X / Y. Doctor : Population ratio. Male : Female ratio. WB C : R B C r a ti o

67. A part/share or number considered in comparative relation to a whole. U s u a ll y e xpr e s s e d a s a pe r cen t a g e %

68. This is also relation /magnitude between two quantities, And numerator is always part of denominator . And expressed as percentage -Proportion of female students . -Proportion of anemic mothers ( 60 % m othe r s are a n e m i c )

69. Incidence Occurrence of new cases • Prevalence Existence of all new & old cases.

70. Prevalence:- how many people in a population currently have the disease. Incidence:- how many people are diagnosed each year

71. Cure rate

72. The rate at which acute disease is spreading - - used during epidemics & expressed in %. Attack rate %of exposed persons developing disease after primary case exposure Secondary attack rate

73. Prevalence at any given point of time. 4 % T B c a s e s o n 1 s t Ap r i l Point p r e v a l e n c e Prevalence at a given period of time. Period will be 1year. Period prevale n c e

74. Longer duration of the disease. Prolongation of life, with treatment. If incidence increases. Immigration of new cases. Better reporting of cases. Emigration of healthy people.

75. Longer duration of disease Incidence i n c r eas e s. P ro l on g a t i o n of life without c ure . 20

76. Shorter duration of diseases. Improved cure rate. Incidence decreases. Emigration of new cases. Under reporting of cases. Immig r atio n o f hea lt h y people.

77. Improved cure rate. Short duration of disease. Incidence decreases

78. Crude Death Rate. Specific death rate. Case fatality rate. Proportional mortality rate. Survival rate. Standardized death rate.

79. Nu m be r o f d e a t h s f r o m a l l c a u s e s , p e r 10 e s t i m at e d m i d y e a r p o pul a t i o n in one year in a given place. No deaths during one year M i d yea r popu l a ti o n CD R = X 100

80. C a us e S p ec i f i c d e a t h r a t e li k e disease death rate, Road accident… Age specific- IMR, Child Mortality rate Sex specific death rate – MMR/female Period specific death rate– Death in May

81. Percentage of particular cases dying during particular disease epidemic. Killing power of disease particularly acute diseases No of deaths due to cholera CF R = - - - - - - - - - - - - - - - - - - - - - - - X 100 Total No of cholera cases

82. Proportion or %of deaths due to particular cause out of total deaths. I t m e a s ures t h e di seas e bu r d e n . Under 5, proportional = mortality rate No of deaths below 5 years - - - - - - - - - - - - - - - - - - - - X 100 Total No all of deaths

83. Percentage of the treated patients remaining alive at the end of 5 years treatment. Yard stick for assessing the standard of therapy in cancer. S u r v iva l Rate pts alive at the end of 5 yrs = - - - - - - - - - - - - - - - - - - - - - - Total No of pts treated X 100

84. CDR can not be useful for comparison. Death rate need to be standardized for comparisons. Standardization can be done by- :adjusting death rate age wise, :also can be done sex/race wise

85. Epidemiological Methods

86. EPIDEMIOLOGICAL METHODS 1. OBSERVATIONAL STUDIES Descriptive studies Analytical studies 2. EXPERIMENTAL STUDIES Randomized control trials Field trials Community trials

87. OBSERVATIONAL STUDIES Do not have control over the circumstances Allow nature to take its own course, the investigator measures but does not intervene 1.Descriptive Epidemiology: Desc r i p ti v e epid e mio l o g y is t h e s tudy o f a m ou n t and distribution of disease or health status with in a population by person, place and time. When is the disease occurring?–time distribution. Where is it occurring? –place distribution. Who is getting the disease?-person.

88. USES OF DESCRIPTIVE EPIDEMIOLOGY Provide data regarding the magnitude of the disease load & types of disease problems in the community in terms of morbidity & mortality rates & ratios. Provide clues to disease aetiology & help in the formulation of an etiological hypothesis. Provide back ground data for planning, organizing , & evaluating preventive & curative services. Contribute to research by describing variation in disease occurrence.

89. Procedures in descriptive studies Define the population to be studied Defines the disease Describe the disease Time, place and person Measurement of disease Comparing with known indices Formulation of hypothesis.

90. Defining the population to be studied Descriptive studies are investigations of populations not individuals .The defined population can be: The whole population A representative sample

91. 2. DEFINING THE DISEASE UNDER STUDY The epidemiologist looks out for an "operational definition", i.e..a definition by which the disease or condition can be identified and measured in the defined population with a degree of accuracy

92. 3.DESCRIBING THE DISEASE Describes the occurence and distribution of disease by time, place and person and identifying those characteristics associated with presence or absence of the disease in individuals TIME PLACE PERSON Y ea r , se a son Cl i m a tic zones age Birth order Month, week Country, region sex Family size Da y , hou r of onset Urban/rural Marr i tal state Heigh t , w e i gh t duration T o w n s , citi e s Occupation, social status, education B P , b l o o d cholestrol, pe rs ona l h a b b its

93. 4.PLACE DISTRIBUTION: International variations:(cancer) National variations:(distribution of goitre, fluorosis, leprosy, malaria etc) Rural –Urban variations(chronic bronchitis, accidents, mental illness in urban areas, soil transmitted helmenthies, skin, zoonotics diseases) PERSON DISTRIBUTION: Age; measels-child hood Middle age-D.M,cancer. Old age-cardiovascular disease

94. TIME DISTRIBUTION Short term fluctuations: Cholera, Measels Periodic fluctuations: Seasonal like respiratory diseases in winter Long-term fluctuations: Cancer

95. 5.Measurement of Disease The amount of the disease ‘disease load’ in the p o p u lation.T h is information sh o uld be av a ilable in terms of mortality, mobidity, disability and so on. Measurement of Mortality is straightforward. Morbidity has 2 aspects, Incidence prevelence

96. 6. COMPARING WITH KNOWN INDICES By making comparison between different populations, by sub groups of the population. so we can identified the increased risk for diseases.

97. 7.FORMULATION OF ETIOLOGICAL HYPOTHESIS By studying the distribution of disease to formulate hypothesis relating the disease aetiology. E.g. cegirrate smoking causes lung cancer- incomplete hypothesis. The smoking of 30-40 cigarettes per day smoking causes lung cancer in 10%of smokers after 20 years of exposure.

98. The case report is the presentation of the experience of a single patient. A case report is a detailed report of the symptoms , signs , diagnosis , treatment, and follow-up of an individual patient. Case reports may contain a demographic profile of the patient, but usually describe an unusual or novel occurrence. contain a literature review of other Some case reports also reported cases. Case reports are often referred to as Hypothesis - generating because these bring forth evidence that supports a Hypotheses or conclusion. 1) Case series/ Case report: A . Ca s e R e p ort :

99. B. C A SE S E R I E S : When the common experiences of more than one patient are presented, this is referred to as case series. Greater the number of experiences stronger the evidences. EXAMPLE: if five patients developed aplastic anemia due to the same medication, this would raise questions. A good example is the case series of 24 patients showing vuvular heart abnormalities from concurrent fenfluramine which lead to its withdrawal from the market

100. 2) Cross-sectional studies Also known as prevelance study. It is the simplest form of the observation study. Prevalence is the frequency of cases at a given time. They provide a snap shot of the frequency and characteristics of a disease in a population at a particular point in time . It is a single examination of a cross section of population at one time and the results can be projected on the whole population Doesnot tell us about the history of the disease but only the Ddistribution tell.

101. However since exposure & disease status are measured at the same point in time, it may not be possible to distinguish whether the exposure proceeded or followed the disease and thus Cause and effect are not certain. For example the study of hypertension Advantages ; Several outcomes Short duration Disadvantages: Not feasible for rare diseases Prov i de le s s info r mati o n ab o ut the hi s to r y of the disease or the rate of occurance

102. It involves a repeated observation of the same variables over longer period of time, often many decades by means of follow-up examination. Also known as INCIDENCE study. Incidence is the development of new cases in a population at risk. It is often used in psychology to study developmental trends across the life span and in sociology to study life events throughout life time and generation. Long i tudinal stu d ies

103. Long i tudinal studies: ADVANTAGES: 1. study the natural history of disease Risk factors Incidence rate DISADVANTAGES: difficult to organize Time consuming

104. ANALYTICAL STUDIES The subject of interest is individual within the population. 2 distinct types; 1.Case control studies 2.Cohort studies

105. Analytical epidemiology Testing a specific hypothesis about a relationship of a disease to a specific cause. Analytical studies comprise 2 distinct types Case control study Cohort study

106. Case control study(retrospective study) 3 distinct features Both exposure and outcome have occurred before the start of the study It uses a control/comparison group The study proceeds backwards from effect to cause. Involves 2 populations Cases Controls

107. Adv a n t a g es can obtain findings quickly can often be undertaken with minimal funding efficient for rare diseases A l lo w s the study of several d i f fer ent aeti o l o g i cal factors eg. Smoking, physical activity etc. No attrition problems, because case control donot require follow up of individuals into the future generally requires few study subjects s tudies Disadvantages cannot generate incidence data, can only estimate relative risk subject to bias

108. COHORT STUDY FEATURES ARE: Cohorts are identified prior to the appearance of disease under investigation. Study groups are observed for a period of time to determine the frequency of disease among them. Study proceeds forward from cause to effect

109. FRAMEWORK OF COHORT STUDY Study cohort: exposed to a particular factor Control cohort: not exposed Example: smokers and non smokers associated with lung cancer GENERAL CONSIDERATIONS: The cohorts must be free from the disease Both the groups should be equally susceptible to the disease under study eg. Males over 35 years would be appropriate for studies on lung cancer Both the groups should be comparable in respect of all the possible variables which may influence the frequency of the disease

110. There are four basic steps in conducting a case control study: Selection of cases and controls Matching Measurement of exposure, and Analysis and interpretation.

111. COHORT STUDY

112. Advantages: Establish sequence of events Short duration Relatively cheap Can study several outcomes Dose response ratios can be estimated Disadvantages: Often requires large sample sizes Not feasible for rare diseases Requires long period of follow up The study itself may alter people’s behaviour It is not unusual to loose a substantial proportion of the original cohort,they may migrate or loose interest

113. Experimental Epidemiology Experimental , where the epidemiologists have control over the circumstances from the start it is the study of the relationships of various factors determining the frequency and distribution of diseases in a community. It provides a specific proof. It can provide the strongest evidence for cause and effect.

114. TYP E S Randomised controlled trials. Non randomised or non experimental trails.

115. Randomized Controlled Trial (RCT) (Synonym: Randomized Clinical Trial) ”An epidemiological experiment in which subjects in a population are randomly allocated into groups, usually called study and control groups to receive and not receive an experimental preventive or therapeutic procedure, or intervention” John M.Last, 2001

116. Basic steps of RCT The protocol Selecting reference and experimental populations Randomization Intervention Follow up Assessment

117. Eg; u.v rays of the sun effects on the skin Select a suitable population Select a suitable sample. Make who are eligible/not eligible. Randamize Expermental c o n t r o l . Manipulatio( or) intervention. Fallow up. Out come.

118. 1. The protocol Rationale Aims and objectives, Research questions Design of the study: selection of study and control groups Ethics: patient consent, adverse events Documentation -Procedure Selecting Reference and Experimental Populations Reference or target population - population to which the findings of the trial, if found successful, are expected to be applicable (eg. drugs, vaccines, etc.) Experimental or study population – actual population that participates in the experimental study

119. Participants must fulfil the following criteria: - Must give informed consent - Should be representative of the population - Should be qualified or eligible for the trial

120. 3. Randomization Heart of the control trial Procedure: Participants are allocated into study and control groups Eliminates bias and allows comparability Both groups should be alike with regards to certain variables that might affect the outcome of the experiment Best done by using table of random numbers

121. Manipulation of Interventions: Pharmaceutical (Therapeutic or Preventive) Device Procedure Behaviour modification Follow Up Implies examination of the experimental and control group subjects at defined intervals of time, in a standard manner, with equal intensity, under the same given circumstances

122. Randomised controlled trials design

123. NON-RANDOMIZED CONTROL TRIALS

124. USES 1 T o stu d y t he h i story of the d i se a se Trends of a disease for the prediction of trend Results of studies are useful in planning for health services for public health Community diagnosis What are the diseases, conditions, injuries disorders, disabilities, defects causing illness health problems, or death in a community or region. risks of individuals as they affect populations What are the risk factors, problems, behaviours that affect groups are studied by doing risk factor and disease assessments Assessment, evaluation and research assessments: health screening , medical exams How well do public health and health services meet the problems and needs of the population Effectiveness; efficiency; quality; access; availability of services to treat, control or prevent disease

125. 5.Completing the clinical picture Identification and diagnostic process to establish that a condition exists or that a person has a specific disease Cause effect relationships are determined, e.g. strep throat can cause rheumatic fever Identification of syndromes Help to establish and set criteria to define syndromes, some examples are: fetal alcohol, sudden death in infants, etc. Determine the causes and sources of diseases Findings allow for control prevention, and elimination of the causes of disease, conditions, injury, disability, or death