Basic Epidemiology Lecture 4 th YEAR BDS

Basic Epidemiology Lecture 4 th yeardental students

1. Basic Epidemiology Dr. Halima A lnagi Assistant Professor 3/4/2024 Dr. Hala Ben Ghasheer Lecturer

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4. 3/4/2024 Definition of Epidemiology The word epidemiology comes from the Greek words: epi , meaning on or upon demos , meaning people , and o logy , meaning 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 . (as given by John M. Last in 1988) -

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6. 3/4/2024 Key terms in this definition 1. Distribution : - is concerned with the frequency and pattern of health events in a population. Frequency includes not only the number of events in a population, but also the risk of disease in the population. Pattern of health events refers to occurrence of health-related events by time, place & person, by asking three questions ( when, where, who?). Who (persons), is affected more by a disease or who remain free from it within a population. Where (place) a health related event has occurred When, (time) such event has occurred or existed.

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8. Health determinants 2. Determinants : Include both causes and factors that influence the risk of disease. Determinants can be both causal & preventive factors

9. Aims of epidemiology: 1 . To describe the distribution and size of disease problems in human populations. 2. To identify aetiological factors in the pathogenesis of disease. 3. To provide the data essential to the planning, Implementation and evaluation of services for the prevention, control and treatment of disease and to the setting up of priorities among those services. 3/4/2024

10. USES OF EPIDEMIOLOGY 1- Historical study: Is the community improving? We can decide only by comparing experience (rates) over time, because it is well known that the health and disease pattern in communities never constant . There are fluctuations both over short and long periods of time.   2. Community diagnosis : generally refers to the identification and quantification of health problems in a community in terms of mortality and morbidity rates and ratios. 3. Planning and evaluation: is essential for rational use of the limited resources.. 4. Evaluation of individual’s risks and chances: It measures degree of risks in the population. . 3/4/2024

11. USES OF EPIDEMIOLOGY 5. Syndrome Identification : rising number of syndromes 6. Completing the natural history of disease 7. Searching for causes and risk factors:. Ex:Cigarette smoking is a causal factors of oral cancer . 3/4/2024

12. Sources of data in epidemiology : Vital statistics, Birth and death records of municipality. Birth, death, morbidity reports “monthly, quarterly annual from Hospitals/Health care facilities. Special disease registries at polyclinics / Hospitals e.g.: Cancers, Hypertension, and CHD. Health surveys. Reports from practicing physicians. Laboratory registers (Hospitals, polyclinics, etc ). Employment records (service, industry, and mines). Epidemic reports 3/4/2024

13. Concept of disease occurrence : Factors to be studied in epidemiology : 3/4/2024

14. 3/4/2024 Epidemiological triad model

15. Host Factor A susceptible human or animal who harbors and nourishes a disease-causing agent The host must be highly resistance to prevent disease. Hosts’ resistance depends on: Age Sex Race Genetic influence People’s response to stress Lifestyle: diet, exercise, sleep patterns, healthy and unhealthy habits Certain diseases are more common in males than females or vice versa 3/4/2024

16. Agent A factor that causes or contributes to a health problem or condition. 1. Biological agent : Bacteria, viruses, fungi, allergy or nutrients S mutans cause dental caries Actinomuces causes root caries Vitamin c deficiency causes scurvey Herps virus causes herpetic gingivostomatitis 2. Chemical agents: chemical toxins as fluoride ex: fluorosis 3. Physical agents: Radiation, heat, cold or trauma Ex: head and neck radiotherapy cause salivary gland destruction and hence acute caries 3/4/2024

17. Environment Aggregate of all external condition and influence affecting life and development of an organism, human behaviour or society Physical environment : Geography, Climate, Weather Water, air and soiled Water may have high fluoride content High temperature more water drinking 3/4/2024

18. biological environment : Diet and nutrition Presence of animals, Plants, Insects Deficiency of protein and vitamin during tooth formation lead to poor tooth structure 3/4/2024

19. Social environment: Education , occupation or outcome Any factor affect social condition can affect general health. Educated people have better oral hygiene 3/4/2024

20. Interaction between factors The environment considered as fulcrum arm between agent and host The greater the resistance of host , it outweighs the agent and health wins 3/4/2024

21. The greater the virulence of agent , it outweighs the host resistance and disease happens 3/4/2024

22. The environment can be shifted either toward host or agent 3/4/2024

23. Interplay of these factors (Seesaw effect) 3/4/2024

24. Time In the center of the triangle is time. Most infection disease have an incubation period, the time between when the host is infected and when disease symptoms occur. Time may describe the duration of the illness or the amount of time a person can be sick before death or recovery occurs . Time also describes the period from an infection to the threshold of an epidemic for a population 3/4/2024

25. Epidemiological terms Outbreak: is sudden increase in the disease frequency, related to time, place, and observed population. For example , a cluster of children absent from school due to gastrointestinal illness could represent an outbreak if they are found to have the same infectious disease . Endemic: constant presence of disease that affect the population in a definite area . Eg : malaria disease is endemic in some parts of the world. Epidemic: unusual occurrence of a disease in any region. Pandemic: when a disease affects large number of population worldwide. Eg:COVID-19 3/4/2024

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27. 3/4/2024 The WHO defines pandemics, epidemics, and endemic diseases based on a disease's rate of spread. Thus, the difference between an epidemic and a pandemic isn't in the severity of the disease, but the degree to which it has spread .

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29. Prevalence : the number of all current cases at present time of given population Measured by proportion and percentage ( to 1 if expressed as proportion, to 100 if expressed as percentage) Proportion = Number of existing cases \ Number of total population Percentage = Number of existing cases\Number of total population × 100 Incidence: is a measure of the new occurrence of a disease event within a defined time period in a specified population Incidence rate =the number of the new cases/ total population Mortality : is the measure of death in a population Mortalty rate = number of death/ total population Morbidity :is the measure of illness in a population. Morbidity rate = number of diseased/ total population 3/4/2024

30. Risk factor: it is exposure or attribute that increase probability of disease occurrence, can be identified only in longitudinal studies & can be modified. EX: smoking is risk factor in periodontal disease. Demographic risk factor : it is exposure or attribute that increase probability of disease occurrence & can not be modified, such as age, sex, SES…… Risk marker (risk predictor): it is exposure or attribute that increase probability of disease occurrence & not necessary to be cause, EX: gingival bleeding. Exposure : is the quantity or intensity of a factor which supposedly causes a disease. 3/4/2024

31. Association: a relationship between an exposure and a disease, that is, the presence of one alters the probability of observing the presence of the other. Causality: The determination of “cause and effect”. The ability to be able to state with certainty that “A” causes “B” (a specific exposure has been shown to cause a specific outcome) 3/4/2024

32. TYPES OF EPIDEMIOLOGICAL STUDIES 3/4/2024

33. Why important ? Research Question Study Design Appropriate study design to achieve objectives of study 30/09/2023 33 DR.HALA BEN GHASHEER

34. to avoid faulty conclusion that ultimately will affect patient care t o get an accurate and precise results of study one of sources of error  to reduce error in research Why important ? 30/09/2023 34 DR.HALA BEN GHASHEER

35. Two broad research designs Quantitative and Qualitative Most biomedical studies are quantitative : numerical data is collected and analyzed Subjective phenomena such as feelings, attitudes and emotional responses  qualitative Qualitative: in-depth exploration and description, rather than numerical measurement, of variables Results in a rich and deep understanding of the topic under study Study Design 30/09/2023 35 DR.HALA BEN GHASHEER

36. Quantitative and Qualitative RQ: In patients suffered from stroke that involves facial nerve, how much it affects speech, taste and weight ? RQ: What challenges faced by families and patients after suffering from stroke that involves facial nerve ? Study Design 30/09/2023 36 DR.HALA BEN GHASHEER

37. Study designs Intervene or Observe? Intervention Observation Looking for causality? Analytical Descriptive Cohort Case control Cross sectional (prevalence) Case series/ Case report Ecologic Correlational 30/09/2023 37 DR.HALA BEN GHASHEER

38. Study designs Intervene or Observe? Intervention Observation Looking for causality? NO Analytical Descriptive Cohort Case control Cross sectional (prevalence) Case series/ Case report Ecologic Correlational 30/09/2023 38 DR.HALA BEN GHASHEER

39. Study designs Intervene or Observe? Intervention Observation Looking for causality? YES Analytical Descriptive Cohort Case control Cross sectional (prevalence) Case series/ Case report Ecologic Correlational 30/09/2023 39 DR.HALA BEN GHASHEER

40. Study designs Intervene or Observe? Intervention (Analytical) Observation Randomised controlled trial Non-RCT/ Quasi experimental study 30/09/2023 40 DR.HALA BEN GHASHEER

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44. Observational (non-experimental): In this type of study the researcher: does not intervene . does not artificially introduce an exposure factor only reports the data that could be gauged through observation . They are mainly used to assess the etiology of the phenomena ( assess the causality ). Usually , observational studies are a first step towards the elucidation of health determinants 3/4/2024

45. 30/09/2023 DR.HALA BEN GHASHEER 45 Descriptive studies : The study is descriptive when the researcher solely intends to describe the pattern of the occurrence of diseases with variables related to the person, time, and place. - Such as case report, case series, cross-sectional (prevalence). - Analytical studies: When specific hypotheses of causal association between variables are tested, the study is said to be analytical. - Such as case-control (retrospective), cohort (prospective, longitudinal).

46. Study designs Intervene or Observe? Intervention Observation Looking for causality? NO Analytical Descriptive Cohort Case control Cross sectional (prevalence) Case series/ Case report Ecologic Correlational 30/09/2023 46 DR.HALA BEN GHASHEER

47. TYPES OF DESCRIPTIVE STUDIES: 1. Case Report Study : The simplest type of research. They descript the experience of a single patient with unusual diagnosis or exposure It is done for one case of unexpected outcome or previously unknown side effect of a drug Example fibrosis of the retina and blindness of newly born when subjected to hyperbaric oxygen in NICU 3/4/2024

48. 2. Case series Study : it is collection of case reports. It may indicate an impending epidemic of a disease . For example: hairy leukoplakia, one of the oral manifestations of Acquired Immune Defiency Syndrome (AIDS), was initially reported in a series of case report. 3/4/2024

49. 3. Correlation studies : It uses data from entire populations to compare disease frequency between different groups during the same period of time or in the same population at different points in time. Example. correlation between number of cigarettes smoked per day and annual oral cancer . Higher number of cigarettes smoked per day was related to increase in annual orals cancer. 3/4/2024

50. Cross sectional surveys : prevalence study . Cross-sectional study is the simplest of all the observational studies. It is based on a single examination of a cross-section of population at one point in time The results can be projected on the whole population provided the sampling has been done correctly. It is more useful for chronic than acute diseases. 3/4/2024

51. Example: In a study of dental caries among children , we can collect data during the survey about age, sex, sugar intake and other variables of interest. Such a study tells us about the distribution of a disease in population rather than its a etiology. Doesn’t prove the risk factor. A ‘confounding factor’ is one which is associated with both exposure and disease , and not equally distributed in study and control groups, e.g. age of mother is related to birth weight of the child 3/4/2024

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54. Advantages short time. Provide a wealth of data that can be used in health sys­tems research. Cheap & simple. Easy to conduct compared to longitudinal studies. Disadvantages Do not estimate the incidence of the disease. Prone to selection bias, information bias, confounding bias. Not suitable for rare diseases and remission 3/4/2024

55. Study designs Intervene or Observe? Intervention Observation Looking for causality? YES Analytical Descriptive Cohort Case control Cross sectional (prevalence) Case series/ Case report Ecologic Correlational 30/09/2023 55 DR.HALA BEN GHASHEER

56. ANALYTICAL STUDIES   ( How? Why?) It is the second major type of epidemiological studies. In contrast to descriptive studies that look at entire populations, in analytical studies, the subject of interest is the individuals within the population. The Objective is to test hypotheses.   Types of analytical studies : Case control study Cohort study 3/4/2024

57. A. CASE CONTROL ( RETROSPECTIVE ) STUDY It involves two populations - case and control . The unit of study is individual rather than group . It is a comparison study. The study starts with the manifestation of the outcome, and it aims to investigate the differential effect of several causal factors to which both groups were differentially exposed in the past . Assess the relationship of existing disease to exposure (possible cause) in the past 3/4/2024

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60. Cases : people who have the disease. Control: people without the disease, but should resemble the case in all respect except for the presence of disease Matching : is defined as the process by which we select controls in such a way that they are similar to cases with regard to certain variables, e.g. age & sex which are known to influence the outcom e of the disease and which, if not adequately matched for comparability, could distort or confound the results . 3/4/2024

61. Advantages of case control study: 1-Relatively easy to carry out 2-Rapid and inexpensive 3-Suitable to investigate rare diseases 4-No risks to subjects 5-Several etiological factors can be studied 6-No attrition problems ( no loss of follow up ) 7-Ethical problems minimal . 3/4/2024

62. Disadvantages 1-Recall Bias, relies on memory or past records the accuracy of, which may be uncertain ,difficult to validate the information obtained. 2- Selection of appropriate control group may be difficult. 3-We cannot measure incidence and can only estimate the relative risk. 3/4/2024

63. E xample A study conducted in order to investigate the differential effect of common foods as a risk factor for oral cancer, Characteristics such as sex, age, family income, smoking, and use of a dental prosthesis ( back to history ) were matched for the controlled assessment of the association between food consumption and oral cancer . 3/4/2024

64. Cohort studies ( prospective cohort study) Is form of longitudinal observation, whose central objective is to assess the incidence of a given disease or health condition. Cohort is a group of people having common characteristic, for example, in a cohort of live births, all research subjects have in common the same birth period. The study start with group of people who are free of disease that classified into 2 group , one exposed to exposure (factor or interest) & the other not exposed, then the 2 group followed up to see how subsequent development of new cases differs between the two groups (prospective). 3/4/2024

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67. Follow -up : may be very long a certain percentage of losses to follow-up (attrition) are inevitable due to death, change of residence, migration 95 % follow-up as possible. . 3/4/2024

68. Indication for cohort studies: When there is good evidence of an association between exposure and disease ,. When exposure is rare , but the incidence of disease is high among exposed e.g. special exposure groups like those exposure to X- rays . When attrition of study population can be minimized , When funds are available 3/4/2024

69. Advantages of cohort studies : Incidence can be calculated . Several possible out comes related to exposure can be studied simultaneously . Reduced recall & selection bias.   3/4/2024

70. Disadvantage : Cohort studies involve a large number of people . Unsuitable for investigating un common diseases or diseases with low incidence in the population. It takes a long time to complete the study and obtain results. Expensive . Ethical problems . Loss of participant 3/4/2024

71. 3/4/2024   Differences between case control and cohort studies:

72. 3/4/2024 Case Control studies Cohort studies 1. Proceeds backward from effect to cause 2. Starts with people with the disease 3. Test whether the suspected cause occurs more frequently in those with the disease than among those without the disease 4. Involves fewer subjects 5. Yields relatively quick results 6. Suitable for the study of rare disease Proceeds from cause to effect 2. Starts with people free from disease. 3. Tests whether the disease occurs more frequently in those exposed than in those not similarly exposed 4. Large number of subjects 5. Long follow-up period 6. Inappropriate if disease and exposure is rare

73. Case Control studies Cohort studies 7 . It measures Odd’s ratio, can’t measure incidence 8. Cannot yield information of diseases other than that selected for study 9. Less expensive       7 . Can measure Incidence Rate, Relative Risk &, Attributable Risk 8. Can yield information about more than one disease outcome 9. More expensive 3/4/2024  

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75. EXPERIMENTAL STUDIES The experimental studies involve some actions, interventions or manipulations attempting to change a variable in one or more groups of people. 3/4/2024

76. EXPERIMENTAL STUDIES Two types: Clinical trial . Field trial. 3/4/2024

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79. The aims of experimental studies may be stated as follows: To provide scientific proof of aetiological (or risk) factors which may permit the modification (s) or control of those diseases. To provide methods of measuring the effectiveness and efficiency of health services for the prevention, control and treatment of diseases and improve the health of the community. . Experimental studies can be conducted in animals or human beings 3/4/2024

80. Clinical trial: Can only be used to examine interventions with a positive outcome for the participants. It is unethical to use an RCT design to examine the aetiology of disease. The participant classified to two groups : 1- Test or intervention group who receiving the therapeutic or preventive agent under study. 2-Control group not receive the agent under study.  The two groups must be similar in distribution of age, gender, race, SES, disease level & differ only in receiving agent.  The primary objective of clinical trials is to evaluate endpoint treatment results, the cure of diseases, the survival of patients Clinical trial can be randomized or non randomized. 3/4/2024

81. Randomized Controlled trial Randomized controlled trial (RCT) is often considered as the “gold standard” and the most reliable resources to produce evidence in health Experimental studies maintain the greatest control over the research setting. Randomized controlled trials (RCT’s) are used for evalu­ating both the effectiveness and side effects of new types of intervention. 3/4/2024

82. Use of control: by classified the participant into sub group: control & study group , that should be the 2 groups similar in distribution of age , gender, race….. except agent under investigation. study group Positive control: receive an active treatment (traditional treatment). 3/4/2024

83. Negative control: absent of active agent called placebo (is an inert substance that similar in appearance to test but without active ingredient, it is useful to the subjects unaware whether are in test or control group) 3/4/2024

84. Bias in R C Ts : i . Subject variation bias: the participants subjectively feel better or report improvement if they knew that they were receiving a new form of treatment. ii . Observer bias: the investigator measuring the outcome of a therapeutic trial / intervention may be influenced, if he knows beforehand the particular procedure or therapy to which the patient has been subjected. These biases cannot be prevented by randomization or by increasing the size of the sample, but can be minimized by a technique known as blinding. 3/4/2024

85. iii. Evaluation bias : the investigator may subconsciously give a favourable report of the outcome of the trial if the evaluator is aware of the details of the study. 3/4/2024

86. Blinding: Blinding can be done in three ways: i. Single blind trial : the participant is not aware whether s/he belongs to the study group or control group. ii . Double blind trial : neither the investigator nor the participant is aware of the group allocation and the treatment received. iii. Triple blind trial : the participant, the investigator, and the person analyzing the data are all unaware. 3/4/2024

87. Field Trials Are experiments on people without the disease in ques­tion to determine the efficacy of a preventive or thera­peutic agent or procedure . .  Treatment groups are communities like schools or markets rather than individuals .  The fluoridation of public water supply is an excellent example of this type of study 3/4/2024

88. Community Intervention Trials In this type of field trial the intervention is done on a community wide basis rather than individuals. 3/4/2024

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