Introduction to Epidemiology (Year 2 A &B).pptx

Made simple

1. Scope of epidemiology What is epidemiology? The study of the distribution and determinants of health related states and events in populations and the application of this study to control of health problems Last JM: A Dictionary of Epidemiology The study of the distribution of a disease or a physiological condition in human populations and of the factors that influence this distribution Lilienfeld A: in Foundations of Epidemiology

2. Health related states and events Epidemics of communicable diseases – original focus Current scope: endemic communicable diseases non-communicable infectious diseases chronic diseases, injuries, birth defects, maternal-child health, occupational health, and environmental health h ealth-related behaviors: exercise, seat belt use, …..

3. Distribution Includes frequency and pattern Frequency: the number of health events (e.g. number of cases of diabetes in a population), also the relationship of that number to the size of the population Pattern: the occurrence of health-related events by time , place , and person Time patterns : annual , seasonal, weekly, daily, hourly, weekday versus weekend, Place patterns: geographic variation, urban/rural differences, and location of work sites or schools Personal characteristics: demographic factors (age , sex, marital status, and socioeconomic status), as well as behaviors and environmental exposures

4. Determinants Causes and other factors that influence the occurrence of disease and other health-related events Illness does not occur randomly in a population, but happens only when the right accumulation of risk factors or determinants exists in an individual

5. Epidemiology as Population Science E pidemiological concept of population important P opulations are made up of distinct individuals I ndividuals are generally organized into some kind of societal grouping family other larger grouping / sub-cultures T hinking about population and specifically about health (and disease) in populations W hat extent do individuals and their societies have effects?

6. Importance of Population D efine population (of interest) with view to drawing sample E xamples –men aged 45-64 for CHD events study why leave women out? –implies belief in different risk for women studying pregnancy and childbirth –restrict population to females (of child bearing age) L ooking to generate study research findings generalize these to wider population

7. Epidemiology and Demography-Interdependent Population Science Taking a sample –where do we start? Need information about population Census data –every 5 years in Sierra Leone Varies between countries Planning future health care needs –reliant on some demographic data need to know the size of a problem now, plus some indication of future trends

8. Epidemiology as Disease Distribution Science Disease Distribution refers to analysis of disease patterns according to Person, Place and Time Triad of epidemiological questions: Time, Place, Person -exposure variables Person: Age Sex Race Ethnic Group Socioeconomic Status Occupation Religion and Marital Status

9. Epidemiology as Disease Determinants Disease determinants are factors that bring about a change in a person’s health. These are factors that either cause a healthy individual to become sick or cause a sick person to recover It include both causal and preventive factors Determinants include: Individual, Environmental and Societal Individual Determinants Genetic make-up Gender Age Immunity Diets Behaviors Existing Diseases

10. Environmental/Societal Determinants Presence of infectious agents Reservoirs in which the organism multiplies Vectors that transport the agents Poor and crowded housing conditions Political instability

11. Dahlgren & Whitehead (1991) Influences on Health (Cited Speller, 2007: no pagination)

12. Two Broad Types of Epidemiology Examining the distribution of a disease in a population, and observing the basic features of its distribution in terms of time , place , and person Typical study design: community health survey (approximate synonyms - cross-sectional study, descriptive study) Testing a specific hypothesis about the relationship of a disease to a putative cause, by conducting an epidemiologic study that relates the exposure of interest to the disease of interest Typical study designs: cohort, case-control DESCRIPTIVE EPIDEMIOLOGY ANALYTIC EPIDEMIOLO GY

13. The 5W's of descriptive epidemiology What = health issue of concern Who = person Where = place When = time Why/how = causes, risk factors, modes of transmission Analytic epidemiology Tests hypotheses about: Why How Comparing groups with different rates of disease occurrence and with differences in demographic characteristics, genetic or immunologic make-up, behaviors, environmental exposures, and other potential risk factors

14. An epidemiologist An epidemiologist: Counts Divides Compares Counting based on case definition i.e. a set of standard criteria for classifying whether a person has a particular disease, syndrome, or other health condition Divide by the number of cases divided by the size of the population or by the size of the population per unit of time

15. RATE OF A DISEASE IN A POPULATION Attack rate Morbidity rate Mortality rate Incidence Prevalence Epidemic Pandemic Types of Disease Frequency The two basic types are Incidence Prevalence

16. Incidence as Disease Frequency Incidence is the occurrence of new cases of disease that develop in a candidate population over a specific time period . New disease events Candidate population Specific amount of time Incidence cases: Types of Incidence Cumulative incidence-is defined as the proportion of a candidate population that becomes diseased over a specific period of time. # of new cases of disease/#of candidate pop over specific time period Incidence Rate-is the occurrence of new cases of disease during a person time of observation. # of new cases of disease/Person-time of observation in candidate population.

17. Prevalence as Disease Frequency Prevalence is defined as the proportion of the total population that is diseased. Point Prevalence Period Prevalence Prevalence case: Example: Thus a population with a heart disease prevalence of 0.25 indicates What?

18. Risk as Disease Frequency Risk , also known as incidence, cumulative incidence, incidence proportion, or attack rate (although not really a rate at all) is a measure of the probability of an unaffected individual developing a specified health outcome over a given period of time. For a given period of time (i.e.: 1 month, 5 years, lifetime): Example: A 5-year risk of 0.10 indicates that an individual at risk has a 10% chance of developing the given health outcome over a 5-year period of time Risk= #of new cases/Total number of individual at risk Another way to look at risk: Risk is the proportion of an at-risk population that develops a specific health outcome within a specified amount of time. The numerator for risk is incident cases, and the denominator includes only those at-risk of developing the outcome of interest at the beginning of study follow-up.

19. Use of Incidence and Prevalence Incidence is most helpful for evaluating the effectiveness of a program that try to prevent disease from occurring in the first place Prevalence are useful for estimating the needs of medical facilities for allocating resources for treating people who already have a disease.

20. Characteristics of Incidence and Prevalence Measure Type of # Units Range Types of cases Major use Cumulative incidence Proportion None 0 to 1 New Prevention/ Tx of diseases Incidence Rate Time Rate 1/time 0 to infinity New Prevention/ Tx of diseases Prevalence Proportion None 0 to 1 Existing Resources Planning

21. Comparing measures of occurrences

22. Other measures of Disease Frequency Crude Mortality rate ( or death) : Total number of deaths from all causes per 100,000 population per year. Crude means the rate is based on raw numbers Cause –specific mortality ( or death) rate: Number of death from specific causes per 100,000 per year. Age-Specific mortality (or death) : Total umber of deaths from all causes among individuals in a specific age category per 100,000 population per year in the age category. Years of potential life lost : The number of years that an individual was expected to live beyond his or her death.

23. Other measures of Disease Frequency Livebirth rate: Total number of Livebirth per 1000 population per year. A Livebirth is a pregnancy that results in a child who after separation, breathes or shows any other evidence of life. Infant mortality rate: Number of deaths of infants less than one year of age per 1000 Livebirth per year. It can be neonatal deaths occurring during the first 27 days following births or it post-neonatal deaths occurring from 28 days through 12 months. Birth defects (congenital anomaly or malformation) rate: Number of children born with defects per 10,000 births. The denominator and numerator often include live and stillbirths

24. Other measures of disease frequency Morbidity rate: Number of existing or new cases of a particular disease or condition per 100 population. It is a general word that can apply to a disease, condition or event. Case fatality rate: Number of deaths per number of cases of a disease. Survival rate: Number of living cases per number of disease.

25. Measuring frequency To measure frequency of a disease or event, pay attention to the numerator (cases) and the denominator (population at risk) Key point in making sense of the numbers

26. Measures of disease frequency ratios proportions prevalence , incidence risks , rates, odds all functions of numerators (cases) and denominators (population at risk or those at risk but disease free) R atios : the relative magnitudes of two quantities (usually expressed as a quotient) (A/B) P roportions : a ratio that relates the part (the numerator) to the whole (the denominator) — numerator always part of the denominator (A/A+B)

27. Prevalence The prevalence of a disease or condition in a population is defined as: The total number of cases (existing cases) of the disease in the population at a given time or T he total number of cases in the population, divided by the number of individuals in the population It is a proportion and is usually expressed as a percentage Incidence The incidence of a disease in a population is defined as: The total number of NEW cases of the disease in a population at risk of the disease in a defined time period or The total number of NEW cases in the population, divided by the total number of individuals at risk of the disease in the population Again , it is a proportion (RISK) and can be expressed as a percentage

28. Odds of disease Provides an alternative way to express a probability (likelihood of an event) Risk = A / N Odds = A / (N-A) Odds = probability / ( 1 + odds ) Probability = odds / ( 1 - odds ) Risk and odds Risk is number of events over number of possible events Odds is defined as the number of events to the number of non-events Example : number of cases in exposed group 60, number of cases in unexposed group 10, odds are six to one (60/10) and risk is 86% (60/70) The odds has properties that make it very useful in epidemiology

29. Rate Rate or velocity at which new cases of a particular disease (or outcome of interest) occur in a population at risk for the disease Calculated as: Number of individuals developing disease over specified time period ---------------------------------------- Sum of the “disease-free” time experienced by study participants at risk of disease Measures of association Measure the strength of association between the exposure and outcome, e.g. How likely are cigarette smokers likely to develop lung cancer? Could be relative (ratios) or absolute (differences) Risk ratio Odds ratio

30. Risk ratio Risk ratio = R e/ R u = (120/5000)/(50/5000) = 2.4 Case Control Exposed a b Unexposed c d Risk in exposed (R e ) = a/( a+b ) Risk in exposed (R u )= c/( c+d ) Risk ratio = R e/ R u

31. Odds ratio Odds ratio = R e/ R u = (120/4880)/(50/4950) = 2.4 Case Control Exposed a b Unexposed c d Odds of a case being exposed (R e ) = a/b Odds of a control being exposed (R u )= c/d Odds ratio = R e/ R u = (a/b)/(c/d) = ad/ bc

32. Features of odds ratios Often the only measure calculable for case-control studies Approximates the risk ratio when the disease is rare Based on artificially sampled case and control populations, which may not reflect the population rate or risk of disease I f the prevalence of disease is high (high initial risk), the odds ratio can under- or overestimate the risk ratio Often used in genomic epidemiology because the largest set of studies are case-control designs based on disease definitions and often sampled from patient populations

33. Infectious Disease Model Model Host Pathogen Environment disease

34. Incidence and prevalence of infectious diseases Incidence of an infectious disease: number of new cases in a given time period expressed as percent infected per year (cumulative incidence) or number per person time of observation (incidence density). Prevalence of an infectious disease: number of cases at a given time expressed as a percent at a given time. Prevalence is a product of incidence x duration of disease, and is of little interest if an infectious disease is of short duration (i.e. measles), but may be of interest if an infectious disease is of long duration (i.e. chronic hepatitis B).

35. Epidemic “ The unusual occurrence in a community of disease, specific health related behavior, or other health related events clearly in excess of expected occurrence ” ( epi = upon; demos= people) Epidemics can occur upon endemic states too . Endemic It refers to the constant presence of a disease or infectious agent within a given geographic area or population group. It is the usual or expected frequency of disease within a population. (En = in; demos = people)

36. Hyperendemic and holoendemic The term “ hyperendemic ” expresses that the disease is constantly present at high incidence and/or prevalence rate and affects all age groups equally. The term “ holoendemic ” expresses a high level of infection beginning early in life and affecting most of the child population, leading to a state of equilibrium such that the adult population shows evidence of the disease much less commonly than do the children (e.g. malaria)

37. Pandemic and Exotic An epidemic usually affecting a large proportion of the population, occuring over a wide geographic area such as a section of a nation, the entire nation, a continent or the world, e.g. Influenza pandemics. Exotic diseases are those which are imported into a country in which they do not otherwise occur, as for example, rabies in the UK.

38. Sporadic The word sporadic means “ scattered about ” . The cases occur irregularly, haphazardly from time to time, and generally infrequently. The cases are few and separated widely in time and place that they show no or little connection with each other, nor a recognizable common source of infection e.g. polio, meningococcal meningitis, tetanus … . However, a sporadic disease could be the starting point of an epidemic when the conditions are favorable for its spread.

39. Parameters of an infection

40. The epidemic curve of an extended source epidemic in a limited population (simplified).

41. Fig. 2.3. Epidemic types

42. Investigation of a point-source epidemic.

43. Investigation of a propagated-source epidemic.

44. Basic reproductive rate increasing, i.e. >1. Maximal transmission: every infection produces a new case.

45. Fig. 2e decreasing , i.e. <1. Unsustained transmission: each transmission gives rise to less than one new case and the infection dies out.

46. Fig. 2.8. The focality of endemicdisease . (A) A universally homogeneous prevalence rate is measured in an area. (B) Once control measures have been implemented, foci of persistent transmission are revealed.

47. Fig. 2.9. Theoretical environmental control of schistosomiasis.

48. Prevalence of disease is a measure of burden – how many people have the illness. Population of a place – often a particular geographic area (city, state) Defined period of time. Could be a particular point in time (point prevalence) or during a defined time period, e.g., over a year (period prevalence) May be expressed as a percentage or other ratio (per thousand) Basic formula: Number of persons with the disease Number of persons in the population Prevalence: Definition and Calculation

49. Prevalence data are typically available from routine surveillance systems and surveys collected by health agencies at the local, state or national levels. For example the US CDC collects and provides asthma prevalence data https://www.cdc.gov/asthma/asthmadata.htm Example from Shikowski et al. 2014 In the European Community Respiratory Health Survey cohort COPD prevalence was 3.4% Prevalence: Data and Examples

50. Incidence of disease is the number of new cases of disease Defined place – often a particular geographic area (city, state) Population at risk Defined period of time May be expressed as a percentage or other ratio (per thousand) Basic formula: Number of new cases of disease in a population over defined time Number of persons at risk in the population during that time Incidence: Definition and Calculation

51. Incidence data are typically available from routine surveillance systems and surveys collected by health agencies at the local, state or national levels. Incidence data for cancer are gathered and disseminated by cancer registries Example from Shikowski et al. 2014 In the European Community Respiratory Health Survey COPD incidence was 3.4% Measures of Association and Risk Relative risk (RR) Odds ratio (OR) Attributable risk (AR) Incidence: Data and Examples

52. Relative risk is a ratio of risk comparing two groups on the basis of their exposure status Used to determine if a particular exposure increases or decreases risk or probability of developing a disease Exposures could be to chemical, microbial, physical or psychosocial stressors Basic formula: Incidence in exposed group Incidence in un-exposed group Relative risk: Data and Examples Relative risk can be calculated from cohort study data Cohort studies follow groups of people defined by exposure status over time to see whether disease develops (or not) Example from Rajagopalan et al 2018 Short-term increases in exposure to PM 2.5 increase the relative risk of cardiovascular mortality by 1% to 3% Relative risk: Definition and Calculation

53. Odds ratio (or relative odds) is defined as a ratio of the odds of developing disease in exposed persons to the odds of developing disease in un-exposed persons Odds ratios are similar to relative risk Basic formula= A/B ÷ C/D Odds ratio: Definition and Calculation Exposed Developed Disease Did not develop disease Yes A B No C D

54. Odds ratios are calculated from case-control studies A case-control study starts by identifying those with and without disease absent other knowledge of the incidence of disease in the underlying population. Then exposures are assessed in both cases and controls to examine potential association with disease. Example from Lee et al. 2014 All studies in this review that assessed the association of carbon monoxide (CO) exposure and allergic diseases reported odds ratios greater than 1, indicating increased risk with exposure Attributable risk: Definition Attributable risk is a measure of how much of the disease risk is due to a certain exposure, after accounting for the background risk of disease (in unexposed people). Attributable risk is determined by subtracting the risk of disease in the unexposed group from risk in the exposed group Odds ratio: Data and Examples

55. Attributable risk: Calculation Attributable risk measures In Exposed Group In Total Population Incidence attributable to exposure [Incidence in exposed group] - [Incidence in unexposed group] [Incidence in total population] - [Incidence in unexposed group] Proportion of incidence attributable to exposure [Incidence in exposed group] - [Incidence in unexposed group] ÷ [Incidence in exposed group] [Incidence in total population] - [Incidence in unexposed group] ÷ [Incidence in total population]

56. Attributable risk data are developed from a combination of health risk research and population health statistics. Example: “Air pollution, both outdoor and household burning of solid fuels, was the fifth leading risk factor for mortality following diet, high blood pressure, tobacco and high fasting blood glucose, contributing to 4.9 million deaths worldwide, or 8.7% of global mortality in 2017.” (Boogaard et al. 2019, pg. 418) Attributable risk: Data and Examples

57. BREAK THE CYCLE THEN CONTROL THE INFECTION Chain of Infection This refers to a logical sequence of factors or links of a chain that are essential to the development of the infectious agent and propagation of disease. The six factors to consider in disease transmission Infectious agent (etiology or causative agent) Reservoir Portal of exit Mode of transmission Portal of entry Susceptible host Infectious Agents An organism that is capable of producing infection or infectious disease. On the basis of their size, etiological agents are generally classified into: Metazoa (multicellular organisms e.g. Helminths ). Protozoa (Unicellular organisms e.g. Ameobae ) Bacteria (e.g. Treponema pallidum , Mycobacterium tuberculosis) Fungus (e.g. Candida albicans ) Virus (e.g. Chickenpox, polio)

58. Reservoir of infection Any person, animal, arthropod, plant, soil or substance (or combination of these) in which an infectious agent normally lives and multiplies. on which it depends primarily for survival and where it reproduces itself in such a manner that it can be transmitted to a susceptible host . Types of Reservoir Man: There are a number of important pathogens that are specifically adapted to man, such as: measles, smallpox, typhoid, meningococcal meningitis, gonorrhea and syphilis. The cycle of transmission is from human to human Animals : Some infective agents that affect man have their reservoir in animals. The term “zoonosis” is applied to disease transmission from animals to man under natural conditions Bovine tuberculosis - cow to man ƒ Brucellosis - Cows, pigs and goats to man Non-living things: Many of the agents are living in soil and fully adapted to live freely in nature. Tetani etiologic agent of Tetanus Clostridium welchi etiologic agent of gas gangrene

59. Portal of Exit This is the site through which the agent escapes from the reservoir. Examples include: GIT : typhoid fever, bacillary dysentery, amoebic dysentery, cholera etc. Respiratory : tuberculosis, common cold, etc. ƒ Skin and mucus membranes: Syphilis Mode of transmission ( Direct) The mechanisms by which an infectious agent is transferred from one person to another or from a reservoir to a new host. Transmission may be direct or indirect. Direct Transmission- Direct Vertical : transplacental transmission of syphilis, HIV Direct horizontal Direct touching, biting, kissing, sexual intercourse, sneezing, coughing, spitting or talking; Usually limited to a distance of about one meter or less.

60. Mode of Transmission (Indirect) Indirect Transmission Vehicle-borne transmission : Indirect contact through contaminated inanimate objects: Bedding , toys, handkerchiefs, soiled clothes, cooking, eating utensils, surgical instruments. Contaminated food and water Biological products like blood, serum, plasma, IV-fluids A ny substance serving as intermediate means by which an infectious agent is transported and introduced into a susceptible host through a suitable portal of entry . The agent may or may not multiply or develop in the vehicle before it is introduced into man

61. Mode of Transmission(Indirect) Vector-borne transmission : Occurs when the infectious agent is conveyed by an arthropod (insect) to a susceptible host. Mechanical transmission : The arthropod transports the agent by soiling its feet or proboscis, in which case multiplication of the agent in the vector does not occur. (common house fly.) Biological transmission : This is when the agent multiplies in the arthropod before it is transmitted, such as the transmission of malaria by mosquito Air-borne transmission : Dissemination of microbial agent by air to a suitable portal of entry, usually the respiratory tract Dust: small infectious particles of widely varying size that may arise from soil and be re-suspended by air currents. Droplet nuclei : Small residues resulting from evaporation of fluid.They usually remain suspended in the air for long periods of time

62. Portal of Entry The site in which the infectious agent enters to the susceptible host . Mucus membrane Skin Respiratory tract   GIT Blood Susceptible Host Susceptible host (host factors): A person or animal lacking sufficient resistance to a particular pathogenic agent to prevent disease if or when exposed. Occurrence of infection and its outcome are in part determined by host factors. The term “immunity” is used to describe the ability of the host to resist infection.

63. Infection Resistance Resistance to infection is determined by non-specific and specific factors: Non-specific factors Skin and mucus membrane Mucus , tears, gastric secretion Reflex responses such as coughing and sneezing. Specific factors Genetic-hemoglobin resistant to Plasmodium Naturally acquired or artificially induced immunity. Active immunity- acquired following actual infection or immunization. Passive immunity- pre-formed antibodies given to the host

64. Types of Carrier A carrier is an infected person or animal who does not have apparent clinical disease but is a potential source of infection to others. Healthy or asymptomatic carriers : These are persons whose infection remains unapparent. For example, in poliovirus and hepatitis virus infections, there is a high carrier rate. Incubatory carriers : These are individuals or persons who excrete the pathogen during the incubation period- before the onset of symptoms examples measles , mumps, chickenpox and hepatitis. Convalescent Carriers : These are those who continue to harbor the infective agent after recovering from the illness. E.g. Diphtheria, Hepatitis B virus. Chronic Carriers : The carrier state persists for a long period of time. E.g. Typhoid fever, Hepatitis B virus infection

65. Time Course of Infectious Diseases Incubation period : It is the interval of time between infection of the host and the first appearance of symptoms and signs of the disease . Prodormal period : It is the interval between the onset of symptoms of an infectious disease and the appearance of characteristic manifestations (In a measles patient, fever and coryza occur in the first three days and Koplick spots in the buccal mucosa) Period of communicability : The period during which that particular communicable disease (infectious agent) is transmitted from the infected person to the susceptible host

66. What designs exist to identify and investigate factors in disease?

67. What designs exist to identify and investigate factors in disease? Study Designs Case report Case series Descriptive Epidemiology Descriptive RCT Before-After study Cross-sectional study Case-Crossover study Case-Control study Cohort study Analytic Ecologic study

68. Timeframe of Studies Prospective Study - looks forward, looks to the future, examines future events, follows a condition, concern or disease into the future time Study begins here

69. Timeframe of Studies Retrospective Study - “to look back”, looks back in time to study events that have already occurred time Study begins here

70. Study Design Sequence Case reports Case series Descriptive epidemiology Analytic epidemiology Clinical trials Animal study Lab study Cohort Case- control Cross- sectional Hypothesis formation Hypothesis testing

71. Descriptive Studies Case-control Studies Cohort Studies Develop hypothesis Investigate it’s relationship to outcomes Define it’s meaning with exposures Clinical trials Test link experimentally Increasing Knowledge of Disease/Exposure

72. Descriptive Studies Case Reports Detailed presentation of a single case or handful of cases Generally report a new or unique finding e.g. previous undescribed disease e.g. unexpected link between diseases e.g. unexpected new therapeutic effect e.g. adverse events

73. Case Series Experience of a group of patients with a similar diagnosis Assesses prevalent disease Cases may be identified from a single or multiple sources Generally report on new/unique condition May be only realistic design for rare disorders

74. Case Series Advantages Useful for hypothesis generation Informative for very rare disease with few established risk factors Characterizes averages for disorder Disadvantages Cannot study cause and effect relationships Cannot assess disease frequency

75. Case Report Case Series Descriptive Epidemiology Study One case of unusual findings Multiple cases of findings Population-based cases with denominator

76. Analytical Studies Study Designs - Analytic Epidemiology Experimental Studies Randomized controlled clinical trials Community trials Observational Studies Group data Ecologic Individual data Cross-sectional Cohort Case-control Case-crossover

77. Experimental Studies treatment and exposures occur in a “controlled ” environment planned research designs clinical trials are the most well known experimental design. Clinical trials use randomly assigned data. Community trials use nonrandom data Observational Studies non-experimental observational because there is no individual intervention treatment and exposures occur in a “non-controlled” environment individuals can be observed prospectively, retrospectively, or currently

78. Cross-sectional studies An “observational” design that surveys exposures and disease status at a single point in time (a cross-section of the population) time Study only exists at this point in time

79. Cross-sectional Design time Study only exists at this point in time Study population No Disease Disease factor present factor absent factor present factor absent

80. Cross-sectional Studies Often used to study conditions that are relatively frequent with long duration of expression (nonfatal, chronic conditions) It measures prevalence, not incidence of disease Example: community surveys Not suitable for studying rare or highly fatal diseases or a disease with short duration of expression

81. Cross-sectional studies Disadvantages Weakest observational design, (it measures prevalence, not incidence of disease). Prevalent cases are survivors The temporal sequence of exposure and effect may be difficult or impossible to determine Usually don’t know when disease occurred Rare events a problem. Quickly emerging diseases a problem

82. Epidemiologic Study Designs Case-Control Studies an “observational” design comparing exposures in disease cases vs. healthy controls from same population exposure data collected retrospectively most feasible design where disease outcomes are rare

83. Case-Control Studies Cases: Disease Controls: No disease

84. Case-Control Design Study population Cases (disease) Controls (no disease) factor present factor absent factor present factor absent present past time Study begins here

85. Case-Control Study Strengths Less expensive and time consuming Efficient for studying rare diseases Limitations Inappropriate when disease outcome for a specific exposure is not known at start of study Exposure measurements taken after disease occurrence Disease status can influence selection of subjects

86. Hypothesis Testing: Case-Crossover Studies Study of “triggers” within an individual ”Case" and "control" component, but information of both components will come from the same individual ”Case component" = hazard period which is the time period right before the disease or event onset ”Control component" = control period which is a specified time interval other than the hazard period

87. Epidemiologic Study Designs Cohort Studies an “observational” design comparing individuals with a known risk factor or exposure with others without the risk factor or exposure looking for a difference in the risk (incidence) of a disease over time best observational design data usually collected prospectively (some retrospective)

88. Cohort Design time Study begins here Study population free of disease Factor present Factor absent disease no disease disease no disease present future

89. Timeframe of Studies Prospective Study - looks forward, looks to the future, examines future events, follows a condition, concern or disease into the future time Study begins here

90. Prospective Cohort study Measure exposure and confounder variables Exposed Non-exposed Outcome Outcome Baseline time Study begins here

91. Timeframe of Studies Retrospective Study - “to look back”, looks back in time to study events that have already occurred time Study begins here

92. Retrospective Cohort study Measure exposure and confounder variables Exposed Non-exposed Outcome Outcome Baseline time Study begins here

93. Cohort Study Strengths Exposure status determined before disease detection Subjects selected before disease detection Can study several outcomes for each exposure Limitations Expensive and time-consuming Inefficient for rare diseases or diseases with long latency Loss to follow-up

94. Experimental Studies investigator can “control” the exposure akin to laboratory experiments except living populations are the subjects generally involves random assignment to groups clinical trials are the most well known experimental design the ultimate step in testing causal hypotheses

95. Experimental Studies In an experiment, we are interested in the consequences of some treatment on some outcome. The subjects in the study who actually receive the treatment of interest are called the treatment group . The subjects in the study who receive no treatment or a different treatment are called the comparison group .

96. Epidemiologic Study Designs Randomized Controlled Trials (RCTs) a design with subjects randomly assigned to “treatment” and “comparison” groups provides most convincing evidence of relationship between exposure and effect not possible to use RCTs to test effects of exposures that are expected to be harmful, for ethical reasons

97. Experimental Design time Study begins here (baseline point) Study population Intervention Control outcome no outcome outcome no outcome baseline future RANDOMIZATION

98. Randomized Controlled Trials Disadvantages Very expensive Not appropriate to answer certain types of questions it may be unethical, for example, to assign persons to certain treatment or comparison groups Review Questions (Developed by the Supercourse team ) Describe the link between exposure and disease Describe study design sequence Describe strengths and weaknesses of each design Epidemiologic Study Designs Randomized Controlled Trials (RCTs) the “gold standard” of research designs provides most convincing evidence of relationship between exposure and effect trials of hormone replacement therapy in menopausal women found no protection for heart disease, contradicting findings of prior observational studies

99. Surveillance for priority diseases, conditions and events in human health, animal health and environment Public Health Surveillance Ongoing, systematic collection , analysis , and interpretation of health-related data essential to the planning , implementation , and evaluation of public health practice, closely integrated with the timely dissemination of these data to those responsible for preventing and controlling disease and injury (Stephen Thacker, CDC) “The reason for collecting, analyzing, and disseminating information on a disease is to control that disease. Collection and analysis should not be allowed to consume resources if action does not follow” ( William Foege et al ) DATA FOR ACTION

100. Uses of surveillance data Utility Examples 1. Immediate detection of Epidemics Newly emerging health problems Changes in distribution of at risk populations 2. Periodic dissemination for Estimating the magnitude of a health problem, including cost Assessing control activities Determining risk factors for disease Monitoring changes in health practices 3. Stored information for Describing natural history of disease Epidemiologic and laboratory research

101. Reporting 1/4 Every level of the one health system has a role in carrying out ongoing surveillance for priority diseases , conditions and events . If a disease is identified at a local level, for example, but the information is not reported to the next level, an opportunity for timely response is lost. Reporting 2/4 Gathering data about diseases, conditions and events in a health facility, district or other administrative areas helps the one health teams to use the data for action and to: Identify emerging problems and plan appropriate responses Take action in a timely way Monitor disease trends in the area Evaluate the effectiveness of the response

102. Reporting 3/4 What is reported to each level and how often is usually guided by national policy. The policy will specify whether the data are reported immediately, weekly, monthly, or quarterly. How the information is reported depends on the capacity in your area. For example, reporting may be done by electronic methods such as email or other electronic transmission, by regular mail, or by radiophone or cell phone SMS text reporting Reporting 4/4 . The decision about what, when and where to report disease information will depend on specific disease control priorities and activities in your country or district. In addition to priority diseases that are targets of national policy, districts should also report any unusual event that has the potential to affect human health.

103. Immediately Report Information About Acute Epidemic-Prone Diseases or Events Immediate reporting means that information about a disease, condition, or event is reported to the next level as soon as an epidemic-prone disease is suspected. The information that is reported immediately is often referred to as case-based reporting . This means that specific information about each case is included in the report.

104. Diseases Requiring Immediate Reporting Acute haemorrhagic fever syndrome(Ebola, Lassa, Marburg, CCHF etc ) Acute Jaundice Syndrome Adverse effects following immunization (AEFI) Animal Bites (Dog and Snake bite Anthrax Bacterial Meningitis Chikungunya Cholera Dengue fever Diarrhoea with blood (Shigella) Human Rabies Cholera Dengue 12. Maternal deaths Monkey pox Measles Plague SARS Yellow fever Dracunculiasis 19. Plague 20. SARIs** 21. Typhoid fever 22. Yellow fever 23. Zika virus disease 24. Also: A cluster of deaths in the community (animal or human deaths) A cluster of unwell people or animals with similar symptoms

105. Disease, condition and events for IDSR weekly reporting (New List) 1. Acute haemorrhagic fever syndrome (Ebola Virus disease, Marburg, Lassa Fever, RVF, Crimean- Congo) 15. Measles 2. Acute Jaundice Syndrome 16. Monkey Pox 3. Adverse effects following immunization (AEFI) 17. Neonatal Tetanus 4a. Animal Bites (Dog) 18. Non-Neonatal tetanus 4b. Animal Bite (Snake) 19. Perinatal and Neonatal deaths 5. Anthrax 20. Plague 6. Bacterial Meningitis 21. Poliomyelitis (Acute Flaccid Paralysis) (AFP) 7. Buruli Ulcer 22. Rabies (Human) 8. Cholera 23. Yellow fever 9. Diarrhoea with blood (Shigella) 24. MDR/XDR Tuberculosis – Lab. Surveillance 10. Diarrhoea with severe dehydration less than 5 years of age 25. Severe malnutrition in children under 5 years of age 11. Dracunculiasis (Guinea Worm disease 26. Severe pneumonia less than 5 years of age 12 Dracunculiasis (Guinea worm disease) 27. Typhoid fever 13. Maternal death 28. Any public health event of concern (infectious, zoonotic, food borne, chemical, radio nuclear or due to an unknown condition) 14. Malaria 29. Unexplained cluster of illness/ death from human or animals/birds.

106. Disease, condition and events for IDSR Monthly reporting or quarterly (New List) 1. Lymphatic filariasis 10. Injuries (Road traffic Accidents) 2. Noma 11. Sickle Cell Disease (SCD) 3. Onchocerciasis 12. Soil Transmitted Helminthiasis (STH) 4. Yaws 13. STIs 5. Asthma 14. Trachoma 6. Diabetes Mellitus 15. Trypanosomiasis 7. Epilepsy 16. Tuberculosis –(quarterly) 8. HIV/AIDS (new cases) 17. Leprosy –(quarterly) 9.Hypertension Laboratory : Newly diagnosed HIV infection, TB (MDR/XDR)

107. Surveillance capacity e.g. Pandemic influenza A system that can detect, analyze and report events (including rumors and other ad hoc reports) that are a potential risk to public health Laboratory capacity to identify influenza viruses with pandemic potential, or rapid access to outside laboratory facilities with this capacity and the ability to ship samples; Ability to collect and share samples under the pandemic influenza preparedness (PIP) framework

108. Surveillance capacity e.g. Pandemic Influenza Epidemiological expertise to carry out the initial investigation of signal events (including clusters), data analysis and reporting National IHR focal point to report PHEIC to WHO Outbreak response and pandemic preparedness plans Materials and personnel for rapid containment of outbreaks of influenza with pandemic potential

109. Environmental Public Health Surveillance Surveillance on hazards, exposures, and health outcomes. Challenging due to difficulty in linking specific environmental causes to adverse health outcomes. Exposure data (e.g., air sampling) may be difficult to obtain in developing countries. Biologic markers (e.g., blood lead levels) are useful and feasible.

110. Surveillance Limitations Completeness Unreported cases Incomplete reports Consistency of reporting

111. Quality of the Data Completeness of case ascertainment Assessment of completeness, accuracy, and timeliness of reports ‘Tip of the iceberg’

112. Points to Remember Report priority diseases to the next level Know which diseases and events require immediate reporting and monthly reporting Be sure to know who to send the report to and the reporting format Involve the labs and community to foster communication and develop a clear profile for the disease and target populations