Epidemiological Churva Flashcards
1
Q
Proportion of people suffering from disease at a given instant of time
A
Prevalence Rate:
2
Q
risk of developing disease per year
A
Incidence Rate
3
Q
Types of mortality
risk of dying from a specific disease
A
Cause-specific Mortality Rate
4
Q
risk of dying for a specific age group
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Age-Specific Mortality Rate
5
Q
Killing power of a disease
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Case Fatality Rate
6
Q
proportion of total deaths ascribed to a specific disease
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Proportionate Mortality Rate
7
Q
risk of a woman dying associated with pregnancy, delivery and puerperium
A
Maternal Mortality Rate:
8
Q
Stillbirth or fetal mortality rate:
A
risk of losing the product of conception before delivery
9
Q
risk of dying during first year of life
A
Infant Mortality Rate:
10
Q
sum of stillbirth and neonatal death rates
A
Perinatal Mortality Rate:
11
Q
Study of the distribution of disease or physiological condition in human population and of the factors that influence this distribution” (Lilienfeld, 1976)
A
EPIDEMIOLOGY
12
Q
groups of people which may be defined by geographic boundaries or characteristics or attributes (e.g. age, gender)
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Population
13
Q
occurrence of disease or condition
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Distribution
14
Q
variable responsible for the observed distribution of the condition (e.g. drinking of alcohol among adolescents – factors: self-efficacy and family function)
A
Factor
15
Q
John Graunt
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Collected and organized Bills of Mortality
• Identified broad causes of mortality: acute and “chronical diseases”
• Constructed the first known life table from collected data
DEMOGRAPHY
16
Q
James Lind (1747)
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etiology and treatment of scurvy.
17
Q
Daniel Bernoulli
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1760-Epidemiolgic analysis on smallpox inoculation
18
Q
Pierre Charles-Alexandre Louis
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One of first modern epidemiologists
Pioneered in emphasizing statistical methods in medicine
19
Q
First to use vital statistics and other demographic data for epidemiologic purposes.
Developed the concept of mortality surveillance
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William Farr
20
Q
Robert Koch. (1883)
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identified the cholera vibrio.
21
Q
William Budd
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typhoid fever
- Argued against the miasmatic origin of typhoid fever
- Inferred that typhoid fever was a “contagious and self-propagating fever”
22
Q
Edgar Sydenstricker
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Extensive epidemiologic studies identified the etiology of pellagra and made it possible to develop interventions
23
Q
role of cigarette smoking in the epidemic of lung cancer.
A
Bradford Hill
24
Q
Harold Dorn
A
Sought to use the First National Cancer Survey as basis for an epidemiologic profile of cancer.
25
• The study of the amount & distribution of disease within a population by person, place & time
Descriptive Epidemiology
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Cross-sectional or Survey Studies
• Ad-hoc Survey: Special Surveys to establish incidence and prevalence
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Analytic Epidemiology
Study of the determinants of disease or reason for relatively high or low frequency of disease in specific groups
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Types of Analytic Studies
Cohort studies in which the groups to be studied are defined in terms of whether they are not exposed to the suspected factors are followed for a period of time to determine the frequency (Incidence) of the alleged effect (Disease) among them (Exposed) and not exposed
Concurrent
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Types of Analytic Studies
Cohort studies in which both exposure and the effect have occurred prior to the tie of investigation
Non-concurrent
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affects utilization of medical care services for a variety of reasons:
o Limited financial reasons
o Restricted access to medical care
o Tend to underutilize available preventive service
Poverty
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OCCUPATION HAZARD
Pulmonary fibrosis
silica
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OCCUPATION HAZARD
Mesothelioma, lung CA, GIT CA
asbestos exposure
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aniline dyes
Bladder CA
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chromate worker
Lung cancer
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Blood type: A - risk of
gastric CA
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O - more likely to have
duodenal ulcer
37
Three major kinds of change with time:
1. Secular trends
2. Cyclic change
3. Clustering in time
38
SECULAR TRENDS
Long term variations over a period of time, years or decades
• Ex. Cancers: lung cancer, breast cancer
• *Death closely parallel incidence rates only if the disease is fatal and if death happens nearly after diagnosis
39
CYCLIC CHANGE
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Recurrent alterations in the frequency of diseases cycles maybe annual / seasonal or may have some other periodicity
Examples:
o Measles
o Influenza A epidemic: every 2-3 yrs.
o Influenza B: every 4-6 yrs.
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40
CLUSTERING IN TIME
Epidemic: reported number of cases exceeds expected or unused number for that period
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Occurrence of more cases of disease than expected in a given area among a specific group of people over a particular period of time or two or more linked cases of the same illness
Outbreak
42
An assertion or proposition about the relationship between 2 or more variables, adopted to explain facts and to guide in the investigation of others; supposition arrived at from observation or reflection that leads to refutable predictions
Hypo thesis
43
STUDY DESIGNS
Descriptive Studies
1. Case-Report
2. Case-Series
3. Cross-Sectional
4. Ecologic Studies
44
STUDY DESIGNS :
Analytic Studies
1. Observational – Cohort, Case-Control, Cross-Sectional
| 2. Experimental – Clinical Trials, Community Trials
45
describe only those with the disease
Case-Report and Case-Series
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Ecologic Studies –
data being used are secondary on population aggregates
47
investigator simply observes the natural course of events, noting who is exposed and (who is not exposed) and who has not developed the outcome of interest
Observational Studies
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the members of the population at risk are classified in terms whether they had been exposed or unexposed to the factor of interest and followed up to determine who will develop the disease/condition being investigated
FOLLOWED UP
Cohort Studies
49
identifies a group of subjects who already have the disease/condition and a comparison group who do not have the disease/condition. Information on past exposure are then obtained and compared between the cases and controls
COMPARISON
Case-Control Studies –
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measurements of cause and effect related to the same point in the study members’ lives; limited to studies of causes that are long standing characteristics of the individual
CAUSE AND EFFECT
Cross-Sectional Studies
51
the investigator assigns the study subjects to the exposure status usually in a random manner
Experimental Studies
Notes
2. 1. Clinical Trials – individual subjects
2. 2. Community Trials – among population groups
52
✓ Health gap measure that extends the concept of potential years of life lost due to premature death (PYLL) to include equivalent years of “healthy” life lost by virtue of being in states of poor health or disability
✓ Calculated as the sum of the years of life lost due to premature mortality (YLL) in the population and the years lost due to disability (YLD)
DALY (Disability Adjusted Life Year)
53
Removal of agent from environmental or minimizing the amount of agent present
▪ Protection of the susceptible host from exposure
PRIMARY PREVENTION
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Screening tests
SECONDARY PREVENTION
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~Lifestyle modification (and rehab)
TERTIARY PREVENTION
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• The ability of an agent to invade and multiply (produce infection) in a host
INFECTIVITY
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Minimum number of particles or agents required to establish infection in 50% of a group of hosts of the same species
ID50
58
Ability to produce clinically apparent illness in an infected population
= # of infected persons with disease
—————————————————-
Total number of infected persons
PATHOGENICITY
> Factors that may affect pathogenicity:
✓ Host and environmental factors
✓ Dose, route of entrance of infection, source of infection
59
The extent to which severe disease is produced in a population with clinically manifest disease
Proportion of clinical cases resulting in severe clinical manifestations
VIRULENCE
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Determined How much of the afflicted die from the disease
CASE FATALITY RATE
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# Of deaths from a specified cause
# Of cases of the same disease X 100
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-Capacity of an agent to produce a toxin or poison
| • Disease results from the toxin produced by the agent rather than from the agent itself
TOXIGENICITY
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• Infection’s ability to produce specific immunity in the host (e.g. measles)
IMMUNOGENICITY
May be humoral immunity, cellular immunity or both
• Affected by host factors: age, nutrition, dose, and virulence
• May produce local immunity only—agents that replicate in local areas: rhinoviruses, gonococci
• Agent’s differ in intrinsic ability to induce an effective, lasting immune response
63
A living organism or inanimate matter in which an infectious agent normally lives and multiplies.
RESERVOIR
Notes:
Reservoir is an essential component of the cycle by which an infectious agent maintains and perpetuates itself
• The specific reservoir for an agent is thus intimately related to the life cycle of that agents
64
Zoonosis
infectious diseases that have vertebrate animal reservoirs; they are potentially transmissible to humans under natural conditions
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any person or animal that harbors a particular infectious agent without discernible clinical disease and serves as a potential source of infection
Carrier
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infection present on surface of body—organism propagating at a rate sufficient to maintain its numbers without producing identifiable eveidence of any reaction in host
Colonization
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organism not only multiplying but also causes a measurable reaction that is however not clinically detectable
Inapparent or subclinical infection
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organism causes clinically detectable reaction
Symptomatic infection
69
Considered direct transmission because these are heavy so they do not tend to travel more than 6 feet from the infected person
- A susceptible person who is not near an infected person will not become infected
- droplets spread
| - The spread of disease by respiratory droplets usually requires extended contact
70
Period between receipt of infection by the host and maximal communicability of that host
• Roughly equivalent to incubation period
Generation Time
71
Immunity of a group or community
| • Resistance of a group to invasion because of the high proportion of immunized members of the group
Herd immunity
72
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SAR= # new cases in a group-initial cases
————————————————————-
# Of susceptible persons in group-initial cases
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Secondary attack rates
73
Latency Period ?
Incubation Period?
the time between infection agent and onset of infectiousness
the time between infection and onset of symptoms
74
*Refers to Minimum proportion (p) of population that needs to be immunized in order to obtain herd immunity
• Important concept for immunization programs and eradiation of an infectious disease
HERD IMMUNITY THRESHOLD
75
Number of current cases per population at risk
- Old: persistent active disease contracted previously
- New: onset of active disease
DISEASE PREVALENCE RATE
76
Prevalence at a specific point in time?
Prevalence over a given time interval?
Point prevalence
Period prevalence
- - Prevalence over a given time interval
• Usage:
➢ Measure amount of illness in the community
➢ Determine health care needs of the community
77
Number of new disease cases per population at risk
- High incidence implies high disease occurrence
- Low incidence implies low disease occurrence
• Measured over a given time interval
DISEASE INCIDENCE RATE
Usage:
➢ Determine probability of developing a specific disease
➢ Used to detect etiologic factors
78
Estimates the probability of the population being ill at the period of time being studied
Useful in the study of the burden of chronic diseases and implication for health services
PREVALENCE
79
Expresses the risk of becoming ill
The main measure of acute diseases or conditions; but also used for chronic diseases
Most useful for studies of causation
INCIDENCE
80
➢ Refers to the proportion of the population who developed the disease in a given interval of time
➢ For investigating etiologic factors
➢ A measure of the risk of developing the disease in the population at risk of the disease
Incidence Measures
81
Can be computed if all the members of the population are followed up for the same period of time
Cumulative Incidence
82
➢ Numerator – still the number of new cases over the specified period of time
➢ Denominator – the accumulated person-time observation or follow-up time
Incidence Rate or Incidence Density
83
➢ Measures the impact of mortality in a population
➢ Tells how fast deaths are occurring in a specific population
➢ Used to compare mortality in different populations or groups of individuals
Crude Death Rate
84
➢ Special type of specific death rate
➢ Numerator – includes those who die of a certain disease
➢ Denominator – includes the number of cases of the said disease
Case Fatality Rate
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# of deaths from specific cause
= —————————————————
# of cases of same specific cause
```
85
➢ The proportion of all deaths that is attributed to this cause
➢ Measures the relative contribution of a specific cause to the deaths in a population
➢ Used for comparing the importance of causes of death within a population
Proportionate Mortality Rate
PMR = # of death of specific cause
———————————————
# of cases of same specific cause
86
➢ Single (summary) measures that are computed for the population
➢ Obtained by dividing the number of cases (diseased individuals or deaths) by the size of the population form where these cases come from in a specified period of time
Crude Rates
87
➢ Measures that are derived for subgroups of the population
➢ More suitable for comparisons of two different populations
➢ Computed in the same manner as crude rates except that the items counted in the numerator and denominator are limited to those who meet the criteria for membership in the subgroup
➢ Ex. Mortality rate among children 1-4 years old
Specific Rates
88
➢ Measures how fast individuals in a population are dying from a specific cause
Cause specific death rate
Death from specific cause
——————————————
Total population
89
➢ Used for comparing populations that have different distributions
➢ Ex: death rate of males
Death Rate for Specific Subgroup
90
• Single summary measures that have been adjusted for the purpose of removing the effects of differences in the populations (e.g. age differences) when comparing these populations
Adjusted Rates
91
Methods of Adjusting Rates
1. Direct Standardization
➢ Uses the distribution (according to the variable of adjustment) of the standard population and computed an adjusted (or standardized) rate
➢ Used for adjusted comparisons
➢ Derived by dividing the total expected deaths by the total population of the standard
2. Indirect Standardization
➢ Makes use of standard population also
➢ If age is the variable for adjustment, the age-specific rates in the standard population are employed (these rates are then multiplied to the age-specific population sizes of the population under study to arrive at the expected number of cases in this population
Observed # of cases
SMR = ————————————-
Expected # of cases
