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41 Cards in this Set
- Front
- Back
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What is the interrelationship b/w prevalence and incidence?
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Prevalence of a disease is proportional to incidence rate (I) x duration of a disease (D)
Interrelationship: P = I x D |
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What may reflect high prevalence?
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high risk
prolonged survial w/o cure |
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What may reflect low prevalence?
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Low risk
Rapid fatal disease progression Rapid cure |
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What are the characteristics of crude mortality rates?
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-numerator of the rate = number of deaths that occurred in the specified population
-Denominator is obtained from a census or estimates of the population |
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what is the equation of crude death rate?
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(Number of deaths in 12 months) X (population size at the same period)
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What is the relationship b/w numerator and denominator in crude death rate?
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-Numerator represents individuals who died
-Denominator represents individuals who were T risk of death |
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What are the 2 mortality rates that we know?
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crude mortality rate
Cause-Specific Rate |
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Age and crude death rate?
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the older a population, the larger the crude death
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What is the cause-specific rate?
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(mortality or frequency of a given disease) / 9Population size at midpoint of time period) X 1000
-Refer to a particular subgroup of the population defined |
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What are some examples of particular subgroup of the population defined in a cause-specific rate?
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race, age, sex, or specific to some single cause of death or illness
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What are th eunique features of infectious disease epidemiology?
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1-a case may also be a risk factor for a subsequent case
2-People may become immune |
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What are the science related to epidemiology of infectious disease?
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Ecology + Evolution
Epidemiology of infectious disease is an extension of ecology and evolution |
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What is fundamental to the survival for an infectious agent?
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transmission from one host to another is fundamental to the survival of the infectious agent
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What re the main mode of transmission of infectious disease?
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1-Direct transmission
2-Indirect Transmission |
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What is a direct transmission ?
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Direct Transmission = person-to-person spread of an infectious disease
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What are some examples of disease with direct transmission?
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1-Sexually Transmitted Disease
2-Influeza 3-Acute Respiratory Infections |
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What is an indirect transmission of an infectious disease?
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the spread of infection through an intermediary source
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What are the elts of indirect transmission?
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-Vehicle
-Fomites -Vectors |
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What is vehicles?
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things that indirectly transmit disease agents or provide an environment in which the agents can multiply or produce toxins
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Examples of vehicles
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food, blood, water
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What are fomites?
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inanimated objects able to harbor and transmit disease agents
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Examples of fomites?
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clothing, bed sheets, handkerchiefs, eating untensils, door knobs, key boards, laryngoscopes, syringes, surgical scalpels
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What are vectors?
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living organismssuch as insects or animals, which do not cause disease themselves, but which transmit disease from one host to another: mosquitoes, fleas, tics, deer mice
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How to measure infectious disease outbreaks?
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1- Attack Rate (AR)
2- Secondary Attack Rate (SAR) 3- Case Fatality Rate |
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Wha tis the Attack Rate (AR)?
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an incidence rate: # new cases of disease / unit population/unit time
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When is attack rate used?
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1- When the occurence of the disease among population at risk increases greatly over a short period of time after a specific exposure
2-Used to describe outbreaks of food-borne illnesses, othe rinfectious diseases, and othe acute epdemics |
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What is secondary attack rate(SAR)?
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a rate that yields an index of the spread of a disease w/in a household or similar circumscribed unit
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What does SAR measure?
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1-contagiousness
2-Useful in evaluating control measure 3-Used to evaluate the efficacy of a prophylactic agent (specific vaccine or gamma globulin) 4-Used to trace 2ry spread of a disease of unknown etiology to determine whether there is a transmissible agent |
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What the second definition of SAR?
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The number of cases of infection that occur among contacts w/in the incubation period following exposure to a primary case in relation to the total # of exposed contacts
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What does Case Fatality Rate (CFR) show?
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CFR provides an index of the lethality of a particular disease w/in a specific population
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What is the Case Fatality Rate (CFR)?
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proportion of the # of deaths from a certain disease among those that have the disease during an interval of time
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What are the disease w/ high CFR?
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rabies, untreated bubonic plague, untreated cholera
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What is the basic reproductive number, Ro?
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expected number of new infectious hosts that one infectious host will produce during her/his period of infectiousness in a large population tha is completely susceptible
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What are Ro change and its significance?
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If Ro < 1, then the disease will disappear
If Ro = 1, ENDEMY If Ro > 1----EPIDEMY |
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What are the parameters of Ro?
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Beta: transmission probability per contact
K: number of contacts per unit time D: duration of infectivity (measured in the same time unit as K) |
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What is the transmission probability in random heterosexual sex in North America?
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Beta = 0.001
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What is the transmission probability in blood transfusion with HIV + Blood?
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Beta < or = 1.0
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What is herd immunity?
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immunity of a population, group, or community against a disease because of either VACCINATION or PAST INFECTION
NOT ALL MEMBERS OF THE IMMUNE POPULATION NEEDS TO BE IMMUNIZED |
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What are the types of epidemic curve ?
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1-Point-source outbreak
2-Continuous-source outbreak Person-to-person (or propagated) outbreak |
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What is the characteristic of point-source outbreak?
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-All cases are infected at the same time
-Exple: Outbreak of Trichonosis (Trichinella spiralis) from eating improperly cooked grizzly meat -Curve---cluster of curves around a peak value |
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What is the characteristics of Continuous-source outbreak?
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continous source of contamination such as E. coli contamined water, contmainated food
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