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28 Cards in this Set
- Front
- Back
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Attack Rate |
number of people at risk in whom a certain disease develops / total number of people at risk -cumulative incidence -total number includes cases and non cases -time is implicit |
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Epidemic Curve |
a histogram of the frequency of cases by time of symptom onset |
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spot map |
a detailed map identifying the location of cases in a discrete area |
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type of outbreak |
-common source -propagated -mixed -other |
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Common Source |
-point source -continuous -intermittent |
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Point Source Outbreak |
-Population is exposed briefly / simultaneously / at a single point in time -occur suddenly and after a brief peak period of time, fall off in a logarithmic fashion |
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Continuous Outbreak |
-Exposure occurs over a period of day, weeks or longer -Cases arise suddenly and continue to arise as more individuals continue to be exposed to the source -Peaks in epidemic curve may represent two or ore incubation periods -the range of exposure and incubation periods tend to flatten and widen the peaks of the epidemic cure |
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Intermittent Outbreak |
-Exposure occurs over a period of day, weeks or longer -Cases arise suddenly and continue to arise as more individuals continue to be exposed to the source -Peaks in epidemic curve may represent two or ore incubation periods -the epidemic curve often has a pattern reflecting the intermittent nature of the exposure |
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Propagated outbreaks |
person to person outbreaks there are multiple points to the epidemic curve two or more peaks as secondary cases occur from person to person spread epidemic usually wanes after a few generations |
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Determinants of propagated outbreaks |
-balance between proportion of susceptible and immune individuals in the population -immunity may be innate or acquired -effective contact between agent and suspecting host -virulence of the organism |
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Mixed outbreak |
has features of both common-source and propagated epidemics -exposure to measles at disneyland and then person to person transmission |
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Other outbreaks |
neither common source nor propagated outbreaks of zoonotic or vector borne disease may result from sufficient prevalence of infection in host species, sufficient presence of vector, sufficient human vector |
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Herd Immunity |
-the relative resistance of a group to an outbreak of a disease when a critical proportion but not all of the group is immune -helps prevent person-to-person transmission -the greater proportion of the groups that is immune the less likely -encounter between infected person and a susceptible person become more rare -# of those vaccinated depends on the reproductive number of the disease |
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Risk Difference |
(ARexposed) – (ARnon-exposed) |
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Risk Ratio |
(ARexposed) / (ARnon-exposed) |
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-develop, test and refine hypothesis |
-examine distribution of cases by time and place -look for time-place interactions -examine possible interactions among potential exposures -incorporate existing knowledge about disease -refine hypothesis and collect additional data |
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Incubation period |
the time interval from infection to apparent of first signs or symptoms -can be used to identify potential infectious agents which may have caused the epidemic |
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Median Incubation period |
50th percentile observation at the middle odd number then the median is the middle value if the observation is even, then the median is the average of the two middle values |
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Dose Response Relationship |
A gradient in the attack rate in relation to the amount of the exposure provides strong evidence that the exposure is the cause of the disease adequate dose to get a response |
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Investigation steps |
-determine existence of epidemic -case definition -identify cases and population at risk -obtain information on time, place, and person -collect specimens for lab analysis -Analyze date develop, test, and refine hypothesis -implement control measure -prepare report and disseminate finding |
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How to determine the existence of epidemic |
info from local health officers observed versus expected |
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Case Definition |
clinical features and known causes what test to confirm diagnosis start with a simple case definition and the refine as you go what happens when you change the case definition |
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Identify cases and population at risk |
identify source for finding cases collect information to provide clues to determine population at risk natural history of epidemic characteristics of the ill |
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Information of person time and place |
time of occurrence place characteristic of persons affected |
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collect specimans for lab analysis |
collect from people vectors or formats -serologic test x-rays |
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analyze data |
-calculate attak rates -create epidemic curve -create spot map |
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implement control measures |
control of current outbreak prevention of future similar outbreaks directed at source -modify environment, quarantine, treat directed at susceptible -modify behaviors to reduce risk to self |
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prepare report and disseminate findings |
document for action and medical. legal issue |
