Central nervous system infections Central nervous system infections.
Epidemiology 101: Understanding Infections in...
Transcript of Epidemiology 101: Understanding Infections in...
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Epidemiology 101: Understanding Infections in Communities
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“We owe all the great advances in knowledge to those who endeavor to find out how much there is of anything.”
- James Maxwell (physicist)
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Agenda 1. How do we define disease?
2. How to we measure disease occurrence?
Prevalence Incidence
3. Methodological issues
→ Expect: 20-30 minutes of a short lecture, 10-15 minutes of practice, rest of time: discussion/Q&A
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“If you wish to converse with me, define your terms.”
- Francois Voltaire
Case Definition
Clinical Diagnosis
Population
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Testing Accuracy • Case definition relies on
confirmed laboratory cases
• How do we measure the accuracy of testing?
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Measures of Disease Frequency
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What is the Prevalence of a disease? Count of prevalent cases = number of persons in the population who have a disease
Prevalence = Defined as the number of affected persons present in the population at a specific time divided by the number of persons in the population at that time
At a specific time,
Prevalence = # 𝑜𝑓 𝑐𝑎𝑠𝑒𝑠 𝑜𝑓 𝑎 𝑑𝑖𝑠𝑒𝑎𝑠𝑒 𝑝𝑟𝑒𝑠𝑒𝑛𝑡 𝑖𝑛 𝑡ℎ𝑒 𝑝𝑜𝑝𝑢𝑙𝑎𝑡𝑖𝑜𝑛
# 𝑜𝑓 𝑝𝑒𝑜𝑝𝑙𝑒 𝑖𝑛 𝑡ℎ𝑒 𝑝𝑜𝑝𝑢𝑙𝑎𝑡𝑖𝑜𝑛
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What is Incidence of a disease? Incidence is the number of new cases of a disease that occur during a specified period of time in a population at risk.
Count of Incident Cases = Number of new cases during a specific time period
Incidence Rate = 𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑖𝑛𝑐𝑖𝑑𝑒𝑛𝑡 𝑐𝑎𝑠𝑒𝑠
𝐴𝑚𝑜𝑢𝑛𝑡 𝑜𝑓 𝑎𝑡−𝑟𝑖𝑠𝑘 𝑒𝑥𝑝𝑜𝑠𝑢𝑟𝑒→ Denominator is person-time
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https://www.cdc.gov/csels/dsepd/ss1978/lesson1/section9.html
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Methodological Challenges • Numerator issues
• Denominator issues
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Examples
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Example from WA State DOH
Which is the incident case count?
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Example from WA State DOH
Which is the prevalent case count?
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How do we interpret this?
What does
this number
represent?
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What is the sensitivity and specificity of the following test?
Results
of test
Disease No
Disease
Total
Positive 80 100 180
Negative 20 800 820
Total 100 900 1,000
Sensitivity = 80
100= 80%
Specificity = 800
900= 89%
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Questions and answers• What questions do YOU have?
• Please feel free to ask questions by:
Asking them now
Posting them in the chat window
Emailing them to [email protected] – I will get back to you when I can
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Evaluation• Link to anonymous four question survey:
https://www.surveymonkey.com/r/6T5DMFK
• This is an ongoing class that I want to develop and make better. Your feedback helps!
• If you don’t want to click the link please feel free to leave feedback in the chat window or by emailing me at [email protected]
• Thanks for tuning in!
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Next Classes• Next classes:
Epi 102: Tuesday 9am PST [noon EST, 6pm GMT+2 (Cape Town)]
Epi 103: Wednesday 9am PST [noon EST, 6pm GMT+2 (Cape Town)]
Epi 101: Friday 2pm PST [5pm EST, 11pm GMT+2 (Cape Town)]
Epi 102: Saturday 2pm PST [5pm EST, 11pm GMT+2 (Cape Town)]
Epi 103: Sunday Friday 2pm PST [5pm EST, 11pm GMT+2 (Cape Town)]
• Additional resources for more reading & learning can be found at: http://karabensley.org/epidemiology-for-our-new-reality