Epi 103: Outbreaks in

Communities

Agenda

How do we track an outbreak?

Exponential growth

Basic reproduction number

Herd Immunity

Attack Rate

Incubation Period

Outbreak investigations and surveillance

Expect: ~40 minutes of short lectures on different topics interspersed with

examples and discussions, followed by Q&A for the remainder of the time

Understanding the Spread of Disease in

Communities

“Life can only be understood backwards, but it must be lived forwards.”—

Soren Kierkegaard

What is exponential growth?

https://www.worldometers.info/coronavirus/coronavirus-cases/

Basic Reproductive Number (R0)

Expected number of secondary cases produced by a single infection in a

completely susceptible population

Example:

https://blossoms.mit.edu/legacy/FluGames/simulation01.html

Smieszek, T., Salathé, M. A low-cost method to assess the epidemiological importance of individuals in controlling infectious disease outbreaks. BMC Med 11, 35 (2013). https://doi.org/10.1186/1741-7015-11-35

Herd Immunity

Herd immunity is the resistance to an attack by a disease to which a large

proportion of the population are immune.

Example:

https://blossoms.mit.edu/legacy/FluGames/simulation05.html

Other Key Terms for Outbreak

Investigations

Endemic

Epidemic

Pandemic

Attack Rate

An attack rate is a measure of the speed of spread of a disease in the

population often used during outbreaks.

Attack rate = 𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑝𝑒𝑜𝑝𝑙𝑒 𝑎𝑡 𝑟𝑖𝑠𝑘 𝑤ℎ𝑜 𝑑𝑒𝑣𝑒𝑙𝑜𝑝 𝑎 𝑐𝑒𝑟𝑡𝑎𝑖𝑛 𝑑𝑖𝑠𝑒𝑎𝑠𝑒

𝑇𝑜𝑡𝑎𝑙 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑝𝑒𝑜𝑝𝑙𝑒 𝑎𝑡 𝑟𝑖𝑠𝑘

Incubation Period

Lauer SA, Grantz KH, Bi Q, et al. The Incubation Period of Coronavirus Disease 2019 (COVID-19) From Publicly Reported Confirmed Cases: Estimation and Application. Ann Intern Med. 2020; [Epub ahead of print 10 March 2020]. doi: https://doi.org/10.7326/M20-0504

Steps of an

Outbreak

Investigation

Establish a case definition

Enhance Surveillance

Describe occurrence of cases according to time, place, and person

Develop hypotheses about the nature of

the exposure

Conduct analytic studies, if

appropriate

Implement disease-control interventions

Communicate results of the investigation

Koepsell & Weiss, Epidemiological Methods: Studying the Occurrence of Disease

Final Word

As a final note I want to leave you with this thought:

“All models are wrong, but some are useful.”—George Box (statistician, 1919–)

We are in an unprecedented time of massive information sharing. Be

thoughtful, be patient, and be suspicious of anyone who says something is

GOING to happen or that they have certainty about some aspect of COVID-

19. Its new and we don’t know much yet.

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 kmbensley@gmail.com – I will get back to you when I can

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 kmbensley@gmail.com

Thanks for tuning in!

Next Classes

Next classes:

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