Explaining Epidemics

PUBHLTH 405
Social Epidemiology of Infectious Disease
University of Michigan School of Public Health

Jon Zelner
[email protected]
epibayes.io

Agenda

  • Pathogen project groups and logistics (5m)

  • Configuration, contamination, and predisposition. (10m)

  • How can and should we use infection history as a guide for pandemic preparedness? (15m)

  • Integrating ideas of configuration and contamination into CDC definitions and guidelines. (~30m)

  • Prep for weds workshop

Pathogen Project Groups

Group Assignments

Contamination & Configuration Assignments

  • Contamination assignment workday this Weds 9/11

  • Contamination assignment due by Sun 9/22

  • Configuration in-class workday Weds 9/25

  • Configuration assignment due by Sun 10/13

Characterizing Epidemic Causes

Today’s Theme: Transmission and its causes

How do pathogens get from one host to another?

How do we describe the mechanisms of transmission?

Not all transmission is direct

How would we characterize the causes of environmentally-mediated transmission?

Indirect transmission conditions are often a function of the larger ecosystem

Representation of the ways climate change impacts waterborne disease risks from (Semenza 2020)

Our understanding of transmission is always socially constructed

Early causal diagram explaining AIDS risk as a function of gay male promiscuity and immune ‘overload’ from STIs (Sonnabend, Witkin, and Purtilo 1984)

Explaining Epidemics

CDC Epidemic Types

What are the different modes of common-source outbreaks and epidemics outlined by the CDC?

  • Point Source

  • Continuous

  • Intermittent

A recent example of a non-infectious point-source event

What characterizes a propagated epidemic?

Transmission!

What about a mixed outbreak?

Rosenberg’s parts of an epidemic explanation

What do the mechanisms that Rosenberg identifies in ‘Explaining Epidemics’ cover?

  • Contamination 🦠

  • Configuration 🧩

  • Predisposition ❓

What are the differences between these modes of explanation?

https://pollev.com/jonzelner

Why is it important to understand the explanations that are - and have historically - been used?

Perception implies explanation. Certainly this is the case in epidemics when fear and anxiety create an imperative need for understanding and thus reassurance. (Rosenberg 1992, 293)

This is not to suggest a democracy among hypothetical etiologies; some explanations approximate the natural world a great deal better than others (and thus provide different real-world choices). But the continuity that I seek to emphasize relates to function, not specific content; and that function is the unavoidable act of explanation itself. (Rosenberg 1992, 294)

How would you summarize the critique that is made in the Mamelund piece?

  • What common fallacy about pandemics do Mamelund and Dimka identify?

  • What motivations do they identify for deeper study of the 1918 influenza pandemic in the context of COVID?

  • How might Rosenberg describe the way we ended up here?

  • Thinking back to the Krishnan piece from the beginning of the term, do they come up with a similar or different conclusion?

Multi-level socio-biological framework from Mamelund & Dimka

The myth of the equal opportunity infector comes from of an overemphasis on contamination over configuration

How could a pathogen actually be an equal opportunity infector?

  • Susceptibility is uniformly distributed across the population.

  • Host and pathogen biology are the primary important factors in determining infectiousness.

  • Protective health behaviors are equally available to everyone.

  • Social and spatial differences in exposure by race and wealth are dwarfed by these biological factors.

If this is so clearly false, why do we often fall into this kind of trap?

Continuing to revise CDC’s definitions

  • Get back into your groups from last Weds.

  • If you weren’t here, link up with an existing group.

  • Open up this document and read the instructions for Part II to get started.

  • If you have time, go back and clean up edits etc. from last session.

Next Time

Contamination Assignment Workday

References

Rosenberg, Charles E., ed. 1992. “Explaining Epidemics.” In Explaining Epidemics, 293–304. Cambridge: Cambridge University Press. https://doi.org/10.1017/CBO9780511666865.015.
Semenza, Jan C. 2020. “Cascading Risks of Waterborne Diseases from Climate Change.” Nature Immunology 21 (5): 484–87. https://doi.org/10.1038/s41590-020-0631-7.
Sonnabend, J. A., S. S. Witkin, and D. T. Purtilo. 1984. “A Multifactorial Model for the Development of AIDS in Homosexual Men.” Annals of the New York Academy of Sciences 437: 177–83. https://doi.org/10.1111/j.1749-6632.1984.tb37134.x.