Communicating Complication Risks
from Influenza A (H1N1)
Tom´s J. Arag´n, MD, DrPH
a
o
Health Officer, City & County of San F...
Individual risk of complication vs number of complications
For simplicity, we focus on complications (e.g., death)
Types o...
Number of complications from influenza during a season
Epidemic equation
Number of complications = Pr(Complication) × NS
= ...
Components of transmission probability (p)

Infectiousness of source
Susceptibility of host
Infection control

Tom´s J. Ar...
What explains increase in number of H1N1 deaths in
2013-2014 season?
Assuming no changes in the virulence of H1N1 (i.e., c...
Upcoming SlideShare
Loading in …5
×

Communicating Complication Risks from Influenza A (H1N1)

1,064 views

Published on

0 Comments
0 Likes
Statistics
Notes
  • Be the first to comment

  • Be the first to like this

No Downloads
Views
Total views
1,064
On SlideShare
0
From Embeds
0
Number of Embeds
418
Actions
Shares
0
Downloads
11
Comments
0
Likes
0
Embeds 0
No embeds

No notes for slide

Communicating Complication Risks from Influenza A (H1N1)

  1. 1. Communicating Complication Risks from Influenza A (H1N1) Tom´s J. Arag´n, MD, DrPH a o Health Officer, City & County of San Francisco Director, Population Health Division (PHD) San Francisco Department of Public Health Adjunct Faculty, Division of Epidemiology UC Berkeley School of Public Health Email: tomas.aragon@sfdph.org February 7, 2014 Tom´s J. Arag´n, MD, DrPH (SFDPH) a o Influenza Risk Communication February 7, 2014 1/5
  2. 2. Individual risk of complication vs number of complications For simplicity, we focus on complications (e.g., death) Types of individual risks Risk of complication given infectiona Risk of complication given influenza seasonb a b driven by individual susceptibility driven by individual susceptibility and prevalence of circulating subtype It is important to distinguish the difference between the types of individual risk and the number of cases in a season. You can have low individual risks but large number of cases if there are many susceptibles. However, the large number of complications may give the perception that the individual risks are large. In the next slide, we use the epidemic equation to help understand the components that go into individual risks and number of complications. Tom´s J. Arag´n, MD, DrPH (SFDPH) a o Influenza Risk Communication February 7, 2014 2/5
  3. 3. Number of complications from influenza during a season Epidemic equation Number of complications = Pr(Complication) × NS = c × P × p × Pr(D | I) × Pr(C | D) × NS c = contact rate to potential infectious influenza cases P = prevalence of influenza in the community* p = transmission probability given contact with influenza case* I = infection (transmission) D = disease (symptomatic flu)** C = complication (e.g., death)** NS = number of susceptibles in population * drivers for transmission of novel strains (i.e., spread) ** function of host predisposition (e.g., obesity) and novel strain virulence Tom´s J. Arag´n, MD, DrPH (SFDPH) a o Influenza Risk Communication February 7, 2014 3/5
  4. 4. Components of transmission probability (p) Infectiousness of source Susceptibility of host Infection control Tom´s J. Arag´n, MD, DrPH (SFDPH) a o Influenza Risk Communication February 7, 2014 4/5
  5. 5. What explains increase in number of H1N1 deaths in 2013-2014 season? Assuming no changes in the virulence of H1N1 (i.e., chance of complication given infection), the only plausible explanation would be a combination of the following: Increase in circulating H1N1 (P , prevalence) Large susceptible population (NS ) In an influenza pandemic, not everyone becomes infected with the pandemic strain. In a non-pandemic season, the risk of infection is about 10%. This means a large proportion of the population remained susceptible (NS ) to H1N1 assuming they did not get natural H1N1 infection (a reasonable chance), or did not get vaccinated. Since 2009, H1N1 and H3N2 have been competing, and which dominates will depend on available susceptibles. Finally, even with a stable and low individual risk of complications (like H1N1), we can see many deaths if the number of sususceptibles is large. Nonetheless, this gives the perception that H1N1 may be worse (more virulent). Tom´s J. Arag´n, MD, DrPH (SFDPH) a o Influenza Risk Communication February 7, 2014 5/5

×