SARS Outbreak Study 2

Outbreak Control

At this point in the outbreak investigation, your primary concern is to contain the spread of SARS. Looking at the very different experiences of the two Epiville hospitals, you see the importance of public health measures which were instituted at the Epiville General Hospital, where no secondary transmission occurred.

Reproductive rate (R 0 ) , is the number of secondary infections per 1 infected case. This measure is useful in determining the outbreak control measures. It is defined by the following equation:

R 0 = β * c * D


β = average probability a contact will be infected over duration of a relationship (depends on the biology and behavior of infection)

c = average rate of getting into contact (isolation and quarantine minimize this parameter because infectious persons and those who are suspected to be infected are in minimal contact with healthy individuals)

D = average duration of infectiousness (this parameter represents length of symptomatic disease; we can modify D by shortening duration of infectiousness. This could be achieved by proper treatment of cases, as well as improving the general health of the at risk population.)

8. There are a number of important policy implications derived from this formula. Which parameter of R 0 would you expect each of these to alter?

  1. Wearing masks
  2. Closing schools
  3. Public advisory on attending public gatherings (cinemas were closed in Hong Kong during the SARS epidemic)
  4. Precautionary measures at the hospitals (negative pressure wards and properly clothed personnel)
  5. Travel advisories
  6. Early identification and treatment of symptoms
Answer (a) — Paramenter of R 0 : β
Answer (b) — Paramenter of R 0 : c
Answer (c) — Paramenter of R 0 : c
Answer (d) — Paramenter of R 0 : β
Answer (e) — Paramenter of R 0 : c
Answer (f) — Paramenter of R 0 : D


The objective of this exercise is to understand how R 0 changes with varying of its parameters:
β, c, and D

Directions for this exercise:

  • This interactive map reflects the epidemic outbreak given 66 cases that occurred in Amoy Apartment Complex and 22 cases of secondary transmission in the Star Hospital.
  • Use the dropdown boxes to demonstrate the effect that changing each of the parameters has on the magnitude of the outbreak