Epidemiology in outbreak

definition of outbreak by CDC

• epidemic limited to localised increase in the incidence of disease
• Epidemic Disease Occurrence - Level of disease

what to do when to investigate an outbreak

• Steps of an Outbreak Investigation

1. Prepare for field work
2. Establish the existence of an outbreak
3. Verify the diagnosis
4. Construct a working case definition
5. Find cases systematically and record information
6. Perform descriptive epidemiology
7. Develop hypotheses
8. Evaluate hypotheses epidemiologically
9. As necessary, reconsider, refine, and re-evaluate hypotheses
10. Compare and reconcile with laboratory and/or environmental studies
11. Implement control and prevention measures
12. Initiate or maintain surveillance
13. Communicate findings

second attack rate (SAR)

• proportion of individuals who are exposed to an infectious agent who become ill

[math]\displaystyle{ SAR=\frac{number_of_becoming_ill}{number_of_exposed} }[/math]

reproduction number

basic reproduction number

• average number of secondary cases caused by a single primary case in a fully susceptible population

effective reproduction number

• actual number of secondary cases per single primary case

time course

• incubation period
  • followed by symptomatic p.
• symptomatic p.

• latent (pre-infectious) p.
  • followed by infectious p.
• infectious p.

• serial interval
  • time from illness onset of primary case to illness onset of secondary case caused by primary case
• generation time
  • time from infection of primary case to /u>infection of secondary case caused by primary case

SIR model

• S = susceptible
• I = infected
• R = recovered
• β = transmission coefficient (S→I)
• γ = recovery rate (I→R)