SIR and the spread of disease (11/11/2008)

1. Main Points

In todays reading I learned how to apply differential equations to predict epidemic outbreaks just like the CDC. The model used for an epidemic is the S-I-R model, where S is the number susceptible, I the number of infected and R the number of recovered.

dS/dt =-(Rate susceptible get sick)= -aSI

dI/dt=(Rate susceptible get sick)-(Rate of infected get removed=aSI-bI

The constant a measures how infectious the disease is, meaning how quickly it is transmitted from the infected to the susceptible.

a=-(dS/dt)/SI

The constant b represents the rate at which infected people are removed from the infected population.

Threshold population = b/a

If the initial number of susceptible is above b/a, then there is an epidemic, if the initial number of susceptible is below b/a, then there is no epidemic.


2. Challenging about the material

Looking at an epidemic in terms of a phase plane was a little confusing I thought, maybe we can go over this example in class?

3. Intriguing

This was one of the more interesting readings for me yet in this book. I am currently taking medical anthropology where we are talking a lot of epidemic outbreaks and containment of such. Therefore I found it very interesting how to interpret epidemics mathematically!