#### Answer

$\frac{1}{1000}$

#### Work Step by Step

If the odds against event E are a to b, then the probability of the event is
given by
P(E) =$\frac{b}{a+b}$
The odds against contracting an airborne disease are: 999 to 1
P(E) = $\frac{1}{999 + 1}$ = $\frac{1}{1000}$