Question

For an outbreak of a waterborne disease to occur, ____ people must get sick from the water source.

Answer 1

For an outbreak of a waterborne disease to occur, a large number of people must get sick from the water source.  an outbreak needs a group of people, a large enough group of people, to get sick and at least some of them to seek some kind of medical care so that the cause could be identified. 

Answer 2

Answer:

As the happening of waterborne diseases will take pace, greater number of people will get sick.  

Explanation:

An outbreak of the ailment will be resulting into so many greater number of people to fall into with. It is important to seek away the medical care treatment to highlight the ailment as early as possible.