Hi, I am new

[justdoit]

Welcome to this site.

[laky]

Hi Laky,

Try this:

Pertussis is a common illness among children under 4 years old
or
Pertussis is often contracted by children under 4 years old

Okie, thanks for your correction. Most of the time I seem to get stuck with the vocabularies, esp when speaking and writing. Hope that I can learn from you more.