I have answered this for you HERE.
The fact that only 22 persons became ill, and of those only 5 died, is a tribute to the rapid and effective response of the clinicians and public health workers involved.
My question: How to explain the grammar structure of "of those" in the above sentence?
It simply means that the "of those" is in reference to 22 people. Meaning, 5 died out of 22 who became ill.
Your comments are useful, hlbert03, and greatly welcomed. However, please take a look at the other posts in the thread before posting. The question has already been answered.
Can I use 'of which' instead of 'of those' in the sentence given? Is this correct?
The fact that only 22 people became ill, and of which only five died, ........