This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Social & Preventive Medicine
Which of the following is the best parameter to predict virulence of acute infectious illness? 
Select and explain. 
A. Incidence, B. Secondary attack rate, C. Case fatality rate, D. Crude death rate
C: Case fatality rate
Answer: C: Case fatality rate 
Explanation: Case fatality rate is directly related to the killing power of the disease. It denotes the virulence of an organism. But utility of case fatality rate is limited to acute illnesses and is not of much value for chronic diseases. Ref: Park 21st edition, page 55.