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
Best tool to measure communicability of an infectious disease? 
Select and explain. 
A. Secondary attack rate, B. Generation timeSerial interval, C. Serial interval, D. Incubation period
A: Secondary attack rate
Answer: A: Secondary attack rate 
Explanation: Ans. is 'a' i.e., Secondary attack rate Secondary attack rateSAR is defined as "the number of exposed persons developing the disease within the range of incubation period, following exposure to primary case.