This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Epidemiology, Subject name: Social & Preventive Medicine
Communicability of disease is assessed by? 
Select and explain. 
A. Secondary attack rate, B. Generation time, C. Serial interval, D. Incubation period
A: Secondary attack rate
Answer: A: Secondary attack rate 
Explanation: Secondary attack is defined as the number of exposed persons developing the disease within the range of incubation period following exposure to primary case. It is useful in detecting whether a disease of unknown etiology is communicable or not and in evaluating the effectiveness of control measures such as isolation and immunization. Ref: 25th edition, Park's Textbook of Preventive and Social Medicine, Page no. 108