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
Main period of communicability of whooping cough? 
Select and explain. 
A. Incubation period, B. Paroxysmal stage, C. Catarrhal stage, D. Convalescent stage
C: Catarrhal stage
Answer: C: Catarrhal stage 
Explanation: Ans. is 'c' i.e.,Catarrhal stage Peussis, also called '100 day cough', is caused by Bordetella peussis (only 5% cases are caused by B. parapeussis).there is no cross immunity between B. peussis and B. parapeussis.Period of infectivity (communicability) extends from a week after exposuse to about 3 weeks after the onset of paroxysmal stage. Catarrhal stage is most infective. Secondary attack rate is high, i.e. 90%.