A Young Couple Brings Their 3-Month Old Baby to the Emergency

A young couple brings their 3-month old baby to the emergency department where you work as a triage nurse. The parents tell you that the baby had a runny nose, low grade fever, and mild cough two days earlier, which they assumed was a cold. However, the cough has become significantly worse and they are really worried about the gasping sound the child makes when breathing in after a coughing spell. The baby's cough is so bad that she has been vomiting and is refusing to feed. You are concerned that the baby has pertussis, commonly known as whooping cough. You give the parents some information while they are waiting for a physician to examine their child.
-You explain to the parents that pertussis is a highly contagious disease, meaning that

A) it is a disease that can be easily transmitted from one host to another.
B) it is a disease that is not easily transmitted from one host to another.
C) it is a disease that is acquired by inhaling the pathogen.
D) it is a disease that is acquired via the placenta.
E) it is a disease caused by an opportunistic pathogen.