Which of the following is NOT a symptom of pertussis?

Muscle rigidity is not a symptom of pertussis. Pertussis, also known as whooping cough, is primarily characterized by several distinctive symptoms that reflect irritability of the respiratory tract.

The hallmark of pertussis is the paroxysmal cough, which is characterized by intense coughing fits that can often lead to the whooping sound as the individual struggles to breathe in. Severe coughing spells are common and frequently occur in bouts, particularly in young children. In infants under one year, these severe symptoms can escalate and lead to hospitalization due to the potential for complications, such as pneumonia or dehydration.

In contrast, muscle rigidity is more often associated with other conditions, such as tetanus or certain neurological disorders, rather than pertussis. It does not play a role in the clinical presentation of whooping cough, making it the option that does not align with the typical symptoms of the illness.