What are the key clinical features to consider when diagnosing pertussis in a patient presenting with a persistent cough?

Key clinical features for diagnosing pertussis in a patient with persistent cough include:

• A prolonged paroxysmal cough lasting more than two weeks, often characterized by sudden, intense coughing fits that may end with a characteristic 'whoop' sound, especially in children.
• The cough is typically non-productive and may be worse at night, with episodes sometimes followed by vomiting or post-tussive cyanosis.
• In infants, pertussis may present atypically without the classic whoop but with episodes of apnea or cyanosis, and a persistent cough.
• Close contact with a confirmed or suspected case of pertussis or belonging to a high-risk group (infants under 6 months, pregnant women) increases suspicion.
• Absence of fever or only low-grade fever during the catarrhal phase, differentiating it from other respiratory infections.
• Clinical signs of respiratory distress such as tachypnea, use of accessory muscles, or cyanosis may indicate severe disease requiring urgent assessment.
• History of incomplete or absent vaccination against pertussis supports the diagnosis.

These features should prompt consideration of pertussis, especially when the cough is persistent and paroxysmal, and in the context of epidemiological risk factors. Laboratory confirmation may be required but clinical suspicion based on these features is critical for early diagnosis and management NICE CKS Frumkin 2013.