Pertussis

Pertussis is a highly contagious respiratory infection caused by Bordetella pertussis. Disease is particularly dangerous in young infants, who may develop apnoea, hypoxaemia, pneumonia, seizures and death without the classic whoop.

Disease typically evolves through three phases.

Catarrhal phase

• Coryza
• Mild cough
• Low grade fever

Paroxysmal phase

• Repeated bursts of coughing
• Inspiratory whoop
• Post tussive vomiting
• Cyanosis
• Exhaustion

Infants may present primarily with:

• Apnoea
• Cyanotic episodes
• Poor feeding
• Minimal cough

Convalescent phase

Cough gradually decreases but may persist for weeks.

Clinical suspicion is particularly important in prolonged paroxysmal cough.

Confirm with:

• PCR from nasopharyngeal specimen, especially early in illness

Culture is highly specific but less sensitive and slower.

Marked lymphocytosis may support the diagnosis, particularly in young infants.

Macrolide therapy reduces transmission and is most effective when given early.

Azithromycin

For infants younger than 6 months:

10 mg/kg PO once daily for 5 days

For children 6 months and older:

10 mg/kg PO on day 1, maximum 500 mg, then
5 mg/kg PO once daily on days 2 to 5, maximum 250 mg/day.

Alternative macrolides include clarithromycin or erythromycin.

Admit young infants with apnoea, cyanosis, hypoxaemia, feeding difficulty or severe paroxysms.

Provide oxygen and respiratory support as required.

Treat close contacts according to public health guidance, particularly households containing high risk infants or pregnant women.