Pertussis can affect people of all ages. In unimmunized populations, pertussis peaks in pre-school years. In immunized populations, pertussis peaks in infants (<1 year old). Incidence of pertussis is increasing in children and adolescents. Note: Recent pertussis vaccination should not preclude consideration of this diagnosis in patients with compatible illness.
The disease occurs in 3 phases after an incubation period of 7-10 days:
- Catarrhal phase (1-2 weeks)
- Paroxysmal phase (2-4 weeks)
- Convalescent phase (1-3 months)
In the paroxysmal phase, typical clinical presentations include spasmodic, repetitive coughing spells, often followed by a forced inspiratory effort producing a "whoop" sound. These bursts of coughing occur more commonly at night and are due to difficulty in expelling thick mucus. Intensity of cough is most severe during the first 1-2 weeks of the paroxysmal phase, decreasing gradually after 3 weeks. During a spasm, there may be neck vein distention, gagging, cyanosis, tongue protrusion, and bulging eyes. Paroxysms of cough can occur spontaneously or be triggered by external stimuli. They are usually followed by post-tussive vomiting and exhaustion. During this phase, infants and young children often appear very ill and distressed.
Following the paroxysmal stage, the convalescent phase ensues, and the intensity of cough continues to subside over next 1-3 months. Hence, pertussis is nicknamed "100-day cough" in China.
Fever is uncommon; if present, consider superinfection. Neurologic events like seizures or encephalopathy can occur, likely secondary to hypoxia from paroxysmal events.
Complications most often occur during the paroxysmal stage. They include apnea, pneumonia, and weight loss in young children from feeding difficulties and post-tussive vomiting. Other complications are subconjunctival hemorrhage, subdural hematoma, epistaxis, pneumothorax, abdominal and inguinal hernias, rectal prolapse, urinary incontinence, truncal and facial petechiae, rib fracture, carotid artery aneurysm, and cough syncope. Most deaths from pertussis occur in infants younger than 6 months, and the case fatality rate of pertussis among this age group is estimated to be 1%.
10% of infants develop B. pertussis pneumonia (diffuse bilateral infiltrates). Primary pertussis pneumonia is associated with markedly elevated leukocytosis (>60,000 cells/µL) and thus increased mortality in young infants. In older children and adults, pneumonia is usually due to secondary bacterial infection, commonly with encapsulated organisms like Streptococcus pneumoniae or Haemophilus influenzae.