Pertussis Infection and Immunity

Etiology

• Causative organisms of pertussis: Bordetella pertussis and Bordetella parapertussis
• Bordetella is spread by airborne droplets and is highly contagious
• Pertussis often affects 100% of non-immune household contacts
• Immunity wanes to 50% 12 years after completing a vaccination series
• Immunocompromised persons can also contract Bordetella bronchiseptica, which typically affects animals and is commonly known as “kennel cough”

History and Physical

• Incubation period: 1 to 3 weeks
• Three distinct stages: catarrhal phase, paroxysmal phase, and convalescent phase
• Catarrhal phase: fever, fatigue, rhinorrhea, and conjunctival injection, lasts 1 to 2 weeks
• Paroxysmal phase: paroxysms of staccato cough, resolution of fever, and characteristic “whoop”
• Patients are nontoxic-appearing between paroxysms, but may exhibit cyanosis, diaphoresis, or apnea during coughing episodes
• Convalescent phase: residual cough persists for weeks to months, triggered by exposure to another upper respiratory infection or irritant
• Atypical presentations common in infants: tachypnea, apnea, cyanosis, and episodic bradycardia
• Increased intrathoracic pressure from coughing may result in petechiae, subconjunctival hemorrhage, and epistaxis

Evaluation

• Testing for pertussis: not readily available in the emergency department
• Nasopharyngeal culture and polymerase chain reaction may yield laboratory confirmation
• Cultures require specialized media, typically not positive for 3 to 7 days
• Polymerase chain reaction is more sensitive and specific than culture
• Leukocytosis with lymphocytosis may raise suspicion for pertussis
• Chest x-ray findings: nonspecific, may show peribronchial thickening, atelectasis, or infiltrates

Treatment / Management

• Treatment is largely supportive: oxygen, suctioning, hydration, and avoidance of respiratory irritants
• Parenteral nutrition may be necessary
• Hospitalization indicated for patients with superimposed pneumonia, hypoxia, central nervous system complications, or who are unable to tolerate nutrition and hydration by mouth
• Patients less than 1 year old: should be hospitalized regardless of symptoms
• Neonates: should be admitted to an intensive care setting
• Antibiotics: decrease the carriage and spread of disease, not proven effective when started in the paroxysmal phase
• First-line treatment: erythromycin (40 to 50 mg/kg per day, maximum 2 g per day, in 2 to 3 divided doses)
• Alternative treatments: azithromycin, clarithromycin, and trimethoprim-sulfamethoxazole
• Macrolides not recommended for infants less than 4 weeks old
• Strict isolation important while the patient remains infectious
• Postexposure prophylaxis with erythromycin recommended for all household contacts

Complications

• Secondary pneumonia or otitis media may occur
• Superimposed pneumonia: a major cause of mortality in infants and young children
• Fever should subside during the catarrhal phase, and its presence during the paroxysmal phase should raise suspicion for pneumonia
• Central nervous system complications: seizures, encephalopathy, and cerebral bleeding
• Rare complications: periorbital edema, pneumothorax, pneumomediastinum, subcutaneous emphysema, diaphragmatic rupture, umbilical and inguinal hernias, and rectal prolapse
• Pertussis toxin causes histamine hypersensitivity and increased insulin secretion
• Infants are particularly prone to bradycardia, hypotension, and cardiac arrest
• Development of pulmonary hypertension: a factor contributing to infantile mortality