What are the clinical presentation, diagnosis, and treatment options for a patient, particularly infants and young children, presenting with symptoms of pertussis (whooping cough)?

Whooping Cough (Pertussis): Clinical Presentation, Diagnosis, and Treatment

Clinical Presentation

Pertussis presents in three distinct phases: catarrhal (1-2 weeks), paroxysmal (4-6 weeks), and convalescent (2-6 weeks or longer), with the paroxysmal phase characterized by the hallmark triad of paroxysmal cough, post-tussive vomiting, and inspiratory whoop. 1

Catarrhal Phase (1-2 weeks)

• Nonspecific symptoms including coryza, intermittent cough, sneezing, lacrimation, and minimal or absent fever 1
• Clinically indistinguishable from minor respiratory infections 1
• Most infectious period despite least specific symptoms 1

Paroxysmal Phase (4-6 weeks)

• Paroxysmal cough: Series of rapid expiratory bursts with high sensitivity (93.2%) but low specificity (20.6%) 1
• Post-tussive vomiting: Low sensitivity but high specificity (77.7% in adults, 66.0% in children) 1, 2
• Inspiratory whoop: Low sensitivity but high specificity (79.5%) when present 1
• Paroxysms occur more frequently at night and can be precipitated by stimulation 3

Age-Specific Variations

• Infants <12 months: May present with apneic spells and minimal cough initially, appearing well between episodes despite severe disease 3, 1
• Adolescents and adults: Often milder illness with absent whoop, especially in previously vaccinated individuals 1
• Physical examination is often surprisingly unremarkable between coughing episodes 1

Convalescent Phase (2-6 weeks or longer)

• Gradual improvement with decreasing frequency of coughing bouts 1
• Nonparoxysmal cough can persist for months 1

Diagnosis

When a patient has cough lasting ≥2 weeks accompanied by paroxysms of coughing, post-tussive vomiting, and/or inspiratory whooping sound, diagnose pertussis unless another diagnosis is proven. 4

Clinical Diagnosis

• Absence of fever is important: Pertussis is unlikely if fever is present 1
• Absence of paroxysmal cough makes pertussis unlikely given its 93.2% sensitivity 1
• Confirmed diagnosis requires either positive culture or compatible clinical picture with epidemiologic linkage to a confirmed case 4

Laboratory Confirmation

Order nasopharyngeal aspirate or Dacron swab for culture and/or PCR testing when pertussis is suspected. 4

Preferred Testing Methods

• PCR testing of nasopharyngeal specimens: Preferred confirmatory test per CDC 1
• Culture: 100% specific but isolation of bacteria is the only certain way to make the diagnosis 4, 1
• Important caveat: PCR is not recommended by ACCP guidelines as there is no universally accepted, validated technique for routine clinical testing (Grade I evidence) 4

Alternative Testing

• Serology: Paired acute and convalescent sera showing fourfold increase in IgG or IgA antibodies to PT or FHA (72%-100% specific) 4, 1
• Oral fluid testing: 91%-99% specific 1

Common Pitfall

• Do not wait for laboratory confirmation to initiate treatment - antibiotics should be started when pertussis is clinically suspected to prevent transmission 1
• Leukocytosis with lymphocytosis is frequently absent and should not be relied upon for diagnosis 1

Treatment

All children and adults with confirmed or probable whooping cough should receive a macrolide antibiotic (preferably azithromycin) and be isolated for 5 days from the start of treatment. 4

Antibiotic Therapy (Grade A Evidence)

First-Line Treatment

• Macrolide antibiotics, preferably azithromycin 3, 1, 5
• Timing is critical: Early treatment within the first few weeks diminishes coughing paroxysms and prevents disease spread 4
• Treatment beyond 3 weeks after cough onset may be offered but the patient is unlikely to respond 4
• Antibiotics are effective in eliminating B. pertussis from the nasopharynx but do not alter the subsequent clinical course if started late 6

Alternative Therapy

• Trimethoprim/sulfamethoxazole for 7 days is effective in cases of macrolide allergy or intolerance 5, 6

Short-Course vs. Long-Course

• Short-term antibiotics (azithromycin 3-5 days, clarithromycin or erythromycin 7 days) are as effective as long-term (erythromycin 10-14 days) in eradicating B. pertussis but have fewer side effects 6

Supportive Care for Infants <12 Months

Infants under 12 months with suspected pertussis should be hospitalized for continuous cardiorespiratory monitoring due to high risk of severe and life-threatening complications including apneic spells, bradycardia, cyanosis, and death. 3

Monitoring Requirements

• Continuous pulse oximetry and apnea monitoring 3
• Respiratory status assessment between paroxysms 3
• Monitor for complications: pneumothorax, subconjunctival hemorrhage, subdural hematoma, seizures, secondary bacterial pneumonia, otitis media, and neurologic complications 3

Nutritional Support

• Frequent small feedings to prevent aspiration and maintain nutrition 3
• Offer smaller, more frequent feeds immediately after coughing episodes when infant is less likely to cough 3
• Consider nasogastric or intravenous hydration if vomiting causes dehydration or significant weight loss 3

Environmental Modifications

• Maintain calm, quiet environment to minimize coughing triggers 3
• Reduce environmental irritants and tobacco smoke exposure 3
• Ensure adequate humidification of inspired air 3

Sleep Management

• Expect significant sleep disturbance as paroxysms occur more frequently at night 3
• Position infant safely for sleep while facilitating secretion drainage 3

Treatments That Should NOT Be Used (Grade D Evidence)

Do not offer long-acting β-agonists, antihistamines, corticosteroids, or pertussis immunoglobulin to patients with whooping cough as there is no evidence they benefit these patients. 4

Isolation Requirements

• Isolate for 5 days from start of antibiotic treatment 4
• Patients are most infectious during catarrhal stage and first 3 weeks after cough onset 1

Prevention

All children should receive complete DTaP primary vaccination series followed by a single dose DTaP booster early in adolescence. 4

• Five doses of DTaP vaccine before 7 years of age 5
• Tdap booster between 11-18 years of age 5
• For all adults up to age 65, administer TDap vaccine according to CDC guidelines 4
• Vaccination during pregnancy (second half of every pregnancy) is critical to protection of the newborn 7, 8

Critical Pitfalls to Avoid

• Do not discharge infants <12 months prematurely - paroxysmal stage lasts 2-6 weeks and complications can occur throughout 3
• Do not assume infant's appearance between paroxysms indicates improvement - they often appear well between episodes despite severe disease 3
• Do not dismiss pertussis in vaccinated adolescents and adults - illness can be milder with absent whoop in previously vaccinated individuals 1