What are the testing and cough characteristics that suggest pertussis and how is it treated?

Pertussis: Clinical Characteristics, Testing, and Treatment

Clinical Characteristics That Suggest Pertussis

Suspect pertussis when a patient presents with cough lasting ≥2 weeks accompanied by paroxysms of coughing, post-tussive vomiting, and/or an inspiratory whooping sound. 1, 2

Key Clinical Features by Phase

The disease progresses through three distinct phases that help identify pertussis:

• Catarrhal phase (1-2 weeks): Nonspecific symptoms including coryza, intermittent cough, sneezing, lacrimation, and minimal fever—clinically indistinguishable from minor respiratory infections and the most infectious period 3

• Paroxysmal phase (4-6 weeks): The hallmark features emerge:

  • Paroxysmal cough (high sensitivity 93.2%, low specificity 20.6%) 3
  • Post-tussive vomiting (low sensitivity, high specificity 77.7%) 3
  • Inspiratory whoop (low sensitivity, high specificity 79.5%) 3

• Convalescent phase (2-6 weeks or longer): Gradual improvement with decreasing coughing frequency, though nonparoxysmal cough can persist for months 3

Important Clinical Caveats

• Do not dismiss pertussis in vaccinated adolescents and adults—the illness can be milder with absent whoop in previously vaccinated individuals 3
• Infants may present atypically with apneic spells and minimal cough rather than classic whooping 3
• Physical examination is often surprisingly unremarkable between coughing episodes, with normal lung auscultation common 3
• Fever argues against pertussis—its presence should prompt consideration of alternative diagnoses 3

Diagnostic Testing Approach

When to Test

Begin testing as early as possible in the course of illness, ideally within the first 2-3 weeks of cough onset, as diagnostic sensitivity drops dramatically after this period. 2

Testing Algorithm

1. First-line test: Nasopharyngeal PCR 2

• PCR has superior sensitivity (80-100%) compared to culture (30-60%) 2
• PCR is 2-3 times more likely than culture to detect B. pertussis when classic symptoms are present 2
• Results available within 24-48 hours 2
• PCR should only be ordered when the clinical case definition is met (>2 weeks of cough with paroxysms, inspiratory "whoop," or post-tussive vomiting) 2

2. Culture (nasopharyngeal aspirate or Dacron swab) 1, 2

• 100% specific but only 30-60% sensitive in practice 2
• Isolation of bacteria is the only certain way to make the diagnosis 1
• Requires 1-2 weeks for definitive negative results 2
• Sensitivity decreases after 2+ weeks of cough, antimicrobial treatment, or previous vaccination 2
• Despite limitations, culture remains essential for antimicrobial susceptibility testing and molecular subtyping 2

3. Serology (paired acute and convalescent sera) 1

• A fourfold increase in IgG or IgA antibodies to pertussis toxin (PT) or filamentous hemagglutinin (FHA) is consistent with recent infection 1
• Results become available too late (weeks) to guide acute management 2
• Cannot differentiate between recent infection, remote infection, or vaccination response 2

Confirmed Diagnosis Criteria

A confirmed diagnosis requires one of the following 1, 2:

• Isolation of B. pertussis from nasopharyngeal culture, OR
• Clinical case with PCR confirmation, OR
• Compatible clinical picture with epidemiologic linkage to a confirmed case

Testing After Antibiotic Initiation

If antibiotics have already been started, PCR is the gold standard investigation as culture sensitivity drops dramatically after 2 days of antibiotics. 2

Treatment

Antibiotic Therapy

All patients with confirmed or probable pertussis should receive a macrolide antibiotic and be isolated for 5 days from the start of treatment. 1

Do not delay treatment while awaiting test results—initiate antibiotics when pertussis is clinically suspected. 2, 3

Macrolide Regimens (First-line)

• Erythromycin: 500 mg four times daily for adults (or 333 mg delayed-release three times daily); 40-50 mg/kg/day for children for 14 days 1

• Azithromycin (preferred for tolerability): 10 mg/kg on day 1, then 5 mg/kg/day for days 2-5 for infants and children; standard adult dosing for 5-7 days 1, 4

• Clarithromycin: 500 mg twice daily for adults; 15-20 mg/kg/day in two divided doses for children for 10-14 days 1

Alternative for Macrolide Intolerance

• Trimethoprim-sulfamethoxazole: One double-strength tablet twice daily for adults; 8 mg/kg/day TMP, 40 mg/kg/day SMX in 2 divided doses for children for 14 days (avoid in pregnant women at term, nursing mothers, and infants <2 months) 1

Treatment Timing and Efficacy

• Early treatment within the first few weeks will diminish coughing paroxysms and prevent disease spread 1
• Treatment beyond 3 weeks may be offered but the patient is unlikely to respond 1
• Antibiotics eliminate the organism from the nasopharynx but may not alter the clinical course if started late 3, 4

Therapies That Do NOT Work

Long-acting β-agonists, antihistamines, corticosteroids, and pertussis immunoglobulin should NOT be offered to patients with whooping cough because there is no evidence that they benefit these patients. 1

Isolation and Infection Control

• Isolate patients for 5 days after starting antibiotic therapy 1, 2
• If unable to take antimicrobial treatment, isolate for 21 days after cough onset 1
• Healthcare workers within 3 feet of a patient with confirmed or suspected pertussis should wear a surgical mask 1

Prophylaxis for Close Contacts

Administer a macrolide to any person who has had close contact with pertussis patients (same regimens as treatment) 1

Prevention

• All children should receive complete DTaP primary vaccination series followed by a single dose DTaP booster early in adolescence 1
• All adults up to age 65 should receive TDap vaccination according to CDC guidelines 1
• All pregnant patients should receive Tdap between 27-36 weeks' gestation with each pregnancy 4