How is pertussis (whooping cough) diagnosed and managed, including appropriate laboratory testing, antibiotic treatment, prophylaxis for contacts, and vaccination recommendations?

Whooping Cough (Pertussis): Diagnosis and Treatment

Clinical Diagnosis

Diagnose pertussis when a patient has cough lasting ≥2 weeks accompanied by paroxysms of coughing, post-tussive vomiting, and/or an inspiratory whooping sound, unless another diagnosis is proven. 1, 2

Key Clinical Features by Stage

• The catarrhal stage (1-2 weeks) presents with nonspecific symptoms including nasal congestion, runny nose, mild sore throat, mild dry cough, and minimal or no fever—indistinguishable from minor respiratory infections 1, 2
• The paroxysmal stage (4-6 weeks) is characterized by severe coughing paroxysms, often followed by an inspiratory "whoop" and post-tussive vomiting 1, 2
• The convalescent stage (2-6 weeks or longer) shows gradual improvement with decreasing frequency of coughing bouts, though nonparoxysmal cough can persist for months 1, 2
• Infants may present atypically with apneic spells and minimal cough rather than classic whooping 1, 2

Diagnostic Clinical Features

In adults, the presence of whooping or post-tussive vomiting strongly suggests pertussis (specificity 79.5% and 77.7% respectively), while absence of paroxysmal cough or presence of fever makes pertussis unlikely. 3

• Paroxysmal cough has high sensitivity (93.2%) but low specificity (20.6%) in adults—its absence effectively rules out pertussis 3
• Post-tussive vomiting has low sensitivity (32.5%) but high specificity (77.7%) in adults—its presence strongly suggests pertussis 3
• Inspiratory whoop has low sensitivity (29.8%) but high specificity (79.5%) in adults 3
• In children, post-tussive vomiting has moderate sensitivity (60.0%) and specificity (66.0%), making it less diagnostically useful than in adults 3
• Vaccinated adolescents and adults often have milder illness with absent whoop, so do not dismiss pertussis based on vaccination history 1, 4

Laboratory Confirmation

Order nasopharyngeal PCR testing as the primary diagnostic test when clinical criteria are met, as it has superior sensitivity (80-100%) compared to culture (30-60%) and provides results within 24-48 hours. 5

Diagnostic Testing Algorithm

• Collect specimens using a Dacron or rayon nasopharyngeal swab from the posterior nasopharynx (not anterior nares), or use nasopharyngeal aspirate for highest yield 5
• PCR is 2-3 times more likely than culture to detect B. pertussis when classic symptoms are present and maintains sensitivity even after antibiotic initiation 5
• Culture remains 100% specific and is essential for antimicrobial susceptibility testing and molecular subtyping, but requires 1-2 weeks for results 1, 5
• Culture sensitivity drops dramatically after 2 weeks of cough (only 1-3% after 3 weeks), after antimicrobial treatment, or in previously vaccinated individuals 5
• A confirmed diagnosis requires either positive culture, PCR confirmation with compatible clinical picture, or clinical case with epidemiologic linkage to a confirmed case 1, 2

Serology

• Paired acute and convalescent sera showing a fourfold increase in IgG or IgA antibodies to pertussis toxin (PT) or filamentous hemagglutinin (FHA) can provide presumptive diagnosis 1
• Single-sample serology is not endorsed by the CDC for routine diagnostic use because it cannot differentiate between recent infection, remote infection, or vaccination response 5
• Serology results become available too late (weeks) to guide acute management 5

Critical Timing Considerations

• Begin testing as early as possible in the illness course, ideally within the first 2 weeks of cough 5
• Do not delay treatment while awaiting test results—start antibiotics immediately when pertussis is clinically suspected 5, 2

Treatment

All children and adults with confirmed or probable whooping cough should receive a macrolide antibiotic and be isolated for 5 days from the start of treatment. 1, 2

Antibiotic Regimens

• Azithromycin is the preferred first-line antibiotic for both treatment and prophylaxis 6
  • Adults: 500 mg on day 1, then 250 mg daily for 4 days (total 5 days) 1
  • Children: 10 mg/kg on day 1, then 5 mg/kg daily for 4 days 1
• Alternative macrolides include:
  • Erythromycin: 1 g/day for adults or 40-50 mg/kg/day for children for 14 days 1, 4
  • Clarithromycin: 500 mg twice daily for adults or 15-20 mg/kg/day in two divided doses for children for 10-14 days 1, 4
• For macrolide allergy or intolerance: Trimethoprim-sulfamethoxazole 320 mg/1600 mg per day for adults or 8 mg/40 mg/kg/day for children for 14 days 1, 4

Treatment Efficacy and Timing

• Early treatment within the first 2-3 weeks diminishes coughing paroxysms and prevents disease spread 1, 5
• Treatment beyond 3 weeks after cough onset may be offered but the patient is unlikely to respond clinically 1
• Antibiotics eradicate B. pertussis from the nasopharynx but do not alter the subsequent clinical course if started late 7, 8
• Shorter antibiotic courses (azithromycin 3-5 days, clarithromycin or erythromycin 7 days) are as effective as longer courses (erythromycin 10-14 days) in eradicating bacteria but have fewer side effects 7

Isolation Requirements

• Isolate patients for 5 days from the start of antibiotic treatment 1, 5, 2
• Patients are most infectious during the catarrhal stage and first 3 weeks after cough onset 1, 2

Ineffective Treatments

Do not offer long-acting β-agonists, antihistamines, corticosteroids, or pertussis immunoglobulin to patients with whooping cough, as there is no evidence of benefit. 1

Prophylaxis for Contacts

All household and other close contacts of persons with pertussis should receive antibiotic prophylaxis for 14 days (or 5-7 days for azithromycin), regardless of age and vaccination status. 4

Prophylaxis Regimens

• Use the same antibiotic regimens as for treatment (azithromycin preferred) 4, 6
• Prophylaxis is most effective when initiated promptly after exposure 4
• High-risk contacts requiring prophylaxis include infants, immunocompromised individuals, pregnant patients in third trimester, and those in close contact with high-risk individuals 6
• Healthcare workers exposed to pertussis who remain asymptomatic can continue patient care while receiving chemoprophylaxis 4

Vaccination for Exposed Contacts

• Close contacts <7 years of age who have not completed the four-dose primary DTaP series should complete it with minimal intervals 4
• Those who completed primary series but have not received pertussis vaccine within 3 years of exposure should receive a booster dose 4

Vaccination Recommendations

All children should receive the complete DTaP primary vaccination series (5 doses at ages 2,4,6,15-18 months, and 4-6 years), followed by a single Tdap booster between 11-18 years of age. 1

Adolescent and Adult Vaccination

• All adolescents aged 11-18 years should receive a single dose of Tdap 1, 9
• All adults aged 19-64 years should receive a single dose of Tdap if not previously administered 1, 9
• All pregnant patients should receive Tdap between 27-36 weeks' gestation with each pregnancy to convey immunity to the newborn 6
• Tdap may replace any dose of tetanus-diphtheria (Td) vaccine 6

Important Vaccination Considerations

• Neither vaccination nor natural disease confers complete or lifelong immunity—immunity wanes 5-10 years after the last pertussis vaccine dose 1, 4
• Vaccinated individuals can still contract and transmit pertussis, which is why cocooning (vaccinating only close contacts) is no longer recommended 6
• A history of seizure or hypotonic-hyporesponsive episodes after prior pertussis vaccination is no longer a contraindication to immunization 6
• Vaccination coverage must remain high (>90%) to prevent disease transmission, as the secondary attack rate exceeds 80% among susceptible persons 1