In a 6-year-old girl presenting with a three-week dry cough and a white blood cell count of 12.4 ×10⁹/L with lymphocytosis, what is the appropriate management?

Pertussis (Whooping Cough) Management

This 6-year-old girl with 3 weeks of dry cough and lymphocytosis most likely has pertussis and should be treated with azithromycin (10 mg/kg on day 1, followed by 5 mg/kg/day for days 2-5) to reduce transmission, even though antibiotics at this stage will not significantly alter her clinical course. 1

Clinical Reasoning

Why Pertussis is the Leading Diagnosis

The combination of:

• 3-week dry cough (pertussis typically lasts 29-61 days depending on vaccination status)
• Lymphocytosis with WCC 12.4 (characteristic of pertussis, which causes marked lymphocytosis)
• Age 6 years (school-age children are common vectors)

This clinical picture strongly suggests pertussis 2. The 2017 CHEST guidelines specifically recommend testing for Bordetella pertussis when clinically suspected in children with chronic cough (>4 weeks) 2.

Critical Timing Consideration

At 3 weeks into illness, this child is in the paroxysmal phase of pertussis. While macrolide antibiotics are most effective when started in the catarrhal phase (first 1-2 weeks), treatment is still indicated at 3 weeks primarily to:

• Reduce transmission to others (especially vulnerable infants)
• Render the patient non-infectious within 5 days
• Potentially modestly reduce symptom duration 1

Specific Management Algorithm

1. Immediate Actions

Diagnostic Testing:

• PCR for Bordetella pertussis (most sensitive at this stage)
• Chest radiograph to rule out complications 2
• Consider pertussis serology if PCR unavailable

Do NOT routinely order: skin prick tests, Mantoux, bronchoscopy, or CT scan unless specific clinical features suggest alternative diagnoses 2

2. Antibiotic Treatment

First-line: Azithromycin

• Day 1: 10 mg/kg (maximum 500 mg)
• Days 2-5: 5 mg/kg once daily (maximum 250 mg/day)

Alternatives if azithromycin contraindicated:

• Clarithromycin: 15 mg/kg/day in 2 doses for 7 days
• Erythromycin: 40 mg/kg/day in 4 doses for 14 days (more side effects, poorer adherence)
• TMP-SMZ if macrolide allergy 1

Rationale: Azithromycin is preferred over erythromycin due to better tolerability, fewer side effects, shorter course (5 vs 14 days), and once-daily dosing improving adherence 1

3. Contact Management - CRITICAL

Identify and treat close contacts:

• Household members
• Classmates with prolonged exposure
• Any infants <12 months who had contact

Postexposure prophylaxis (same dosing as treatment) should be given to:

• All household contacts within 21 days of cough onset
• Any setting with infants <12 months present
• Pregnant women in third trimester 1

4. Monitoring for Complications

Watch for red flags requiring hospitalization:

• Respiratory distress or apnea
• Cyanosis during coughing paroxysms
• Post-tussive vomiting with dehydration
• Severe leukocytosis (WCC >50) - can indicate malignant pertussis with risk of pulmonary hypertension 3, 4, 5

At WCC 12.4, this patient is not in the danger zone, but serial monitoring may be warranted if symptoms worsen.

5. What This is NOT

Do not empirically treat for:

• Asthma (dry cough alone without wheeze, exercise symptoms, or documented airway hyperreactivity does not warrant asthma treatment) 2, 6
• GERD (no features described)
• Upper airway cough syndrome/rhinosinusitis (no nasal symptoms mentioned) 2

The 2017 CHEST guidelines explicitly state that empirical treatment for these conditions should NOT be used unless specific features are present 2.

Common Pitfalls to Avoid

1. Assuming "too late to treat" - While symptom benefit is limited at 3 weeks, treatment prevents transmission and is still indicated 1

2. Missing contact tracing - The primary benefit at this stage is preventing secondary cases, especially in vulnerable infants who can develop life-threatening disease 1

3. Empirical asthma treatment - Most children with isolated dry cough do NOT have asthma; this approach wastes resources and delays correct diagnosis 6, 7

4. Over-investigating - Chest X-ray is appropriate, but avoid routine allergy testing, TB testing, or advanced imaging unless clinical features warrant 2

Expected Clinical Course

• Cough will likely persist for several more weeks (total 4-8 weeks typical) despite antibiotics
• Paroxysms may continue but patient becomes non-infectious after 5 days of appropriate antibiotics
• Reassure family that prolonged cough is expected and does not indicate treatment failure 1, 6