Bordetella pertussis respiratory infection with paroxysmal cough and inspiratory whoop.
Also known as: pertussis, whooping cough, Bordetella pertussis, 100-day cough
Overview
Highly contagious respiratory infection caused by the gram-negative coccobacillus Bordetella pertussis, characterized by prolonged paroxysmal cough, inspiratory whoop, and post-tussive emesis. Severe and potentially fatal in young infants.
Epidemiology
Endemic worldwide with cyclic outbreaks every 2-5 years. US incidence has risen since the 1990s despite vaccination, partly from waning acellular vaccine immunity. Highest morbidity and mortality in infants <6 months who are too young to be fully vaccinated.
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Question 1PulmonaryMedium
A 9-year-old has paroxysmal coughing spells followed by an inspiratory whoop and post-tussive emesis. Which of the following is the most appropriate treatment?
AOseltamivir for the patient and contacts
BAzithromycin for the patient and contacts
CDaily inhaled fluticasone for the patient
DHigh-dose oral amoxicillin for the patient
Reveal answer & full explanation
Correct answer: B — Azithromycin for the patient and contacts
AOseltamivir for the patient and contacts
BAzithromycin for the patient and contacts✓
CDaily inhaled fluticasone for the patient
DHigh-dose oral amoxicillin for the patient
Why Azithromycin for the patient and contacts is correct
Paroxysmal cough with inspiratory whoop and post-tussive emesis is classic pertussis (Bordetella pertussis).
A macrolide such as azithromycin is first-line; it shortens infectivity, and household and close contacts need the same agent as postexposure prophylaxis.
Treating early in the catarrhal/paroxysmal phase limits transmission even though it does not reverse established cough.
Why the others are wrong
Oseltamivir for the patient and contacts — A neuraminidase inhibitor targets influenza and has no activity against Bordetella; this is the respiratory-virus buzzword trap.
High-dose oral amoxicillin for the patient — Amoxicillin does not reliably eradicate pertussis or cover contacts the way a macrolide does; this is the antibiotic-familiarity trap.
Daily inhaled fluticasone for the patient — An inhaled steroid does not eradicate the organism or curb spread and has no proven benefit in pertussis cough; this is the symptom-control trap.
Question 2PulmonaryMedium
A 4-year-old boy is brought to the clinic for a cough that began 3 weeks ago. It started as a runny nose and mild cough, but over the past 2 weeks he has had sudden fits of rapid coughing that end with a high-pitched gasp on inhalation, and he often vomits afterward. His face turns red during the spells, but between episodes he appears well and is playful. He has been afebrile throughout. His immunizations are not up to date because the family missed several visits. Lungs are clear to auscultation, and a CBC shows a white blood cell count of 24,000/μL with marked lymphocyte predominance. Which of the following is the most likely diagnosis?
AAsthma exacerbation in a child
BRespiratory syncytial virus (RSV)
CBordetella pertussis infection
DMycoplasma pneumoniae infection
Reveal answer & full explanation
Correct answer: C — Bordetella pertussis infection
AAsthma exacerbation in a child
BRespiratory syncytial virus (RSV)
CBordetella pertussis infection✓
DMycoplasma pneumoniae infection
Why Bordetella pertussis infection is correct
The classic triad of paroxysmal coughing fits, an inspiratory whoop (the high-pitched gasp), and post-tussive emesis lasting more than 2 weeks in a child is the hallmark of Bordetella pertussis infection.
Supporting features here are a catarrhal (URI) prodrome that progressed to paroxysms, an afebrile and well-appearing child between fits, incomplete vaccination, and marked lymphocytosis (WBC greater than 20,000 with lymphocyte predominance), a CBC finding classic for pertussis.
This meets the CDC clinical case definition (cough at least 2 weeks with paroxysms, whoop, OR post-tussive emesis); confirm with nasopharyngeal PCR and treat with a macrolide such as azithromycin to reduce transmission.
Why the others are wrong
Respiratory syncytial virus (RSV): causes bronchiolitis in infants under 2 years with wheeze, tachypnea, and hypoxia, not paroxysmal cough with whoop and post-tussive emesis in a well-appearing 4-year-old.
Mycoplasma pneumoniae infection: typically affects adolescents and young adults with a persistent cough, headache, and low-grade fever; it lacks the classic whoop, post-tussive emesis, and marked lymphocytosis of pertussis.
Asthma exacerbation in a child: produces reversible wheeze with atopy that responds to bronchodilators; it does not cause a catarrhal prodrome, an inspiratory whoop, or the marked lymphocytosis seen here.
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Infants <6 months (especially <2 months — too young for vaccination)
Inadequate or waning vaccination (acellular DTaP immunity wanes 5-10 years)
Pregnant women in third trimester (and infants of unvaccinated mothers)
Close contact with infected person (household transmission very efficient)
Healthcare workers, daycare workers
Adolescents and adults with waning immunity — often the source for infant cases
Pathophysiology
Bordetella pertussis attaches to ciliated respiratory epithelium via filamentous hemagglutinin and pertactin. Toxins (pertussis toxin, tracheal cytotoxin, adenylate cyclase toxin) impair ciliary function, kill respiratory cells, and produce systemic effects (lymphocytosis). Three classic phases: catarrhal, paroxysmal, convalescent.
Clinical presentation
Symptoms
Catarrhal phase (1-2 weeks): mild URI symptoms — rhinorrhea, low-grade fever, mild cough; most contagious period
Paroxysmal phase (2-8 weeks): sudden severe coughing fits ending with inspiratory whoop and post-tussive emesis; cyanosis with paroxysm; afebrile between fits
Convalescent phase (weeks to months): gradual reduction in frequency and severity
Adolescents/adults often have ATYPICAL presentation: prolonged cough (≥2 weeks) without classic whoop
Infants <6 months: may present with apnea WITHOUT classic cough — 'whoop' less common; high risk of death
Signs / physical exam
Between paroxysms: often appears well
During paroxysm: facial plethora, cyanosis, subconjunctival hemorrhage, lacrimation, post-tussive emesis
Inspiratory whoop (classic in children; uncommon in adults and young infants)
Generally afebrile (high fever suggests alternative diagnosis or complication)
Classic findings
Paroxysmal coughing fits with inspiratory whoop and post-tussive emesis lasting >2 weeks in a child or adolescent. Apnea (not cough) in young infant.
Differential diagnosis
Bronchiolitis (RSV) — Infant with wheeze, tachypnea, hypoxia; less paroxysmal cough; RSV PCR positive
Acute viral bronchitis — Self-limited, no paroxysmal pattern, lacks whoop and post-tussive emesis
Asthma — Reversible wheeze, atopy, responds to bronchodilators
Postnasal drip / upper airway cough syndrome — Chronic cough with allergic rhinitis features; responds to antihistamines/intranasal steroids
Diagnostic workup
Diagnostic criteria
CDC clinical case definition: cough ≥2 weeks with paroxysms, inspiratory whoop, OR post-tussive emesis without other apparent cause. Laboratory confirmation: positive culture, PCR, or seroconversion.
Labs
Nasopharyngeal swab/aspirate for B. pertussis PCR (highest sensitivity in first 3-4 weeks of cough)
Bacterial culture on Bordet-Gengou or Regan-Lowe medium (specific but slow and lower sensitivity; useful for surveillance and antimicrobial susceptibility)
Serology (anti-pertussis toxin IgG) — useful later in illness (>2-4 weeks); positive in vaccinated patients may be confounding
CBC — marked LYMPHOCYTOSIS classic (especially infants and unvaccinated children); WBC >20,000 with lymphocyte predominance
Pertussis case reporting to public health is mandatory in the US
Imaging
Chest radiograph: often normal or shows perihilar infiltrate ('shaggy heart border'); rules out pneumonia and other complications
Diagnostic algorithm
Phase
Duration
Features
Catarrhal
1-2 weeks
URI symptoms (rhinorrhea, low fever, mild cough); MOST CONTAGIOUS
Paroxysmal
2-8 weeks
Severe coughing fits ± whoop and post-tussive emesis; afebrile between
Convalescent
Weeks to months
Gradual reduction in cough frequency; '100-day cough'
Classic phases of pertussis (Bordetella pertussis) infection.
Treatment
First-line
Antibiotic treatment primarily REDUCES TRANSMISSION; clinical benefit greatest if started in catarrhal or early paroxysmal phase
Macrolide first-line:
Azithromycin: infants <1 month 10 mg/kg/day × 5 days; older children/adults 500 mg day 1 then 250 mg days 2-5
Clarithromycin or erythromycin alternatives (avoid erythromycin in infants <1 month due to pyloric stenosis risk)
Macrolide alternative if intolerant or resistant: TMP-SMX (NOT for infants <2 months due to kernicterus risk)
Supportive care: hydration, nutritional support, gentle suctioning of secretions
Hospitalize infants <6 months and those with severe disease (apnea, cyanosis, dehydration, complications)
Treat as soon as suspected; do not wait for confirmation in high-suspicion cases
Bronchodilators, corticosteroids, antitussives NOT effective
Isolation (droplet precautions) until 5 days of effective antibiotic therapy completed; if untreated, until 21 days of cough
Second-line / adjunct
Post-exposure prophylaxis (same antibiotic regimen as treatment) for all household contacts and high-risk contacts (infants <12 months, late pregnancy, healthcare workers caring for infants/pregnant women), regardless of vaccination status
Pregnant women should receive Tdap during each pregnancy (preferably 27-36 weeks) — passive antibody transfer protects newborn before infant vaccinations
Routine childhood vaccination: DTaP at 2, 4, 6, 15-18 months and 4-6 years
Adolescent and adult Tdap booster (single dose ≥age 11, then Td or Tdap every 10 years)
Cocoon strategy — vaccinate close contacts of newborns
Complications
Apnea, hypoxia, and death in young infants (highest risk <2 months)
Pulmonary hypertension (severe pertussis, especially with extreme lymphocytosis)
Tdap during each pregnancy (27-36 weeks) is the single most important intervention for protecting newborns from pertussis — vaccinate even if recently received.
Macrolide treatment is primarily aimed at reducing transmission; symptomatic benefit is limited once paroxysmal phase begins.
Erythromycin is associated with hypertrophic pyloric stenosis in infants <1 month — use azithromycin instead.
Marked lymphocytosis (WBC >20,000, lymphocyte predominance) supports pertussis diagnosis in infants; lymphocytosis correlates with disease severity.
Adolescents and adults are often the source of infant pertussis — vaccinate adolescents, parents, grandparents, and healthcare workers (Tdap).
References
CDC 2005 — Recommended Antimicrobial Agents for the Treatment and Postexposure Prophylaxis of Pertussis (Tiwari et al., MMWR Recomm Rep 2005)
ACIP — Updated Recommendations for Use of Tdap in Pregnant Women — ACIP 2013 (Sawyer et al., MMWR 2013)
Cochrane — Antibiotics for Whooping Cough (Pertussis) (Altunaiji et al., Cochrane Database Syst Rev 2007)
AAP Red Book — Pertussis (Whooping Cough) — AAP Committee on Infectious Diseases, Red Book 2024
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