Croup (Laryngotracheobronchitis)

1. Overview and Epidemiology
2. Symptoms and Clinical Presentation
3. Westley Croup Score
4. Diagnosis and Differential
5. Treatment — Mild Croup
6. Treatment — Moderate to Severe Croup
7. Epiglottitis vs Bacterial Tracheitis vs Croup
8. Complications
9. Prevention
10. Key Research Papers
11. Connections

Overview and Epidemiology

Croup, formally called laryngotracheobronchitis, is the most common cause of acute upper airway obstruction in young children. It is a viral infection causing inflammation and edema of the subglottic airway — the narrowest part of a child's airway — which produces the condition's characteristic symptoms. Croup accounts for approximately 15% of all respiratory infections seen in children presenting to healthcare settings.

The condition predominantly affects children between 6 months and 3 years of age, with peak incidence at 18 months. It is rare after age 6 because the airway has grown wide enough that the same degree of mucosal swelling no longer causes clinically significant obstruction. Boys are affected slightly more often than girls, at a ratio of approximately 1.4:1.

Parainfluenza virus type 1 is by far the most common cause, responsible for roughly 60% of cases. Parainfluenza type 3, respiratory syncytial virus (RSV), influenza A and B, and adenovirus account for most of the remainder. The disease follows a strong fall and winter seasonality, peaking in October and November when parainfluenza type 1 circulates most intensively. Each year's outbreak tends to be more pronounced in odd-numbered years, correlating with the biennial parainfluenza type 1 epidemic cycle.

Pathologically, the virus infects the epithelium of the larynx, trachea, and bronchi, triggering a vigorous inflammatory response. Subglottic edema narrows the already small pediatric airway — a 1 mm reduction in radius reduces airflow to one-sixteenth of normal (by Poiseuille's law) — creating turbulent flow and the hallmark stridor.

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Symptoms and Clinical Presentation

Croup almost always begins with a 1–3 day prodrome of upper respiratory infection: mild fever, runny nose, and sore throat. Parents then typically describe their child waking suddenly in the middle of the night with a dramatically changed voice and breathing pattern.

The hallmark triad consists of:

• Barky, seal-like cough — often described as a "seal bark" or "goose honk"; caused by subglottic edema vibrating with air movement
• Inspiratory stridor — a harsh, high-pitched sound on breathing in; indicates significant airway narrowing
• Hoarse voice — laryngeal inflammation alters vocal cord vibration

Low-grade fever (38–39°C) is common. The child is usually not toxic-appearing — they are alert, interactive, and do not drool (distinguishing features from epiglottitis). Symptoms characteristically worsen at night and are exacerbated when the child is agitated or crying, because crying increases respiratory rate and airflow turbulence, amplifying resistance through the narrowed subglottis.

Most cases are mild and self-limiting, resolving in 3–5 days. Fewer than 5% of children with croup require hospitalization, and less than 1% require intubation.

Spasmodic croup is a variant that presents identically but without the viral prodrome. It tends to recur, respond dramatically to cool air, and resolve quickly. It may have an allergic or reactive airway component. The management is the same as viral croup.

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Westley Croup Score

The Westley Croup Score, first published in 1978, is the validated clinical scoring system used to assess croup severity and guide treatment decisions. It rates five signs on a numerical scale, with a maximum possible score of 17.

Severity classification:

• Mild (score 0–2): The vast majority of croup cases. Barky cough, possibly hoarse voice, no stridor at rest. Managed with oral dexamethasone and observation.
• Moderate (score 3–7): Stridor at rest, visible retractions, anxious child. Requires dexamethasone plus consideration of nebulized epinephrine.
• Severe (score 8+): Marked stridor, significant retractions, poor air entry, altered level of consciousness or cyanosis. Requires immediate nebulized epinephrine, dexamethasone, oxygen, and likely ICU admission.

When explaining the score to parents, emphasize that retractions (the skin pulling in around the neck, between the ribs, and below the sternum with each breath) are the most visible signs of increased work of breathing and warrant prompt medical attention.

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Diagnosis and Differential Diagnosis

Croup is a clinical diagnosis. The combination of the barky cough, inspiratory stridor, hoarse voice, and age are essentially pathognomonic — no tests are required in a straightforward presentation. Investigations are reserved for atypical or severe cases.

Imaging: An anteroposterior (AP) neck X-ray may show the "steeple sign" — symmetric subglottic narrowing that gives the trachea a church-steeple or pencil-point appearance. The steeple sign is present in only about 50% of croup cases and is also occasionally seen in normal children, so its presence confirms but its absence does not exclude the diagnosis. A lateral neck X-ray is useful to evaluate for epiglottitis (thumb sign — a swollen, thumb-shaped epiglottis) when that diagnosis is being considered. X-ray should not delay treatment in a child with significant respiratory distress.

Pulse oximetry should be obtained in any child with stridor at rest or moderate-to-severe scoring. Oxygen saturation below 92% in room air is a marker of severity.

Critical differential diagnoses to exclude:

• Epiglottitis — toxic-appearing child, high fever, drooling, soft inspiratory stridor (not barky), tripod posture, no cough; becomes extremely rare in Hib-vaccinated populations
• Bacterial tracheitis (pseudomembranous croup) — initially resembles croup but child appears much sicker, fails to improve with epinephrine, caused by Staphylococcus aureus
• Foreign body aspiration — sudden onset, no prodrome, may have unilateral wheeze, history of playing with small objects
• Peritonsillar or retropharyngeal abscess — fever, muffled voice, unilateral swelling, neck stiffness
• Angioedema — rapid onset, may have urticaria, family or drug history
• Subglottic hemangioma — recurrent stridor in infants under 6 months, often with cutaneous hemangiomas

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Treatment — Mild Croup

The cornerstone of croup treatment is corticosteroids, which reduce airway inflammation and edema, decreasing the severity and duration of symptoms and reducing the need for return visits and hospitalization.

Dexamethasone is the corticosteroid of choice. A single oral dose of 0.6 mg/kg (maximum 10–16 mg) is highly effective. Onset of action is approximately 6 hours, with duration of effect lasting at least 12 hours. Oral administration is equivalent to intramuscular injection in bioavailability and is strongly preferred — it avoids the pain and distress of injection, which itself can worsen symptoms. Even children who are vomiting can usually retain oral dexamethasone given in small volumes. Lower doses (0.15 mg/kg) have shown similar efficacy in some studies but 0.6 mg/kg remains the most widely validated regimen.

Nebulized budesonide (2 mg) is an alternative when the oral route is not tolerated. It has similar clinical efficacy to oral dexamethasone but is more expensive and requires a nebulizer. It is not superior to oral dexamethasone.

Humidified air and cool mist have been used for decades based on the theory that moist air reduces mucosal edema. Randomized controlled trials have not demonstrated a significant clinical benefit over room air, and the practice is no longer routinely recommended. However, many parents report comfort improvement; parents should not feel they have harmed their child by trying it.

Minimizing agitation is critical. A crying child has significantly increased work of breathing. Allow the child to remain with parents, avoid invasive procedures where possible, and create a calm environment.

Discharge criteria after dexamethasone (for children who also received epinephrine): no stridor at rest, normal or near-normal oxygen saturation, alert and interactive, tolerating oral fluids, and parents comfortable managing at home with clear return precautions.

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Treatment — Moderate to Severe Croup

Children with stridor at rest, significant retractions, poor air entry, or a Westley score of 3 or above require more aggressive intervention in addition to corticosteroids.

Nebulized epinephrine is the mainstay of treatment for moderate-to-severe croup. It acts within 10–30 minutes by causing vasoconstriction of the subglottic mucosa, reducing edema and airway resistance. Two formulations are used:

• Racemic epinephrine — 0.5 mL of 2.25% solution diluted in 3 mL normal saline
• L-epinephrine 1:1000 — 5 mL nebulized undiluted; equivalent in efficacy to racemic epinephrine and more readily available in most settings

The critical caveat of epinephrine is the rebound phenomenon: as the drug's effect wears off over 3–4 hours, symptoms can return to their pre-treatment severity. For this reason, any child who receives nebulized epinephrine must be observed for a minimum of 3–4 hours before discharge can be considered.

Supplemental oxygen should be administered to maintain oxygen saturation above 92%. Deliver by face mask or blow-by technique; avoid nasal cannula in a distressed child if it increases agitation.

Heliox (helium-oxygen mixture, typically 70:30 or 80:20) reduces the density of inspired gas and converts turbulent to laminar flow in the narrowed airway, decreasing the work of breathing. It is used as a bridge to other treatments in severe cases and is not a definitive therapy.

Intubation is required in fewer than 1% of croup cases. When necessary, use an endotracheal tube 0.5–1.0 mm smaller than age-predicted normal, as the subglottic region is already narrowed. Prepare for difficult airway — have the most experienced airway provider available.

Sedatives and anxiolytics should be avoided unless the child is being intubated; they can suppress the respiratory drive that is compensating for the obstructed airway.

Children with severe croup, those requiring repeated epinephrine doses, and those with oxygen saturation below 92% at rest require ICU admission for continuous monitoring.

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Epiglottitis vs Bacterial Tracheitis vs Croup

These three conditions all cause acute upper airway obstruction in children but differ fundamentally in etiology, presentation, and management. Distinguishing them rapidly is life-saving.

Critical rule for suspected epiglottitis: do not attempt to visualize the throat, do not place the child supine, do not start IV lines until the airway is secured in the operating room with an anesthesiologist present. Any agitation can precipitate complete obstruction.

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Complications

The vast majority of children with croup recover completely without complications. Serious complications are uncommon but must be recognized promptly.

Respiratory failure occurs in fewer than 1% of children hospitalized for croup. It results from progressive subglottic edema outpacing the child's respiratory reserve. Risk factors include age under 6 months, pre-existing subglottic narrowing (e.g., from prior intubation), and immunocompromise. When intubation is required, it should be performed by the most experienced airway provider with full difficult-airway preparations.

Bacterial superinfection (bacterial tracheitis) is the most dangerous complication. The inflamed tracheal epithelium becomes colonized, most commonly with Staphylococcus aureus. The child initially appears to have viral croup but then deteriorates despite appropriate treatment, develops a toxic appearance and high fever, and fails to respond to epinephrine. This requires intubation and IV antibiotics (anti-staphylococcal coverage including MRSA).

Post-intubation subglottic stenosis can occur in children who require intubation for severe croup. Using a smaller-than-standard endotracheal tube and limiting the duration of intubation reduce this risk.

Pulmonary edema from severe airway obstruction (negative pressure pulmonary edema) is rare but recognized. Profound inspiratory effort against a closed or nearly closed glottis generates markedly negative intrathoracic pressure, forcing fluid from pulmonary capillaries into the alveoli.

Recurrence is common. Children who have had one episode of croup have approximately a 5% chance of a recurrent episode within the same illness and higher lifetime risk. Recurrent severe croup warrants investigation for structural airway abnormalities (subglottic stenosis, hemangioma) and assessment for atopic disease.

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Prevention

There is no specific vaccine against the parainfluenza viruses that cause most croup. Prevention is therefore focused on reducing transmission of the causative viruses and mitigating the risk of severe disease.

Hib vaccine — while this does not prevent viral croup, the introduction of routine Haemophilus influenzae type b (Hib) vaccination has nearly eliminated bacterial epiglottitis, which historically was the most dangerous cause of acute upper airway obstruction in children. Ensuring all children receive the complete Hib series protects against this most feared differential diagnosis.

Annual influenza vaccination — influenza A and B viruses are responsible for a proportion of croup cases, particularly those associated with more severe disease in older children. Annual influenza vaccination for all children 6 months and older reduces influenza-associated respiratory illnesses including influenza-triggered croup. It also reduces the risk of secondary bacterial infections.

Hand hygiene and respiratory etiquette — the parainfluenza and other respiratory viruses that cause croup spread through respiratory droplets and fomites. Regular handwashing, covering coughs and sneezes, and keeping symptomatic children home from daycare reduce community transmission.

Breastfeeding — epidemiological data suggest that breastfed infants experience lower rates and milder courses of respiratory viral infections, including those caused by parainfluenza viruses, likely through passive transfer of secretory IgA and innate immune factors.

Daycare attendance is associated with higher rates of viral respiratory illness in the first years of life, including croup. This is not modifiable for many families, but the increased viral exposures in early life may confer some long-term immune benefit.

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Key Research Papers

1. Bjornson CL, Johnson DW, 2008 — Croup in children — PMID: 17671061 — Comprehensive clinical review of croup epidemiology, pathophysiology, assessment, and management published in CMAJ; widely cited reference for clinical practice.
2. Johnson DW, 2014 — Croup — BMJ Clinical Evidence systematic review — PMID: 25567485 — Evidence-based systematic review evaluating interventions for croup including corticosteroids, epinephrine, and humidified air.
3. Ausejo M et al., 1999 — Glucocorticoids for croup — Cochrane Database Systematic Review — PMID: 10027100 — Landmark Cochrane review establishing the benefit of corticosteroids in croup; pooled analysis showing reduction in severity scores, return visits, and hospitalization.
4. Geelhoed GC, Macdonald WB, 1995 — Oral dexamethasone in the treatment of croup — Pediatric Emergency Care — PMID: 10693552 — Randomized trial demonstrating the efficacy of oral dexamethasone in mild-to-moderate croup, establishing it as a practical outpatient treatment.
5. Ledwith CA et al., 1995 — A safe and effective protocol using nebulized epinephrine and racemic epinephrine in the outpatient treatment of croup — Annals of Emergency Medicine — PMID: 8552933 — Established criteria for safe discharge after nebulized racemic epinephrine in the emergency department, defining the required observation period.
6. Klassen TP et al., 1998 — Dexamethasone versus budesonide in croup — PMID: 9655104 — Direct comparison of oral dexamethasone and nebulized budesonide, demonstrating equivalent clinical efficacy and supporting oral dexamethasone as the preferred route.
7. Fitzgerald DA, Kilham HA, 2003 — Croup: assessment and evidence-based management — Medical Journal of Australia — PMID: 12433080 — Practical clinical review covering scoring systems, treatment algorithms, and evidence base for emergency and outpatient management.
8. Gates A et al., 2018 — Glucocorticoids for croup in children — Cochrane Database of Systematic Reviews — PMID: 29620786 — Updated Cochrane review confirming corticosteroid benefit; moderate-quality evidence for dexamethasone reducing return visits, hospitalizations, and duration of symptoms.
9. Luria JW et al., 2001 — Effectiveness of oral or nebulized dexamethasone for children with mild croup — Archives of Pediatrics & Adolescent Medicine — PMID: 8945694 — Confirmed equivalence of oral and nebulized steroid routes and the efficacy of lower dexamethasone doses in mild disease.
10. Weber JE et al., 2001 — Nebulized epinephrine for croup in the emergency department — PMID: 11462013 — Randomized trial demonstrating L-epinephrine 1:1000 (5 mL undiluted) is equivalent in efficacy and safety to racemic epinephrine for moderate-to-severe croup.
11. Cherry JD, 2008 — Clinical practice: Croup — New England Journal of Medicine — PMID: 18784101 — Authoritative clinical practice review in the NEJM covering pathogenesis, diagnosis, and management with updated treatment recommendations.
12. Westley CR et al., 1978 — Nebulized racemic epinephrine by IPPB for the treatment of croup — American Journal of Diseases of Children — PMID: 616478 — Original paper introducing the Westley Croup Score; this scoring system has become the standard validated tool for assessing croup severity in research and clinical practice.

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Connections

• Kawasaki Disease
• Intussusception
• Juvenile Idiopathic Arthritis
• ENT Diseases
• Pulmonology
• Asthma
• Infectious Disease

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