Version July 2025
INTRODUCTION —
Croup is a respiratory illness characterized by inspiratory stridor, barking cough, and hoarseness. These symptoms result from inflammation in the larynx and subglottic airway. Although croup usually is a mild and self-limited illness, significant upper airway obstruction and respiratory distress can occur.
The clinical features, evaluation, and diagnosis of croup will be discussed here. The management of croup is discussed separately. (See "Croup: Management".)
DEFINITIONS —
The term "croup" has been used to describe a range of upper respiratory conditions in children. For the purpose of this topic review, we will use the term "croup" to refer to viral laryngotracheitis, as defined below.
Laryngotracheitis (croup) — Croup is a respiratory illness characterized by inspiratory stridor, barking cough, and hoarseness. These symptoms result from inflammation in the larynx and subglottic airway.
Viral croup — Viral croup (also called classic croup) refers to the typical croup syndrome that occurs most commonly in children six months to three years of age. As the name implies, it is caused by respiratory viruses and so viral symptoms (eg, nasal congestion, fever) are usually present. Viral croup is usually a self-limited illness; the cough typically resolves within three days [1]. (See 'Clinical presentation' below and 'Clinical course' below.)
Spasmodic croup — Spasmodic croup also occurs in children six months to three years of age. Spasmodic croup always occurs at night. The onset and cessation of symptoms are abrupt, and the duration of symptoms is short, often with symptoms subsiding by the time of presentation for medical attention. Fever is typically absent. Episodes can recur within the same night and for two to four successive evenings. A striking feature of spasmodic croup is its recurrent nature, hence the alternate descriptive term "frequently recurrent croup." There may be a familial predisposition to spasmodic croup, and it appears to be more common in children with a family history of allergies [2]. Because there is some clinical overlap with atopic diseases, it is sometimes referred to as "allergic croup."
Early in the clinical course, spasmodic croup may be difficult to distinguish from viral croup. Over time, the episodic nature of symptoms and relative wellness of the child between attacks differentiate spasmodic croup from viral croup, in which the symptoms are continuous.
Although the initial presentation can be dramatic, the clinical course is usually benign. Symptoms are almost always relieved by comforting the anxious child and administering humidified air.
Recurrent episodes of croup also are labeled "atypical croup" or "recurrent croup," with varying definitions and etiologic considerations [3]. (See 'Recurrent croup' below.)
Other related terms — The following conditions are related to croup, but we consider these distinct clinical entities:
●Laryngitis – Laryngitis refers to inflammation limited to the larynx which manifests as hoarseness. It usually occurs in older children and adults and, similar to croup, is frequently caused by a viral infection. Laryngitis is discussed separately. (See "Common causes of hoarseness in children", section on 'Acute laryngitis'.)
●Laryngotracheobronchitis – Laryngotracheobronchitis occurs when inflammation extends into the bronchi, resulting in lower airway signs (eg, wheezing, crackles). It tends to be a more severe illness compared with laryngotracheitis alone. However, the two entities overlap and the term laryngotracheobronchitis is commonly used interchangeably with laryngotracheitis. Extension of inflammation further into the lower airways results in laryngotracheobronchopneumonitis, which can be complicated by bacterial superinfection (ie, pneumonia).
●Bacterial tracheitis – Bacterial tracheitis (sometimes called "bacterial croup") is an invasive exudative bacterial infection of the soft tissues of the trachea (picture 1). In some cases, there is extension to the subglottic laryngeal structures or the upper bronchial tree. Bacterial tracheitis may occur as a primary infection or as a complication of viral croup. With secondary infection, patients typically present with symptoms of viral croup and then have marked worsening with high fevers, toxic appearance, and severe respiratory distress. Bacterial tracheitis is discussed in greater detail separately. (See "Bacterial tracheitis in children: Clinical features and diagnosis".)
EPIDEMIOLOGY —
Croup is one of the most common respiratory illnesses in young children. It occurs mostly in children ≤6 years old, with a peak incidence between six months to three years of age; it is uncommon in children >6 years old [4,5]. A study of emergency department (ED) visits in the United States from 2007 to 2014 estimated that there were approximately 350,000 to 400,000 croup-related ED visits each year, accounting for 1.3 percent of all ED visits [6]. Children <2 years old accounted for 43 percent of the visits, children ages two to seven years made up 50 percent of visits, and children ≥7 accounted for only 7 percent. Croup is more common in boys, with reported male:female ratios ranging from 1.4:1 to 2:1 [4-8].
Family history of croup is a risk factor for croup and recurrent croup. In a case-control study, children whose parents had a history of croup were 3 times more likely to have an episode of croup and 4 times as likely to have recurrent croup compared with children without parental history of croup [9]. Parent/caregiver smoking, a well-recognized risk factor for other respiratory tract infections in children, does not appear to increase the risk of croup [9,10]. (See "Secondhand smoke exposure: Effects in children", section on 'Respiratory symptoms and illness'.)
In temperate climates, most cases of croup occur in the fall or early winter, with the major incidence peaks coinciding with parainfluenza type 1 activity. (See "Parainfluenza viruses in children", section on 'Seasonality'.)
Additional peaks may occur during periods of respiratory syncytial virus, influenza, and COVID-19 activity. (See "Seasonal influenza in children: Clinical features and diagnosis", section on 'Influenza activity' and "Respiratory syncytial virus infection: Clinical features and diagnosis in infants and children", section on 'Epidemiology' and "COVID-19: Epidemiology, virology, and prevention", section on 'Geographic and temporal distribution'.)
ED visits for croup are most frequent between 10:00 PM and 4:00 AM [11]. A morning peak in ED visits for croup between 7:00 AM and 11:00 AM also has been noted [8].
Hospital admissions for croup have declined steadily since the late 1970s [12]. In studies conducted in the contemporary era, <10 percent of children with croup presenting to the ED require hospitalization. This is discussed separately. (See "Croup: Management", section on 'Indications for hospital admission'.)
MICROBIOLOGY
Viral causes — Croup is usually caused by viruses:
●Parainfluenza viruses – Parainfluenza virus type 1 is the most common cause of acute laryngotracheitis, especially during fall and winter epidemics [13-16]. The microbiology, pathogenesis, and epidemiology of parainfluenza infections are discussed separately. (See "Parainfluenza viruses in children".)
●Rhinovirus, respiratory syncytial virus (RSV), and adenoviruses – Rhinovirus, RSV, and adenoviruses are relatively frequent causes of croup. For children with RSV infection, the laryngotracheal component of disease is usually less significant than that of the lower airways. (See "Respiratory syncytial virus infection: Clinical features and diagnosis in infants and children", section on 'Clinical manifestations' and "Pathogenesis, epidemiology, and clinical manifestations of adenovirus infections", section on 'Clinical presentation'.)
●Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) – SARS-CoV-2 has become a relatively common cause of croup [14,17-24]. (See "COVID-19: Clinical manifestations and diagnosis in children".)
●Influenza – Influenza virus is a relatively uncommon cause of croup. However, children hospitalized with influenzal croup tend to have longer hospitalization and greater risk of readmission for relapse of laryngeal symptoms than those with parainfluenzal croup. (See "Seasonal influenza in children: Clinical features and diagnosis", section on 'Pneumonia and respiratory tract complications'.)
●Other human coronaviruses – HCoV-NL63 has been associated with croup and other respiratory illnesses in children [25-28], as have human coronaviruses OC43 HKU1 [29]. (See "Common cold coronaviruses", section on 'Respiratory syndromes'.)
●Measles – Measles is an important cause of croup in areas where measles remains prevalent or during outbreaks. (See "Measles: Clinical manifestations, diagnosis, treatment, and prevention".)
●Others – Enteroviruses (especially coxsackie types A9, B4, and B5 and echovirus types 4, 11, and 21) and herpes simplex virus are occasional causes of sporadic cases of croup that are usually mild. (See "Enterovirus and parechovirus infections: Clinical features, laboratory diagnosis, treatment, and prevention" and "Epidemiology, clinical manifestations, and pathogenesis of rhinovirus infections".)
Human metapneumovirus causes primarily lower respiratory tract disease similar to RSV, but upper respiratory tract symptoms have been described [30]. (See "Human metapneumovirus infections".)
Bacterial infection — Croup is rarely caused by bacterial infection with the exception of Mycoplasma pneumoniae, which can cause a mild croup-like illness [31]. (See "Mycoplasma pneumoniae infection in children", section on 'Other respiratory manifestations'.)
Secondary bacterial infection (ie, bacterial tracheitis) can occur, though this is uncommon. The most common bacterial pathogens in this setting include Staphylococcus aureus, Streptococcus pyogenes, and Streptococcus pneumoniae [4]. This is discussed in detail separately. (See "Bacterial tracheitis in children: Clinical features and diagnosis".)
PATHOGENESIS
Pathology
●Viral croup – The viruses that cause croup typically infect the nasal and pharyngeal mucosal epithelia initially and then spread locally along the respiratory epithelium to the larynx and trachea.
The anatomic hallmark of croup is narrowing of the subglottic airway, the portion of the larynx immediately below the vocal folds. The cricoid cartilage of the subglottis is a complete cartilaginous ring, unlike the tracheal rings, which are horseshoe shaped. Because it is a complete ring, the cricoid cannot expand, causing significant airway narrowing whenever the subglottic mucosa becomes inflamed. In addition to this "fixed" obstruction, dynamic obstruction of the extrathoracic trachea below the cartilaginous ring may occur when the child struggles, cries, or becomes agitated. The dynamic obstruction occurs as a result of the combination of high negative pressure in the distal extrathoracic trachea and the floppiness of the tracheal wall in children.
Laryngoscopic evaluation is rarely necessary for patients with viral croup, but, when performed, it typically shows redness and swelling in the area just below the vocal folds (picture 2). In severe cases, the subglottic airway may be reduced to a diameter of 1 to 2 mm. In addition to mucosal edema and swelling, fibrinous exudates and, occasionally, pseudomembranes can build up on the tracheal surfaces and contribute to airway narrowing. The vocal folds and laryngeal tissues also can become swollen, and cord mobility may be impaired [32-34]. Autopsy studies in children with laryngotracheitis show infiltration of histiocytes, lymphocytes, plasma cells, and neutrophils into edematous lamina propria, submucosa, and adventitia of the larynx and trachea [35-37].
●Spasmodic or recurrent croup – In spasmodic or recurrent croup, findings on direct laryngoscopy may demonstrate noninflammatory edema, suggesting that there is no direct viral involvement of the tracheal epithelium in children with this presentation [32]. In a retrospective case series of 197 children with recurrent croup who underwent endoscopy at a single center from 2002 to 2012, 21 percent had evidence of subglottic stenosis and 20 percent had abnormal esophageal biopsies (including evidence of reflux esophagitis, eosinophilic esophagitis, and candidal esophagitis) [38]. Children with subglottic stenosis tended to be younger compared with those without (mean age 35 versus 58 months). In another case series of 103 children with recurrent croup who underwent endoscopy at a single center from 2004 to 2013, 44 percent had a history of prior intubation, subglottic stenosis, or previous airway procedure [39]. Other common underlying conditions included asthma (64 percent), gastroesophageal reflux disease (60 percent), and seasonal allergies (48 percent). Endoscopy was normal in 65 percent of the children in this series; 9 percent of children had moderate to severe findings (including subglottic stenosis, cyst, and hemangioma).
Though a causal relationship between gastroesophageal reflux disease and recurrent croup has been postulated, the evidence to support this is limited. A systematic review of observational studies found that a temporal association between treatment with antireflux medication and reduction of croup symptoms was often reported; however, the retrospective nature of the data and lack of control group made it difficult to draw conclusions about causality [40].
●Bacterial tracheitis – Patients with bacterial tracheitis have a bacterial superinfection that causes thick pus to develop within the lumen of the subglottic trachea (picture 1). Ulcerations, pseudomembranes, and microabscesses of the mucosal surface occur. The supraglottic tissues usually are normal. This clinical entity is discussed in greater detail separately. (See "Bacterial tracheitis in children: Clinical features and diagnosis", section on 'Pathogenesis and pathology'.)
Host factors — Only a small subset of children with a parainfluenza viral infection develop overt croup. This suggests that host (or genetic) factors play a role in the pathogenesis. Host factors that may contribute to the development of croup include functional or anatomic upper airway narrowing, variations in immune response, and predisposition to atopy [8].
Underlying host factors that predispose to clinically significant narrowing of the upper airway include:
●Congenital and acquired airway abnormalities, such as laryngomalacia, laryngeal clefts, subglottic stenosis, vallecular cysts, or subglottic hemangiomas [41]. Subglottic hemangiomas grow in the first few months of life, and affected patients typically present with symptoms mimicking croup (ie, stridor and barking cough). (See "Congenital anomalies of the larynx" and "Infantile hemangiomas: Epidemiology, pathogenesis, clinical features, and complications", section on 'Airway hemangiomas'.)
●Hyperactive airways, perhaps aggravated by atopy or gastroesophageal reflux, as suggested in some children with spasmodic croup or recurrent croup [2,42,43]. (See 'Spasmodic croup' above.)
CLINICAL PRESENTATION —
Croup typically occurs in children ≤6 years old, with a peak incidence between six months to three years of age (see 'Epidemiology' above). The illness begins with typical viral upper respiratory symptoms (rhinorrhea, cough, congestion) and progresses to signs of airway inflammation and obstruction (barking cough, stridor, respiratory distress).
Presenting signs and symptoms — Symptoms usually begin with nasal discharge and congestion and progress over 12 to 48 hours to include fever, hoarseness, barking cough, and stridor. There is minimal, if any, pharyngitis.
As airway narrowing progresses, stridor develops and there may be mild tachypnea with a prolonged inspiratory phase. If upper airway obstruction worsens, severe respiratory distress can develop. Rapid progression or signs of concurrent lower airway involvement suggests a more serious illness (eg, bacterial tracheitis, pneumonia, or impending complete upper airway obstruction). (See 'Differential diagnosis' below.)
The severity of upper airway obstruction is evident on physical examination, as summarized in the table (table 1) and described below (see 'Severity assessment' below). Biphasic stridor (stridor heard on both inspiration and expiration) at rest is a sign of significant airway obstruction. If airway obstruction progresses, the child may become restless or anxious. When airway obstruction becomes severe, suprasternal, subcostal, and intercostal retractions may be seen. Breath sounds can be diminished. Agitation, which generally is accompanied by increased inspiratory effort, exacerbates the subglottic narrowing by creating negative pressure in the airway. This can lead to further respiratory distress and agitation.
Clinical course — Croup is a self-limited illness that typically resolves within 24 to 72 hours, though the cough may persist for up to a week [1]. Complications of croup (eg, secondary bacterial infection, respiratory failure) are uncommon. (See "Croup: Management", section on 'Complications'.)
Deviation from this expected course should prompt consideration of diagnoses other than croup. (See 'Differential diagnosis' below.)
EVALUATION
Overview — The evaluation of children with suspected croup is aimed at promptly identifying patients with severe upper airway obstruction or those at risk for rapid progression of upper airway obstruction and excluding other conditions with presentations similar to croup that require specific evaluations and/or interventions. (See 'Differential diagnosis' below.)
During the evaluation, efforts should be made to make the child as comfortable as possible. The increased inspiratory effort that accompanies anxiety and fear in young children can exacerbate subglottic narrowing, further diminishing air exchange and oxygenation. (See 'Pathogenesis' above.)
Rapid assessment and initial management — Rapid assessment of general appearance (including the presence of stridor at rest), vital signs, pulse oximetry, airway stability, and mental status is necessary to identify children with severe respiratory distress and/or impending respiratory failure (table 1). Children who have severe respiratory distress require immediate treatment, as summarized in the figure (algorithm 1) and discussed in detail separately. (See "Croup: Management", section on 'Moderate to severe croup' and "Croup: Management", section on 'Respiratory care'.)
In addition, the child's hydration status should be assessed. Moderate to severe croup may be associated with decreased oral intake and increased insensible losses from fever and tachypnea, resulting in dehydration. (See "Clinical assessment of hypovolemia (dehydration) in children".)
Once treatment is underway and the child is more stable, the remainder of the evaluation can proceed.
History — The history should elicit details of the onset, duration, and progression of symptoms. Factors associated with increased risk of severe croup include:
●Sudden onset of symptoms
●Rapidly progressing symptoms (ie, symptoms of upper airway obstruction after fewer than 12 hours of illness)
●Previous episodes of croup
●Underlying abnormality of the upper airway
●Medical conditions that predispose to respiratory failure (eg, neuromuscular disorders)
The review of symptoms can help distinguish croup from other causes of acute upper airway obstruction.
Signs and symptoms that are characteristic of croup include [4,44]:
●Fever and other viral symptoms – Most children with viral croup have fever and/or other signs of viral illness (eg, rhinorrhea, congestion). Stridor occurring without associated viral symptoms should prompt consideration of noninfectious etiologies (eg, spasmodic croup, subglottic cyst, subglottic hemangioma, foreign body aspiration). (See 'Differential diagnosis' below.)
●Barking cough – The classic physical finding in a patient with subglottic inflammation is a barky, seal-like cough.
●Hoarseness – Hoarseness may be present in croup, particularly in older children, whereas hoarseness is not a typical finding in epiglottitis or foreign body aspiration.
Signs and symptoms that are not typical of croup and suggest another etiology include:
●Difficulty swallowing – Difficulty swallowing may occur in acute epiglottitis. Rarely, a large ingested foreign body may lodge in the upper esophagus, where it distorts and narrows the upper trachea, thus mimicking the croup syndrome (including barking cough and inspiratory stridor). (See "Epiglottitis (supraglottitis): Clinical features and diagnosis" and "Foreign bodies of the esophagus and gastrointestinal tract in children".)
●Drooling – Drooling more commonly occurs in children with peritonsillar or retropharyngeal abscesses, retropharyngeal cellulitis, and epiglottitis. In an observational study, drooling was present in approximately 80 percent of children with epiglottitis but only 10 percent of those with croup [44]. (See "Retropharyngeal infections in children" and "Epiglottitis (supraglottitis): Clinical features and diagnosis".)
●Throat pain – Complaints of dysphagia and sore throat are more common in children with epiglottitis than croup (approximately 60 to 70 versus <10 percent) [44].
●Angioedema, urticaria, wheezing, and/or hypotension – Stridor associated with these findings suggests anaphylaxis. (See "Anaphylaxis: Acute diagnosis", section on 'Symptoms and signs'.)
The differential diagnosis of croup is discussed in greater detail below. (See 'Differential diagnosis' below.)
Examination — The objectives of the examination of the child with croup include assessment of severity of upper airway obstruction and exclusion of other causes of acute upper airway obstruction, both of which are necessary in making management decisions.
The initial examination often can be accomplished by observing the child in a comfortable position with their caretaker. Minimizing agitation is paramount, especially in patients with moderate or severe croup.
Severity assessment — The severity of croup is determined by the presence or absence of stridor at rest, degree of chest wall retractions, air entry, presence or absence of pallor or cyanosis, and mental status. There are several clinical scoring systems for croup. We use the Westley croup score since it is the most extensively studied tool (table 1) (calculator 1) [45,46].
●Mild croup (Westley croup score ≤2) – Children with mild croup have a barking cough, hoarse cry, no stridor at rest (although stridor may be present when upset or crying), and either no or only mild chest wall/subcostal retractions [4,47,48].
●Moderate croup (Westley croup score 3 to 7) – Children with moderate croup have stridor at rest. They have at least mild retractions and may have other mild to moderate symptoms or signs of respiratory distress [4,47,48].
●Severe croup (Westley croup score ≥8) – Children with severe croup have significant stridor at rest, although the intensity of the stridor may decrease with worsening upper airway obstruction and poor air entry [4,47,48]. They have severe retractions (including indrawing of the sternum) and other signs of significant distress. They may appear anxious, agitated, or pale and fatigued.
●Impending respiratory failure (Westley croup score ≥12) – Croup occasionally results in severe airway obstruction with impending respiratory failure, heralded by the following signs [4,47,48]:
•Fatigue and listlessness
•Marked retractions (although retractions may decrease as the child becomes increasingly fatigued or obtunded)
•Decreased or absent breath sounds
•Cyanosis or pallor
•Depressed level of consciousness
Prompt recognition and treatment of children with severe croup are paramount, as discussed separately. (See "Croup: Management", section on 'Moderate to severe croup'.)
Croup clinical scores are widely used in clinical practice and in clinical trials evaluating the efficacy of different treatments for croup. However, it is important to understand that these scores are somewhat subjective and there can be substantial interobserver variability [46,49]. Nevertheless, the croup score remains a useful guide for assessing severity of illness and responses to therapies.
In an observational study of 192 patients with croup who had Westley croup scores assessed, the two components of the score that correlated most strongly with the need for hospital admission and duration of hospitalization were the degree of retractions and air entry [50].
Assessing for other causes — Components of the physical examination that are useful in distinguishing croup from other causes of acute upper airway obstruction and respiratory distress include [44,47]:
●Preferred posture – Children with epiglottitis usually prefer to sit up in the "tripod" or "sniffing position" (neck is mildly flexed, and head is mildly extended) (picture 3A-B). However, children with very severe croup may also have tripod posture.
●Quality of the voice – Children with croup may have a hoarse voice or diminished cry. A muffled "hot-potato" voice is suggestive of epiglottitis, retropharyngeal abscess, or peritonsillar abscess.
●Examination of the oropharynx for the following signs:
•Pharyngitis, typically minimal in croup, may be more pronounced in epiglottitis, retropharyngeal abscess, parapharyngeal abscess, or peritonsillar abscess
•Excessive salivation, suggestive of acute epiglottitis, peritonsillar abscess, parapharyngeal abscess, or retropharyngeal abscess
•Diphtheritic membrane
•Tonsillar asymmetry or deviation of the uvula suggestive of peritonsillar abscess
•Midline or unilateral swelling of the posterior pharyngeal wall suggestive of retropharyngeal abscess
•Cherry-red, swollen epiglottis, suggestive of epiglottitis
For most patients who have a clinical picture consistent with viral croup, direct visualization of the epiglottis is not necessary and cautious examination of the child's throat is sufficient. The approach to diagnosing epiglottitis, including which patients should undergo attempts at direct visualization, is discussed separately. (See "Epiglottitis (supraglottitis): Clinical features and diagnosis".)
●Examination of the cervical lymph nodes, which can be enlarged in patients with retropharyngeal or peritonsillar abscesses.
●Lung examination – Expiratory wheezing suggests small or medium airway obstruction (eg, asthma or bronchiolitis). Crackles (rales) suggests lower respiratory tract disease (eg, pneumonia).
●Other physical findings may be present, depending on the particular inciting virus. As an example, rash, conjunctivitis, exudative pharyngitis, and adenopathy are suggestive of adenovirus infection.
●Otitis media (acute or with effusion) may be present as a primary viral or secondary bacterial process.
The differential diagnosis of croup is discussed in greater detail below. (See 'Differential diagnosis' below.)
Radiographs
●Indications – Radiographic confirmation of acute laryngotracheitis is not required in the vast majority of children with croup. Radiographic evaluation of the chest and/or upper trachea is indicated if:
•The course is atypical and/or the diagnosis is in question
•The child has severe symptoms and does not respond as expected to therapeutic interventions
•There is suspicion for an inhaled or swallowed foreign body (although the majority are not radiopaque) (see "Airway foreign bodies in children")
•The child has recurrent episodes of croup and has not previously had airway radiographs performed (see 'Recurrent croup' below)
●Findings – In children with croup, a posterior-anterior chest radiograph demonstrates subglottic narrowing, commonly called the "steeple sign" (image 1A). The lateral view may demonstrate overdistention of the hypopharynx during inspiration and subglottic haziness (image 1B). The epiglottis should have a normal appearance.
Laboratory studies — Laboratory studies are rarely indicated in children with croup and are of limited diagnostic utility.
Blood tests — The white blood cell (WBC) count is not helpful in the diagnosis of croup. It can be low, normal, or elevated; WBC counts >10,000 cells/microL are common. A large number of band-form neutrophils is suggestive of primary or secondary bacterial infection. Croup is not associated with any specific alterations in serum chemistries, but children with dehydration may have low serum bicarbonate and/or elevated blood urea nitrogen. (See "Clinical assessment of hypovolemia (dehydration) in children", section on 'Laboratory testing'.)
Microbiology — Confirmation of etiologic diagnosis is not necessary for most children with croup, since croup is a self-limited illness that usually requires only symptomatic therapy. However, identification of a specific viral etiology may be necessary to make decisions regarding isolation. When an etiologic diagnosis is necessary, rapid diagnostic tests are performed on secretions from the nasopharynx, as discussed below. (See 'Etiologic diagnosis' below.)
DIAGNOSIS
Clinical diagnosis — Croup is diagnosed clinically, based upon the characteristic barking cough and stridor, especially during a typical community epidemic of one of the causative viruses. (See 'Clinical presentation' above and 'Viral causes' above.)
Neither radiographs nor laboratory tests are necessary to make the diagnosis. However, radiographs may be helpful in select cases to exclude other causes if the diagnosis is in question. In children with croup, the characteristic radiographic finding is subglottic narrowing ("steeple sign") (image 1A). (See 'Radiographs' above and 'Differential diagnosis' below.)
Etiologic diagnosis — Although not typically required in most cases of croup, identification of a specific viral etiology may be necessary to make decisions regarding isolation for patients requiring hospitalization or for public health/epidemiologic monitoring purposes. In particular, SARS-CoV-2 testing may be appropriate given the infection control and quarantine implications. (See "COVID-19: Diagnosis" and "COVID-19: Infection prevention for persons with SARS-CoV-2 infection".)
Testing for influenza is indicated if the results will influence decisions regarding treatment, prophylaxis of contacts, or performance of other diagnostic tests; laboratory confirmation should not delay the initiation of antiviral therapy for influenza when clinical and seasonal considerations are compatible with influenza as the potential etiology of croup. (See "Seasonal influenza in children: Management", section on 'Timing' and "Seasonal influenza in children: Clinical features and diagnosis", section on 'Whom to test'.)
Diagnosis of a specific viral etiology can be made with rapid polymerase chain reaction (PCR), rapid antigen testing, or viral culture of secretions from the nasopharynx. Multiplex tests (eg, respiratory viral panel), which simultaneously assess the presence of multiple agents in one specimen (typically using PCR), are widely available [51,52]. The diagnosis of specific viral infections is discussed in detail in individual topic reviews:
●Parainfluenza (see "Parainfluenza viruses in children", section on 'Diagnosis')
●Influenza (see "Seasonal influenza in children: Clinical features and diagnosis", section on 'Diagnosis')
●Respiratory syncytial virus (see "Respiratory syncytial virus infection: Clinical features and diagnosis in infants and children", section on 'Laboratory confirmation')
●Coronavirus (all types) (see "Common cold coronaviruses", section on 'Diagnosis' and "COVID-19: Clinical manifestations and diagnosis in children", section on 'Laboratory tests for SARS-CoV-2')
●Adenovirus (see "Diagnosis, treatment, and prevention of adenovirus infection", section on 'Diagnostic tests of choice for different adenovirus syndromes')
●Metapneumovirus (see "Human metapneumovirus infections", section on 'Diagnosis')
●Measles (see "Measles: Clinical manifestations, diagnosis, treatment, and prevention", section on 'Diagnosis')
●Enteroviruses (see "Enterovirus and parechovirus infections: Clinical features, laboratory diagnosis, treatment, and prevention", section on 'Laboratory diagnosis')
RECURRENT CROUP —
A child who has recurrent episodes of classic viral croup may have an underlying condition predisposing them to clinically significant narrowing of the upper airway. Recurrent episodes of croup-like symptoms occurring outside of the typical age range for "viral croup" (ie, six months to three years) and recurrent episodes that do not appear to be simple "spasmodic croup" should raise suspicion for airway lesions, gastroesophageal reflux or eosinophilic esophagitis, or atopic conditions [38,39,41,53-57]. (See 'Differential diagnosis' below.)
Children who have recurrent croup should be referred to an otolaryngologist. Radiographic evaluation, laryngoscopy, bronchoscopy, and/or esophagoscopy may be warranted. (See 'Radiographs' above and "Assessment of stridor in children".)
DIFFERENTIAL DIAGNOSIS —
The differential diagnosis of croup includes other causes of stridor and/or respiratory distress. (See "Assessment of stridor in children", section on 'Causes of stridor'.)
The primary considerations are those with acute onset (particularly those that may rapidly progress to complete upper airway obstruction) and those that require specific therapy. Underlying anatomic anomalies of the upper airway also must be considered since they may contribute to more severe disease. (See 'Host factors' above.)
Important considerations include (table 2 and table 3) [4,5]:
●Acute epiglottitis – Epiglottitis, which is rare in the era of vaccination against Haemophilus influenzae type b, is distinguished from croup by the absence of barking cough and the presence of anxiety that is out of proportion to the degree of respiratory distress. Onset of symptoms is usually rapid. Affected patients usually have high fevers and appear pale and ill-appearing. Difficulty swallowing and drooling are characteristic features. Affected children usually prefer to sit up and seldom have observed cough [44]. The lateral radiograph in virtually all children with epiglottitis demonstrates swelling of the epiglottis, sometimes called the "thumb sign" (image 2). (See "Epiglottitis (supraglottitis): Clinical features and diagnosis".)
●Bacterial tracheitis – Bacterial tracheitis (sometimes called "bacterial croup") is an invasive exudative bacterial infection of the soft tissues of the trachea. It may occur as a primary infection or as a complication of viral croup. With secondary infection, patients typically present with symptoms of viral croup and then have marked worsening with high fevers, toxic appearance, and severe respiratory distress. The lateral radiograph in children with bacterial tracheitis may demonstrate only nonspecific edema or intraluminal membranes and irregularities of the tracheal wall (image 3). (See "Bacterial tracheitis in children: Clinical features and diagnosis".)
●Peritonsillar, parapharyngeal, or retropharyngeal abscesses – Children with deep neck space abscesses, cellulitis of the cervical prevertebral tissues, or other painful infections of the pharynx may present with fever, drooling, neck stiffness, lymphadenopathy, and varying degrees of toxicity. Barking cough and stridor are usually absent. (See "Peritonsillar cellulitis and abscess", section on 'Clinical manifestations'.)
●Foreign body – In foreign body aspiration, there often is a history of the sudden onset of choking and symptoms of upper airway obstruction in a previously healthy child. If an inhaled foreign body lodges in the larynx, it will produce hoarseness and stridor. If a large foreign body is swallowed, it may lodge in the upper esophagus, resulting in distortion of the adjacent soft extrathoracic trachea and producing a barking cough and inspiratory stridor. Ingestion of a nonobstructive but subsequently erosive foreign bodies such as a button battery may produce stridor more remote from the time of ingestion that persists or recurs [58]. (See "Airway foreign bodies in children" and "Foreign bodies of the esophagus and gastrointestinal tract in children".)
●Allergic reaction or acute angioneurotic edema – Allergic reaction or acute angioneurotic edema has rapid onset without antecedent cold symptoms or fever. The primary manifestations are swelling of the lips and tongue, urticarial rash, dysphagia without hoarseness, and, sometimes, inspiratory stridor [4,5]. There may be a history of allergy or a previous attack. (See "An overview of angioedema: Clinical features, diagnosis, and management", section on 'Clinical features'.)
●Upper airway injury – Injury to the airway from smoke or thermal or chemical burns should be evident from the history. The child typically does not have fever or a viral prodrome. (See "Inhalation injury from heat, smoke, or chemical irritants".)
●Anomalies of the airway – Stridor can be caused by congenital or acquired anomalies of the upper airway (table 2 and table 3), including laryngeal webs, laryngomalacia, congenital subglottic stenosis, subglottic hemangioma, bronchogenic cyst, laryngeal papillomas, and vocal cord paralysis (which can be secondary to laryngeal nerve injury from trauma or surgery or due to neurologic disease [eg, Chiari malformation, Guillain-Barré syndrome, brain or spinal cord tumor]) [59]. Most of these tend to have a more chronic course with absence of fever and symptoms of upper respiratory tract illness, unless the child presents because the airway narrowing is exacerbated by a concomitant viral infection. Subglottic hemangioma (picture 4 and picture 5) should be considered in any young infant who presents with a barking cough and no other signs of a viral infection, particularly if there is a visible hemangioma present in the beard distribution. Often, these infants will respond temporarily to the usual treatment for croup (steroids and nebulized epinephrine); however, the symptoms will recur within a few days of treatment completion. (See "Assessment of stridor in children" and "Congenital anomalies of the larynx" and "Infantile hemangiomas: Epidemiology, pathogenesis, clinical features, and complications", section on 'Airway hemangiomas'.)
SOCIETY GUIDELINE LINKS —
Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Croup".)
INFORMATION FOR PATIENTS —
UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5th to 6th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10th to 12th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.
Here are the patient education articles that are relevant to this topic. We encourage you to print or email these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword[s] of interest.)
●Basics topic (see "Patient education: Croup (The Basics)")
●Beyond the Basics topic (see "Patient education: Croup in infants and children (Beyond the Basics)")
SUMMARY AND RECOMMENDATIONS
●Etiology – Croup is a respiratory illness characterized by inspiratory stridor, barking cough, and hoarseness resulting from inflammation in the larynx and subglottic airway. Croup is usually caused by viruses, most commonly parainfluenza virus type 1. Other common causes include rhinovirus, respiratory syncytial virus (RSV), adenoviruses, and COVID-19. Bacterial infection may occur secondarily, though this is uncommon. (See 'Definitions' above and 'Microbiology' above.)
●Epidemiology – Croup is one of the most common respiratory illnesses in young children. It occurs mostly in children ≤6 years old, with a peak incidence between six months to three years of age. In temperate climates, most cases occur in the fall or early winter. Host factors that may contribute to the development of croup include functional or anatomic susceptibility to upper airway narrowing. (See 'Epidemiology' above and 'Host factors' above.)
●Clinical presentation – Symptoms usually begin with nasal discharge and congestion and progress over 12 to 48 hours to include fever, hoarseness, barking cough, and stridor. If airway obstruction worsens, severe respiratory distress can develop. Croup is usually a self-limited illness that resolves within three days, though the cough may persist for up to a week. (See 'Clinical presentation' above.)
●Rapid assessment – The objectives of the evaluation of the child with croup include assessment of severity (table 1) (calculator 1) and exclusion of other causes of upper airway obstruction. Rapid assessment of general appearance, vital signs, pulse oximetry, airway stability, and mental status are necessary to identify children with severe respiratory distress and/or impending respiratory failure. (See 'Evaluation' above and 'Rapid assessment and initial management' above.)
●Diagnosis – Croup is diagnosed clinically, based upon the characteristic barking cough and stridor. Neither radiographs nor laboratory tests are necessary to make the diagnosis. However, radiographs may be helpful in select cases to exclude other causes if the diagnosis is in question. The characteristic radiographic finding in croup is subglottic narrowing ("steeple sign") (image 1A-B). (See 'Diagnosis' above and 'Radiographs' above.)
●Differential diagnosis – The differential diagnosis of croup includes other causes of stridor and/or respiratory distress. The primary considerations are those with acute onset (particularly those that may rapidly progress to severe upper airway obstruction) and those that require specific therapy. (See 'Differential diagnosis' above.)
Important considerations include (see "Assessment of stridor in children"):
•Acute epiglottitis (see "Epiglottitis (supraglottitis): Clinical features and diagnosis")
•Peritonsillar abscess (see "Peritonsillar cellulitis and abscess")
•Retropharyngeal abscess(see "Retropharyngeal infections in children")
•Foreign body aspiration (see "Airway foreign bodies in children")
•Acute angioedema (eg, anaphylaxis) (see "Anaphylaxis: Acute diagnosis")
•Upper airway injury(eg, from a caustic ingestion) (see "Caustic esophageal injury in children" and "Button and cylindrical battery ingestion: Clinical features, diagnosis, and initial management")
•Congenital abnormalities of the upper airway (table 2) (see "Congenital anomalies of the larynx")
●Recurrent croup – Recurrent episodes of croup-like symptoms that are atypical for simple croup (ie, severe or prolonged symptoms) or that occur outside of the typical age range (ie, earlier than six months or beyond age five or six years) should raise suspicion for another underlying condition (eg, congenital airway abnormalities (table 2), gastroesophageal reflux, eosinophilic esophagitis, atopic conditions). Children with recurrent croup should be referred to an otolaryngologist for further evaluation. (See 'Recurrent croup' above and "Assessment of stridor in children".)
