What is croup? what causes croup?

What is croup? what causes croup?

Croup is a term used to describe inflammation of the larynx and trachea in children.

A variety of inflammatory conditions can cause croup, which is characterized by varying degrees of inspiratory stridor (airway obstruction), barking cough and hoarseness due to obstruction in the region of the larynx.

The upper respiratory tract includes the following organs, structures and tissues:

  1. Larynx (voice box with vocal chords)
  2. Pharynx (top of throat where the openings of the mouth and nose meet)
  3. Epiglottis (flap of tissue in the throat that prevents food and liquids from entering the windpipe)
  4. Trachea (windpipe that leads to bronchi)
  5. Bronchi (tubes that branch off the trachea and lead into the lungs).

The main symptoms of croup include a "barking" cough which can sound similar to a barking seal or sea lion and which often has a sudden overnight onset

The barking cough characteristic of croup is a result of swelling and inflammation around the vocal chords and windpipe (i.e., the larynx and trachea). Although most children with croup improve within a few days, hospitalization may be necessary in severe cases.

You will also see introductions at the end of some sections to any recent developments that have been covered by Medical-Diag.com's news stories. Also, look out for links to information about related conditions.

  • Croup accounts for 15% of respiratory illness in children, but almost never occurs in teenagers or adults
  • Croup may occur in 3% of children up to the age of 6, with 1.5-31% of these admitted to the hospital
  • Average age for viral croup is 1-6 years, with peak incidence between 6 months and 3 years
  • Up to 80% of cases are due to parainfluenza viruses 1, 2 and 3, with types 1 and 2 accounting for around 66% of cases
  • The most severe cases of croup are due to influenza A
  • The most common type of croup is a viral type affecting the upper respiratory tract (laryngotracheitis)
  • Bacterial and viral agents can cause disease lower in the respiratory tract (laryngotracheobronchitis and laryngotracheobronchopneumonitis, for example)
  • Common bacterial agents responsible for bacterial croup (also known as bacterial tracheitis) include Staphylococcus aureusStreptococcus pyogenes and Streptococcus pneumonia
  • The main symptom of croup is a distinctive "barking cough"
  • The majority of cases of croup are mild and can be managed at home
  • Before 1970, diphtheria was a common cause of croup (most children are now vaccinated against diphtheria).

What is croup?

Croup is categorized either by the cause (e.g., virus, bacteria) or by specific symptoms that may accompany the cough. Below is an overview of viral and bacterial croup.

Viral croup (most common)

Viral croup is the most common type and is caused by viruses, such as adenoviruses (cold viruses) and influenza (flu) viruses.

Laryngotracheitis is most often caused by a virus, as is recurrent (spasmodic) croup, and they have a similar presentation, making it difficult to distinguish between the two clinically. Some researchers argue that spasmodic croup may be linked to allergens such as pollen, a bee sting or allergic reaction to viral antigens, rather than a direct result of a viral infection.6,7,8

Spasmodic croup Laryngotracheitis
  • Sudden night time onset
  • Harsh, vibratory sound associated with mild upper respiratory tract infection
  • No inflammation.
  • Inflammation of the larynx
  • Inflammation of the trachea.
Typical age at occurrence
  • 3 months - 3 years
  • 3 months - 3 years

Bacterial croup

Bacterial croup is caused by a bacterial infection. This type is significantly less common than viral croup and can be subdivided into bacterial tracheitis, laryngotracheobronchitis (LTB), laryngotracheobronchopneumonitis (LTBP) and laryngeal diphtheria.6,8

Laryngotracheobronchitis (LTB) and laryngotracheobronchopneumonitis (LTBP) Laryngeal diphtheria
  • Inflammation of the larynx
  • Inflammation of the trachea
  • Inflammation of the bronchi
  • Inflammation of the lung.
  • Infection of larynx
  • Infection of other airway areas due to corynebacterium diphtheriae, resulting in progressive airway obstruction.
Typical age at occurrence
  • 3 months - 3 years
  • All ages

What causes croup?

Viral croup

Human parainfluenza viruses types 1, 2 and 3 account for 80% of all cases of croup. Human parainfluenza virus 1 (HPIV-1) is the most common cause of croup, with parainfluenza types 1 and 2 accounting for around 66% of all cases of croup. Type 4, with subtypes 4A and 4B, have been associated with milder illness, but are not well understood.

Studies suggest that respiratory syncytial virus, metapneumovirus, influenza A and B, adenovirus, coronavirus and mycoplasma cause the remaining cases of croup.9

Viral infection that escalates to croup typically takes the following course:9

  1. The virus infects the nose and throat
  2. The virus spreads along the respiratory tract (back of throat) to the larynx and trachea
  3. As the infection progresses, the top part of the trachea becomes swollen
  4. The space available for air to enter the lungs becomes narrower
  5. Children compensate for this narrowing by breathing more quickly and deeply, leading to symptoms of croup
  6. The child may become restless or anxious (agitated) as breathing becomes more difficult. Agitation can also cause constriction (narrowing) of the throat, which increases breathing difficulties and can exacerbate agitation. The effort required to breathe faster and harder is tiring, and the child may become exhausted and unable to breathe on his or her own in severe cases.

Summary table of possible causes of viral croup:8

Cause Spasmodic croup Laryngotracheitis
Individual and family history
  • Possible family history of croup
  • Possible previous attack.
  • Possible family history of croup.
Microbiologic findings
  • Etiologic agents similar to those in laryngotracheitis.

Most commonly caused by:

  • Parainfluenza virus 1, 2, 3
  • Influenza virus A, B
  • Respiratory syncytial virus
  • Metapneumovirus
  • Measles virus
  • Adenoviruses
  • Coronavirus
  • Mycoplasma
  • Rhinoviruses.

Bacterial croup

Bacterial infection usually affects the same areas as viral infection but is typically more severe and requires different treatment. Most instances of illness are due to secondary bacterial infection from: Staphylococcus aureus, other bacteria include Streptococcus pyogenes, Streptococcus pneumonia, Haemophilus influenza and Moraxella catarrhalis.10

Cause Laryngotracheobronchitis (LTB) and laryngotracheobronchopneumonitis (LTBP) Laryngeal diphtheria
Individual and family history
  • Possible family history of croup.
  • Possible family history of croup.
Microbiologic findings
  • May be caused by a virus (e.g., parainfluenza virus 1, 2 or 3 or influenza virus A or B)
  • Bacterial infection from: staphylococcus aureus, other bacteria staphylococcus aureus, streptococcus pyogenes, streptococcus pneumonia, haemophilus influenzae and moraxella catarrhalis.
  • Corynebacterium diphtheriae (identified on smear and culture of membrane).

Signs and symptoms

The main symptoms of croup are a "barking cough" - often compared to the barking of a seal or sea lion - which may begin suddenly during the night.The child may also have a runny nose, sore throat, congestion and mild fever a few days before the cough starts. Croup is usually mild and lasts less than a week. More severe cases are due to difficulty breathing caused by swelling in the upper part of the windpipe.11

85% of children examined at the emergency room have mild croup. Severe croup is rare and accounts for less than 1%.8

The child may also have a runny nose, sore throat, congestions and fever. Croup is usually mild and lasts less than a week.

Other symptoms of croup may include:

  • Noisy breathing - a rasping sound when breathing in or wheezing when breathing out
  • Hoarse throat
  • Other problems with breathing
  • His or her chest moving up and down more than normal during breathing
  • A high fever (40°C or more)
  • Rash
  • Eye redness (conjunctivitis)
  • Swollen lymph nodes
  • Dehydration
  • Low oxygen levels (hypoxia) and blue-tinged skin (cyanosis) can develop, as airflow to the lungs is restricted. Cyanosis may first be noticed in the fingers and toenails, ear lobes, tip of the nose, lips, tongue and inside of the cheek.

Uncommon complications of croup include pneumonia and pulmonary edema and bacterial tracheitis.12

Summary table of possible signs and symptoms of viral croup:8

Symptoms Spasmodic croup Laryngotracheitis
Early symptoms
  • Mild coryza (acute inflammatory contagious disease involving the upper respiratory tract).
  • Usually coryza.
Onset (time to full-blown disease)
  • Sudden
  • Always at night.
  • Moderately rapid but variable
  • Onset mimics that of a cold (nasal irritation, cough, coryza)
  • Fever occurs within first 24 hours
  • Signs of obstructed upper airway and symptoms occur within 12 to 48 hours.
  • Hoarseness
  • Barking cough
  • No dysphagia
  • Minimal-to-moderate inspiratory stridor
  • Nontoxic presentation.
  • Hoarseness
  • Barking cough
  • No dysphagia
  • Minimal-to-severe inspiratory stridor
  • Minimally toxic presentation.
Signs of presentation
  • No fever
  • No pharyngitis (inflammation of the pharynx)
  • Normal epiglottis (the flap of cartilage that covers the windpipe while swallowing).
  • Fever, usually 37.8°C to 40.5°C
  • Minimal pharyngitis
  • Normal epiglottis.
Radiographic findings
  • Subglottic (The lower part of the larynx, the area from just below the vocal cords down to the top of the trachea.) narrowing on posterior-anterior view.
  • Subglottic narrowing on posterior-anterior view.
White cell count
  • Normal.
  • Mildly elevated with >70% polymorphonuclear cells (category of white blood cell).

Summary table of possible signs and symptoms of bacterial croup:8

Symptoms Laryngotracheobronchitis (LTB) and laryngotracheobronchopneumonitis (LTBP) Laryngeal diphtheria
Early symptoms
  • Usually coryza.
  • Usually pharyngitis.
Onset (time to full-blown disease)
  • Gradually progressive over a period of 12 hours to 7 days.
  • Slow, progressing over a period of 2 to 3 days.
  • Hoarseness
  • Barking cough
  • No dysphagia
  • Inspiratory strider, usually severe
  • Typically toxic presentation.
  • Hoarseness
  • Barking cough
  • Usually dysphagia
  • Minimal-to-severe inspiratory stridor
  • Usually nontoxic presentation.
Signs of presentation
  • Fever, 37.8°C to 40.5°C
  • Minimal pharyngitis
  • Normal epiglottis.
  • Fever, 37.8°C to 38.5°C
  • Membranous pharyngitis
  • Epiglottis usually normal but may contain membrane.
Radiographic findings
  • Subglottic narrowing on post-anterior view
  • Irregular soft-tissue densities in trachea on lateral view
  • Bilateral pneumonia.
  • Not useful.
White cell count
  • Usually elevated or abnormally low, with >70% neutrophils and increased percentage of band forms.
  • Usually elevated, with increased percentage of band forms.

Tests and diagnosis

Each year, about 5% of young children develop croup. Croup occurs more often in boys than in girls and some children may be prone to developing croup more than once.9

Croup is typically seen among infants, toddlers and young children between the ages of 3 months and 6 years. As breathing passages are larger in older children and adolescents, upper respiratory tract swelling and inflammation usually do not result in croup symptoms. Although rare, it is possible for children over 6 years old to get croup.

A variety of scoring systems have been developed to evaluate the severity of croup. Below is an indication of how the severity of croup might be analyzed using the Westly and Alberta Clinical Practice Guideline Working Group guidelines.8

Level of Severity Characteristics


Level 0 to 2

  • Occasional barking cough
  • Inspiratory stridor that is absent or intermittent
  • No chest wall retraction or cyanosis
  • Child appears otherwise normal.


Level 3 to 5

  • Barking cough
  • Persistent audible stridor at rest
  • Some tracheal tug and chest wall retraction
  • Child may be agitated but can be placated and is responsive to care givers and the surroundings.


Level 6 to 11

  • Frequent barking cough
  • Prominent inspiratory stridor at rest
  • Marked sternal wall retraction
  • Significant agitation, distress, lethargy
  • Tachycardia may be present with more severe obstructive symptoms.

Impending respiratory failure

Level 12 to 17

  • Barking cough (often not prominent)
  • Audible stridor at rest (occasionally hard to hear)
  • Sternal retractions (may not be marked)
  • Lethargy or decreased level of consciousness
  • Often-dusky appearance in the absence of supplemental oxygen.


Croup is caused by viruses that can spread through coughing, sneezing and respiratory secretions (mucus and droplets from coughing or sneezing), children with croup should be considered contagious for 3 days after the illness begins or until the fever is gone.11

An infection by a virus that causes croup in a young child may cause a cough or sore throat in an older child or adult, but is unlikely to cause the breathing symptoms of croup. However, rarely, symptoms of croup can occur in teenagers or adults.

Different diagnosis

Cases of croup differ in severity and cause, necessitating careful diagnosis to ensure appropriate treatment. Several differential diagnoses exist for croup, with symptoms often caused by one of the following acute obstructive conditions in the region of the larynx:8,9

  • Acute laryngeal fracture
  • Angioedema
  • Arnold-Chiari deformity
  • Burns or thermal injury
  • Dandy-Walker syndrome
  • Epiglottitis
  • Extrinsic obstruction by a vascular ring
  • Foreign body
  • Laryngeal papillomatosis
  • Laryngomalacia
  • Neoplasm or hemangioma
  • Peritonsillar abscess
  • Retropharyngeal abscess
  • Smoke inhalation
  • Subglottic stenosis
  • Vocal cord paralysis.

In recurrent pediatric croup, reflux a possible factor

Children who suffer from several occurrences of croup should be evaluated for reflux disorders, says new research presented at the 2008 American Academy of Otolaryngology - Head and Neck Surgery Foundation (AAO-HNSF) Annual Meeting & OTO EXPO in Chicago, IL.

Treatment and prevention

In cases severe enough to warrant medical attention, a doctor will recommend treatment options for croup, and will decide if admission to hospital is necessary.

The majority of cases of croup are mild and can be managed at home. A single dose of oral dexamethasone is often recommended alongside advice given to a parent or caregiver on how to manage symptoms and when to seek further medical attention.

A single dose of oral dexamethasone, a corticosteroid

Randomized controlled trials (RCTs) have found that, compared with placebo, a single dose of oral dexamethasone in children with mild croup reduces the proportion who re-present with croup in the following 7-10 days. Steroid medicines do not shorten the length of the illness, but they have anti-inflammatory activity and are likely to reduce the severity of breathing symptoms.10,11

Prednisolone may be used as an alternative to dexamethasone in some cases.

Management advice to parents or caregivers

Parents and caregivers are typically given a range of strategies to help manage symptoms of croup in a child in their care.11

Remaining calm and reassuring is important for any caregiver looking after a child with croup. This is because small children with croup can easily become distressed, leading to crying which can make symptoms worse. The child should be placed in an upright position if their breathing is noisy or difficult.

The child needs to be kept calm and soothed. Anxiety and panic can make symptoms worse.

Any caregiver who notices any of the following signs of symptoms should seek further medical help:

  • Breathing becomes difficult
  • The child is very pale or blue
  • The child becomes agitated, delirious, or listless
  • Breastbone is drawn right back on breathing
  • The child has a high temperature and is drooling
  • The parent is concerned for any other reason
  • Severe agitation alongside respiratory distress and/or cyanosis requires immediate referral to the emergency room.

Typically, croup:

  • Resolves within 48 hours, with no residual effects
  • Is followed by symptoms of upper respiratory tract infection (URTI).

More information on managing croup

Paracetamol and ibuprofen can be used to control fever and pain, but tepid-sponging is not recommended to control fever.

It is important to ensure adequate fluid intake, but humidification is not recommended as there is no evidence that it is beneficial in primary or secondary care, and there are risks from humidifiers (including the spread of microbes and mildew) and steam inhalation (burns).

Cough medicines and decongestants are not effective for relieving symptoms of croup.

Parents and caregivers should also be reassured, in the event symptoms occur suddenly at night that croup is usually a self-limiting disease and exposing the child to cool night air may relieve mild respiratory distress.

Antibiotics are not usually prescribed for viral croup as they are not effective unless there is a secondary bacterial infection.

The following have been found to be effective in relieving the symptoms of moderate/severe croup:1,11

  • Oxygen: Oxygen administration should be reserved for children with hypoxia (oxygen on room air saturation less than 92%) and significant respiratory distress
  • Nebulized adrenaline (epinephrine): Required for severe croup only, this is delivered by intermittent positive pressure breathing and offers improvements up to 30 minutes after administration for acute croup. Nebulized adrenaline has been consistently demonstrated by several randomized controlled trials (RCTs) to be of benefit in children with moderate-to-severe croup
  • Glucocorticoids: Dexamethasone, budesonide and prednisone have been shown to be effective up to 12 hours after treatment
  • Intubation: Intubation is only required in about 1% of croup cases, when the airway obstruction is not relieved by conservative treatment and the child's condition continues to deteriorate.

When to seek medical help

A doctor or nurse should always be consulted if there are any concerns about the child's condition. Most children with croup have mild symptoms and will recover with 7 days. However, a minority of children need hospital care.

In particular, a doctor must be seen quickly if:11

  • Breathing symptoms get worse - signs include rapid breathing, needing more effort to breathe, and pulling in of the chest or neck muscles with each breath
  • The child becomes restless or agitated
  • The child looks unusually pale
  • A high fever persists despite giving acetaminophen (paracetamol) or ibuprofen.

An emergency ambulance should be called if the child is:

  • Blue (cyanosed)
  • Unusually sleepy
  • Struggling to breathe
  • Drooling and unable to swallow.

Inhaled epinephrine confirmed quick, effective for croup

For more than 30 years, pediatricians have treated children who have croup with inhaled epinephrine to relieve their symptoms quickly. Now, a new review confirms the value of this approach to treat this common respiratory illness, which sometimes turns serious and, in rare instances, can prove fatal.

Use of high humidity does not improve symptoms for children with croup

For children with moderate to severe croup treated in the emergency department, use of high humidity did not improve symptoms more than low humidity or mist therapy, according to an article in the March 15 issue of JAMA.

Croup: Causes, Symptoms and Treatment | St. Louis Children's Hospital (Video Medical And Professional 2020).

Section Issues On Medicine: Disease