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Medical Professionals

Professional Reference articles are designed for health professionals to use. They are written by UK doctors and based on research evidence, UK and European Guidelines. You may find the Croup article more useful, or one of our other health articles.

Synonyms: acute laryngotracheitis, acute laryngotracheobronchitis

Croup is a common childhood illness causing symptoms which may involve a harsh barking cough, hoarse voice and (inspiratory) stridor. It is usually caused by inflammation of the upper respiratory tract (predominantly the larynx and trachea but it may affect the bronchi) as a result of viral infection.

Some consider that the term croup should not be used to describe illness affecting the bronchi, as there is a higher likelihood of secondary bacterial infection in such cases.

Croup tends to be relatively mild and self-limiting but the distressing symptoms may prompt parents to bring their child to their GP or local emergency department. Severe cases may compromise the upper airway and so the condition of the child needs to be assessed carefully and other causes of upper airway obstruction (such as inhaled foreign body and epiglottitis) must be considered and excluded.

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  • Viruses are detected in up to 80% of patients who have croup with identifiable pathogens.

  • Parainfluenza virus (types 1 to 3) accounts for 75% of all cases, and human parainfluenza virus 1 is the most common type.

  • Other viral causes include influenza A and B, adenovirus, respiratory syncytial virus, rhinovirus and enterovirus.

  • Viral infection of the subglottic region and laryngeal mucosa causes inflammation and oedema, which significantly decrease air movement and lead to respiratory distress and stridor.

  • Bacterial croup is less common and may be caused by Mycoplasma pneumoniae and Corynebacterium diphtheriae.

  • The type of infectious agent does not affect outcomes or initial management.


  • Croup affects about 3% of children per year, mostly between the ages of 6 months and 3 years.

  • Hospital admissions due to croup peak in September to December, but occur throughout the year.

Risk factors

  • Male:female preponderance is about 1.4:1.

  • Genetic studies suggest that the C/C variant of the CD14 C-159T gene had a significantly lower prevalence of croup3 .

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  • Croup normally starts with nonspecific symptoms of viral upper respiratory tract infection (URTI), such as runny nose, sore throat, fever and cough.

  • This progresses over the course of a couple of days to include the characteristic barking cough and hoarseness. These symptoms tend to be worse at night.

  • There is a high degree of variability in clinical findings. There may be a mild-to-moderate fever. Check vital signs (including temperature, pulse and blood pressure).

  • A barking cough and hoarse cry are nearly always present.

  • Stridor (harsh, low-pitched noise heard during inspiration) may be heard at rest or only when the child is agitated or active.

  • Chest sounds are usually normal but can be decreased in volume where there is severe airflow limitation.

  • Respiratory distress with marked tachypnoea and intercostal recession may be noted. It should be recognised that a child whose stridor appears to be improving and in whom intercostal recession has disappeared may in fact be deteriorating with worsening airways obstruction. Such a child may be at high risk of complete airway occlusion2 .

  • Drowsiness, lethargy, and cyanosis despite increasing respiratory distress should be considered as red flags for impending respiratory failure.

  • The illness tends to last for about 3-7 days but can persist for up to two weeks.

Differential diagnosis

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Assessment of severity2

There are many clinical scoring systems for croup. Croup can be classified into mild, moderate or severe4 .

  • Mild - seal-like barking cough but no stridor or sternal/intercostal recession at rest.

  • Moderate - seal-like barking cough with stridor and sternal recession at rest; no agitation or lethargy.

  • Severe - seal-like barking cough with stridor and sternal/intercostal recession associated with agitation or lethargy.

  • Impending respiratory failure - increasing upper airway obstruction:

    • Sternal/intercostal recession, asynchronous chest wall and abdominal movement.

    • Fatigue, pallor or cyanosis, decreased level of consciousness or tachycardia.

    • The degree of chest wall recession may diminish with the onset of respiratory failure as the child tires.

    • A respiratory rate of over 70 breaths/minute is also indicative of severe respiratory distress.

Hospital admission2

Admit all children with features of moderate or severe illness, or impending respiratory failure.

Hospital admission should also be considered for children with a respiratory rate of over 60 breaths/minute or who have a high fever or 'toxic' appearance.

Children with mild illness may require admission if they have factors that warrant a lower threshold for admission, such as:

  • Chronic lung disease (including bronchopulmonary dysplasia).

  • Haemodynamically significant congenital heart disease.

  • Neuromuscular disorders.

  • Immunodeficiency.

  • Age under 3 months.

  • Inadequate fluid intake (50-75% of usual volume, or no wet nappy for 12 hours).

  • Factors that might affect a carer's ability to look after a child with croup, such as adverse social circumstances, or concerns about the skill and confidence of the carer in looking after a child with croup at home, or the carer being able to spot deteriorating symptoms.

  • Longer distance to healthcare in case of deterioration.

While awaiting admission to hospital:

  • Give controlled supplementary oxygen if there are symptoms of severe illness or impending respiratory failure.

  • Give oral dexamethasone (0.15 mg/kg).

  • If the child is too unwell to receive medication, inhaled budesonide (2 mg nebulised as a single dose) or intramuscular dexamethasone (0.6 mg/kg as a single dose) are possible alternatives.


The diagnosis is usually made on clinical grounds but the following investigations may be indicated:

  • A low SaO2 on pulse oximetry (<95%) indicates significant respiratory impairment.

  • It is important to weigh the benefits of investigations such as CXRs and blood tests against the risks of distressing the child and making the symptoms worse5 .

  • A rapid influenza A test can be performed if it is considered vital to do so but even this investigation (which requires a throat swab) can distress the child6 .

  • Direct or indirect laryngoscopy is not usually required but may be employed where the course of the illness is atypical or there is reason to suspect a congenital or other alternative cause for upper airway obstruction.


If hospital admission is not required (mild illness):

  • Prescribe a single dose of oral dexamethasone (0.15 mg/kg) to be taken immediately. Glucocorticoids reduce symptoms of croup at two hours, shorten hospital stays and reduce the rate of return visits to care7 .

  • Advise parents/carers to take the child to hospital if stridor can be heard continually, the skin between the ribs is pulling in with every breath, and/or the child is restless or agitated.

  • Advise parents/carers to call an ambulance if the child:

    • Is very pale, blue, or grey (includes blue lips) for more than a few seconds.

    • Is unusually sleepy or is not responding, is having a lot of trouble breathing (eg, the belly is sinking in while breathing, or the skin between the ribs or over the windpipe is pulling in with each breath; the nostrils may also be flaring in and out).

    • Is upset (agitated or restless) while struggling to breathe and cannot be calmed down quickly.

    • Wants to sit instead of lie down, and/or if they cannot talk, are drooling, or are having trouble swallowing.

Nebulised epinephrine is associated with clinically and statistically significant transient reduction of symptoms of croup 30 minutes post-treatment8 .

Self-care advice

  • Use either paracetamol or ibuprofen to treat a child who is distressed due to fever.

  • Antipyretic agents should not be used with the sole aim of reducing body temperature and should be continued for only as long as the child appears distressed.

  • Consider changing to the other agent if the child's distress is not alleviated, but not to give both agents simultaneously, and only ro alternate these agents if the distress persists, or recurs before the next dose is due.

  • Don't attempt to reduce fever by under-dressing the child, or with use of tepid sponging.

  • Encourage the child to take fluids regularly. For infants who are breastfed, advise continued breastfeeding.

  • Check on the child regularly, including through the night.

  • Arrange follow-up, using clinical judgement to determine the appropriate interval.



  • Symptoms usually resolve within 48 hours.

  • Mild croup tends to be self-limiting even without treatment, with shorter time to resolution with dexamethasone treatment.

  • In most cases of moderate croup, symptoms resolve without significant complications.

  • With dexamethasone and nebulised epinephrine combination treatment, the prognosis for severe croup is excellent.

  • Severe upper airway obstruction can, rarely, lead to respiratory failure and arrest.

  • In children with impending respiratory failure, intubation is required in 1-3% of cases.

  • Death from croup is rare, occurring in about 1 in every 30,000 cases.

Further reading and references

  1. Smith DK, McDermott AJ, Sullivan JF; Croup: Diagnosis and Management. Am Fam Physician. 2018 May 1;97(9):575-580.
  2. Croup; NICE CKS, February 2019 (UK access only)
  3. Rennie DC, Karunanayake CP, Chen Y, et al; CD14 gene variants and their importance for childhood croup, atopy, and asthma. Dis Markers. 2013;35(6):765-71. doi: 10.1155/2013/434920. Epub 2013 Nov 21.
  4. Johnson D; Croup. Clin Evid (Online). 2009 Mar 10;2009. pii: 0321.
  5. Croup (Laryngotracheobronchitis); Nottingham Children's Hospital
  6. Guidance for Clinicians on the Use of Rapid Influenza Diagnostic Tests; Centers for Disease Control and Prevention, 2014
  7. Gates A, Gates M, Vandermeer B, et al; Glucocorticoids for croup in children. Cochrane Database Syst Rev. 2018 Aug 22;8:CD001955. doi: 10.1002/14651858.CD001955.pub4.
  8. Bjornson C, Russell K, Vandermeer B, et al; Nebulized epinephrine for croup in children. Cochrane Database Syst Rev. 2013 Oct 10;(10):CD006619. doi: 10.1002/14651858.CD006619.pub3.

Article history

The information on this page is written and peer reviewed by qualified clinicians.

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