Department of Health

Key messages

  • Croup or bronchiolitis are most often caused by respiratory syncytial virus, parainfluenza viruses, influenza and adenoviruses.
  • In Australia, croup is more common in autumn and affects young children. Bronchiolitis is more common in winter and predominantly affects children in the first year of life.
  • There are no exclusion requirements, but children with croup or bronchiolitis should not attend school or childcare if they are unwell.
  • Public health action is dependent on the setting in which the case has occurred.

Notification requirement for croup or bronchiolitis

Notification is not required.

Primary school and children’s services centre exclusion for croup or bronchiolitis

School exclusion is not required.

Infectious agent of croup or bronchiolitis

Respiratory syncytial virus (RSV), parainfluenza viruses, influenza and adenoviruses are the major causative agents.

Parainfluenza type 1 virus is the most common cause of croup (laryngotracheobronchitis) and RSV the most common cause of bronchiolitis.

Picornaviruses (rhinoviruses and enteroviruses) and bocavirus have also been isolated from patients with croup. Co-infection with rhinoviruses is particularly frequent. Croup can also be an uncommon complication of measles.

Identification of croup or bronchiolitis

Clinical features

Disease is generally characterised by fever and one or more systemic reactions, such as chills, headaches, generalised aches, malaise and anorexia in a young child, usually between 6 months and 3 years of age. Gastrointestinal disturbances may also occur. In young children, general features are often not apparent and disease presents with localising signs at various sites in the respiratory tract.


Croup is an acute respiratory illness characterised by a distinctive barking cough, hoarseness and inspiratory stridor in a young child. It has a prodrome of fever, runny nose and sore throat. Cough is also common. Inflammation at the subglottic level produces a classic high-pitched inspiratory stridor and a hoarse voice. The larger airways are narrowed by inflammation, resulting in various degrees of shortness of breath and increased respiratory rate. Airway obstruction can progress to indrawing of the intercostal spaces and the soft tissues of the neck, cyanosis and death without urgent treatment.


A 1–7 day prodrome of mild fever, coryza and cough is common with bronchiolitis. Disease can rapidly progress to deepening cough, tachypnoea, restlessness, chest wall retraction, nasal flaring and grunting. Audible wheezing is a characteristic feature. It can be accompanied by paroxysms of coughing, vomiting, dehydration, otitis media and diarrhoea.


The diagnosis of croup and bronchiolitis is usually based on characteristic clinical findings. Serologic diagnosis can be unreliable. Identification of the specific viral agent may be accomplished by isolation in microbiological culture from throat, tracheal and nasal wash specimens, or by multiplex polymerase chain reaction (PCR).

Incubation period of croup or bronchiolitis viruses

The incubation period varies from 1 to 10 days.

Public health significance and occurrence of croup or bronchiolitis

There are limited data on the epidemiology of croup and bronchiolitis in Australia. Croup is more common in autumn and affects young children. It peaks in the second year of life. Bronchiolitis is more common in winter and predominantly affects children in the first year of life.

Lower respiratory tract infections due to viral agents are significant causes of infant and childhood morbidity and mortality worldwide. People with underlying cardiac or pulmonary disease or compromised immune systems are at increased risk for serious complications of RSV infection, such as pneumonia and death. RSV infection among recipients of bone marrow transplants has resulted in high mortality rates. Symptomatic RSV disease can recur throughout life because of the limited protective immunity induced by natural infection.

Reservoir of croup or bronchiolitis viruses

Humans are the reservoir.

Mode of transmission of croup or bronchiolitis viruses

RSV is transmitted via oral contact, droplet spread or by contact with hands or fomites soiled by respiratory discharges from an infected person.

Period of communicability of croup or bronchiolitis

RSV is communicable shortly before and for the duration of active disease. Prolonged shedding of RSV has been documented.

Susceptibility and resistance to croup or bronchiolitis

Everyone is susceptible to infection. Re-infection with the agents that cause croup is common, but the infection is generally milder.

Control measures for croup or bronchiolitis

Preventive measures

There is no vaccine available. Basic hygiene can help limit the spread of many diseases, including croup and bronchiolitis.

Control of case

Children with these diseases should not attend school or childcare centres while unwell.

Control of contacts

Investigation of contacts is not necessary, but the diagnosis should be considered in other family or close contacts if they are symptomatic.

Control of environment

Not applicable.

Outbreak measures for croup or bronchiolitis

Public health action is dependent on the setting in which the case has occurred and is based on an assessment of ongoing risk. The risk for nosocomial transmission of RSV increases during community outbreaks. Nosocomial outbreaks of RSV can be controlled by adhering to contact and respiratory precautions.

Reviewed 08 October 2015


Contact details

Do not email patient notifications.

Communicable Disease Section Department of Health GPO Box 4057, Melbourne, VIC 3000

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