Is Croup Contagious?

Croup is caused mostly by viruses, and sometimes bacteria, and it is highly contagious. Croup, a viral respiratory illness, commonly affects children ages six months to three years.

Croup (laryngotracheobronchitis) is a viral respiratory illness characterized by high-pitched, noisy breathing (stridor), hoarseness, and barking cough.

Croup commonly affects children ages six months to three years. 

What Are Symptoms of Croup?

Early symptoms of croup include: 

• Congestion
• Runny nose
• Inflammation of the mucus membranes inside the nose (coryza)

After the initial symptoms, croup progresses over 12 to 48 hours and symptoms include:

• Hoarseness
• Barking cough
• High-pitched, noisy breathing (stridor)
• Fever
• Mild fast, shallow breathing 
• Mild sore throat
• Pneumonia (in severe cases)

The cough associated with croup usually goes away in about three days though other symptoms may continue for up to a week and before gradually resolving.

Most cases of croup are caused by viruses. Secondary bacterial infections may occur.

Viruses that cause croup include: 

• Respiratory syncytial viruses (RSV)
• Adenoviruses 
• Parainfluenza viruses
  • Most cases of croup occur in the fall (often in October) or early winter, which coincides with parainfluenza type 1 activity.  
• Human coronavirus NL63 (HCoV-NL63)
• Measles (in areas where measles remains prevalent)
• Rhinoviruses
• Enteroviruses (especially Coxsackie types A9, B4, and B5, and echovirus types 4, 11, and 21)
• Herpes simplex viruses 
• Metapneumoviruses 
• Influenza viruses (uncommon)

Secondary bacterial infections of croup include: 

• Staphylococcus aureus
• Streptococcus pneumoniae
• Streptococcus pyogenes

Croup may sometimes be caused by bacteria, including Mycoplasma pneumoniae.

Croup is caused mostly by viruses, and sometimes bacteria, and it is highly contagious. Croup is transmitted from person-to-person through respiratory droplets propelled into the air when an infected person coughs or sneezes.

Croup is diagnosed based on a patient’s symptoms of high-pitched, noisy breathing (stridor) and barking cough, especially during a period when one of the causative viruses is active in the community. 

Tests may be used to rule out other conditions, such as:

• Blood tests
  • White blood cell (WBC)
  • Blood urea nitrogen (BUN)
  • Serum bicarbonate 
• Viral culture and/or rapid diagnostic tests that detect viral antigens 
• Chest X-ray

Mild croup may be treated at home to relieve symptoms and includes:

• Drinking enough fluids
• Humidifier/mist
• Fever reducers 

Medication for mild croup may also include a single dose of oral dexamethasone.

Treatment for moderate to severe croup includes: 

• Nebulized epinephrine 
• Dexamethasone
  • Nebulized budesonide is an alternative 
• Supportive care
  • Adequate fluid intake
  • Humidified air or oxygen
  • Fever reducers 
• Supplemental oxygen if needed