Croup is an inflammation of the upper and lower airways due to a viral infection; it is also called laryngotracheitis.
The most common cause is the parainfluenza virus, particularly type1. Occasionally other viruses such as influenza (type A or B), RSV, rhino-, entero- and adenoviruses, Mycoplasma pneumoniae and the measles can also produce this. The typical age group to develop this is aged 6 months to 3 years.
There are seasonal peaks with parainfluenzae virus outbreaks occurring in the fall, whereas RSV and influenza virus cases occur more in the winter and spring.
The virus is causing inflammation of the trachea, the larynx, the bronchial tubes, the small bronchial tubes (bronchioles) and the lung tissue.
However the most prominent feature is the swelling and obstruction due to fibrinous inflammatory material in the subglottic area (thanks to www.andorrapediatrics.com for this image), the area underneath the vocal cords. This leads to an stridor and difficulties breathing. X-rays show the narrowing of the air ways, called the “Steeple” sign.
Typically the child suddenly awakes in the middle of the night with a barking cough, a stridor, fast breathing rate and respiratory distress. If the symptoms were not bad enough in the first night to go to the Emergency Room of the hospital, the symptoms get better during the day, only to worsen the following night. Typically it peaks on day 2 or 3 of the disease. The physician hears a prolonged inspiration with stridor through the stethoscope, often there are wheezes on expiration as well. The more severe cases will likely need hospitalization for a few days until the respiratory distress is over. Patients with an allergic predisposition and patients where the virus has caused viral pneumonia with a lowered oxygen uptake will more likely need hospitalization.
Treatment is supportive and observant. Transcutaneous oximetry is done for monitoring the oxygen uptake at any given moment. Some patients deteriorate and need emergency intubation or tracheotomy and they are the ones where the oximetry monitor (a clip on the finger or the ear lobe) shows a deteriorating oxygen concentration in the blood. The patient is often placed in a croupette, which is a plastic tent where moist air is fortified with oxygen. The moisture allows the swelling in upper airways to subside faster and the oxygen improves the oxygenation of all of the tissues. Most patients do not need intubation and can leave the hospital after 2 or 3 nights. Most of the time there is no bacterial superinfection following the parainfluenza virus infection and the immune system overcomes this by producing specific antibodies. Antibiotics are therefore rarely needed.
1. The Merck Manual, 7th edition, by M. H. Beers et al., Whitehouse Station, N.J., 1999. Chapter 161.
2. TC Dixon et al. N Engl J Med 1999 Sep 9;341(11):815-826.
3. F Charatan BMJ 2000 Oct 21;321(7267):980.
4. The Merck Manual, 7th edition, by M. H. Beers et al., Whitehouse Station, N.J., 1999. Chapter 43.
5. JR Zunt and CM Marra Neurol Clinics Vol.17, No.4,1999: 675-689.
6. The Merck Manual, 7th edition, by M. H. Beers et al., Whitehouse Station, N.J., 1999. Chapter 162.
7. LE Chapman : Antivir Ther 1999; 4(4): 211-19.
8. HW Cho: Vaccine 1999 Jun 4; 17(20-21): 2569-2575.
9. DO Freedman et al. Med Clinics N. Amer. Vol.83, No 4 (July 1999): 865-883.
10. SP Fisher-Hoch et al. J Virol 2000 Aug; 74(15): 6777-6783.
11. Mandell: Principles and Practice of Infectious Diseases, 5th ed., © 2000 Churchill Livingstone, Inc.
12. Goldman: Cecil Textbook of Medicine, 21st ed., Copyright © 2000 W. B. Saunders Company
13. PE Sax: Infect DisClinics of N America Vol.15, No 2 (June 2001): 433-455.
14. David Heymann, MD, Editor: Control of Communicable Diseases Manual, 18th Edition, 2004, American Public Health Association.