Croup is a common disease in children. While rare, can still occur in adults, yet when it does it is more severe, often requiring care in intensive care units.
Croup is caused by inflammation and swelling around the vocal cords, and can cause a harsh barky cough, and may also lead to breathing difficulty if the air passages becomes partially blocked. If severe, it may lead to death.
The simplest treatment for croup may be to place the child in a hot, steamy bathroom. This tends to ease some of the swelling. Another treatment may be to go outside in the cool, fresh air. However, when these simple treatments don't work, a visit to a physician, or an emergency room, may be required. In some instances, a stay in a hospital may be required. Death, however, from croup is rare.
The cause of croup is most often a virus, but occasionally it can be caused by a bacteria. Croup is contagious, as the germs that cause it may be exhaled and transferred through the air in droplets. The best way to prevent the spread of it is to wash your hands frequently, clean up surfaces touched by those who are infected, and to cover your mouth when you sneeze or cough.
While croup is a lot less common in adults than it is in children, it is possible for a rare form of croup to affect adults, so it is best to take precautions to avoid contracting croup, even if you are an adult. Here are some everyday tips on how to keep your lungs clean: http://www.healthcentral.com/copd/cf/slideshows/9-ways-to-keep-your-airways-clear-and-lungs-clean
I found a really nice case study on adult croup by Karger: Medical and Scientific Publishers, "Adult Croup: A Rare but More Severe Condition." Basically, 11 cases of adult croup were reviewed. All required a stay in the hospital ranging anywhere from 3-35 days. While ten of the patients required care in an intensive care unit, none of them died. So, adult onset croup tends to be more severe than child onset croup, although it is not deadly if treated properly.
It's also interesting to note that the presumed reason croup is more common in children is because they have narrower airways than adults. Because their airways are narrow, even slight inflammation may partially block their air passages, causing the symptoms of croup (harsh voice, barky cough, shortness of breath, fever, etc.)