The pathogen that causes croup can easily pass from one person to another through a medium of infectious droplets of saliva sneezed or coughed by the affected child. It can also be spread through doors, furniture, toys, clothes and other objects which might get contaminated with the mucus or sputum of the sick child. A healthy child who comes in contact with such objects, can easily develop the symptoms of croup. This disease commonly affects children younger than 5 years of age, and rarely, adults.