Definition of Strongyloidiasis:

Strongyloidiasis is infection with the roundworm Strongyloides stercoralis (S. stercoralis).

Causes, incidence, and risk factors:

S. stercoralis is a roundworm that is fairly common in warm, moist areas. Rarely, it can be found as far north as Canada.

People catch the infection when they come in contact with soil contaminated with the worms.

The tiny worm is barely visible to the naked eye. Young roundworms can move through a person's skin and into the bloodstream to the lungs and airways. As the worms grow older, they bury themselves in the walls of the intestines. Later, they produce eggs in the intestines. Areas where the worms go through the skin may become red and painful.

This infection is uncommon in the United States. Most cases seen in North America are brought by travelers who have visited or lived in South America or Africa.