The most commonly reported intestinal protozoal infection in the United States is:

A) giardiasis
B) dysentery
C) amebiasis
D) colitis

A) giardiasis
A) Giardiasis is the most commonly reported intestinal protozoal infection in the United States. It is an infection in which trophozoites attach to the mucosa of the duodenum and jejunum, then multiply using binary fission. Most cases of giardiasis are transmitted through contaminated water or food, sexual contact, and other direct contact.