Parasites that infect the intestine cause morbidity in >25% of the world’s population. Prevalent intestinal parasites within the United States include Enterobius vermicularis, Giardia lamblia, Ancylostoma duodenale, Necator americanus, and Entamoeba histolytica. In the United States, high-risk groups include international travelers, refugees, recent immigrants, and international adoptees.

The most prevalent of the previously listed helminthic organisms in the United States is E. vermicularis, or the pinworm. It has the largest geographic range of any helminth. As many as 30% of children and 10% of adults are infected worldwide. The ubiquitous infection occurs when eggs are ingested via fecal-oral route or via oral contact with contaminated hands or fomites. Infection can also occur when eggs are exposed to the air, aerosolized, and ingested. Slumber parties are an excellent source of cross infestation. The eggs hatch in the duodenum and the larvae mature as they migrate to the large intestine. The worms live primarily in the cecum, from which the pregnant female travels out of the anus at night and lays up to 15,000 eggs on the perineum. Male pinworms measure 2 to 5 mm; females measure 8 to 13 mm. Pinworms typically exit to lay eggs between 10 PM and 11 PM. It is easy to see why autoinoculation and reinfection are common. Most eggs dehydrate within 72 hours. If autoinoculation does not occur, the infestation usually resolves in 4 to 6 weeks.