The scotch tape test for Enterobius vermicularis, the common pinworm, is one of the really simple, inexpensive and just plain cool tests used in primary care. In addition the life cycle of the pinworm is well understood and is quite unique (not to mention disgusting) in that it depends completely on humans eating feces repeatedly.
To understand why the scotch tape test work works we need to first review the interesting life cycle of the pinworm. Enterobius vermicularis is known as the pinworm because it is about the size of a common pin. It lives in the human small intestine and proximal colon. After living a few weeks the female worm migrates down the colon, exits the anus and lays its eggs on the skin of the perianal area at night. The female dies after laying her eggs. The worm and the eggs seem to lead to itching, which initiates scratching which helps facilitate the eggs getting on the fingers and then reingested. The infection is most common in children who have less concern about putting their hands in their mouth after scratching or touching their anal area, and self-inoculate themselves. The ingested eggs then hatch in the duodenum, the males and females mate, the male dies and the female moves to the distal small bowel after molting twice as she passes through the bowel, and the process is repeated.
This sounds disgusting but the fecal-oral route of spread is a common way that infections are spread. The unique thing about the pinworm is that it’s probably the only common human infestation that depends on people perpetuating and sustaining the infestation by repeatedly ingesting more eggs over and over. If no eggs were reingested the infestation would die out as the worms die after laying their eggs.
All this sounds terrible, but there are a few good things about pinworms. The first is that the infection is almost harmless. Infection tends to either be asymptomatic, or just cause perianal itching. In girls it can sometimes cause a vaginal itch if the organisms inadvertently crawl into the vagina instead of the rectum after coming out to lay their eggs.
The second good thing is that pinworms are easily diagnosed. When I see a child I suspect of having pinworms I have their parent wake them about 2-3 AM and look at their anus with a flashlight. Often the worms can be seen on the outside. Sometimes they are also seen in the diaper or the toilet after a bowel movement. If not seen the scotch tape test is done by taking a piece of scotch tape, applying the sticky side to the child’s anus on awakening in the morning, and sticking the piece of tape to a microscope slide. I just give a few microscope slides to the parent to collect the specimens at home on two or three mornings, and have them bring the slides in for me to examine. The pinworm eggs are easy to see under the microscope, and a diagnosis is made if eggs are noted.
The third good thing about pinworms is that treatment is very easy and effective. A single dose of mebendazole, a 100 mg chewable tablet, is effective in most cases. We do routinely treat the whole family at once to eradicate the organism from any unsuspecting family members and increase the chance of long term cure.
Unfortunately reinfection is common, especially in children in daycare or when they originally contacted the organism from another child who remains undiagnosed. If your child contacts pinworms, don’t be overly concerned. It’s common, easily treated and not at all serious.