Parasites are a source of significant illness worldwide. In the United States, giardiasis, cryptosporidiosis, cyclosporiasis, and trichinellosis are nationally notifiable conditions. Pinworm, the most common intestinal parasite in children, is not a locally notifiable infection. Intestinal parasites have a wide range of acute and chronic symptoms but should be suspected in those who present with diarrhea lasting more than seven days. Infections most often occur through a fecal-oral route. Symptoms tend to be worse for children, older adults, or immunocompromised individuals. To diagnose Giardia infection, stool microscopy with direct fluorescent antibody testing is recommended; metronidazole, nitazoxanide, or tinidazole is used for treatment. Microscopy with immunofluorescence is sensitive and specific for diagnosing Cryptosporidium infection. This infection is often self-resolving, but treatment with nitazoxanide is effective for symptoms lasting more than two weeks. Microscopy or polymerase chain reaction assays are recommended to diagnose Cyclospora infections, and sulfamethoxazole/trimethoprim may be used to treat patients with persistent diarrhea. Trichinella infection is diagnosed by serum antibody testing, and severe symptoms are treated with albendazole in patients older than one year. Pinworm infections are diagnosed visually or by a tape test or paddle test; albendazole and pyrantel pamoate are both effective treatments.
Intestinal parasites found in the United States include one-celled protozoa and soil-transmitted helminths. Examples of nationally notifiable one-celled protozoa infections include giardiasis, cryptosporidiosis, and cyclosporiasis.1,2 Soil-transmitted helminths are the most common intestinal parasites worldwide, causing an estimated 2.6 billion infections per year.3 The most common soil-transmitted helminth in the United States is Enterobius vermicularis (pinworm).4 Trichinella (roundworm) is another soil-transmitted helminth and is nationally notifiable in the United States.1,2 [corrected] Parasites generally spread through a fecal-oral route. Good hygiene, handwashing, and proper handling of food and water are key to preventing intestinal parasitic infections. Additional specific guidance for prevention is listed in Table 1.5–8
SORT: KEY RECOMMENDATIONS FOR PRACTICE
| Clinical recommendation | Evidence rating | Comments |
|---|---|---|
| In immunocompetent patients without a history of travel to areas with endemic parasites, ova and parasite examination should not be ordered if diarrhea has lasted fewer than seven days.9,10 | C | Choosing Wisely and the 2017 Infectious Diseases Society of America clinical practice guideline |
| Microscopy with direct fluorescent antibody testing is the preferred test for Giardia.18,20 | C | Expert opinion and comparative diagnostic studies |
| A single dose of tinidazole is the most effective treatment for people older than three years with Giardia infection (greater than 90% cure rate).12,13 | A | Systematic review and network meta-analysis |
| Cryptosporidium infection with diarrhea persisting beyond two weeks should be treated with nitazoxanide (Alinia).14 | A | Prospective randomized controlled trial |
A = consistent, good-quality patient-oriented evidence; B = inconsistent or limited-quality patient-oriented evidence; C = consensus, disease-oriented evidence, usual practice, expert opinion, or case series. For information about the SORT evidence rating system, go to https://www.aafp.org/afpsort.
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