July 1, 2019: Washington Post: CDC warns swimmers about ‘Crypto,’ a parasite that can live for days in pools
The Centers for Disease Control and Prevention published a report last week about the increased number of outbreaks caused by the fecal parasite Cryptosporidium, more commonly known as “Crypto.”…
The warning came from the CDC’s recent Morbidity and Mortality Weekly Report, which highlighted an average 13 percent increase in cryptosporidiosis outbreaks each year from 2009 to 2017.
The CDC said that over the past decade, there have been more than 400 reported outbreaks in the United States, leading to nearly 7,500 people becoming sick. Of those, more than 200 people were hospitalized, and one person died as a result of the disease, according to the report…
In about 35 percent of the outbreaks, sicknesses were linked to swimming pools and playgrounds, according to the report.
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A terrific review article (S Mohapatra et al. Am J Gastroenterol 2018; 113: 805-18) provides a great deal of information about gastrointestinal parasites. Thanks to Ben Gold for this reference (& don’t forget to vote for NASPGHAN president).
Generally, the authors dispute the usefulness of testing for ova and parasites (O&P) with three separate specimens. While classic training has noted the intermittent shedding of parasites and the suboptimal sensitivity of O&P, the authors note that a recent study showed a detection of 91% of parasites in the first stool sample. In addition, newer PCR based assays are more appropriate in many clinical situations due to their improved sensitivity.
The authors first review the protozoa, which are single-celled, motile, free-living organisms, in depth & summarized in Table 1; these include the following:
- Amoeba: Entamoeba histolytica (E histolytica),
- Dientamoeba fragilis
- Blastocystis hominis
- Coccidia: Cryptosporidium, Cystiospora, Cyclospora
- Ciliates: Balantidium coli
- Flagellates: Giardia lamblia
- Trypanosoma cruzi
Next, they review the helminths in depth and in Table 2, which are large, multicellular organisms that can be seen with the naked eye and include the following:
- Ascariasis: A lumbridcoides
- Enterobiasis: E vermicularis
- Hookworm disease: A dudenale, N amercanus
- Strongyloides: S stercoralis
- Groups of helminths: trematodes (eg. Schistosomes), cestodes (tapeworms eg. Taenia), and nematodes (roundworms eg. Ascariasis, hookworm, pinworms, and whipworms).
- For E histolytica, ELISA fecal antigen test is superior to O&P as is the PCR assay. If the diagnosis of E histolytica is being considered in the setting of ulcerative colitis, the authors note that this infection must be excluded before the initiation of corticosteroid therapy since steroids can lead to hyperinfection and could be fatal. Also, the so-called “flask shaped” ulcers seen with this infection refers to the microscopic appearance of the ulcer into the submucosa. Most infections (>90%) remain asymptomatic.
- Blastocystis “is the most common parasite identified in stool samples in the US” though the pathogenicity remains controversial and is often self-limited.
- D fragilis “as a pathogen is controversial…[but] recent studies on patients infected only with D fragilis have found an association with diarrhea, abdominal pain, nausea, weight loss, anorexia, and flatus which resolve after eradication.”
- Giardiasis is “the most common intestinal parasitic disease affecting humans in the US.” PCR/molecular methods are highly sensitive (>90%) and specific (nearly 100%)
- Enterobius vermicularis (pinworms). The “CDC does not recommend stool examination for O&P since the yield is low.” The diagnostic test is the “Scotch test” in which tape is left overnight in the perianal region and then examined for captured eggs.
- “Restrict stool examination [for parasites] to patients with persistent diarrheal illness with a duration greater than 7 days.” Do not check O&P in hospitalized patients more than 3 days into their hospitalization.
- The most common parasitic infections, Giardia and Cryptosporidium, are best diagnosed with a stool immunoassay (EIA) rather than O&P. For E histolytica EIA is recommended over O&P.
- In those who are persistently symptomatic and with travel history with likely parasite exposure, stool O&P with wet mount/AFB stain/special stains for detection of rare parasites still is worthwhile. In those without exposure history and with persistent diarrhea (after exclusion of Giardia and Cryptosporidium), consider non-infectious causes of diarrhea.
- We discourage repeating the O&P due to the “very low incremental yield of second and third samples”
My take: This article makes a strong argument that “O&P times three” represents an outdated approach in the diagnosis of parasitic diseases in the US.
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