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O&P
Formal name: Ova and Parasite Exam Related tests: Stool Culture, Giardia, Cryptosporidium, and Entamoeba histolytica antigen tests
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Common Questions
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1. How can I prevent a parasitic infection?
2. Will an O&P detect all parasites?
3. Why does it need to be a fresh stool sample?
4. Are those parasitic worms I’m seeing in my stool sample?
5. Are there other ways to test for parasites besides the microscopic exam?
6. Once I’ve had a parasitic infection, can I be re-infected?
7. Why shouldn’t I take an over the counter anti-diarrhea medicine?
1. How can I prevent a parasitic infection?
The best way is to avoid food and water that is suspected of being contaminated. This is especially true if you travel to developing nations, where ice in a drink or a dinner salad may expose you to parasites. But the clearest mountain stream should also be suspect; it could be contaminated with giardia. You cannot see most parasites; you won’t be able to smell them or taste them in the water. If someone in your family has a parasitic infection, careful handwashing after going to the bathroom can help prevent passing the parasite on to others. The infected person should avoid preparing food for others until their symptoms are gone.
2. Will an O&P detect all parasites?
No, only those that live in the intestines and whose eggs are passed through the feces. There are other tests specific for other parasites, such as pinworms or blood parasites that cause malaria.
3. Why does it need to be a fresh stool sample?
The structure of the parasites may deteriorate in unpreserved stool, which would destroy the identifying characteristics of the parasite and make the infection harder to detect.
4. Are those parasitic worms I’m seeing in my stool sample?
Most of the common parasites are much too small to be seen with the naked eye. What you are probably noticing are undigested food fibers. The only way to be sure though is to look at the sample under the microscope. Parasites have characteristic external and internal structures that fibers do not have.
5. Are there other ways to test for parasites besides the microscopic exam?
Yes, antigen tests have been developed for several common parasites including giardia, cryptosporidium, and E. histolytica. The antigen tests detect protein structures on the parasite, and they can detect the presence of fragments of the parasite in a stool sample. This has the advantage of allowing detection of that particular parasite even if it is not seen in the microscopic O&P examination. Blood antibody tests may be ordered to determine whether or not someone has been exposed to a parasite in the past. This may indicate a past or a chronic infection but is not used to detect a current infection. Sometimes a biopsy of the small intestines is taken, and the small amount of tissue is examined for parasitic infestation.
6. Once I’ve had a parasitic infection, can I be re-infected?
Yes, you can become re-infected if exposed again. This may happen if you have a family member who has an asymptomatic parasitic infection, such as giardiasis (due to giardia), and continues to shed the organisms and re-infects others until everyone is treated.
7. Why shouldn’t I take an over the counter anti-diarrhea medicine?
You should only take this on the advice of your doctor. Diarrhea is one of the methods your body uses to help rid itself of the infection. If you slow down or prevent this from happening by taking anti-diarrhea medication, you can prolong the amount of time that you are ill and may make your infection worse.
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This article was last reviewed on
January 28, 2008.
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