more likely it is that the causative agent will be identified and the infection confirmed. It is often imperative that the laboratory follow up with specific questions for the physician; information received with the test request may be minimal, at best.
Immune Status of the Patient
Certain parasites can cause severe illness in debilitated patients and should be considered when these patients present with relevant symptoms. Infections that may cause few to no symptoms in an immunocompetent host may cause prolonged illness in an immunocompromised patient. Unfortunately, this information is not always readily available. Client education can help to increase awareness of possible infections with human parasites.
Clinical Symptoms
When infectious diseases are suspected, there are a number of possible etiologic agents. When a patient presents with gastrointestinal symptoms, it is difficult to tell whether the cause is infectious and, if so, which microbe might be responsible. These symptoms often have many non-infectious causes, so laboratory findings can be extremely valuable in confirming a suspected infectious organism. The same diagnostic procedures can also be used to rule out specific etiologic agents.
Documented Previous Infection
Many parasitic infections are extremely difficult to cure or may not cause symptoms on a continual basis; past exposure or prior documented disease will provide valuable information to the laboratory. Knowing that the patient may be experiencing a relapse can guide the laboratory in detecting the suspected organism.
Contact with Infected Individuals
In situations where multiple reports of symptomatic patients are confirmed, contacts with these infected patients should be tested, particularly during a potential outbreak. An example of this type of situation would be outbreaks of diarrhea in the nursery school setting. When Cryptosporidium is identified as the causative agent, all nursery school attendees, employees of the school, and family members are often tested for infection. Another example might involve a group of individuals who experience the same symptoms at similar times after attending a function where food was served; the causative agent might be confirmed as Cyclospora cayetanensis.
Potential Outbreak Testing
In potential outbreak situations, laboratories that perform certain tests on request only may revise their protocol and begin to test all specimens for a particular suspected parasite. A potential Cryptosporidium outbreak might require a change from testing on request only to screening all fecal specimens submitted for parasite testing for this particular organism. Often this occurs after consultation among various groups such as health care providers, public health personnel, water company personnel, and pharmacy purchasing agents (who may report an increase in the purchase of antidiarrheal medication).
Occupational Testing
The most common example of occupational testing would involve food handlers and routine testing for intestinal parasites. This practice is less common than in the past, probably due to financial constraints. Each city, county, and state has specific regulations and/or recommendations.
Therapeutic Failure
With few exceptions, patients are generally retested after therapy to confirm therapeutic efficacy. If testing reveals the infection has not been eradicated, there may be several reasons. In some cases, the patient may not have taken the medication correctly or may have failed to take the number of recommended doses; these reasons are more likely than the presence of a drug-resistant organism. However, there are certainly examples where drug resistance is possible and is the more likely reason, often depending on the geographic area involved. Another reason might involve the timing between therapy and posttreatment checks for cure; if the time lag is extended, the patient’s infection may also represent reinfection. This is particularly true if the patient’s living conditions, site, and other epidemiological considerations are not modified.
What Testing Should Be Performed?
Routine Tests
“Routine” can imply a widely used, well-understood laboratory test; it can also imply a low or moderately complex method, rather than a high complexity procedure. Routine diagnostic parasitology procedures could include the ova and parasite examination (O&P exam), preparation and examination of blood films and pinworm tapes/paddles, occult blood tests, and examination of specimens from other body sites (urine, sputum, duodenal aspirates, urogenital specimens, etc.).
The selection and use of routine test procedures often depend on a number of factors including geographic area, population served, overall positivity rate, client preference, number of test orders, staffing, personnel experience, turnaround time requirements, epidemiology considerations, clinical relevance of test results, and cost. Routine tests generally have a wide range in both sensitivity and specificity. As an example, the O&P exam (direct wet mount, concentration, permanent stained smear) could be considered a routine test method for the detection of a number of different intestinal protozoa and helminth infections; this procedure is moderately sensitive but relatively nonspecific. Monoclonal antibody-based test methods tend to be very specific (generally for a single organism such as Giardia lamblia) and more sensitive than the routine O&P exam for specific intestinal protozoa. However, the test results are limited in scope; either the organism is present or it’s not, and none of the other possible etiologic agents have been ruled in or out!
Diagnostic laboratories generally offer tests “on request”; an example would be testing for the presence of Cryptosporidium spp. However, if a potential waterborne outbreak was suspected, this laboratory might change its approach and begin testing all stool specimens submitted for an O&P exam rather than testing only specimens accompanied by a specific test request for Cryptosporidium spp. These decisions require close communication with other entities, as described above for potential outbreak testing.
Special Testing
Special procedures, such as parasite culture, are often performed in limited numbers of laboratories. These procedures require the maintenance of positive control cultures used for quality control checks on all patient specimens; they also require special expertise and time. Many clinical laboratories do not meet these requirements. Although some standardized reagents are now commercially available, many clinical laboratories choose to send their requests for serologic testing for parasitic diseases to other laboratories. Often, the Centers for Disease Control and Prevention (CDC) perform serologic testing on specimens submitted to each state’s Department of Public Health. Generally, specimens for parasitic serologic testing are not submitted directly to CDC but instead are submitted through state public health laboratories. In an emergency situation, consultation with your county or state public health laboratory may allow shipment of a specimen directly to CDC.
Other (Nonmicrobiological) Testing
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