are compromised through underlying illness, chemotherapy, transplantation, AIDS, or age, we are much more likely to see increasing numbers of opportunistic infections, including those caused by parasites. Also, we continue to discover and document organisms that were thought to be nonpathogenic but, when found in the compromised host, can cause serious disease. In assessing the possible cause of illness in this patient population, the possibility of parasitic infections must be considered as part of the differential diagnosis.
Approach to Therapy
As new etiologic agents are discovered and the need for new therapeutics increases, more sensitive and specific diagnostic methods to assess the efficacy of newer drugs and alternative therapies will become mandatory. Skilled laboratorians, physicians, public health personnel, and other health care team members will be required to think globally in terms of infectious diseases caused by bacterial, fungal, parasitic, and viral etiologies, particularly when certain parasitic infections require very specific therapeutic regimens.
Who Should Perform Diagnostic Parasitology Testing?
Laboratory Personnel
Diagnostic procedures in the field of medical parasitology require a great deal of judgmental and interpretative experience and are, with very few exceptions, classified by the Clinical Laboratory Improvement Act of 1988 (CLIA ’88) as high-complexity procedures. Very few procedures can be automated, and organism identification relies on morphologic characteristics that can be very difficult to differentiate. Although morphology can be “learned” at the microscope, knowledge about the life cycle, epidemiology, infectivity, geographic range, clinical symptoms, range of illness, disease presentation depending on immune status, and recommended therapy is critical to the operation of any laboratory providing diagnostic services in medical parasitology. As laboratories continue to downsize and reduce staff, cross-training will become more common and critical to financial success. Maintaining expertise in fields such as diagnostic parasitology has become more difficult, particularly when using standard manual methods. Also, the lower the positive rate for parasitic infections, the more likely it is that the laboratory will generate both false-positive and false-negative laboratory reports. It is important for members of the health care team to thoroughly recognize areas of the clinical laboratory that require experienced personnel and why various procedures are recommended above others.
Nonlaboratory Personnel
Health care delivery settings where physicians provide parasitology diagnostic testing occasionally provide “simple” test results (CLIA ’88 waived tests) based on wet mount examinations. However, in spite of the CLIA classification of these diagnostic methods, wet mount examinations are often very difficult to perform, and results are often incomplete or incorrect. Currently, there are no specific “over the counter” testing methods for parasitic infections; however, the future may see some newer diagnostic developments in this area. The key to performance of diagnostic medical parasitology procedures is formal training and experience. As the laboratory setting continues to change during the 21st century, it is important to recognize that these changes will require a thorough understanding of the skills required to perform diagnostic parasitology procedures and the pros and cons of available diagnostic methods. Laboratories will have a number of diagnostic options; whatever approach is selected by an individual laboratory, the clinical relevance of the approach must be thoroughly understood and conveyed to the “client” user of the laboratory services.
Where Should Diagnostic Parasitology Testing Be Performed?
Inpatient Setting
Most diagnostic parasitology procedures can be performed either within the hospital setting or in an offsite location. There are very few procedures within this discipline that must be performed and reported on a STAT basis. Two procedures fall into the STAT category: request for examination of blood films for the diagnosis of malaria or other blood parasites and examination of cerebrospinal fluid (CSF) for the presence of free-living amebae, primarily Naegleria fowleri. Any laboratory providing diagnostic parasitology procedures must be prepared to examine these specimens on a STAT basis 7 days a week, 24 h a day. Unfortunately, these two procedures can be very difficult to perform and interpret; cross-trained individuals with little microbiology training or experience will find this work difficult and subject to error, and this will cause severe risk management issues for the laboratory. It has been well documented that automated hematology instrumentation lacks the sensitivity to diagnose malaria infections, particularly since most patients seen in an emergency room have a very low parasitemia. However, even a low parasitemia can be life-threatening in an infection with Plasmodium falciparum.
Outpatient or Referral Setting
Diagnostic laboratories outside of the hospital setting are very appropriate settings for this type of diagnostic testing; the test requests, for the most part, are routine and are “batch” tested rather than tested singly. With very few exceptions, STAT requests are not relevant and are not sent to such laboratory locations; therefore, immediate testing and reporting are not required.
Decentralized Testing
Point-of-care testing within the hospital (ward laboratories, intensive care units, emergency rooms, and bedside) is usually not considered appropriate for diagnostic parasitology testing; one exception might be the emergency room, where patients with malaria may first present with fever and general malaise. Alternative sites (outpatient clinics, shopping malls, senior citizen groups and others) are generally not considered appropriate settings for diagnostic parasitology testing, although relevance might be dictated by geographic location and the development of newer, less subjective methods.
Physician Office Laboratories
As mentioned above, the majority of physician office laboratories are not involved in diagnostic parasitology testing; however, as more molecular biology-based (nonmicroscopic) methods are developed, they may become more widely used in this setting. One example would be the fecal immunoassay rapid-lateral-flow cartridges, specifically designed to detect antigen of Cryptosporidium spp., Giardia lamblia, the Entamoeba histolytica/E. dispar group, or Entamoeba histolytica. Rapid tests for the detection of Plasmodium spp., particularly P. falciparum, are also currently available.
Over-the-Counter (Home Care) Testing
Currently no diagnostic tests for medical parasitology are available for this potential market. However, outside of the United States, some of these options are more likely to be available.
Field Sites
Field sites are very relevant for diagnostic parasitology testing, particularly in many areas of the world where instrumentation and automation are not routinely found within clinical laboratories. As the methodology becomes less expensive and easier to use and interpret, testing sites outside of the routine laboratory may become more relevant, particularly when associated with epidemiologic studies.
What Factors Should Precipitate Testing?
Travel and Residence History
Although travel history is generally considered in terms of weeks and/or months, a number of parasitic infections involve potential exposure many years earlier. The patient may become symptomatic years after having left the area of endemic infection. Therefore, it is important