Parasitology Proficiency Testing Program

GENERAL CRITIQUE FOR 03 February 2003

The purpose of the New York State Proficiency Testing Program in the category of Parasitology is to monitor the performance of applicant laboratories in detecting and identifying parasites in fecal emulsions, fecal smears, and blood films.

SAMPLE PREPARATION AND QUALITY CONTROL

All emulsions and slides used in this test were prepared by a commercial source. The emulsions were dispensed into the vials from pools which were continuously mixed during the loading process. Numerous samples of each test specimen were selected at random by the Parasitology Unit of the David Axelrod Institute for Public Health, and were checked to confirm their contents. Extensive quality control tests were also conducted by the supplying vendor and a detailed quality control report was submitted to the New York State Parasitology Laboratory for inspection and verification. Samples were authenticated by 90% of participating laboratories and/or referee laboratories.

RESULTS OF PARTICIPATING LABS

* PLEASE SEE EXPLANATION IN QUALITY CONTROL SECTION

February 2003 DISTRIBUTION OF SCORES

ANSWER KEY

TOTAL POSSIBLE POINTS 100

GRADING

The answer key was derived from the response of all participating laboratories as per CLIA '88 Regulations. These state that 90% or more of participating laboratories or referee laboratories must identify the parasite for it to be correct. Similarly, less than 10% of the participating laboratories or referees finding parasites or ova is an incorrect response. Organisms reported by 10-89% of the laboratories or referees are "Unauthenticated", and are not considered for grading.

Each sample has a maximum value of 20 points. Credit is given according to the formula:

For example: If in sample 03-K you reported the correct answer Hymenolepis nana plus Ascaris lumbricoides (incorrect) your score would be:

If in sample 03-K you reported Hymenolepis nana (correct) plus Trichuris trichiura (no penalty) your score would be:

But, If you reported Trichuris trichiura (no penalty) but failed to report Hymenolepis nana (correct) your score would be:

Quality Control

03-K Participating and referee laboratories agreed that Hymenolepis nana was the correct answer (98 and 100%). Quality control examination of 4% of this sample revealed an average of 12 ova per coverslip. Also present are rare Trichuris trichiura which were seen on quality control examination and by 10% of referee labs so this response was graded as no penalty. Other tests performed included Direct Immunofluorescent Assay and ELISA for Giardia duodenalis and Cryptosporidium sp. which were negative for both organisms. A modified acid-fast stain was also negative.

03-L Participating and referee laboratories agreed that Enterobius vermicularis was the correct response (93 and 100%). Quality control examination of 4% of this sample showed an average of 11 ova per coverslip. Other tests performed included Direct Immunofluorescent Assay and ELISA for Giardia duodenalis and Cryptosporidium sp. which were negative for both organisms. A modified acid-fast stain was also negative.

03-M Participating and referee laboratories agreed that Entamoeba histolytica/dispar was the correct response (95 and 100%). Quality control examination of 4% of this sample showed cysts in every 1-5 100X oil emersion fields. Also present is Blastocystis hominis which was seen by 34% of participating and 20% of referee labs and so was graded as no penalty. Other tests performed included Direct Immunofluorescent Assay and ELISA for Giardia duodenalis and Cryptosporidium sp. which were negative for both organisms. A modified acid-fast stain was also negative.

03-N Participating and referee laboratories agreed that Giardia duodenalis was the correct answer (99 and 100%). Quality control examination of 4% of this sample showed cysts and/or trophozoites in every 2-5 100X oil fields.

03-O Participating and referee laboratories agreed that Plasmodium falciparum was the correct response (97 and 90%). Quality control examination of 4% of this sample revealed at least one organism per every 1-2 oil emersion fields. Primary stage seen was the ring stage trophozoite. Also noted were applique forms, double chromatin, Mauer's dots, and multiply infected cells.

Diagnostic Characteristics

	Hymenolepis nana also known as the dwarf tapeworm is an intestinal cestode acquired by ingesting eggs from the environment or rarely by ingesting infected beetles. Internal autoinfection is also possible. H. nana is the only human tapeworm that doesn't have an intermediate host and transmission occurs from person to person. It has a worldwide distribution and is more commonly seen in children. The diagnostic stage is the egg recovered in stool. These eggs are spherical, thin shelled, and measure 30 to 47 microns in diameter. They have a six hooked oncosphere with two polar thickenings from which filaments arise. These filaments are visible in the space between the embryo and the outer shell. Eggs of H. nana can be confused with the eggs of Hymenolepis diminuta and careful measurement with a calibrated ocular micrometer is essential. The eggs of H. diminuta are much larger measuring 70-85 microns.
	Enterobius vermicularis is an intestinal nematode with a worldwide distribution. It is thought to be the most common human parasitic infection especially in children. Diagnosis is usually made when eggs are detected on cellulose tape preparations. The mature female worms migrate at night out of the anus and deposit their eggs. Eggs may sometimes be found in the stool. The eggs are elongate and flattened on one side with a thick shell. They measure 50-60 microns by 20-30 microns.
	Entamoeba histolytica/dispar is distributed worldwide but is more prevalent in the tropics and subtropics. The trophozoites vary in size from 10-60 microns with an average size of 15 microns. They have a single nucleus that generally has a small centrally located karyosome. The peripheral chromatin is usually smooth and evenly distributed. The cysts measure between 8-15 microns with an average size of 10 microns. The mature cyst has 4 nuclei while the immature cyst can have 1 or 2. Chromatin bars are common and have blunt or rounded ends. Infection occurs by ingesting contaminated food or water. Morphologically E. histolytica/dispar and E. hartmanni are very similar but they differ in size. E. hartmanni is smaller measuring only 5-10 microns for cysts and 8-10 microns for trophozoites. Again careful measurement by a calibrated ocular micrometer is needed.
	Giardia duodenalis is the most commonly diagnosed flagellate in humans. It has a worldwide distribution and is more prevalent in children than in adults. Trophozoites are pear-shaped and measure 10-20 microns. They have 2 nuclei, 4 pair of flagella, 2 axonemes, and 2 median bodies. The infective cysts are oval and measure 11-15 microns. They contain 4 nuclei usually located at one end, filaments, and median bodies.
	Plasmodium falciparum is one of the four species of Plasmodium know to infect humans. It causes the most dangerous and severe form of malaria and is always considered to be a medical emergency. Death may occur rapidly if proper treatment is not started immediately. It's distribution is limited to the tropics, primarily Africa and Asia. P. falciparum invades all ages of RBC's and so the parasitemia can exceed 50%. The usual stages seen in the peripheral blood are rings and gametocytes. Schizogony occurs in the internal organs so it is rare to seen other stages although they may be present in cases of severe malaria. The infected RBC's are not enlarged nor do they contain Schüffner's dots. The rings are generally small, and may have one or two chromatin dots. Applique´ forms are also characteristic. Gametocytes are rounded to banana-shaped and contain a single well defined chromatin and coarse rice-grain like pigment.

IMPORTANT REMINDERS

The next Parasitology Proficiency Test is scheduled for June 02, 2003. You are responsible for notifying us before June 09, 2003 if you do not receive your test. Proficiency test results must be postmarked by June 16, 2003 or you will receive a zero. These requirements are clearly stated in your NYS Proficiency Testing Handbook provided by the NYS Clinical Laboratory Evaluation Program or can be accessed via the internet at http://www.wadsworth.org/labcert/clep/ProgramGuide/WebGuide.pdf

NEWS AND NOTES

Policy changes made by the Clinical Laboratory Evaluation Program now allow for the CQ holder for a particular category to sign the attestation statement instead of the Laboratory Director. Starting with the test event of February 05, 2001 we will now accept Director's and/or CQ holder's signatures on the attestation statement.

The New York State Parasitology Laboratory now has available as an "investigational" tool a Polymerase Chain Reaction(PCR) assay for the detection and species identification of malaria and babesia. Please continue to submit EDTA whole blood samples with all requests for malaria confirmation so we can validate these new assays and make them available as routine diagnostic tests.

The Clinical Parasitology Lab of the NYSDOH now offers two mailing kits for the submission of specimens. One kit contains vials of PVA and Formalin and the other does not. These kits can be ordered by calling 518-474-4175 and requesting kit DOH-2117. Please be sure to specify whether you need preservatives or not.Remember that the NYS Parasitology Lab only accepts specimens preserved in appropriate fixatives for the test requested.

There will be a hands on Malaria workshop held on June 20, 2003 at the Broome County Community College in Binghamton, New York. Details and registration forms will be available soon.

Web site questions or comments or to request a different file format (pdf.,doc.,wpd.) contact:
E-mail: Parasit@wadsworth.org.