C-224. Evaluation of the PlexusTM Parasite Multi-Analyte Diagnostics Test Kit for Detection of Giardia lamblia and Cryptosporidium parvum Antigens in Formalin Fixed Stool Specimens

M. J. Marcon, D. Salamon, K. Mack, K. Everhart, L. Sherman, A. Leber;
Nationwide Children's Hosp., Columbus, OH.

Sensitive and specific laboratory diagnosis of parasitic infection due to Giardia lamblia (Gl) and Cryptosporidium parvum (Cp) is important in many clinical settings. Laboratory diagnosis is commonly performed by traditional ova and parasite microscopic exam of fresh or preserved stool specimens following formalin-ethyl acetate concentration procedures and preparation of permanent-stained smears. More recently, direct antigen detection methods for these pathogens have become popular; these methods are based on either direct fluorescent antibody assay or enzyme immunoassay performed in microwell plates. The Plexus (Focus Diagnostics Inc., Cypress, CA) Parasite Multi-Analyte Assay, not yet commercially available, is a multiplexed micro-particle, bead-based immunoassay performed on a Luminex 200 (Luminex Corp., Austin, TX) platform and designed for qualitative detection of Gl, Cp, and non-dispar Entamoeba histolytica (Eh) antigens in human fecal specimens. In this study, a total of 176 formalin-preserved stool specimens (1 per patient)submitted to the laboratory by physician order for routine ova and parasite exam or Gl/Cp antigen testing (ProspecT Microplate Assay, Remel, Inc. Lenexa, KS) were evaluated in the Plexus Parasite Assay for Gl and Cp antigens. Of the 176 specimens, 37 and 7 (44 total) were pre-selected as “presumed Gl or Cp positives”, respectively, based on routine lab testing. For the presumed Gl positives, 36/37 tested positive in the Plexus Assay for Gl and 1 tested equivocal. All 7 presumed Cp positives tested positive in the Plexus Assay for Cp. The remaining 132 specimens were prospectively collected without selection. Of these, 1 was positive for Gl by both routine testing and Plexus and 1 was similarly positive by both testing methods for Cp. The Plexus Parasite Multi-Analyte Assay performs comparably to current methods used in the laboratory for detection of Gl and Cp in fecal specimens. Further evaluation is needed to confirm these findings and to develop data to support the diagnostic efficiency of this assay for Eh.