title: Comparison of sensitivity and specificity of 4 methods for detection of Giardia duodenalis in feces: immunofluorescence and PCR are superior to microscopy of concentrated iodine-stained samples.
abstract: For decades, microscopy of feces after formol-ethylacetate (FEA) concentration and iodine staining has been the routine test for intestinal protozoa. Lately, polymerase chain reaction or fluorescence-labeled parasite-specific antibodies have been introduced, but their place in everyday routine diagnostics has not yet been established. We compared FEA and salt-sugar flotation (SSF) concentration followed by microscopy of iodine-stained concentrate and immunofluorescence assay (IFA) and real-time polymerase chain reaction (qPCR) for detection of Giardia duodenalis in human feces. The median number of Giardia cysts found by FEA in 19 Giardia-positive samples was 50 cysts per gram (CPG), by SSF 350 CPG, by IFA 76,700 CPG, and by qPCR 316,000 CPG. We next tested 455 consecutive samples for presence of Giardia cysts. Using IFA as reference, qPCR had a sensitivity of 91%, specificity of 95.1%, a false-positive rate of 50%, a false-negative rate of 0.48%, a positive predictive value of 50%, and a negative predictive value of 99.5%. In conclusion, qPCR and IFA were significantly more sensitive than microscopy of iodine-stained concentrates using either FEA or SSF. We suggest, when using qPCR, that positive samples are verified by IFA to prevent false-positive results.
authors.affiliation: Department of Infectious Diseases, Aarhus University Hospital Skejby, Aarhus Denmark.
authors.forename: Helle
authors.initials: H
authors.lastname: Gotfred-Rasmussen
authors.affiliation: Department of Clinical Microbiology, Aarhus University Hospital Skejby, Aarhus Denmark.
authors.forename: Marianne
authors.initials: M
authors.lastname: Lund
authors.affiliation: Norwegian Veterinary Institute, PO Box 750 Sentrum, N-0106 Norway.
authors.forename: Heidi L
authors.initials: HL
authors.lastname: Enemark
authors.affiliation: Department of Public Health, Section for Biostatistics, Aarhus University, Aarhus, Denmark.
authors.forename: Mogens
authors.initials: M
authors.lastname: Erlandsen
authors.affiliation: Department of Infectious Diseases, Aarhus University Hospital Skejby, Aarhus Denmark; Department of Clinical Microbiology, Aarhus University Hospital Skejby, Aarhus Denmark. Electronic address: eskildp@dadlnet.dk.
authors.forename: Eskild
authors.initials: E
authors.lastname: Petersen
mesh_terms: D005243:Feces / Q000469:parasitology*; D005455:Fluorescent Antibody Technique; D016829:Giardia lamblia / Q000235:genetics* / Q000276:immunology*; D005873:Giardiasis / Q000175:diagnosis* / Q000469:parasitology*; D006801:Humans; D008853:Microscopy / Q000379:methods; D016133:Polymerase Chain Reaction / Q000379:methods; D060888:Real-Time Polymerase Chain Reaction; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
keywords: Diagnostic methods; Giardia; Immunofluorescence; Microscopy; PCR