Detection of Giardia lamblia cysts in non-fixed long-term stored human feces by direct immunofluorescence assay

Giardia lamblia cysts in fecal specimens are detected by conventional morphological methods. The direct immunofluorescence monoclonal antibody assay (DFA) is also applied to detect G. lamblia cysts in feces, but little is known about the usefulness of DFA in fecal specimens stored under various conditions. The aim of the present study was to evaluate the DFA for detection of G. lamblia cysts and to compare these results with the direct smear method in long-term storage of non-fixed fecal specimens. Fecal specimens with G. lamblia cysts were stored in a refrigerator at 5 degrees C(14 samples), a freezer at -20 degrees C (9 samples), or in 3.9% formalin-saline solution at room temperature (28 samples). G. lamblia cysts were detected by DFA in all stored specimens, while they were detected in only 56% of refrigerated and 93% of frozen specimens by the direct smear method. The storage period of all samples testing negative by direct smear was more than 24 months. Many degenerated cysts were recognized by DFA when cysts were negative by the direct smear method. Our results indicate that DFA is a useful method for detecting G. lamblia cysts in fecal samples that have undergone long-term storage.