Comparison of methods for identification of Giardia lamblia

Stool specimens from children in daycare centers were screened for Giardia lamblia and intestinal amoebae by staining wet mounts with methylene blue and dilute Lugol's iodine. Merthiolate-iodine-formalin concentrations (MIFC) and permanent smears stained with Wheatley's trichrome method also were done. In addition, stools were preserved with polyvinyl alcohol (PVA) and 10% formalin and tested with trichrome and MIFC, respectively. The effectiveness of each method was based on a quantification scheme. Trichrome and MIFC were the best identification methods for cysts of G. lamblia. Trichrome was the superior method for identification of trophozoites. The other staining procedures were significantly less accurate. The use of preservatives did not improve recovery of G. lamblia compared with same morning processing of fresh stools. This study provides evidence that a permanent stain such as trichrome is an important tool for the diagnosis of G. lamblia and should be included in the processing of any diarrheal stool.