Detection of helminth ova and larvae in trichrome-stained stool smears

The detection and identification of intestinal helminths were studied retrospectively by comparing the Formalin concentration technique with the trichrome-stained smear technique. A total of 3,997 stool samples from 1,570 patients were examined by both methods. Of the 3,997 samples, 31% (1,239 of 3,997) contained helminths or protozoans or both. A total of 11% (434 of 3,997) of the samples representing 14% (221 of 1,570) of the patients were positive for one or more helminth species. A total of 570 separate identifications of helminth ova/larvae were made. Among the helminth ova/larvae identified. 14.6% (83 of 570) were detected only in the trichrome-stained smear, representing 6.3% (14 of 221) of the patients. From these data, it can be concluded that unless a diligent search of the stained smear for helminths is made, a significant number of helminth infections may be missed. It is, therefore, recommended that stained stool smears be used to aid the detection of helminth ova/larvae in conjunction with Formalin concentration. The appearance of the most common helminth ova/larvae in trichrome-stained smears is described, along with specific characteristics that may be used for their identification. In addition, the advantages and disadvantages of the trichrome staining technique for helminth identification are discussed.