Faecal Parasitology: Concentration Methodology Needs to be Better Standardised

Abstract

AimTo determine whether variation in the preservative, pore size of the sieve, solvent, centrifugal force and centrifugation time used in the Ridley-Allen Concentration method for examining faecal specimens for parasite stages had any effect on their recovery in faecal specimens.MethodsA questionnaire was sent to all participants in the UK NEQAS Faecal Parasitology Scheme. The recovery of parasite stages was compared using formalin diluted in water or formalin diluted in saline as the fixative, 3 different pore sizes of sieve, ether or ethyl acetate as a solvent, 7 different centrifugal forces and 6 different centrifugation times according to the methods described by participants completing the questionnaire.ResultsThe number of parasite stages recovered was higher when formalin diluted in water was used as fixative, a smaller pore size of sieve was used, ethyl acetate along with Triton X 100 was used as a solvent and a centrifugal force of 3,000 rpm for 3 minutes were employed.ConclusionsThis study showed that differences in methodology at various stages of the concentration process affect the recovery of parasites from a faecal specimen and parasites present in small numbers could be missed if the recommended methodology is not followed.

Intestinal parasites among rural school children in southern Ethiopia: A cross-sectional multilevel and zero-inflated regression model

“…Single, 41.7-mg thick, Kato-Katz smears were prepared from each stool sample on the same day of specimen collection. Then, 1 g of stool was preserved in 10% formalin solution and processed using the formalin-ether concentration technique (35). The slides were examined by three experienced laboratory technicians.…”

Optimization of routine microscopic and molecular detection of parasitic protozoa in SAF-fixed faecal samples in Sweden

“…Total hands-on time including preparation for the extended method in our is setting estimated to 7-12 min per sample which is less than reported by others [57]. Time of examination per slide is dependent both on the experience and competence of the microscopist, but also on the amount of faecal debris, and optimization of the properties of FEC can decrease time [47] and also, experience decrease time spent per sample. The addition of more staining can be optimized by staining in batch, so that all steps only need to be done once.…”

“…The amount of Cryptosporidium oocysts in this study varied from multiple per vision field to a few per slide. It is important for sediments to have a minimum of faecal debris, especially when detecting the small Cryptosporidium and the properties of FEC vary and several factors influence the ability to decrease faecal debris in the sediment and thereby the result, for instance centrifugation time and speed, filtration pore size, preservative and sample quality [47]. The use of metal sieves may have improved yield, studies have shown that Cryptosporidium can end up in the gauze that is traditionally used for filtration [48], but it was not part of the study.…”

Internal Quality Assurance Status of Stool Examination as Assessed by a Questionnaire in Korean Clinical Laboratories

“…Importantly, the rate of positive stool tests differed markedly according to the laboratory performing the testing (ranging from 0.0% to 6.7%; data not shown). Previously, Manser et al also demonstrated that variations in the procedures for stool examinations could reduce the recovery of parasites at different stages, particularly if present in small numbers [5]. We suggest that the standardization of stool examinations in regards to the overall methodology and QC is needed.…”

“…Most of the responses were from laboratories in medical institutions with 500-1,000 beds (53.8%, 21/39), followed by seven institutions with less than 200 beds (including three referral medical laboratories), seven institutions with 200-500 beds, and four institutions with greater than 1,000 beds (Table 1). Fecal concentration is recommended to increase the chance of detecting parasitic ova, cysts, and larvae, particularly in specimens where they are present in insuf cient numbers to be seen using direct microscopy [5]. Although more than a half of the laboratories (51.3%) performed stool concentration using formalin-ether or Tween 80, a third of the laboratories (30.8%) performed direct smears only.…”