Faecal Parasitology: Concentration Methodology Needs to be Better Standardised.

AIM: To 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. METHODS: A 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. RESULTS: The 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. CONCLUSIONS: This 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.

Comparison between the Midi Parasep and Midi Parasep Solvent Free (SF) faecal parasite concentrators.

AIM: To compare the recovery of parasites in faecal samples using the Midi Parasep with ethyl acetate and Midi Parasep Solvent Free (SF) faecal parasite concentrators. METHODS: 23 preserved and 11 fresh faecal samples were microscopically examined for the presence of parasites using the Midi Parasep concentrator with ethyl acetate centrifuged for 1 and 3 min and the Midi Parasep SF concentrator. RESULTS: The Midi Parasep SF faecal parasite system recovered significantly fewer ova and cysts and resulted in a notably larger deposit than the Midi Parasep concentrator with ethyl acetate. CONCLUSIONS: Parasites present in small numbers that would be detected using the Midi Parasep concentrator with ethyl acetate could be missed using the SF faecal parasite system.

The United Kingdom National External Quality Assessment Service for parasitology: toxoplasma serology scheme.

AIM: To examine performance in the UK National External Quality Assessment Scheme (UKNEQAS) for toxoplasma serology for evidence of discrepant results as compared with the predistribution and postdistribution results supplied by the toxoplasma reference laboratories. METHODS: Analysis of performance in the toxoplasma IgG and IgM schemes was made for the period 1994-2008 to look for trends in performance. RESULTS: For the IgG scheme, a mean of 98% of participants obtained the correct result for detection of toxoplasma-specific antibody. The most common problem was failure to detect low levels of antibody. In some cases this was the result of participants deviating from the manufacturer's instructions and using higher cut-off levels. For the IgM scheme, an average of 95% of participants obtained the correct result for toxoplasma antibody detection. The most common problem was the failure of some enzyme immunoassay kits to detect specific toxoplasma IgM antibody, which was detected by the more sensitive immunosorbent agglutination assay. CONCLUSIONS: Performance standards in the UKNEQAS toxoplasma serology schemes were high. The problems encountered have highlighted the importance of detecting low levels of antibody, adhering to the kit manufacturer's instructions and selecting an appropriate assay for the clinical situation.