An optimised and standardised test to determine the presence of the protozoa Cryptosporidium and Giardia in water

Abstract

With funding from the European Commission, a consortium of members of the European Water Research Institutes is carrying out a programme of work with the objective of optimising and standardising a method for determining the presence in water of (oo)cysts of Cryptosporidium and Giardia. Each of the stages of the conventional analysis procedure (initial concentration, recoveryand identification and enumeration) are being investigated and the relative merits of existing and new methods are being assessed. Newly developed filters (Envirochek and Filta-Max) have been shown to be more efficient for initial recovery of (oo)cysts from water than the previously used Cuno cartridge filters. In addition, for the analysis of raw waters, flocculationwith ferric sulphate has been shown to give recoveries similar to the Envirochek and Filta Max. Modern purification systems such as immunomagnetic separation have also been assessed and found to offer some advantages over flotation although optimisation of the latter has brought improved efficiency. Preliminary assessment of solid phase cytometry has indicated that this technique could offer significant time savings compared to conventional microscopic counting. The results of the study will be used to propose a revised standard method to CEN.

Effect of Particles on the Recovery of Cryptosporidium Oocysts from Source Water Samples of Various Turbidities

“…We found in this study that when silica particles in the size range from 5 to 40 m were added to tap water to increase the turbidity to more than 10 NTU or when particles larger than 40 m were added to tap water to obtain a turbidity of 5 NTU, various amounts of particles remained on the filter after the elution process. Furthermore, a large amount of particles may also affect the IMS step, as reported by Stanfield et al (13) and Campbell and Smith (2). This was also noted from microscopic observations made in this study.…”

“…As shown by the data given above, recovery of oocysts by using a Dynal anti-Cryptosporidium IMS kit yielded excellent results, and the average level of recovery was 95.1% (standard deviation, Ϯ3.4%). Using the same type of kit, Bukhari et al (1) found that the levels of oocyst recovery ranged from 68 to 83% for deionized water, while Stanfield et al (13) reported a mean level of recovery of 96.1% for treated water. The manufacturer-stated levels of recovery fell within the range from 60 to Ͼ95% for treated and raw waters.…”

“…Turbidity was among the possible factors which affected oocyst recovery in the IMS procedure. However, there has not been unanimous agreement concerning turbidity as some studies have shown that turbidity has little effect on oocyst recovery in the IMS procedure (11), while other studies have indicated that samples with high turbidity can result in low levels of oocyst recovery (2,13). It has even been reported there was an optimum turbidity of 500 nephelometric turbidity units (NTU) which could result in the highest level of oocyst recovery (1).…”

Recuento y determinación de viabilidad de giardia spp. y Cryptosporidium spp. en aguas potables y residuales en la cuenca alta del rio Bogotá.

“…Se ha observado que la recuperación con gradientes de sacarosa es poco eficiente, variable y, en cierto grado, afecta la viabilidad de los organismos en la muestra (37). Sin embargo, un estudio más reciente realizado por Stanfield et al (38) demuestra que el Percoll-sacarosa fue el mejor gradiente de densidad para la recuperación de Giardia spp. En cuanto a los resultados para Cryptosporidium spp., se observaron pequeñas diferencias en comparación con otros gradientes de densidad pero, de igual manera, presentaron un alto porcentaje de recuperación.…”

“…De otra parte, y según los estudios realizados por Stanfield et al (38), entre los filtros con mayor porcentaje de recuperación de protozoos en el análisis de aguas potables, se encuentran el Genera Filtra Max, el Cryptoscan (Aldreck) y el Envirocheck®Gelman, este último con porcentajes de recuperación para Giardia del 56,7% y para Cryptosporidium del 58,1%, evaluado a partir de muestras con concentración de 10 4 quistes u ooquistes por 10 litros.…”