Cryptosporidium parvum and Giardia duodenalis can cause severe diarrhoea in infected individuals and their transmissive stages, oocysts and cysts, are voided in large numbers with the faeces of infected hosts. Contaminated sewage effluents are recognised as a potential source of waterborne (oo)cysts. In this investigation methods optimised for the recovery of both from a range of wastewaters were used to determine the occurrence of these organisms in influents, effluents and sludges from seven sewage treatment works in England. The data indicated the presence of small numbers of oocysts both in sewage influent and effluent samples whereas cysts were detected more frequently and at higher concentrations in both influents and effluents. Whilst sludge samples from 1/5 sites contained oocysts, cysts were detected from all five sites. These investigations indicate that discharge of sewage effluents into a watercourse, which may be used for potable water abstraction, can contaminate that watercourse with potentially infectious oocysts. In addition, the application of sludge to land can be responsible for contaminating watercourses with (oo)cysts following run-off or leaching.
ON AS A ND C. R . F RI C KE R. 1999. When determining the recovery efficiency of a procedure for the detection of Cryptosporidium or the removal efficiency of a treatment process, it is necessary to accurately enumerate a 'seed dose'. Conventional techniques for this are highly variable and consequently, can result in misleading data. In this study, a flow cytometric method was developed for the production of suspensions of Cryptosporidium oocysts in which the number of organisms could be precisely determined. A Becton Dickinson FACScalibur flow cytometer was employed to produce oocyst suspensions containing 100 oocysts. Analysis of these suspensions resulted in a mean dose of 99·5 oocysts (S.D. 1·1, %cv 1.1). These results indicate that the use of such suspensions to seed test systems generates far more accurate data than is presently possible using conventional techniques. In addition, the use of immunomagnetic separation (IMS) for the isolation of oocysts from three different water matrices, after seeding with oocysts counted using flow cytometry, was investigated. The recovery efficiency of the IMS procedure was found to be high, with the percentage recovery of oocysts ranging from 82·3 to 86·3%, and the use of precise numbers of oocysts allowed accurate recovery efficiency data to be generated. A laser scanning instrument (ChemScan RDI) was employed for the rapid detection and enumeration of oocysts after capture using membrane filtration. This technique was found to be faster and easier to perform than conventional epifluorescence microscopy. These findings demonstrate that the ChemScan RDI system may be used as alternative procedure for the routine examination of IMS supernatant fluids for the presence of Cryptosporidium.
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