An evaluation of a laser scanning device for the detection of Cryptosporidium parvum in treated water samples.
A laser scanning device, the ChemScan RDI (Chemunex, Paris, France), was compared with manual fluorescence microscopy for the detection of oocysts of Cryptosporidium. Pairs of filters were spiked with approximately 100 oocysts. Over 24 h at least 1000 l of treated water was passed through the filters, then concentrated deposits were subjected to an immunomagnetic separation (IMS) protocol described by the manufacturer (Dynal, Oslo, Norway) and examination by fluorescence microscopy, or an IMS protocol (Chemunex) and detection by ChemScan laser scanning. Subsequently a set of five 1-ml samples containing oocysts over a range of concentrations, including a negative control, were examined blind by the two methods (stage two). In stage 1 the average recovery rates were estimated to be 49% (manual fluorescence microscopy) and 73% (ChemScan). The average ratio of ChemScan to manual fluorescence microscopy counts was 1.54 (range 1.08-2.36). In stage 2, statistical comparison of all but one set of results showed there was no significant difference between methods. Differences for the high count sample may possibly have been caused by duplicate counting of oocysts by manual fluorescence microscopy.
Rushton
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Public Health Laboratory, Bridle Path, York Road, Leeds, Public Health Laboratory, General Hospital, Newcastle Upon Tyne and PHLS North, Newcastle Upon Tyne, UK.
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Lightfoot
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D000818:Animals; D015169:Colony Count, Microbial; D016785:Cryptosporidium parvum / Q000254:growth & development / Q000302:isolation & purification*; D005069:Evaluation Studies as Topic; D018189:Immunomagnetic Separation; D007834:Lasers; D008856:Microscopy, Fluorescence; D014871:Water Microbiology; D018508:Water Purification / Q000592:standards*