AIMS: To develop a filtration unit for efficient recovery of waterborne Cryptosporidium oocysts and Giardia cysts ((oo-)cysts) in drinking water.

METHODS AND RESULTS: This unit utilizes a metallic filter and an ultrasound transducer for eluting (oo-)cysts, with a fixed retentate backwash volume; approx. 400 μl. Changes in the viability was evaluated by seeding wild type (oo-)cysts (1 × 10(4) ) followed by sonication for 5, 10, 20 or 40 s (five replicates for each period). Flow cytometry analysis showed negligible increase in the mortality of (oo-)cysts exposed to 5-10 s of sonication. Recovery rate was assessed by seeding ColorSeed(™) (10 replicates) into the filter unit followed by air backwash to a glass slide and counting of (oo-)cysts by epifluorescent microscopy. High recovery rates (mean ± SD) were found: 84·9% ± 4·8 for Giardia cysts and 70% ± 6·5 for Cryptosporidium oocysts. DNA of seeded wild type (oo-)cysts (1 × 10(2) ; 10 replicates) was successfully amplified using real-time PCR.

CONCLUSIONS: The use of a metallic filter, sonication and 'air backwash' were key factors for creating a highly efficient system for recovery of apparently undamaged protozoa.

SIGNIFICANCE AND IMPACT OF THE STUDY: This reagent-less system can be used for monitoring of parasite contamination in drinking water.