Detection Of Giardia Research Articles

The occurrence of Cryptosporidium and Giardia in the Lake Baroon catchment, Queensland, Australia

Research Article| August 01 2006 The occurrence of Cryptosporidium and Giardia in the Lake Baroon catchment, Queensland, Australia T. Wohlsen; T. Wohlsen 1Public Health Microbiology, Queensland Health Scientific Services, P.O. Box 594, Archerfield, Queensland 4108, Australia Tel.: (+61) 7 3274 9075 Fax: (+61) 7 3274 9175; E-mail: Tracey_Wohlsen@health.qld.gov.au Search for other works by this author on: This Site PubMed Google Scholar J. Bates; J. Bates 2Public Health Microbiology, Queensland Health Scientific Services, Coopers Plains, Australia Search for other works by this author on: This Site PubMed Google Scholar B. Gray; B. Gray 2Public Health Microbiology, Queensland Health Scientific Services, Coopers Plains, Australia Search for other works by this author on: This Site PubMed Google Scholar P. Aldridge; P. Aldridge 3Aquagen, Water and Renewable Energy, Palmwoods, Queensland, Australia Search for other works by this author on: This Site PubMed Google Scholar S. Stewart; S. Stewart 3Aquagen, Water and Renewable Energy, Palmwoods, Queensland, Australia Search for other works by this author on: This Site PubMed Google Scholar M. Williams; M. Williams 3Aquagen, Water and Renewable Energy, Palmwoods, Queensland, Australia Search for other works by this author on: This Site PubMed Google Scholar M. Katouli M. Katouli 4Faculty of Science, Health and EducationUniversity of the Sunshine CoastMaroochydore, QueenslandAustralia Search for other works by this author on: This Site PubMed Google Scholar Journal of Water Supply: Research and Technology-Aqua (2006) 55 (5): 357–366. https://doi.org/10.2166/aqua.2006.044 Article history Received: July 21 2005 Accepted: April 11 2006 Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Cite Icon Cite Permissions Search Site Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAll JournalsThis Journal Search Advanced Search Citation T. Wohlsen, J. Bates, B. Gray, P. Aldridge, S. Stewart, M. Williams, M. Katouli; The occurrence of Cryptosporidium and Giardia in the Lake Baroon catchment, Queensland, Australia. Journal of Water Supply: Research and Technology-Aqua 1 August 2006; 55 (5): 357–366. doi: https://doi.org/10.2166/aqua.2006.044 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex We evaluated the occurrence of Cryptosporidium and Giardia in the Lake Baroon catchment, Queensland, Australia. A total of 132 water samples were collected from 6 sites as well as from raw influent and treated effluent from a local sewage treatment plant (STP), over a 12-month period. Three new sites close to the entrance of the lake were added following initial assessment. The prevalence of faecal indicator organisms, E. coli and enterococci was also examined. There was no clear relationship between the level of indicator organisms, rainfall or the detection of Cryptosporidium and Giardia for most sites. Of the five sites showing levels of contamination with Cryptosporidium, only three coincided with elevated rainfall. The highest level of Cryptosporidium oocysts detected in the raw influent from the STP, coincided with the occurrence of an outbreak of cryptosporidiosis in the local area but no Cryptosporidium was detected in surface water samples during that period. Our results indicate that while the human contribution of Cryptosporidium is minimal, the high level of faecal indicator bacteria in surface water was not always associated with the presence Cryptosporidium in this catchment. catchment, Cryptosporidium, Giardia, health risk This content is only available as a PDF. © IWA Publishing 2006 You do not currently have access to this content.

Detection ofCryptosporidium,GiardiaandEnterocytozoon bieneusiin surface water, including recreational areas: a one-year prospective study

Accidental ingestion of natural waters while bathing carries a risk of infection by waterborne protozoa such as Cryptosporidium, Giardia and, possibly, microsporidia. In order to evaluate this risk, we conducted a one-year prospective study of two recreational lakes and three river sites located near Paris, where bathing and boating are frequent. Twenty-litre water samples were collected monthly from each site. Concentrated samples were submitted to immunomagnetic separation followed by immunofluorescence (IMS-IF) for Cryptosporidium and Giardia detection. PCR and PCR restriction fragment length polymorphism (PCR-RFLP) were used for the genetic characterization of Cryptosporidium species on IMS-IF-positive samples. PCR were systematically performed to detect Enterocytozoon bieneusi. Bacteria counts were also determined. IMS-IF revealed low counts of Giardia cysts and Cryptosporidium oocysts in the recreational lakes, with occasional peaks (max. 165 cysts/10 L and 9 oocysts/10 L). By contrast, the river sites were consistently and sometimes heavily contaminated throughout the year. Enterocytozoon bieneusi was found in only two river samples. PCR-RFLP genotyping showed the presence of C. hominis and C. parvum. No correlation was found between the presence or counts of parasites and bacteria, except between the presence of Giardia and high counts of Escherichia coli and enterococci. Based on a previously developed model for quantitative risk assessment of waterborne parasitic infections, we estimated that the mean risk of infection by Cryptosporidium and Giardia associated with swimming was <10(-4) in the recreational lakes, and frequently higher at the river sites.

Evaluation of seven commercial antigen detection tests for Giardia and Cryptosporidium in stool samples

Stool samples from patients with abdominal symptoms were used to evaluate different copro-diagnostic assays for the detection of Giardia and Cryptosporidium. Results from microscopical examination following conventional stool concentration and direct fluorescent-antibody methods were compared with various commercially available immunochromatographic and enzyme immunoassays. Of 220 samples, 45 were positive for Giardia and 17 for Cryptosporidium. For Giardia, the sensitivities obtained by Ridascreen Giardia, Rida Quick Giardia, Rida Quick Combi and Giardia-Strip were 82%, 80%, 80% and 44%, respectively. For Cryptosporidium, the sensitivities obtained by Rida Quick Cryptosporidium, Ridascreen Cryptosporidium, Rida Quick Combi and Cryptosporidium-Strip were 88%, 82%, 82% and 75%, respectively. The specificity of all tests was > or = 98%. Other intestinal parasites were present in 68 samples, but cross-reactions with other protozoan or helminthic parasites were not observed. Overall, the copro-antigen assays were less time-consuming and easier to perform, but were less sensitive than conventional microscopical methods. Thus, these tests might be a useful addition to, but not a substitute for microscopical methods in the diagnosis of travel-associated giardiasis and cryptosporidiosis.

Using the Flow Cytometry to Quantify the Giardia Cysts and Cryptosporidium Oocysts in Water Samples

The flow cytometry (FC) has been used to detect Giardia cysts and Cryptosporidium oocysts quantitatively and instantaneously in this study. The experimental results showed that FC is potential to become a more precise method for the detection of Giardia and Cryptosporidium in water. This study also evaluated the staining efficiencies for three commercial antibodies. After staining Cryptosporidium oocysts with direct immunofluorescent antibodies in water samples, two populations were detected in the scatter-plots (FL1 versus SSC) of the FC. The Cryptosporidium oocysts and Giardia cysts are significantly separated from other particles while stained with direct immunofluorescent antibodies produced by Meridian Diagnostics and Waterborne Inc.

Detection of Cryptosporidium oocysts and Giardia cysts in swimming pool filter backwash water concentrates by flocculation and immunomagnetic separation

The purpose of the present study was to evaluate techniques for detection of Giardia cysts and Cryptosporidium oocysts in swimming pool filter backwash water. Calcium carbonate flocculation was used for water samples concentration of 1 l filter backwash water samples. Immunomagnetic separation (IMS) was used for separation of cysts and oocysts from detrital material. Cysts and oocysts were then detected using direct immunofluorescence. ColorSeed C&G™ was used as an internal standard. Recoveries were examined at several processing points. Highest recoveries (23% Cryptosporidium, 18% Giardia) were obtained using lower filter backwash volumes, greater IMS volumes, and addition of Tween20™ to backwash samples prior to processing. The combination of CaCO3 flocculation, IMS and direct immunofluorescence was found to be an effective tool for the detection and quantification of Giardia spp. and Cryptosporidium spp. in filter backwash water samples.

Detection of enteric viruses, Giardia and Cryptosporidium in two different types of drinking water treatment facilities

In this study, two types of drinking water treatment facilities (two conventional drinking water treatment plants (DWTPs) and two compact units (Cus)) were compared referring to their production capacity. Water samples were collected from three main points: (a) different water treatment steps (b) washings of sand filters and (c) distribution system at different distances from the water treatment plants. Both viruses and protozoa were concentrated from each water sample by adsorption and accumulation on the same nitrocellulose membrane filters (0.45μm pore size). Enteroviruses were detected by plaque infectivity assay in BGM cells and HAV, HEV and Norovirus were detected by RT-PCR. Giardia and Cryptosporidium were detected by conventional staining methods and PCR. The results revealed that enterovirus load at the intake ranged between 10–15PFU/L for the two compact units and between 4.5 and 75PFU/L for the two conventional DWTPs. The virus load in distribution system of the first type DWTPs at 1km from the plant was the same as that of the intake. Viruses in the other type of treatment plants CUs at 1, 5 and 7km, were much reduced. Investigation of raw water sediments of the two DWTPs showed enterovirus counts between 12 and 17.5PFU/L. Virus count was reduced in sand of filters after washing. Giardia cysts were equally detected by microscopy and PCR in only intake samples of EL-Hawamdia CU (33.3%) and Meet Fares DWTP (50%). Cryptosporidium oocysts were equally detected by microscopy and PCR in intake samples of Abo EL-Nomros CU (100%), EL-Hawamdia CU (66.7%) and Fowa DWTP (50%). At Meet Fares DWTP three positive intake samples for Cryptosporidium were detected by PCR, compared with only two positive samples by microscopy. Giardia cysts and Cryptosporidium oocysts were detected in raw water sediment and sand of filters before washing. Only one sample from Meet Fares DWTP sand of filters after washing was positive for both Giardia and Cryptosporidium. It can be concluded that the poor microbial quality of the water may be due to improper operational skills and management of the various water treatment plants (especially at the two high capacity treatment plants).

Detection of Cryptosporidium and Giardia in molluscan shellfish by multiplexed nested-PCR

A multiplexed nested-PCR procedure (ABC-PCR) previously developed to detect Cryptosporidium spp. and Giardia duodenalis assemblages A and B in whole human faeces was applied to DNA extracted from filter-feeding molluscs. Species of Cryptosporidium and G. duodenalis were identified by restriction fragment analysis of the PCR products and by DNA sequencing. The extraction and ABC-PCR procedures were shown to be suitable for application to shellfish by amplification of specific target sequences using DNA from Cryptosporidium parvum genotype 2 and G. duodenalis assemblages A and B which were spiked into DNA extracted from mussels. Using 49 molluscan shellfish specimens (18 clam, 22 mussel and 9 oyster samples) from Spain, cryptosporidial oocysts were detected in 56% by immunofluorescence microscopy, and in 44% by ABC-PCR. For detection of Cryptosporidium, there was a significant association, but not total agreement, between the results of microscopy and PCR. G. duodenalis assemblage B was detected from one oyster sample by PCR. Amongst 38 specimens (20 mussel and 18 cockle samples) collected in the UK and tested by the ABC-PCR, G. duodenalis was not detected, and Cryptosporidium was detected in 11% of the samples. Overall, the 26 samples where Cryptosporidium was detected, C. hominis/ C. parvum genotype 1 was detected in 1, C. parvum genotype 2 in 22, and the remaining three samples contained either sequences similar to C. parvum genotype 2 or heterogeneous mixtures of Cryptosporidium species. There was no significant association between the level of Escherichia coli detected by conventional microbiological methods and the presence of Cryptosporidium detected by ABC-PCR.

Health risks and parasitical quality of water

This article assesses the risks of acute digestive conditions (ADC) in relation to protozoa Giardia and Cryptosporidium conveyed through drinking water within a French general population. It is a part of the Epidemiology and Microbial Risk Assessment study, which combined a daily epidemiological followup among a panel of volunteers whose water was supplied by vulnerable public water systems. These systems were monitored with a microbiological surveillance of the tap water. Parasitical quality of the water was assessed using cartridge and immunofluorescence assays. The relationship between incidence of ADC and waterborne protozoa was modeled using logistic regression and generalized estimating equations analysis. During the study period, 712 cases of ADC occurred. Thirty‐six tap water samples were collected for parasitical quality analysis. of these, 11 tested positive for at least one protozoan, among which 10 complied with bacterial criteria. The final model included concentrations of Giardia cysts and several confounding factors; unfortunately, Cryptosporidium data were too sparse for analysis. Biostatistical modeling showed that Giardia detection was associated with an increased risk of ADC: relative risk (RR) = 1.19 (95% confidence interval = [0.96–1.48]) for 10 to 20 cysts/100 L, and RR = 1.24 [1.06–1.45] for more than 20 cysts/100 L, compared with absence of detectable cysts. These results suggest the role of Giardia in the endemic level of waterborne infectious diseases and raise the question of protozoa surveillance in drinking water, while traditional bacterial surveillance indicators have been shown to be poor predictors of their presence.

Analysis-only detection of Giardia by combining immunomagnetic separation and two-color flow cytometry.

Giardia is a protozoan parasite of concern to water utilities. Giardia detection relies on cyst isolation and confirmation with the use of fluorescence microscopy. It is of interest to develop a flow cytometric (FCM) method that reliably detects one cyst in 10 L of water. To date all available antibodies have targeted the same epitope on the cyst wall. To achieve a reliable method, two independent probes are required. Giardia cysts were spiked into a backwash water sample with and without prior hybridization to peptide nucleic acid (PNA) probes. Immunomagnetic separation (IMS) as a pre-enrichment step was compared with filtration of the water sample. Cysts were recovered with two-color FCM. Those cysts hybridized with PNA and fluorescein isothiocyanate (FITC) were dual stained with monoclonal antibody (mAb) conjugated to phycoerythrin (PE); those not hybridized to PNA were dual stained with mAb-FITC and mAb-PE. A fourfold increase in fluorescent signal intensity was obtained when combining the mAb-PE and PNA probe compared with two-color antibody staining. When combined with IMS, Giardia was successfully identified by FCM, with no false positives detected. Analysis-only FCM detection of Giardia in water is feasible. Further method development incorporating PNA probe hybridization after IMS is necessary.

Detection of Microsporidia, cryptosporidia and Giardia in swimming pools: a one-year prospective study.

In order to estimate the rate of microsporidia, cryptosporidia and giardia contamination of swimming pools, sequential samples of water were collected during a one-year period in six different swimming pools in Paris, France. Fourty-eight samples were submitted to filtrations. Eluates were examined for microsporidia using polymerase chain reaction (PCR) and for cryptosporidia and giardia using immunofluorescence staining. One of 48 specimens was positive for microsporidia. Using DNA sequence analysis, unknown microsporidia species were identified, which were close to an insect microsporidia Endoreticulatus schubergi. One sample was positive for cryptosporidia and none were positive for giardia. This study shows a low level of swimming pool water contamination by microsporidia, cryptosporidia or giardia, demonstrating the efficacy of cleaning filtration and disinfection procedures used in French swimming pools.

Detection of microsporidia, cryptosporidia and giardia in swimming pools: a one-year prospective study

In order to estimate the rate of microsporidia, cryptosporidia and giardia contamination of swimming pools, sequential samples of water were collected during a one-year period in six different swimming pools in Paris, France. Fourty-eight samples were submitted to filtrations. Eluates were examined for microsporidia using polymerase chain reaction (PCR) and for cryptosporidia and giardia using immunofluorescence staining. One of 48 specimens was positive for microsporidia. Using DNA sequence analysis, unknown microsporidia species were identified, which were close to an insect microsporidia Endoreticulatus schubergi. One sample was positive for cryptosporidia and none were positive for giardia. This study shows a low level of swimming pool water contamination by microsporidia, cryptosporidia or giardia, demonstrating the efficacy of cleaning filtration and disinfection procedures used in French swimming pools.

An IC-PCR method for detection of Cryptosporidium and Giardia in natural surface waters in Finland

We developed an immunocapture-based polymerase chain reaction (PCR) assay for simultaneous detection of Cryptosporidium parvum oocysts and Giardia intestinalis cysts in surface water. Using primer pairs Cry9/Cry15 and LaxA/LaxB for Cryptosporidium and Gdh1/Gdh4 for Giardia, the sensitivity of the entire detection procedure (dealing with concentration, separation, DNA purification and PCR amplification) was at the level of 50–100 oocysts and cysts. Of 54 surface water samples, 4 were positive for Cryptosporidium and 1 for Giardia. Cryptosporidium and Giardia were detected for the first time in surface water in Finland.

Ocorrência de Giardia spp. em bezerros leiteiros no Brasil

Fecal samples were collected from 50 female Holstein calves (1-90 days old) from a commercial dairy cattle farm located in Lavras, Minas Gerais, Brazil and examined for presence of Giardia cysts using the zinc sulfate flotation method. A total of 120 samples were collected from March 1999 to April 2000, and fecal consistency (normal or diarrheic) was noted prior to the examination for Giardia cysts. Giardia spp. cysts were found in 11 (9%) of the 120 faecal samples of calves co-infected with Eimeria spp., in calves from 19 to 58 days of age (38±19). In 82% (9/11) calves assessed for mixed infections with Cryptosporidium spp. and Giardia, oocysts of Cryptosporidium were found in three out of four diarrheic calves (75%) positive for Giardia. Giardia cysts (n= 30) sized 13-16 x 10-12µm (mean of 15 x 11µm). They appeared to belong to the morphological group of G. intestinallis according to the size and morphological characteristic of the cysts. This is the first detection of Giardia spp. in calves in Brazil. Considering that Giardia has the potential to cause clinical disease in calves and that organisms infecting humans and domestic ruminants are morphologically and antigenically similar, and calves can shed Giardia cysts potentially infective for humans, the parasite in calves may be of major epidemiological significance, and suggests that naturally infected calves may be reservoirs of Giardia infections for man.

A Microscope System with a dual-band filter for the simultaneous enumeration of cryptosporidium parvum oocysts and sporozoites

A dual band filter set was designed to allow the simultaneous viewing of two fluorochromes (fluorescein isothiocyanate (FITC) and 4′,6-diamidino-2-phenylindole (DAPI)) so that Cryptosporidium oocysts and sporozoites can be viewed together. Simultaneous viewing increases accuracy and decreases examination time as compared to current Environmental Protection Agency (EPA) Method 1623 for the detection of Cryptosporidium and Giardia in water by filtration/IMS/FA (Immunomagnetic Separation/Fluorescent Antibodies). Additionally, a microscope equipped with a programmable, motorized stage, CCD camera, and display monitor was used to facilitate well slide evaluation in a quick and precise fashion ensuring complete coverage without overlap and eliminating the optical strain associated with counting hundreds of images through an eyepiece.

Size selective continuous flow filtration method for detection of Cryptosporidium and Giardia

We describe a size selective continuous flow filtration method for detecting Cryptosporidium oocyst and Giardia cyst in finished water. Twenty liters of finished water spiked with Cryptosporidium oocysts (110) and Giardia cysts (60) were filtered through macro (5.0–10.0 μm) and micro (3.0 μm) pore-sized polycarbonate-track-etch (PCTE) membrane filters housed into two separate 47 mm diameter filter holders joined with a stainless steel nipple. The macro-pore-sized filters removed larger unwanted particles while allowing the Cryptosporidium oocysts and Giardia cysts to pass through, these being subsequently captured on the micro-pore-sized filter. The eluted oocysts and cysts were transferred onto the well-slide, stained by IFA and examined microscopically. The mean recovery efficiencies obtained for Cryptosporidium oocysts using the filter pairs of macro 5 μm and micro 3 μm, macro 8 μm and micro 3 μm, and macro 10 μm and micro 3 μm were 67.3%, 77.2–85.0% and 76.9–82.2%, respectively. Whereas the recovery rates for Giardia cysts using the same filter pairs were 0, 55 and 77.1%. The filter pair having the pore size of macro 10 μm and micro 3 μm was found to be most efficient in the simultaneous detection of Cryptosporidium and Giardia in the finished water. This method is simple, easy, rapid and economical.

First findings of Cryptosporidium and Giardia in California sea lions (Zalophus californianus).

We report the detection and identification of Cryptosporidium and Giardia from 1 of 3 species of pinnipeds. Fecal samples were collected from Pacific harbor seal (Phoca vitulina richardsi), northern elephant seal (Mirounga angustirostris), and California sea lion (Zalophus californianus) in the northern California coastal area. By means of fluorescently labeled monoclonal antibodies, Cryptosporidium oocysts were detected in 3 samples from California sea lions, 1 of which also contained Giardia cysts. Oocysts of Cryptosporidium and cysts of Giardia were morphologically indistinguishable from oocysts of C. parvum and cysts of G. duodenalis from other animal origins. Oocysts and cysts were then purified using immunomagnetic separation techniques and identified by polymerase chain reaction (PCR), from which species-specific products were obtained. Sequence analysis revealed that the 452-bp and 358-bp PCR products of Cryptosporidium isolated from California sea lion had identities of 98% with sequences of their template fragments of C. parvum obtained from infected calves. Based on morphological, immunological, and genetic characterization, the isolates were identified as C. parvum and G. duodenalis, respectively. The findings suggested that California sea lions could serve as reservoirs in the environmental transmission of Cryptosporidium and Giardia.

Giardia, Cryptosporidium, and Cyclospora and Their Impact on Foods: A Review

While the risk from pathogenic microorganisms in foods has been recognized for hundreds of years, bacterial agents are generally implicated as the contaminants. Although many outbreaks of gastroenteritis caused by protozoan pathogens have occurred, it is only in the last 3 years that attention has focused on protozoan association with foodborne transmission. Recognized as waterborne parasites, Giardia, Cryptosporidium, and Cyclospora have now been associated with several food-borne outbreaks. The oocysts and cysts of these organisms can persist and survive for long periods of time both in water and on foods. While Cyclospora oocysts require a maturation period, Cryptosporidium oocysts and Giardia cysts are immediately infectious upon excretion from the previous host. As a result, these parasites have emerged as public health risks and have become a concern to the food industry. More than 200 cases of foodborne giardiasis (seven outbreaks) were reported from 1979 to 1990. Four foodborne Cryptosporidium outbreaks (with a total of 252 cases) have been documented since 1993. Cyclospora caused a series of sporadic outbreaks of cyclosporasis throughout North America that have affected over 3,038 people since 1995. Control and prevention of protozoan foodborne disease depends upon our ability to prevent, remove, or kill protozoan contaminants. This review will address the biology, foodborne and waterborne transmission, survival, and methods for detection and control of Giardia, Cryptosporidium, and Cyclospora.

Immunochromatographic strip-based detection of Entamoeba histolytica-E. dispar and Giardia lamblia coproantigen.

BIOSITE Triage was 68.3% sensitive and 100% specific for the detection of Entamoeba histolytica-E. dispar (n = 71) compared to Alexon-Trend's ProSpecT test (reference standard) using fresh-frozen stool. Neither test is able to distinguish E. histolytica from E. dispar. Triage was 83.3% sensitive and 100% specific compared to microscopy (formalin-ether concentrates and permanent stains) for the detection of Giardia lamblia.

Improved immunofluorescence assay for detection of Giardia and Cryptosporidium from asymptomatic adult cervine animals.

We tested an improved immunofluorescence assay (IFA) in detecting Giardia and Cryptosporidium from feces of asymptomatic adult cervine animals. Samples were concentrated by sucrose flotation before being stained by fluorescent monoclonal antibody and examined microscopically. The detection limit was determined as 500 G. intestinalis cysts or 200 C. parvum oocysts/g of sample. Among the 82 samples collected from adult fallow deer, Columbian black-tailed deer, and Tule elk in northern California, 3 (3.7%) contained G. intestinalis cysts, which were confirmed by a species-specific polymerase chain reaction (PCR) following immunomagnetic capture (IC) of cysts. C. parvum oocysts were detected in a total of 13 (15.9%) samples, and oocysts from 2 such samples were smaller than oocysts from the other 11 samples. C. parvum identification was also confirmed by specific IC-PCR and sequencing of the PCR product. In addition, a C. muris-like organism was detected in 2 (2.4%) samples. Findings obtained with the improved IFA confirmed that cysts/oocysts may pass unnoticed in adult cervine animals and that subclinically infected individuals could serve as potential carriers of infection for humans and other animals via contaminated feces or water.

Improved detection and vital staining of Cryptosporidium and Giardia with flow cytometry

Flow cytometry with fluorescence activated cell sorting (FACS) was used to purify Cryptosporidium (oo)cysts and Giardia cysts from water. With this purification step Cryptosporidium and Giardia were found in a higher percentage of the samples and significantly higher Giardia concentrations were detected in these positive samples. Because FACS removed most of the debris from the concentrated water sample, the microscopic preparations could be examined more rapidly for the presence of (oo)cysts and the morphological characteristics of the (oo)cysts could be interpreted more unambiguously than with the conventional immunofluorescence microscopy method. The use of FACS made it possible to apply PI-staining on environmental samples to determine the fraction of dead (oo)cysts. Sample processing did not appear to influence the PI-staining characteristics of the Cryptosporidium (oo)cysts, but did increase the percentage of PI-positive Giardia cysts. This suggests that this protocol can be used for determining the percentage of dead Cryptosporidium oocysts in environmental samples. Analysis of environmental samples suggests that reservoir storage increases the percentage of PI-positive (dead) oocysts.