ABSTRACT
Quantitative microbiological risk assessment requires quantitative data to assess consumer exposure to pathogens and the resulting health risk. The aim of this study was to evaluate data sets on the occurrence of Cryptosporidium oocysts in raw water and on the removal of model organisms (anaerobic spores, bacteriophages) to perform such a risk assessment. A tiered approach was used by first calculating approximate point estimates and when the point estimate was close to the required safety level (10(4) annual risk of infection), fitting the data to probability distributions and Monte Carlo analysis to calculate the distribution of the risk of infection. Sensitivity analysis showed that the variability in the Cryptosporidium data in raw water (largely introduced by the variability of the recovery efficiency of the detection method) determined most of the variance in the risk estimate.
Subject(s)
Cryptosporidium/pathogenicity , Water Microbiology , Water Supply , Animals , Cryptosporidium/isolation & purification , Humans , Monte Carlo Method , Public Health , Risk Assessment , Water PurificationABSTRACT
AIMS: The reference methods for enumeration of total coliforms and Escherichia coli as stated in the European Drinking Water Directive were compared with alternative methods. METHODS AND RESULTS: Laboratories used the reference method on Lactose TTC agar (LTTC), the Colilert/18 system, Laurysulphate Agar (LSA), Chromocult Coliform Agar and the E. coli Direct Plating (DP) method. They enumerated more total coliforms on LTTC than on LSA. CONCLUSIONS: LTTC is suitable for analysis of very clean water samples only, due to heavy background growth. Colilert/18 is a good alternative but it enumerates a broader group of total coliforms, resulting in higher counts. The DP method appeared to be the best choice for enumeration of E. coli because Colilert/18 produces lower counts and false-negative results. SIGNIFICANCE AND IMPACT OF THE STUDY: This study shows the limitations of the EU reference method on LTTC due to lack of selectivity and suggests alternative methods for the enumeration of total coliforms and E. coli.
Subject(s)
Enterobacteriaceae/isolation & purification , Escherichia coli/isolation & purification , Predictive Value of Tests , Water Supply/standards , Colony Count, Microbial , Culture Media , EuropeABSTRACT
Se analizan los factores a tener en cuenta para el diseño y la evaluacion de un sistema de tratamiento de agua efectivo en la remocion de Cryptosporidium y Giardia. Las compañias de agua y el gobierno de Holanda han iniciado un programa de investigacion para determinar la probabilidad de transmision de esaots parasitos
