Setback distances between small biological wastewater treatment systems and drinking water wells against virus contamination in alluvial aquifers.

Contamination of groundwater by pathogenic viruses from small biological wastewater treatment system discharges in remote areas is a major concern. To protect drinking water wells against virus contamination, safe setback distances are required between wastewater disposal fields and water supply wells. In this study, setback distances are calculated for alluvial sand and gravel aquifers for different vadose zone and aquifer thicknesses and horizontal groundwater gradients. This study applies to individual households and small settlements (1-20 persons) in decentralized locations without access to receiving surface waters but with the legal obligation of biological wastewater treatment. The calculations are based on Monte Carlo simulations using an analytical model that couples vertical unsaturated and horizontal saturated flow with virus transport. Hydraulic conductivities and water retention curves were selected from reported distribution functions depending on the type of subsurface media. The enteric virus concentration in effluent discharge was calculated based on reported ranges of enteric virus concentration in faeces, virus infectivity, suspension factor, and virus reduction by mechanical-biological wastewater treatment. To meet the risk target of <10-4infections/person/year, a 12 log10 reduction was required, using a linear dose-response relationship for the total amount of enteric viruses, at very low exposure concentrations. The results of this study suggest that the horizontal setback distances vary widely ranging 39 to 144m in sand aquifers, 66-289m in gravel aquifers and 1-2.5km in coarse gravel aquifers. It also varies for the same aquifers, depending on the thickness of the vadose zones and the groundwater gradient. For vulnerable fast-flow alluvial aquifers like coarse gravels, the calculated setback distances were too large to achieve practically. Therefore, for this category of aquifer, a high level of treatment is recommended before the effluent is discharged to the ground surface.

Hydrolysis of 4-methylumbelliferyl-beta-D-glucuronide in differing sample fractions of river waters and its implication for the detection of fecal pollution.

The hydrolysis rate of 4-methylumbelliferyl-beta-D-glucuronide (MUG-HR) was determined in unamended samples, filtered samples, and in corresponding buffer resuspended filter residues of various river waters of slight to excessive fecal pollution covering a four orders of magnitude range. Regression analysis of the log MUG-HR of the unamended water samples versus the log MUG-HR of the filter residues revealed a highly significant linear relationship (R2 = 0.94; p<0.001). The median of the MUG-HR of the filtrated water samples was about 10% the MUG-HR of the corresponding unamended water samples. If MUG-HR determinations were used as a surrogate for estimating fecal coliform contamination, both the MUG-HR of the unamended water samples and the MUG-HR of the filter residues would have been equally adequate techniques at river sites of higher fecal pollution levels. However, at river locations of decreased fecal pollution, MUG-HR determination of filter residues appeared to be the more sensitive technique in order to estimate fecal coliform concentrations.

Rapid enzymatic detection of Escherichia coli contamination in polluted river water.

AIMS: The relationship between the rate of beta-D-glucuronidase hydrolysis (GLUase-HR) and the E. coli concentration in rivers differing in the extent of faecal pollution was investigated. It was hypothesized that the rate of GLUase-HR is a better surrogate parameter for E. coli concentrations than estimated numbers of faecal coliforms (FC). METHODS AND RESULTS: The GLUase-HR of the water sample filter residues was determined as the rate of cleavage of 4-methylumbelliferyl-beta-D-glucuronide. FC and E. coli concentrations were enumerated using mFC and Chromocult Coliform agar, respectively. Regression analysis revealed that a 90% variation of the variable log GLUase-HR was directly related to the variable log E. coli concentrations. The observed relationship between the log of the FC count and the log of the GLUase activity could be explained by the hydrolysis activity of the E. coli population, as E. coli is a part of the FC group. CONCLUSION: The data suggest that the log of the GLUase-HR can be used as a surrogate parameter for the log of the E. coli concentrations. SIGNIFICANCE AND IMPACT OF THE STUDY: GLUase-HR determination may provide a rapid alternative technique to estimate E. coli concentrations in freshwaters.

Comparative analysis of denaturing gradient gel electrophoresis and temporal temperature gradient gel electrophoresis in separating Escherichia coli uidA amplicons differing in single base substitutions.

A set of Escherichia coli freshwater isolates was chosen to compare the effectiveness of denaturing gradient gel electrophoresis (DGGE) vs temporal temperature gradient gel electrophoresis (TTGE) for separating homologous amplicons from the respective uidA region differing in one to seven single base substitutions. Both methods revealed congruent results but DGGE showed a five to eight times higher spatial separation of the uidA amplicons as compared with TTGE, although the experiments were performed at comparable denaturing gradients. In contrast to TTGE, DGGE displayed clear and focused bands. The results strongly indicated a significantly higher discrimination efficiency of the spatial chemical denaturing gradient as compared with the temporal temperature denaturing gradient for separating the uidA amplicons. Denaturing gradient gel electrophoresis proved to be highly efficient in the differentiation of E. coli uidA sequence types.

Simultaneous detection and differentiation of Escherichia coli populations from environmental freshwaters by means of sequence variations in a fragment of the beta-D-glucuronidase gene.

A PCR-based denaturing-gradient gel electrophoresis (DGGE) approach was applied to a partial sequence of the beta-D-glucuronidase gene (uidA) for specific detection and differentiation of Escherichia coli populations according to their uidA sequence variations. Detection of sequence variations by PCR-DGGE and by PCR with direct sequencing correlated perfectly. Screening of 50 E. coli freshwater isolates and reference strains revealed 11 sequence types, showing nine polymorphic sites and an average number of pairwise differences between alleles of the uidA gene fragments (screened fragment length, 126 bp) of 2.3%. Among the analyzed strains a range of dominating to more rarely and/or uniquely observed E. coli sequence types was revealed. PCR-DGGE applied to fecally polluted river water samples simultaneously detected E. coli and generated a fingerprint of the mixed populations by separating the polymorphic uidA amplicons. No significant differences between non-cultivation-based and cultivation-based profiles were observed, suggesting that at least some members of all occurring sequence types could be cultivated. As E. coli is frequently used as a fecal indicator, this work is considered an important step towards a new, practical tool for the differentiation and tracing of fecal pollution in all kinds of waters.

[Home hospitalization for patients with acute illnesses]. / Servicio de internación domiciliaria para pacientes con enfermedades agudas.

This study presents the results of 26 months of work, from January 1996 through February 1998, of the Distinct Home Hospitalization Service for Acute Patients. This service managed 20 home beds with two teams, each with a physician and a nurse, with a care approach similar to that for a room in a hospital. Among the items evaluated were the attributes of the admitted population, their illnesses, the form of administering drugs, the satisfaction of the caregivers, the indices of performance, and the costs with this approach. A total of 1,789 patients had home hospitalizations over the period, with a median stay of 4 days. Of the patients, 76.5% were admitted from in-hospital care. The most frequent illnesses were cardiorespiratory ones (45.5%), and the proportion of patients with a terminal illness was 14.2%. Drugs were administered orally with 74% of the patients and parenterally in 26%. The patients' satisfaction level was very high, and the cost of the hospitalization was 70% of that for in-hospital care. Family involvement was key in this approach to care.