Simultaneous detection of various pathogenic Escherichia coli in water by sequencing multiplex PCR amplicons

Waterborne diseases due to pathogen contamination in water are a serious problem all over the world. Accurate and simultaneous detection of pathogens in water is important to protect public health. In this study, we developed a method to simultaneously detect various pathogenic Escherichia coli by sequencing the amplicons of multiplex PCR. Our newly designed multiplex PCR amplified five genes for pathogenic E. coli (uidA, stx1, stx2, STh gene, and LT gene). Additional two PCR assays (for aggR and eae) were also designed and included in the amplicon sequencing analysis. The same assays were also used for digital PCR (dPCR). Strong positive correlations were observed between the sequence read count and the dPCR results for most of the genes targeted, suggesting that our multiplex PCR-amplicon sequencing approach could provide quantitative information. The method was also successfully applied to monitor the level of pathogenic E. coli in river water and wastewater samples. The approach shown here could be expanded by targeting genes for other pathogens.

Natural and anthropogenic forces on suspended sediment dynamics in Asian estuaries

Climate change and anthropogenic activities are affecting the hydrological conditions of rivers and may have altered nutrient and suspended sediments released into coastal seas. However, testing this hypothesis is difficult, confounded by the lack of observational data and the unavailability of globally accepted suspended sediment concentration (SSC) algorithms. Here, we analyzed the trends in SSC (2000-2020) at the mouths of 10 major Asian rivers using 10 available satellite-SSC algorithms. We identified spatially distinct trends, with SSC decreasing at the mouths of the Yellow, Pearl, and Indus rivers, and increasing trends at the mouths of the Narmada and Ganges-Brahmaputra rivers, while there were no significant trends at the mouths of the remaining rivers. River discharge, dams, and land use changes in basins individually did not suffice, but reproduced the observed SSC trends when used together. Our results imply that anthropogenic activities threaten the marine ecosystem more than climate forcing on Asian coasts.

Analysis of long-term (2002-2020) trends and peak events in total suspended solids concentrations in the Chesapeake Bay using MODIS imagery

Water quality monitoring programs have been widely implemented worldwide to monitor and assess water quality and to understand its trends. However, water quality analysis based on point-source field observations is difficult to perform at large spatial and temporal scales. In this paper, a fully automated Google Earth Engine (GEE) application algorithm was developed to estimate the total suspended solids (TSS) concentration in the Chesapeake Bay based on the Moderate Resolution Imaging Spectroradiometer (MODIS) Terra imagery. Combining long-term archived satellite data (2002-2020) with field observations, the concentrations and spatiotemporal patterns of TSS in the bay water were evaluated. Time series analysis showed a statistically significant decreasing trend in TSS concentration between 2002 and 2020, suggesting that the sediment concentration in the bay has gradually been decreasing over the last two decades. The decreasing trend was observed in 49 out of 60 segments of the bay, implying that substantial progress has been made toward attaining the Chesapeake Bay water quality standards. Based on the monthly TSS analysis, 12 major peak events of TSS were identified in the Chesapeake Bay, which coincided with extreme winter blizzards and summer hurricane events. The GEE application and the results presented herein complement the existing monitoring program in attaining the water quality standards of the bay.

Enhancement of sunlight irradiation for wastewater disinfection by mixing with seawater

There is a need for developing a simple and easy-to-maintain disinfection technique for sewage treatment for use in developing countries and disaster-affected areas. We propose a novel disinfection technology that inactivates bacteria in wastewater via sunlight irradiation under high salt concentration by mixing with seawater. The disinfection efficiency of the proposed method was quantitatively evaluated and examined using fecal indicator bacteria. When the salinity in wastewater was adjusted to 30 practical salinity units by mixing with seawater, the constant of inactivation irradiation energy K_s (m²/MJ) was 1.6-2.2-fold greater than that without seawater for total coliforms and Escherichia coli. By contrast, although enterococci were inactivated by sunlight irradiation, an increase in salinity did not enhance disinfection. On setting the irradiation energy of sunlight to 5.5 MJ/m², >99% of the fecal indicator bacteria were inactivated. Finally, we examined the relationship between the attenuation of irradiance and water depth and accordingly proposed a design of a treatment system wherein wastewater and seawater were adequately mixed and passed via a disinfection tank under the natural flow with sunlight irradiation.

COVID-19 and surface water quality: Improved lake water quality during the lockdown

Human life comes to a standstill as many countries shut themselves off from the work due to the novel coronavirus disease pandemic (COVID-19) that hit the world severely in the first quarter of 2020. All types of industries, vehicle movement, and people's activity suddenly halted, perhaps for the first time in modern history. For a long time, it has been stated in various literature that the increased industrialization and anthropogenic activities in the last two decades polluted the atmosphere, hydrosphere, and biosphere. Since the industries and people's activities have been shut off for a month or more in many parts of the world, it is expected to show some improvement in the prevailing conditions in the aforementioned spheres of environment. Here, with the help of remote sensing images, this work quantitatively demonstrated the improvement in surface water quality in terms of suspended particulate matter (SPM) in the Vembanad Lake, the longest freshwater lake in India. The SPM estimated based on established turbidity algorithm from Landsat-8 OLI images showed that the SPM concentration during the lockdown period decreased by 15.9% on average (range: -10.3% to 36.4%, up to 8 mg/l decrease) compared with the pre-lockdown period. Time series analysis of satellite image collections (April 2013 - April 2020) showed that the SPM quantified for April 2020 is the lowest for 11 out of 20 zones of the Vembanad lake. When compared with preceding years, the percentage decrease in SPM for April 2020 is up to 34% from the previous minima.

Fast, sensitive, and reliable detection of waterborne pathogens by digital PCR after coagulation and foam concentration

The quantification of pathogens is important for assessing water safety and preventing disease outbreaks. Culture-independent approaches, such as quantitative PCR (qPCR) and digital PCR (dPCR), are useful techniques for quantifying pathogens in water samples. However, since pathogens are usually present at low concentrations in water, it is necessary to concentrate microbial cells before extracting their DNA. Many existing microbial concentration methods are inefficient or take a long time to perform. In this study, we applied a coagulation and foam separation method to concentrate environmental water samples of between 1000 and 5000 mL to 100 μL of DNA (i.e., a 1-5 × 10⁴-fold concentration). The concentration process took <1 h. The DNA samples were then used to quantify various target pathogens using dPCR. One gene, the Shiga toxin gene (stx₂) of Shiga toxin-producing Escherichia coli, was detected at 32 copies/100 mL in a river water sample. The coagulation and foam concentration method followed by dPCR reported herein is a fast, sensitive, and reliable method to quantify pathogen genes in environmental water samples.

Lectin-stimulated cellular iron uptake and toxin generation in the freshwater cyanobacterium Microcystis aeruginosa

The lectin family is composed of mono- and oligosaccharide binding proteins that could activate specific cellular activities, such as cell-cell attachment and toxin production. In the present study, the effect of the external addition of lectins to culture media containing the freshwater cyanobacterium Microcystis aeruginosa on its metabolic activities, such as iron uptake and toxin production was investigated. Among the three lectins examined in this study (concanavalin A [Con A], wheat germ agglutinin [WGA] and peanut agglutinin [PNA]), PNA substantially increased the accumulated intracellular and extracellular iron content. The binding of PNA and Con A to M. aeruginosa cells was visualized via fluorescence microscopy using a lectin adjunct with fluorescein isothiocyanate, and resulted in carbohydrate and protein accumulation in the cellular capsule. Given that the highest carbohydrate accumulation was seen in the Con A system (where iron accumulation was relatively lower), carbohydrate quality is likely important factor that influences cellular iron accumulation. Since PNA specifically binds to sugars such as galactose and N-acetylgalactosamine, these saccharide species could be important candidates for intracellular and extracellular iron accumulation and transport. Microcystin biosynthesis was stimulated in the presence of PNA and WGA, whereas cellular iron uptake increased only in the presence of PNA. Thus, the iron uptake was not necessarily congruent with the upregulation of microcystin synthesis, which suggested that the positive effect of lectin on iron uptake is probably attributable to the PNA-assisted iron accumulation around the cell surface. Overall, the present study provides insights into the interactions of lectin that influence cellular metabolic activities such as iron uptake, extracellular polymeric substance accumulation, and toxin production.

A review on recent progress in the detection methods and prevalence of human enteric viruses in water

Waterborne human enteric viruses, such as noroviruses and adenoviruses, are excreted in the feces of infected individuals and transmitted via the fecal-oral route including contaminated food and water. Since viruses are normally present at low concentrations in aquatic environments, they should be concentrated into smaller volumes prior to downstream molecular biological applications, such as quantitative polymerase chain reaction (qPCR). This review describes recent progress made in the development of concentration and detection methods of human enteric viruses in water, and discusses their applications for providing a better understanding of the prevalence of the viruses in various types of water worldwide. Maximum concentrations of human enteric viruses in water that have been reported in previous studies are summarized to assess viral abundances in aquatic environments. Some descriptions are also available on recent applications of sequencing analyses used to determine the genetic diversity of viral genomes in water samples, including those of novel viruses. Furthermore, the importance and significance of utilizing appropriate process controls during viral analyses are discussed, and three types of process controls are considered: whole process controls, molecular process controls, and (reverse transcription (RT)-)qPCR controls. Although no standards have been established for acceptable values of virus recovery and/or extraction-(RT-)qPCR efficiency, use of at least one of these appropriate control types is highly recommended for more accurate interpretation of observed data.

Global Distribution of Human-Associated Fecal Genetic Markers in Reference Samples from Six Continents

Numerous bacterial genetic markers are available for the molecular detection of human sources of fecal pollution in environmental waters. However, widespread application is hindered by a lack of knowledge regarding geographical stability, limiting implementation to a small number of well-characterized regions. This study investigates the geographic distribution of five human-associated genetic markers (HF183/BFDrev, HF183/BacR287, BacHum-UCD, BacH, and Lachno2) in municipal wastewaters (raw and treated) from 29 urban and rural wastewater treatment plants (750-4 400 000 population equivalents) from 13 countries spanning six continents. In addition, genetic markers were tested against 280 human and nonhuman fecal samples from domesticated, agricultural and wild animal sources. Findings revealed that all genetic markers are present in consistently high concentrations in raw (median log₁₀ 7.2-8.0 marker equivalents (ME) 100 mL^-1) and biologically treated wastewater samples (median log₁₀ 4.6-6.0 ME 100 mL^-1) regardless of location and population. The false positive rates of the various markers in nonhuman fecal samples ranged from 5% to 47%. Results suggest that several genetic markers have considerable potential for measuring human-associated contamination in polluted environmental waters. This will be helpful in water quality monitoring, pollution modeling and health risk assessment (as demonstrated by QMRAcatch) to guide target-oriented water safety management across the globe.

Applying a water quality index model to assess the water quality of the major rivers in the Kathmandu Valley, Nepal

Human activities during recent decades have led to increased degradation of the river water environment in South Asia. This degradation has led to concerns for the populations of the major cities of Nepal, including those of the Kathmandu Valley. The deterioration of the rivers in the valley is directly linked to the prevalence of poor sanitary conditions, as well as the presence of industries that discharge their effluents into the river. This study aims to investigate the water quality aspect for the aquatic ecosystems and recreation of the major rivers in the Kathmandu Valley using the Canadian Council of Ministers of the Environment water quality index (CCME WQI). Ten physicochemical parameters were used to determine the CCME WQI at 20 different sampling locations. Analysis of the data indicated that the water quality in rural areas ranges from excellent to good, whereas in denser settlements and core urban areas, the water quality is poor. The study results are expected to provide policy-makers with valuable information related to the use of river water by local people in the study area.

Effect of Surface Sampling and Recovery of Viruses and Non-Spore-Forming Bacteria on a Quantitative Microbial Risk Assessment Model for Fomites

Quantitative microbial risk assessment (QMRA) is a powerful decision analytics tool, yet it faces challenges when modeling health risks for the indoor environment. One limitation is uncertainty in fomite recovery for evaluating the efficiency of decontamination. Addressing this data gap has become more important as a result of response and recovery from a potential malicious pathogen release. To develop more accurate QMRA models, recovery efficiency from non-porous fomites (aluminum, ceramic, glass, plastic, steel, and wood laminate) was investigated. Fomite material, surface area (10, 100, and 900 cm(2)), recovery tool (swabs and wipes), initial concentration on the fomites and eluent (polysorbate 80, trypticase soy broth, and beef extract) were evaluated in this research. Recovery was shown to be optimized using polysorbate 80, sampling with wipes, and sampling a surface area of 10-100 cm(2). The QMRA model demonstrated, through a relative risk comparison, the need for recovery efficiency to be used in these models to prevent underestimated risks.

Temporal dynamics of norovirus determined through monitoring of municipal wastewater by pyrosequencing and virological surveillance of gastroenteritis cases

Norovirus is a leading etiological agent of viral gastroenteritis. Because of relatively mild disease symptoms and frequent asymptomatic infections, information on the ecology of this virus is limited. Our objective was to examine the genetic diversity of norovirus circulating in the human population by means of genotyping the virus in municipal wastewater. We investigated norovirus genogroups I and II (GI and GII) in municipal wastewater in Japan by pyrosequencing and quantitative PCR (qPCR) from November 2012 to March 2013. Virological surveillance for gastroenteritis cases was concurrently conducted in the same area. A total of fourteen distinct genotypes in total (GI.1, 3, 4, 6, 7, GII.2, 4, 5, 6, 7, 12, 13, 14, and 17), with up to eight genotypes detected per sample, were observed in wastewater using pyrosequencing; only four genotypes (GI.6, GII.4, 5, and 14) were obtained from clinical samples. Seventy-eight percent of norovirus-positive stool samples contained GII.4, but this genotype was not dominant in wastewater. The norovirus GII.4 Sydney 2012 variant, which appeared and spread during our study period, was detected in both the wastewater and clinical samples. These results suggest that an environmental approach using pyrosequencing yields a more detailed distribution of norovirus genotypes/variants. Thus, wastewater monitoring by pyrosequencing is expected to provide an effective analysis of the distribution of norovirus genotypes causing symptomatic and asymptomatic infections in human populations.

Detection of Human Parechoviruses in Clinical and Municipal Wastewater Samples in Miyagi, Japan, in 2012-2014

In order to study the epidemiology of human parechovirus (HPeV) infections and to evaluate the feasibility of environmental surveillance, we analyzed 281 stool samples, 265 nasopharyngeal swab samples, and 79 municipal wastewater samples for HPeV. The samples were collected in Miyagi Prefecture, Japan, between April 2012 and March 2014. HPeV was detected by reverse-transcription-PCR targeting the partial 5'-untranslated region and was genotyped by sequencing the capsid VP1 region. Seven stool samples (2.5%) and 1 nasopharyngeal swab sample (0.4%), all of which were from children under 2 years old, and 14 wastewater samples (18%) were positive for HPeV. Clear seasonality was observed: all positive samples were collected between July and December during the study period. All strains detected in the stool and wastewater samples had genotype HPeV1, and the strain from the nasopharyngeal swab sample had genotype HPeV6. A phylogenetic analysis revealed that all HPeV1 strains from the stool samples cluster together with those from the wastewater samples, indicating that the HPeV1 strains circulating in human populations can also be detected in municipal wastewater.

[Infectivity Titers of Each Component of the Influenza Virus in the Live Vaccine Purchased from a Parallel Import Distributing System]

Currently in Japan, the only approved influenza vaccine is the inactivated vaccine which is injected subcutaneously. On the other hand, there is a live vaccine available elsewhere in the world. Flumist, an intranasal influenza live vaccine which contains four strains of infectious viruses, has been used in the United States for more than 10 years; the vaccine has been found effective in clinical trials, while it has some limitations such as those on subjects for the administration, strict storage conditions, relatively short expiration date etc. It is not yet approved in Japan, but available through personal import by some medical institutions, and prescribed based on the decision of the doctor. However, in Japan, there is no checking system whether the vaccine contains appropriate amounts of infectious viruses or not. In the present study, we purchased 2013-14 and 2014-15 years' lots of Flumist from a parallel importer and measured the amount of infectious viruses of each component of them using the focus assay. Consequently, for type A influenza viruses, the titers of both of H1N1pdm09 and H3N2 viruses in the 2013-14's lot were 1/30 of the lower limit of those shown in the package insert and 1/10 in 2014-15's lot, while those of type B viruses, both of B/Massachusetts and B/Brisbane viruses marginally cleared the lower limit. The digital PCR analysis showed that the absolute genome copy numbers of type A viruses were 1/10 of those of type B viruses. The relatively higher titer of B/Massachusetts also gradually decreased over time during its storage at 4°C and finally reached the lower limit at about one week before the expiration date. In case it is approved officially in the future to be used in Japan, some studies will be required to elucidate the minimum viral titers of the components necessary for effective live vaccine. In addition, there should be a system to check the titer during the distribution process in Japan.

Impacts of urbanization on the prevalence of antibiotic-resistant Escherichia coli in the Chaophraya River and its tributaries

River water samples were taken from 32 locations around the basin of Chaophraya River and its four major tributaries in Thailand to investigate resistance ratios of Escherichia coli isolates to eight antibiotic agents of amoxicillin, sulfamethoxazole/trimethoprim, tetracycline, doxytetracycline, ciprofloxacin, levofloxacin, norfloxacin and ofloxacin. Principal component analysis was performed to characterize resistance patterns of the samples. Relevancy of the obtained principal components with urban land use and fecal contamination of the river were examined. The ratio of antibiotic-resistant bacteria is likely to increase when urban land use near the sampling site exceeds a certain ratio. The resistance ratio to fluoroquinolones tends to be high in a highly populated area. Meanwhile, no significant contribution of fecal contamination was found to increase the resistance ratio. These results suggest that an antibiotic-resistance ratio is dependent on conditions of local urbanization rather than the upstream conditions, and that the major sources of antibiotic-resistant bacteria in the Chaophraya River basin are possibly point sources located in the urban area which contains a high ratio of resistant bacteria.

Monosaccharide composition of the outer membrane lipopolysaccharide and O-chain from the freshwater cyanobacterium Microcystis aeruginosa NIES-87

AIMS

Bacterial lipopolysaccharide (LPS) protruding from the outermost layer of the outer membrane is expected to play an important role in cell physiology by interacting with molecules in the extracellular milieu; however, the structural and functional characteristics of these components in cyanobacteria remain largely unknown. We isolated water-soluble fractions of LPS and O-chain from the bloom-forming freshwater cyanobacterium Microcystis aeruginosa NIES-87 and identified their monosaccharide compositions.

METHODS AND RESULTS

SDS-PAGE followed by silver staining demonstrated that the isolated total LPS was the smooth type with different numbers of repeating sugar units in the O-chain region. GC/MS analysis after acid hydrolysis, reduction and acetylation treatments indicated that the neutral monosaccharide components of the total LPS include glucose, rhamnose, mannose, galactose and xylose (in decreasing order of weight percentage), while only glucose was detected in the purified O-chain fraction. MALDI-TOF MS analysis suggested that the O-chain fraction is composed of repeating glucose and methylated glucose disaccharide units.

CONCLUSIONS

Our results indicate that the monosaccharide composition of M. aeruginosa O-chain is relatively simple.

SIGNIFICANCE AND IMPACT OF THE STUDY

Although further studies are necessary, these findings provide fundamental information for understanding the structural and functional properties of cyanobacterial LPS and O-chain.

Adsorption characteristics of an enteric virus-binding protein to norovirus, rotavirus and poliovirus

BACKGROUND

Water contamination with human enteric viruses has posed human health risks all over the world. Reasonable and facile methodologies for recovering and quantifying infectious enteric viruses in environmental samples are needed to address the issues of waterborne viral infectious diseases. In this study, a bacterial protein that has a binding capability with several enteric viruses is discovered, and its binding characteristics were investigated for utilizing it as a viral adsorbent in virus recovery and detection technologies.

RESULTS

A gene of an enteric virus-binding protein (EVBP), derived from a monomer of a bacterial chaperon protein GroEL, was successfully acquired from a genomic DNA library of activated sludge microorganisms with nested PCR. Equilibrium dissociation constants between EVBP and norovirus-like particles (NoVLPs) of genotypes GI.7 and GII.4, estimated with quartz crystal microbalance method, were 240 and 210 nM, respectively. These values of equilibrium dissociation constant imply that the binding affinity between EVBP and NoVLPs is 1 to 3-log weaker than that in general antigen-antibody interactions, but about 2-log stronger than that in weak specific interactions of proteins with cations and organic polymers. The adsorptions of EVBP to norovirus, group A rotavirus and poliovirus type 1 were found to be significant in enzyme-linked immunosorbent assay. Meanwhile, the binding of native GroEL tetradecamer to viral particles was weaker than that of EVBP, presumably because of a steric hindrance. The small molecule of EVBP could have an advantage in the access to the surface of viral particles with rugged structure.

CONCLUSIONS

EVBP that has a broad binding spectrum to enteric viruses was newly discovered. The broad binding characteristic of EVBP would allow us to utilize it as a novel adsorbent for detecting diverse enteric viruses in clinical and environmental samples.

Water reclamation redesign for reducing Cryptosporidium risks at a recreational spray park using stochastic models

Recreational outbreaks associated with sprayparks are well recognized, and may be partly due to the engineering designs used for their water reclamation systems are problematic to control. This work is based on an outbreak of cryptosporidiosis linked to a spraypark in New York State, where it was determined, specifically that the spraypad (the main attraction) was the primary exposure point. We first determined the likely dose the spraypad users were exposed to, then modeled the efficacy of the treatment system and used this to inform a Monte Carlo method to estimate the probability of infection and illness for the users of the spraypad. The current treatment system which consists of; two holding tanks, a dual media filter and chlorine injection as well as two design change recommendations were modeled using three independent Markov chain models. Within the current treatment system design the receiving tank for the treatment train is also connected with a second pipe to the spraypad used to deliver the return (treated) water, this return pipe is acting potentially as a bypass for the treatment train. Based on the risk assessments performed it is recommended that the bypass pipe be removed from the treatment system since in doing so the probability of infection and illness were reduced appreciably. Secondarily including an ozone contactor was shown to slightly reduce the risk further and provide a multiple barrier.

Identification and characterization of coagulation inhibitor proteins derived from cyanobacterium Microcystis aeruginosa

The excess growth of cyanobacteria in semi enclosed water areas caused by eutrophication brings about coagulation inhibition in drinking water treatment processes. In this study, coagulation inhibitor proteins produced by Microcystis aeruginosa, a major cyanobacterium in algal bloom, were acquired by a phage display technique, an aluminum-immobilized affinity chromatography and a protein expression technique using Escherichia coli cells. Two cyanobacterial peptides with a high ratio of metallophilic amino acids were recovered, which were a part of homologues of a thiol oxidase enzyme Ero1p and a trans-acting repressor ArsR. It was also shown that the homologue of ArsR exhibited a stronger inhibitory effect on the coagulation of kaolin suspension with polyaluminum chloride than the control proteins. This is the first report to identify a cyanobacterial cell component to inhibit coagulation. The compositions of polar amino acids were critical to explain the strength of coagulation inhibition potential. Polar proteins from cyanobacteria could collectively consume coagulants or stabilize clay particles, which would be plausible explanations for causing coagulation inhibition. Meanwhile, results from the kaolin coagulation tests using the control proteins implied that the neutralization of positive charges of coagulant constituents by simple electrostatic interactions might not be the key mechanism on the protein-induced coagulation inhibition.

Surface-retained organic matter of Microcystis aeruginosa inhibiting coagulation with polyaluminum chloride in drinking water treatment

Algogenic organic matter produced by the excess growth of cyanobacteria in semi-closed water areas causes coagulation inhibition in drinking water production. In this study, hydrophilic substances of Microcystis aeruginosa, which were mainly composed of lipopolysaccharide (LPS) and RNA, were prepared, and the involvement of these cyanobacterial hydrophilic substances in coagulation inhibition was investigated. As a result, it was found that the negatively charged hydrophilic substances with a molecular weight higher than 10 kDa have a significant role in coagulation inhibition. Further fractionation of cyanobacterial hydrophilic substances revealed that surface-retained organic matter (SOM), including LPS, could exhibit a potent inhibitory effect on the coagulation using polyaluminum chloride (PACl), presumably because of the direct interaction of hydrophilic SOM with cations originated from PACl, which could impede the hydrolysis of the coagulant.

Characterizing the risk of infection from Mycobacterium tuberculosis in commercial passenger aircraft using quantitative microbial risk assessment

Quantitative microbial risk assessment was used to predict the likelihood and spatial organization of Mycobacterium tuberculosis (Mtb) transmission in a commercial aircraft. Passenger exposure was predicted via a multizone Markov model in four scenarios: seated or moving infectious passengers and with or without filtration of recirculated cabin air. The traditional exponential (k = 1) and a new exponential (k = 0.0218) dose-response function were used to compute infection risk. Emission variability was included by Monte Carlo simulation. Infection risks were higher nearer and aft of the source; steady state airborne concentration levels were not attained. Expected incidence was low to moderate, with the central 95% ranging from 10(-6) to 10(-1) per 169 passengers in the four scenarios. Emission rates used were low compared to measurements from active TB patients in wards, thus a "superspreader" emitting 44 quanta/h could produce 6.2 cases or more under these scenarios. Use of respiratory protection by the infectious source and/or susceptible passengers reduced infection incidence up to one order of magnitude.

Quantitative risk assessment of noroviruses in drinking water based on qualitative data in Japan

Noroviruses are one of the major causes of viral gastroenteritis in Japan. A quantitative risk assessment was conducted to evaluate the health risk caused by this virus in drinking water. A Monte Carlo analysis was used to calculate both the probability of infection and the disease burden using disability-adjusted life years (DALYs). The concentration of noroviruses in tap water was estimated based on qualitative data and a most probable number (MPN) method with an assumed Poisson lognormal distribution. This numerical method was evaluated using two sets of available count data of Cryptosporidium: that collected from a river and that found in tap water in Japan. The dose-response relationships for noroviruses were estimated using assumed ID50 (10 or 100). The annual risk was higher than the US-EPA acceptable level (10(-4) [infection/ person-year]) but around the WHO level (10(-6) [DALYs/ person-year]). As suggested by others, since microbial concentrations are generally lognormally distributed, the arithmetic mean was directly related to the annual risk, suggesting that the arithmetic mean is more useful in representing the degree of microbial contamination than the geometric mean.

Quantification and genotyping of Cryptosporidium spp. in river water by quenching probe PCR and denaturing gradient gel electrophoresis

A new detection method was developed for the simultaneous quantification and genotyping of Cryptosporidium spp. in river water. Several modifications made to the US EPA Method 1623 enabled high and stable recovery of Cryptosporidium from 40 L of river water (geometric mean = 35%, standard deviation = 8.7%). Quenching probe PCR (QProbe PCR) was used to quantify the 18S rRNA gene of Cryptosporidium spp. This method could successfully detect single oocysts in a sample, and the lower quantitation limit was as low as 2.5 oocysts/sample. In addition, denaturing gradient gel electrophoresis (DGGE) followed by DNA sequencing was used to identify the genotypes. These methods were applied to detect Cryptosporidium spp. in the Koyama River, Japan. The positive ratio was 69% (11/16) with the maximum concentration of 59 oocysts/100 L. Seven genotypes including two novel ones were identified. These results showed that this detection method could provide valuable information on Cryptosporidium in river water, both in the concentration and in the genotypes, which is essential for the precise assessment of waterborne risk to human health.

Cryptosporidium monitoring system at a water treatment plant, based on waterborne risk assessment

The water volume required for daily monitoring of Cryptosporidium (which can statistically ensure an annual risk of infection below 10(-4)), was assessed by evaluating the applicability of the Poisson lognormal (PLN) distribution in microbial risk assessment. PLN showed as good a fit to the observed data as to the negative binomial distribution. From the estimated PLN distributions for the source and finished water, the efficacy of the oocyst removal by the conventional water treatment process was estimated to follow log-normal distribution (median = 3.16 log10, 95% CI = 4.27-2.05 log10). The 365 consecutive negative results of daily monitoring for 180 L of finished water were found to be statistically equivalent to the annual risk of infection below 10(-4). This research also suggested the possibility of applying a qualitative detection method, such as CC-PCR, as a routine monitoring method for the quantitative risk management.

Assessment of risk of infection due to Cryptosporidium parvum in drinking water

The risk of infection of Cryptosporidium via drinking water was assessed using Monte Carlo simulation with the field survey data of the Sagami River watershed. The levels of Cryptosporidium in this river were found to follow the lognormal distribution. From the counted data, the median level of the Miyayama sampling point was estimated to be 5.7 oocysts per 100L. To calculate the annual risk of infection due to Cryptosporidium in drinking water, the Cryptosporidium level of Miyayama sampling point was used as the water source of the waterworks. The 95% percentile of the annual risk of infection was found to be 10(-2.60). If the daily risk was eliminated when the level of Cryptosporidium in treated water exceeded 1 oocyst per 20L, the 95% percentile of the annual risk was reduced by about 1 log. To reduce the 95% value of the annual risk lower than 10(-4), the risk of days with levels of Cryptosporidium in treated water exceeding 1 oocyst per 80L should be eliminated.