Quantitative assessment of risk reduction from hand washing with antibacterial soaps

The Centers for Disease Control and Prevention have estimated that there are 3,713,000 cases of infectious disease associated with day care facilities each year. The objective of this study was to examine the risk reduction achieved from using different soap formulations after diaper changing using a microbial quantitative risk assessment approach. To achieve this, a probability of infection model and an exposure assessment based on micro-organism transfer were used to evaluate the efficacy of different soap formulations in reducing the probability of disease following hand contact with an enteric pathogen. Based on this model, it was determined that the probability of infection ranged from 24/100 to 91/100 for those changing diapers of babies with symptomatic shigellosis who used a control product (soap without an antibacterial ingredient), 22/100 to 91/100 for those who used an antibacterial soap (chlorohexadine 4%), and 15/100 to 90/100 for those who used a triclosan (1.5%) antibacterial soap. Those with asymptomatic shigellosis who used a non-antibacterial control soap had a risk between 49/100,000 and 53/100, those who used the 4% chlorohexadine-containing soap had a risk between 43/100,000 and 51/100, and for those who used a 1.5% triclosan soap had a risk between 21/100,000 and 43/100. The adequate washing of hands after diapering reduces risk and can be further reduced by a factor of 20% by the use of an antibacterial soap. Quantitative risk assessment is a valuable tool in the evaluation of household sanitizing agents and low risk outcomes.

A risk assessment of emerging pathogens of concern in the land application of biosolids

Since the development of the United States Environmental Protection Agency's 503 biosolids Rule, which includes treatment requirements to reduce the threat of pathogen transmission, many new pathogens have been recognized which could be transmitted by biosolids. A risk analysis was performed assess which emerging pathogens would be most likely to survive treatments required for Class B biosolids before land application. The literature was reviewed on the resistance of emerging pathogens to temperature and other environmental factors to assess their probability of surviving various biosolids treatment processes. In addition existing information on occurrence in biosolids and dose response models for each pathogen was reviewed. It was concluded that adenoviruses and hepatitis A virus are the most thermally resistant viruses and can survive for prolonged periods in the environment. The protozoan parasites microsporidia and Cyclospora were unlikely to survive the temperatures achieved in anaerobic digestion and do not survive well under low moisture conditions. A risk model was used to assess the risk of infection and illness from enteric viruses after application of class B biosolids.

Fate of indicator microorganisms, Giardia and Cryptosporidium in subsurface flow constructed wetlands

Limited information is available on the ability of subsurface flow wetlands to remove enteric pathogens. Two multi-species wetlands, one receiving secondary sewage effluent and the other potable (disinfected) groundwater were studied from February 1995 to August 1996, at the Pima County Constructed Ecosystems Research Facility in Tucson, Arizona. Each wetland had a retention time of approximately 4 days. The objectives of this study were (1) to evaluate the ability of multi-species subsurface wetlands to physically remove Giardia cysts; Cryptosporidium oocysts, total and fecal coliforms, and coliphages; and (2) to determine the likely impact of local wildlife on the occurrence of these indicators and pathogens. In the wetland receiving secondary sewage effluent, total coliforms were reduced by an average of 98.8% and fecal coliforms by 98.2%. Coliphage were reduced by an average of 95.2%. Both Giardia cysts and Cryptosporidium oocysts were reduced by an average of 87.8 and 64.2%, respectively. In the wetland receiving disinfected groundwater, an average of 1.3 x 10(2) total coliforms/100 mL and 22.3 fecal coliforms/100 mL were most likely contributed by both flora and fauna. No parasites or coliphages were detected.

Direct exposure to animal enteric pathogens

Humans have very close interactions with working, food-producing, and companion animals. According to the American Veterinary Medical Association, there are more than one hundred million cat and dog pets in the United States. Furthermore, non-traditional pets like reptiles and exotic birds are not unusual companion animals in households. In addition to sharing with animals our living and/or working space and time, we also share, unfortunately, many disease causing microorganisms. In the past few years, we have become aware that several enteric pathogens that were thought to be mostly restricted to animals are a major cause of human disease. Examples of such pathogens include the protozoan parasite Cryptosporidium parvum and bacteria such as Campylobacter spp. This review will examine the characteristics of zoonotic enteric pathogens including bacterial (Helicobacter spp., Campylobacter spp., Salmonella spp., and verotoxin-producing Escherichia coli); parasitic (Toxoplasma gondii, Giardia spp., Cryptosporidium spp.); and viral (rotavirus, norwalk-like virus, hepatitis E virus), and the status of our knowledge with regard to the impact of such pathogens on human health.

ICC/PCR detection of enteroviruses and hepatitis A virus in environmental samples

This study applied the integrated cell culture/polymerase chain reaction methodology (ICC/PCR) for rapid and specific detection of both cytopathogenic and noncytopathogenic viruses. Results of this study showed that the use of direct RT-PCR or conventional cell culture alone may yield erroneous results with the analysis of environmental samples. The purpose of this study was to compare cultural, molecular, and combined assays for the most effective method of virus detection in variable environmental samples. Using ICC/PCR, stock enterovirus inocula of > or =10 PFU were PCR positive in at least 4/5 replicate flasks after only 5 h of incubation in cell culture, and in all flasks after > or =10 h. An inoculum of one PFU was detected by PCR after 20 h of cell culture incubation while for concentrations of virus below one PFU, 25 h of incubation was sufficient. Similarly, hepatitis A virus (HAV) inocula of 100 MPN/flask, produced indeterminate CPE in cell culture, but were clearly detected by ICC/PCR following 48 h of incubation. Lower levels of HAV, 1 and 10 MPN, were detected by ICC/PCR after 96 to 72 h of incubation, respectively. Cell culture lysates from 11 environmental sample concentrates of sewage, marine water, and surface drinking water sources, were positive for enteroviruses by ICC/PCR compared to 3 positive by direct RT-PCR alone. Results from ICC/PCR eventually agreed with cell culture but required < or =48 h of incubation, compared to as long as 3 weeks for CPE following incubation with BGM and FRhK cells.

Chemical and microbial characterization of household graywater

In arid areas, the search for efficient methods to conserve water is of paramount importance. One of the methods of water conservation available today is graywater recycling--the reuse of water from the sinks, showers, washing machine, and dishwasher in a home. The purpose of this project was to characterize the chemical and microbial quality of graywater from a single-family home with two adults. Water samples from a graywater holding tank were analyzed over a seven-month period for total coliforms, fecal coliforms, fecal streptococci, Staphylococcus aureus (S. aureus), Pseudomonas aeruginosa (P. aeruginosa), and coliphages. The pH, turbidity, biological oxygen demand (BOD), suspended solids (SS), electrical conductivity (EC), sulfates (SO4), and chlorides (Cl) were also measured. The mean numbers of total coliforms, fecal coliforms, fecal streptococci, and P. aeruginosa were 8.03 x 10(7), 5.63 x 10(5), 2.38 x 10(2), and 1.99 x 10(4) CFU/100 mL, respectively. S. aureus and coliphages were not detected. In the chemical analysis, mean values of 7.47 for pH, 43 nephelometric turbidity units (NTU) for turbidity, 64.85 mg/L for BOD, 35.09 mg/L for SS, 0.43 mS/cm for EC, 59.59 mg/L for SO4, and 20.54 mg/L for Cl were measured. These data were compared to data taken in 1986 and 1987, when two adults and one child lived in the household. Analysis showed no statistically significant difference in levels of total coliforms and suspended solids between the two data sets. There were statistically significant differences in levels of fecal coliforms, pH, turbidity, chlorides, sulfates, and BOD between the two households. Fecal coliforms, turbidity, and BOD were higher in the household with two adults and one child. Levels of Cl, SO4, and pH were higher in the household with two adults.

Removal of bacterial indicators and pathogens from dairy wastewater by a multi-component treatment system

Microbial removal by a multi-component treatment system for dairy and municipal wastewater is being studied in Arizona, USA. The system consists of paired solids separators, anaerobic lagoons, aerobic ponds and constructed wetlands cells. The organisms under study include: total coliform, fecal coliform, enterovirus, Listeria monocytogenes, Clostridium perfringens, coliphage, Giardia lamblia and Cryptosporidium parvum. Organism removal rates from dairy wastewater varied from 13.2 per cent for fecal coliform to 94.9 per cent for coliphage. It appears that the much higher turbidity of the dairy wastewater, nearly 1,300 NTU, decreased the treatment systems' ability to remove some microbial indicators and pathogens. Information from this study can be used to determine the adequacy of multi-component treatment systems for the control of wastewater-borne pathogens, both in municipal treatment systems as well as in confined animal feeding operations (CAFO). This information also can assist municipalities and the CAFO industry in the implementation of rational and efficient treatment strategies for appropriate reuse of wastewaters.

Removal of pathogenic and indicator microorganisms by a constructed wetland receiving untreated domestic wastewater

Wetlands containing floating, emergent and submergent aquatic plants, and other water-tolerant species have been found to economically provide a mechanism of enhancing the quality of domestic wastewater. The use of constructed wetlands for the removal of indicator bacteria (total and fecal coliforms), coliphages, protozoan parasites (Giardia and Cryptosporidium) and enteric viruses was investigated. A pilot scale constructed wetland consisting of two cells, one planted with bulrush and the other unplanted bare sand, were used to compare their efficiency in removing pathogens from raw sewage. Overall more than 90 percent of all microorganisms studied were removed by either of the two systems with a 1 to 2 day retention time. Removal of all mentioned microorganisms was greater from the surface flow in the unplanted cell than in the planted cell, except for Giardia and Cryptosporidium, although the differences were not statistically significant. Enteric viruses, coliphages and indicator bacteria were found to penetrate 2 m below the surface, although concentrations were reduced by greater than 99 percent in both cells. Less virus penetration into the sand occurred in the planted wetland versus the unplanted wetland. Water temperature was found to be the most important factor in the removal of enteric bacteria and viruses, while turbidity reduction was related to Giardia removal. These results demonstrate that significant reductions of pathogenic microorganisms can occur in constructed wetlands receiving untreated domestic wastewater with only a 1-2 day retention time.

Development of a dose-response relationship for Escherichia coli O157:H7

E. coli O157:H7 is an emerging food and waterborne pathogen. The development of acceptable guidelines for exposure to this organism based on quantitative microbial risk assessment requires a dose response curve. In this study, a prior animal study was used to develop a dose response relationship. The data was adequately fit by the beta-Poisson dose response relationship. This relationship was validated with reference to two outbreaks of this organism. It was found that the low dose extrapolation of the animal data using the beta-Poisson relationship provided estimates of risk concordant with those noted in the outbreaks. The fitted dose response relationship in conjunction with population estimates of the prevalence of E. coli O157:H7 illness indicates that the overall exposure is quite low in the US.

Use of integrated cell culture-PCR to evaluate the effectiveness of poliovirus inactivation by chlorine

Current standards, based on cell culture assay, indicate that poliovirus is inactivated by 0.5 mg of free chlorine per liter after 2 min; however, integrated cell culture-PCR detected viruses for up to 8 min of exposure to the same chlorine concentration, requiring 10 min for complete inactivation. Thus, the contact time for chlorine disinfection of poliovirus is up to five times greater than previously thought.

Microbiological water purification without the use of chemical disinfection

OBJECTIVE

Point-of-use (POU) water treatment systems are self-contained units that can be used by recreational enthusiasts who normally obtain drinking water from untreated sources (i.e., rivers, lakes, etc). Microbiological water purifier units are capable of removing all waterborne pathogens. The purpose of this study was to evaluate a new technology (Structured Matrix) capable of micro-biologically purifying the water without the use of chemical disinfectants or an external power requirement.

METHODS

Each of 3 identical portable water filtration units were evaluated for their ability to remove Klebsiella terrigena, poliovirus type 1, rotavirus SA-11, and Cryptosporidium parvum oocysts. Units were operated according to the manufacturer's instructions to process 378 L of water. Each unit was challenged with test organisms after 0, 94, 190, 227, 284, 340, and 378 L had passed through it. For the 227-L and 284-L challenges, a "worst-case" water quality (4 degrees C, pH 9, and turbidity 30 NTU) was used that contained 1500 mg/L dissolved solids and 10 mg/L humid acid. At 340-L and 378-L challenges, worst-case water quality was adjusted to pH 5.0. Units were tested after stagnation for 48 hours following passage of 190, 340, and 378 L of water.

RESULTS

The geometric average removal exceeded 99.9999% for bacteria, 99.99% for viruses, and 99.9% for Cryptosporidium parvum oocysts.

CONCLUSION

These units comply with the criteria guidelines for microbial removal under the United States Environmental Protection Agency's "Guide Standard and Protocol for Testing Microbiological Water Purifiers."

Evaluation of methodologies including immunofluorescent assay (IFA) and the polymerase chain reaction (PCR) for detection of human pathogenic microsporidia in water

Microsporidia is a term used to describe a group of emerging protozoan pathogens whose environmental occurrence has only recently been documented due to lack of detection methodologies. This study evaluates and describes current methods for detection of microsporidia in water. Standard methods, for the collection and processing of large volumes of water to detect protozoa, showed only a 4.8% recovery, of microsporidia spores, from 100 l volumes of tap. Immunofluorescent assay (IFA) analysis was assessed using two different antibodies specific for human pathogenic microsporidia. Results indicated that the use of IFA for routine screening of water for microsporidia was not an acceptable approach. The antibodies tested for the IFA resulted in false positives and false negatives and did not react with Enterocytozoon bieneusi, which is an important human pathogenic microsporidia. Finally, the small sizes of the human pathogenic microsporidia prevent confirmation and species determination by light microscopic methods. Two methods for isolating microsporidia DNA from water for use in polymerase chain reaction (PCR) amplification of microsporidia target sequences were assessed. Both of these DNA isolation methods when combined with the PCR showed the ability to detect less than ten spores in purified water concentrates. Thus, this study represents the first documentation and evaluation of current methods for the detection of human pathogenic microsporidia in water.

Confirmation of the human-pathogenic microsporidia Enterocytozoon bieneusi, Encephalitozoon intestinalis, and Vittaforma corneae in water

Microsporidia, as a group, cause a wide range of infections, though two species of microsporidia in particular, Enterocytozoon bieneusi and Encephalitozoon intestinalis, are associated with gastrointestinal disease in humans. To date, the mode of transmission and environmental occurrence of microsporidia have not been elucidated due to lack of sensitive and specific screening methods. The present study was undertaken with recently developed methods to screen several significant water sources. Water concentrates were subjected to community DNA extraction followed by microsporidium-specific PCR amplification, PCR sequencing, and database homology comparison. A total of 14 water concentrates were screened; 7 of these contained human-pathogenic microsporidia. The presence of Encephalitozoon intestinalis was confirmed in tertiary sewage effluent, surface water, and groundwater; the presence of Enterocytozoon bieneusi was confirmed in surface water; and the presence of Vittaforma corneae was confirmed in tertiary effluent. Thus, this study represents the first confirmation, to the species level, of human-pathogenic microsporidia in water, indicating that these human-pathogenic microsporidia may be waterborne pathogens.

Incidence of enteroviruses in Mamala Bay, Hawaii using cell culture and direct polymerase chain reaction methodologies

The consequence of point and nonpoint pollution sources, discharged into marine waters, on public recreational beaches in Mamala Bay, Hawaii was evaluated using virus cell culture and direct reverse transcriptase-polymerase chain reaction (RT-PCR). Twelve sites, nine marine, two freshwater (one stream and one canal), and one sewage, were assessed either quarterly or monthly for 1 year to detect the presence of human enteric viruses. Water samples were concentrated from initial volumes of 400 L to final volumes of 30 mL using Filterite electronegative cartridge filters and a modified beef extract elution procedure. Cell culture was applied using the Buffalo Green Monkey kidney cell line to analyze samples for enteroviruses. Positive samples were also evaluated by RT-PCR, using enterovirus-specific primers. Levels of RT-PCR inhibition varied with each concentrated sample. Resin column purification increased PCR detection sensitivity by at least one order of magnitude in a variety of sewage outfall and recreational marine water samples but not in the freshwater canal samples. Using cell culture, viable enteroviruses were found in 50 and 17% of all outfall and canal samples, respectively. Samples were positive at beaches 8% of the time. These data illustrate the potential public health hazard associated with recreational waters. Using direct PCR, viruses were detected at the outfall but were not found in any beach or canal samples, in part, owing to substances that inhibit PCR. Therefore, conventional cell culture is the most effective means of detecting low levels of infectious enteroviruses in environmental waters, whereas direct RT-PCR is rendered less effective by inhibitory compounds and low equivalent reaction volumes.

PCR amplification and species determination of microsporidia in formalin-fixed feces after immunomagnetic separation

The term microsporidia is used to describe several species of opportunistic protozoan parasites. Encephalitozoon intestinalis and Enterocytozoon bieneusi have been found in stools of more than 40% of AIDS patients with diarrhea. Diagnosis of infection with these small protozoans has been difficult, and until recently their occurrence has not been well documented. Formalin is widely used to preserve clinical specimens, but due to the nature of the fixation process, subsequent analysis, especially analysis by the PCR, is difficult. This study evaluated methods used to prepare formalin-fixed fecal specimens for PCR amplification of microsporidial DNA. Two methods were devised to allow PCR detection and subsequent identification of microsporidia in formalin-fixed fecal specimens to the species level. One method involved immunomagnetic separation to concentrate microsporidial spores from fecal specimens. In the second method Chelex resin (Bio-Rad, Hercules, Calif.) was used to remove inhibitory substances, followed by a DNA concentration step. Both methods resulted in reproducible, confirmed detection of microsporidia in formalinized fecal specimens and subsequent species determination by PCR sequencing. The detection sensitivity was two in vitro culture-derived spores (Encephalitozoon intestinalis) for the direct PCR. The reproducible detection sensitivity for DNA amplification from formalin-fixed fecal samples was 200 spores for either the Chelex method or the immunomagnetic bead separation method. Thus, we developed two methods for rapid, inexpensive detection of microsporidial spores in formalin-fixed fecal specimens.

Persistence of MS-2 and PRD-1 bacteriophages in an ultrapure water system

The persistence of bacteriophages MS-2 and PRD-1 was evaluated in tap water, in reverse osmosis (RO) permeate, and in three locations within an ultrapure water system; ultrapure samples included pre- and post-UV sterilization and post-mixed bed ion exchange tank. The inactivation rates for MS-2 were calculated as log10 reduction per hour and per day: k = -(log 10 Ct/C0)/t. PRD-1 was found to persist with no significant loss of infectivity in all water purity environments evaluated. Inactivation of MS-2 was dependent on water quality and pH. Short-term inactivation rates for chlorinated tap water, post-RO, pre-UV, post-UV and post-ion exchange sample locations were 0.028, 0.455, 0.231, 0.191 and 0.168 log10 h-1, respectively. Long-term inactivation rates for chlorinated tap water, post-RO, pre-UV, post-UV and post-ion exchange sample locations were 0.485, 0.911, 0.605, 0.632 and 0.684 log10 day-1, respectively. Since phages were found to remain intact as well as to lyse in the ultrapure water environment, the phages have the potential to contaminate the ultrapure water environments of the microelectronics, pharmaceutical and power generation industries in both colloidal and dissolved form. Further work is proceeding to generate standardized and cost-effective methods to detect viruses in water environments.

Efficacy of iodine water purification tablets against Cryptosporidium oocysts and Giardia cysts

The ability to control water-borne diseases is critical for soldiers, hikers, and others who may need to drink directly from an outdoor source. Water-borne protozoan parasites that are specifically of concern are Giardia and Cryptosporidium because of their resistance to halogen disinfection. The purpose of this study was to determine the effectiveness of iodine tablets against Giardia and Cryptosporidium under general- and worst-case water conditions that might be found in the field. Giardia cysts and Cryptosporidium oocysts were exposed to iodine according to manufacturer's instructions (two tablets/L = 13-18 mg/L for 20 minutes). This dose inactivated 3-log10 of Giardia in general-case water and pH 9. In worst-case water, however, only about 35% of cysts were inactivated at pH 5. Fifty minutes were required to achieve a 3-log10 reduction at pH 5. Cryptosporidium oocysts were more difficult to inactivate. Only 10% were inactivated after a 20-minute exposure to iodine according to manufacturer's instructions; even after 240 minutes of exposure to iodine only 66-81% oocysts were inactivated. These data strongly suggest that iodine disinfection is not effective in inactivating Cryptosporidium oocysts in water. Because this organism is common in all surface waters, it is recommended that another method of treatment be used before ingestion.

Risk assessment of opportunistic bacterial pathogens in drinking water

This study was undertaken to examine quantitatively the risks to human health posed by heterotrophic plate count (HPC) bacteria found naturally in ambient and potable waters. There is no clear-cut evidence that the HPC bacteria as a whole pose a public health risk. Only certain members are opportunistic pathogens. Using the four-tiered approach for risk assessment from the National Academy of Sciences, hazard identification, dose-response modeling, and exposure through ingestion of drinking water were evaluated to develop a risk characterization, which estimates the probability of infection for individuals consuming various levels of specific HPC bacteria. HPC bacteria in drinking water often include isolates from the following genera: Pseudomonas, Acinetobacter, Moraxella, Aeromonas, and Xanthomonas. Other bacteria that are commonly found are Legionella and Mycobacterium. All these genera contain species that are opportunistic pathogens which may cause serious diseases. For example, the three nonfermentative gram-negative rods most frequently isolated in the clinical laboratory are (1) Pseudomonas aeruginosa, (2) Acinetobacter, and (3) Xanthomonas maltophilia. P. aeruginosa is a major cause of hospital-acquired infections with a high mortality rate. Aeromonas is sometimes associated with wound infections and suspected to be a causative agent of diarrhea. Legionella pneumophila causes 4%-20% of cases of community-acquired pneumonia and has been ranked as the second or third most frequent cause of pneumonia requiring hospitalization. The number of cases of pulmonary disease associated with Mycobacterium avian is rapidly increasing and is approaching the incidence of M. tuberculosis in some areas. Moraxella can cause infections of the eye and upper respiratory tract. The oral infectious doses are as follows in animal and human test subjects: P. aeruginosa, 10(8)-10(9); A, hydrophila, > 10(10); M. avium, 10(4)-10(7); and X. maltophilia, 10(6)-10(9). The infectious dose for an opportunistic pathogen is lower for immunocompromised subjects or those on antibiotic treatment. These bacteria have been found in drinking water at the following frequencies: P. aeruginosa, < 1%-24%; Acinetobacter, 5%-38%; X. maltophilia, < 1%-2%; Aeromonas, 1%-27%; Moraxella, 10%-80%; M. avium, < 1%-50%; and L. pneumophila, 3%-33%. These data suggest that drinking water could be a source of infection for some of these bacteria. The risk characterization showed that risks of infection from oral ingestion ranged from a low of 7.3 x 10(-9) (7.3/billion) for low exposures to Aeromonas to higher risks predicted at high levels of exposure to Pseudomonas of 9 x 10(-2) (98/100). This higher risk was only predicted for individuals on antibiotics. Overall, the evidence suggests that specific members of HPC bacteria found in drinking water may be causative agents of both hospital- and community-acquired infections. However, the case numbers may be very low and the risks represent levels generally less than 1/10,000 for a single exposure to the bacterial agent. Future research needs include (1) determining the seasonal concentrations of these bacteria in drinking water, (2) conducting adequate dose-response studies in animal subjects or human volunteers, (3) determining the health risks for an individual with multiple exposures to the opportunistic pathogens, and (4) evaluating the increase in host susceptibility conferred by antibiotic use or immunosuppression.

Detection of viable Giardia cysts by amplification of heat shock-induced mRNA

Primers obtained from gene sequences coding for heat shock proteins (HSP) were used to specifically detect enteric protozoans of the genus Giardia. The HSP primers amplified Giardia DNA or the corresponding RNA sequences obtained from lysed cysts and gave a 163-bp product. Since the presence of the product did not indicate whether the cysts were viable, these amplifications are a presence/absence test only. In contrast, amplification of heat shock-induced mRNA utilizing the same HSP primers was indicative of viable Giardia cysts. The limit of sensitivity of the presence/absence test was 1 cyst, whereas for the viability test it was 10 cysts. Thus, viable Giardia cysts can be rapidly and specifically detected with great sensitivity through the use of PCR amplifications.

Prevalence of shigellosis in the U.S.: consistency with dose-response information

Every year there are estimated 300000 cases of Shigella in the United States (Bennett et al., 1987, Am. J. Prev. Med. 3, 102-114). A beta-poisson model was fit to human dose-response information on pathogenic Shigella using the Maximum Likelihood Estimation technique (Haas, 1983, Am. J. Epidemiol. 118, 573-582). Pooled and separate data sets for the Shigella species were fit to the beta-Poisson model and 95% confidence limits and regions were calculated. Shigella dysentariae and Shigella flexneri confidence regions and limits overlapped with each other and with the pooled data set, suggesting that this model can describe Shigella in general. The pooled Shigella model as well as the upper and lower confidence limits of the three data sets showed average exposures based on the estimated U.S. caseload of pathogenic Shigella of 0.01 to 0.014 organisms (confidence limits 0.001-0.05) for a 7-day per annum period of exposure and ranges from 0.07 to 0.1 organisms (confidence limits 0.006-0.4). for a 1-day per annum period of exposure. The plausibility of the pooled dose-response model was then evaluated by comparison with two known cruise ship outbreaks. The pooled model estimated that the two outbreaks studied could have been due to ingestion of 344 (confidence limits 72-915) Shigella cells per meal and 10.5-12 (confidence limits 1-44) Shigella cells per glass of water by passengers.

Sensitive populations: who is at the greatest risk?

The purpose of this article was to review the existing literature to define those groups of individuals who would be at the greatest risk of serious illness and mortality from water and foodborne enteric microorganisms. This group was found to include the very young, the elderly, pregnant women, and the immunocompromised. This segment of the population currently represents almost 20% of the population in the United States and is expected to increase significantly by the beginning of the next century, because of increases in life-span and the number of immunocompromised individuals. More than half of documented deaths from gastroenteritis and hepatitis A illness occur in the elderly in developed countries. The overall case fatality ratio for foodborne bacterial gastroenteritis outbreaks in nursing homes is 10 times greater than the general population. Pregnant mothers suffer from a case fatality ratio from hepatitis E infections ten times greater than the general population during waterborne disease outbreaks. Enteric diseases are most common and devastating among the immunocompromised. Cryptosporidium is a serious problem among patients with acquired immuno-deficiency syndrome (AIDS). Cancer patients undergoing chemotherapy and transplant patients, are also at significantly greater risk of dying from enteric viral infections than the general population. This review indicates the need for consideration of enhanced protection for certain segments of the population who will suffer the most from food and waterborne pathogens.

Detection of infectious enteroviruses by an integrated cell culture-PCR procedure

Rapid detection of infectious enteroviruses in environmental samples was made possible by utilizing an integrated cell culture-reverse transcriptase PCR approach. By this method, the presence of infectious enterovirus was confirmed within 24 h, compared with > or = 3 days by cell culture alone. The combined methodology eliminated typical problems normally associated with direct reverse transcriptase PCR by increasing the equivalent volume of environmental sample examined and reducing the effects of inhibitory compounds.

Increased sensitivity of poliovirus detection in tap water concentrates by reverse transcriptase-polymerase chain reaction

This study developed a methodology to increase the sensitivity of enteric virus detection in tap water concentrates. Polymerase chain reaction (PCR) detection of virus in reduced volumes of virus-containing water concentrates was successful following removal of PCR inhibitory substances. Poliovirus 1 and coxsackievirus B3 were seeded into 378 l of tap water, concentrated with 1MDS filters, and reconcentrated by organic flocculation. The volume of concentrates was successfully reduced from 25 to 5 ml without loss of virus recovery. PCR detection of virus after treatment of a water concentrate (1.1 x 10(5)-fold concentration) with a Sephadex G-100 plus Chelex-100 column, or Sephadex G-50 plus Chelex-100 column, followed by heat treatment to release viral RNA, was compared with direct phenol-chloroform-isoamyl alcohol (PCI) extraction of viral RNA. The Sephadex G-50 plus Chelex-100 column did not remove inhibitory substances efficiently. The Sephadex G-100 plus Chelex-100 column could remove inhibitory substances, however, 99% of the viruses were also removed by the column. PCI extraction was found to be sufficient to remove inhibitory substances for reverse transcriptase (RT)-seminested PCR with a sensitivity of 0.2 plaque-forming units/10 microliters (0.2 PFU/l tap water).

Comparison of PCR and cell culture for detection of enteroviruses in sludge-amended field soils and determination of their transport

PCR and cell culture assays for enteroviruses were conducted on soil samples collected from an experimental farm that had received mesophilic anaerobically digested sludge for the past 7 years. Of 24 samples assayed, 21 samples were positive by PCR, implying that at least some viral nucleic acid sequences remained intact. However, these viral particles were unable to infect the Buffalo Green Monkey cell line used in subsequent cell culture assays. It is significant that positive PCR detection of nucleic acid sequences occurred even though the most recent sludge application was 3 months prior to soil sampling. Viral nucleic acid sequences were detected by PCR at points vertically and laterally displaced from sludge injections, illustrating significant transport of viruses. Rainfall and irrigation events may have contributed to viral transport.