Norovirus and human adenovirus occurrence and diversity in recreational water in a karst aquifer in the Yucatan Peninsula, Mexico

AIMS

To determine the seasonal occurrence and diversity of norovirus (NoV) and human adenovirus (HAdV) in groundwater from sinkholes, and brackish water used for recreational activities in the karst aquifer of the Yucatan Peninsula, Mexico.

METHODS AND RESULTS

Hollow fibre ultrafiltration was used to concentrate viruses and standard plaque assay methods were used to enumerate somatic and F+ specific coliphages as viral indicators. Real-time quantitative polymerase chain reaction assays were used to estimate the number of genome copies for NoV strains GI, and GII, and HAdVs. The predominant NoV genotypes and HAdV serotypes were identified by comparative sequence analysis. Somatic and male F+ specific coliphages were detected at concentrations up to 94 and 60 plaque-forming units per 100 ml respectively. The NoV genogroup I (GI) was associated with 50% of the sampled sites during the rainy season only, at concentrations ranging from 120 to 1600 genome copies per litre (GC l^-1 ). The NoV genogroup II (GII) was detected in 30 and 40% of the sampled sites during the rainy and dry seasons, respectively, at concentrations ranging from 10 to 290 GC l^-1 . During the rainy and dry seasons, HAdVs were detected in 20% of the sites, at concentrations ranging from 24 to 690 GC l^-1 . Identification of viral types revealed the presence of NoV GI.2, GII.Pe, GII.P16 and GII.P17, and HAdV F serotypes 40 and 41.

CONCLUSIONS

These findings demonstrate that NoVs and HAdVs are prevalent as virus contaminants in the karst aquifer, representing potential health risks particularly during the rainy season, in one of the most important areas used for tourism in Mexico.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is one of the few studies conducted in karst aquifers that provide a foundational baseline of the distribution, concentrations and diversity of NoVs and HadVs in these particular environments.

Modelling of ultraviolet light inactivation kinetics of methicillin-resistant Staphylococcus aureus, vancomycin-resistant Enterococcus, Clostridium difficile spores and murine norovirus on fomite surfaces

AIMS

Quantitative data on the doses needed to inactivate micro-organisms on fomites are not available for ultraviolet applications. The goal of this study was to determine the doses of UV light needed to reduce bacteria and murine norovirus (MNV) on hard surface fomites through experimentation and to identify appropriate models for predicting targeted levels of reduction.

METHODS AND RESULTS

Stainless steel and Formica laminate coupons were selected as they are common surfaces found in healthcare settings. Test organisms included methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococcus (VRE), Clostridium difficile and MNV. The fomites were inoculated with 10⁵ -10⁷ bacteria or virus and exposed to a range of UV doses. The order of resistance to UV irradiation was virus, bacterial spore and vegetative cell. The best fitting inactivation curves suggested nonlinear responses to increasing doses after a 3-4 log reduction in the test organisms. The average UV doses required for a 3 log reduction in the C. difficile, MRSA and VRE were 16 000, 6164 and 11 228 (mJ-s cm^-2 ) for stainless steel, respectively, and 16 000, 11 727 and 12 441 (mJ-s cm^-2 ) for Formica laminate, respectively.

CONCLUSIONS

Higher UV light doses are required to inactivate bacteria and viruses on hard surfaces than in suspension. Greater doses are needed to inactivate bacterial spores and MNV compared to vegetative bacteria.

SIGNIFICANCE AND IMPACT OF THE STUDY

Quantitative data and models on UV light doses needed to inactivate bacteria and MNV on hard surfaces are now available. The generalizable results of this study can be used to estimate required UV dosages to achieve targeted levels of inactivation based on estimated levels of contamination or to support quantitative microbial risk assessments.

Temporal variations in genotype distribution of human sapoviruses and Aichi virus 1 in wastewater in Southern Arizona, United States

AIMS

To investigate the molecular epidemiology, especially temporal variations in genotype distribution, of sapoviruses and Aichi virus 1 (AiV-1) in Arizona, United States, by examining wastewater.

METHODS AND RESULTS

A total of 26 wastewater samples (13 influent and 13 effluent) were collected monthly from a wastewater treatment plant and viral strains were identified through nested reverse transcription-PCR followed by cloning and sequencing analysis. Identified sapovirus strains were classified into seven genotypes belonging to three genogroups (GI, GII, and GV): GI.1, GI.2, GI.3, GII.1, GII.2, GII.8 and GV.1, with a clear temporal shift. The majority of AiV-1 strains identified from the wastewater samples were classified into genotype B, and genotype A strains were identified in only two samples.

CONCLUSIONS

We identified a number of sapovirus and AiV-1 strains belonging to multiple genotypes in wastewater samples collected over a 13-month period. Our results suggested a temporal shift in prevalent genotypes in the community.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first study elucidating the genotype distribution of human sapoviruses and AiV-1 in wastewater in the United States. Wastewater surveillance is especially useful for understanding molecular epidemiology of viruses that are less commonly tested in clinical diagnosis, including sapoviruses and AiV-1.

Persistence analysis of poliovirus on three different types of fomites

AIMS

The goal of this study was to explore various models for describing viral persistence (infectivity) on fomites and identify the best fit models.

METHODS AND RESULTS

The persistence of poliovirus over time was studied on three different fomite materials: steel, cotton and plastic. Known concentrations of poliovirus type 1 were applied to the surface coupons in an indoor environment for various lengths of time. Viruses were recovered from the surfaces by vortexing in phosphate buffer. Seven different mathematical models of relative persistence over time were fit to the data, and the preferred model for each surface was selected based on the Bayesian information criterion.

CONCLUSIONS

While the preferred model varied by fomite type, the virus showed a rapid initial decay on all of the fomite types, followed by a transition to a more gradual decay after about 4-8 days. Estimates of the time for 99% reduction ranged from 81 h for plastic to 143 h for cotton. A 6 log reduction of recoverable infectivity of poliovirus did not occur during the 3-week duration of the experiment for any of the fomites.

SIGNIFICANCE AND IMPACT OF THE STUDY

In protected indoor environments poliovirus can remain infective for weeks. The models identified by this study can be used in risk assessments to identify appropriate strategies for managing this risk.

Impact of disinfectant wipes on the risk of Campylobacter jejuni infection during raw chicken preparation in domestic kitchens

AIMS

In the present study, we conducted a quantitative microbial risk assessment forecasting the exposure to Campylobacter jejuni contaminated surfaces during preparation of chicken fillets and how using a disinfectant-wipe intervention to clean a contaminated work area decreases the risk of infection following the preparation of raw chicken fillet in a domestic kitchen.

METHODS AND RESULTS

Using a Monte Carlo simulation of the risk of transferring Camp. jejuni strain A3249, from various surfaces to hands and subsequently transferring it to the mouth was forecasted. The use of a disinfectant-wipe intervention to disinfect contaminated surface area was also assessed. Several assumptions were used as input parameters in the classical Beta-Poisson model to determine the risk of infection. The disinfectant-wipe intervention reduced the risk of Camp. jejuni infection by 2-3 orders on all fomites.

CONCLUSIONS

The use of disinfectant wipes after the preparation of raw chicken meat reduces the risk of Camp. jejuni infections.

SIGNIFICANCE AND IMPACT OF THE STUDY

This risk assessment shows that the use of disinfectant wipes to decontaminate surface areas after chicken preparation reduces the annual risk of Camp. jejuni infections up to 99·2%, reducing the risk from 2 : 10 to 2 : 1000.

Reduction of risk of Salmonella infection from kitchen cleaning clothes by use of sodium hypochlorite disinfectant cleaner

The objective of this study was to evaluate the reduction of infection risk due to exposure to Salmonella sp. in kitchen cleaning clothes by the use of a bleach (sodium hypochlorite) cleaner utilizing a continuous-time dynamic exposure model. The only route of exposure considered was hand contamination during cloth use. The occurrence and numbers of Salmonella was studied in 60 homes over a 6-week period in which half disinfected kitchen cleaning clothes with a sodium hypochlorite based disinfectant cleaner. This study demonstrated that a significant risk exists for Salmonella infection from kitchen cleaning clothes in Mexican homes and that this risk can be reduced by almost 100-fold by soaking cleaning clothes in a bleach product. The risks of infection and illness could likely be further reduced by developing a more effective procedure for reducing Salmonella in cleaning clothes treated twice a day with a sodium hypochlorite disinfectant (i.e. longer soaking time) or using a greater concentration of the disinfectant.

SIGNIFICANCE AND IMPACT OF THE STUDY

Hygiene intervention is a key strategy to reduce the potential risk of disease-causing micro-organisms in households. There is a lack of understanding of the human health risk associated with the use of contaminated kitchen cleaning cloths. The study used a quantitative microbial risk assessment to estimate the risk associated with the use of kitchen cleaning clothes by using disinfectant products. The results showed that the use of prescribe protocols can reduce the risk of Salmonella infections in household kitchens.

Detection of pathogenic micro-organisms on children's hands and toys during play

AIMS

This study aimed to determine if the children's leisure activities impact the presence of pathogens on their hands and toys.

METHODS & RESULTS

To assess the microbiological hazard in playground areas, a pilot study that included 12 children was conducted. We then conducted an intervention study; children's hands and toys were washed before playing. Faecal coliforms, pathogenic bacteria and Giardia lamblia were quantified by membrane filtration, selective media and flotation techniques, respectively; rotavirus, hepatitis A and rhinovirus by RT-PCR. Pilot study results revealed faecal contamination on children's hands and toys after playing on sidewalks and in public parks. Pathogenic bacteria, hepatitis A and G. lamblia on children's hands were also found. In the intervention study, Staphylococcus aureus and Klebsiella pneumoniae were found on children's hands at concentrations up to 2·5 × 10(4) and 1 × 10(4) CFU hands(-1), respectively. E. coli and Kl. pneumoniae were detected on toys (2·4 × 10(3) and 2·7 × 10(4) CFU toy(-1), respectively). Salmonella spp, Serratia spp and G. lamblia cysts were also present on toys.

CONCLUSION

Children's play activities influence microbial presence on hands and toys; the transfer seems to occur in both ways.

SIGNIFICANCE AND IMPACT OF THE STUDY

Control strategy needs to be implemented to protect children from infectious diseases.

Microbial contamination in kitchens and bathrooms of rural Cambodian village households

AIMS

To quantify microbial contamination on kitchen and bathroom surfaces (fomites) in rural Cambodian homes and to compare these concentrations to similar data from the United States and Japan.

METHODS AND RESULTS

This study monitored the numbers of faecal coliforms (i.e. thermotolerant coliforms), total coliforms, Escherichia coli and heterotrophic plate count bacteria on household surfaces in a rural village of Cambodia. Faecal coliform levels in Cambodia were highest on moist locations such as the plastic ladle used for sink water, the toilet seat surface and the cutting board surface with 100-fold higher levels of faecal coliform bacteria than E. coli and 100-fold higher levels of faecal coliforms than the US and Japanese studies.

CONCLUSIONS

A single public health intervention barrier, such as an improved latrine, is only partially effective for household sanitation. For complete sanitation, multiple environmental barriers may be necessary. These barriers occur in a house constructed with easily washable surfaces, a chlorinated water distribution system, house climate control and cleaning product availability.

SIGNIFICANCE AND IMPACT OF THE STUDY

Results of this study can be used to emphasize the importance of increasing household environmental sanitation barriers.

Impact of prescribed cleaning and disinfectant use on microbial contamination in the home

AIMS

To identify and quantify the presence of Escherichia coli, Staphylococcus aureus, Salmonella, hepatitis A and norovirus in households and to assess the effect of chlorine and quaternary ammonium-based disinfectants following a prescribed use.

METHODS AND RESULTS

Eleven sites distributed in kitchen, bathroom, pet and children's areas of two groups of 30 homes each: (i) a nonprescribed disinfectant user group and (ii) a disinfectant protocol user group. During the 6-week study, samples were collected once a week except for week one when sample collection occurred immediately before and after disinfectant application to evaluate the disinfectant protocol. The concentration and occurrence of bacteria were less in the households with prescribed use of disinfectants. The greatest reductions were for E. coli (99%) and Staph. aureus (99·9999%), respectively. Only two samples were positive for HAV, while norovirus was absent. Disinfection protocols resulted in a significant (P < 0·05) microbial reduction in all areas of the homes tested compared to homes not using a prescribed protocol.

CONCLUSIONS

The study suggests that disinfectant product application under specific protocol is necessary to achieve greater microbial reductions.

SIGNIFICANCE AND IMPACT OF THE STUDY

Prescribed protocols constitute an important tool to reduce the occurrence of potential disease-causing micro-organisms in households.

Persistence of viruses in desert soils amended with anaerobically digested sewage sludge

Pima County, Ariz., is currently investigating the potential benefits of land application of sewage sludge. To assess risks associated with the presence of pathogenic enteric viruses present in the sludge, laboratory studies were conducted to measure the inactivation rate (k = log(10) reduction per day) of poliovirus type 1 and bacteriophages MS2 and PRD-1 in two sludge-amended desert agricultural soils (Brazito Sandy Loam and Pima Clay Loam). Under constant moisture (approximately -0.05 x 10 Pa for both soils) and temperatures of 15, 27, and 40 degrees C, the main factors controlling the inactivation of these viruses were soil temperature and texture. As the temperature increased from 15 to 40 degrees C, the inactivation rate increased significantly for poliovirus and MS2, whereas, for PRD-1, a significant increase in the inactivation rate was observed only at 40 degrees C. Clay loam soils afforded more protection to all three viruses than sandy soils. At 15 degrees C, the inactivation rate for MS2 ranged from 0.366 to 0.394 log(10) reduction per day in clay loam and sandy loam soils, respectively. At 27 degrees C, this rate increased to 0.629 log(10) reduction per day in clay loam soil and to 0.652 in sandy loam soil. A similar trend was observed for poliovirus at 15 degrees C (k = 0.064 log(10) reduction per day, clay loam; k = 0.095 log(10) reduction per day, sandy loam) and 27 degrees C (k = 0.133 log(10) reduction per day, clay loam; k = 0.154 log(10) reduction per day, sandy loam). Neither MS2 nor poliovirus was recovered after 24 h at 40 degrees C. No reduction of PRD-1 was observed after 28 days at 15 degrees C and after 16 days at 27 degrees C. At 40 degrees C, the inactivation rates were 0.208 log(10) reduction per day in amended clay loam soil and 0.282 log(10) reduction per day in sandy loam soil. Evaporation to less than 5% soil moisture completely inactivated all three viruses within 7 days at 15 degrees C, within 3 days at 27 degrees C, and within 2 days at 40 degrees C regardless of soil type. This suggests that a combination of high soil temperature and rapid loss of soil moisture will significantly reduce risks caused by viruses in sludge.

Effect of ionic composition of suspending solution on virus adsorption by a soil column

The effect of various electrolytes on the adsorption of poliovirus was measured in 250-cm-long soil columns with ceramic samplers at different depths. Viruses suspended in deionized water moved much farther through the soil than those suspended in tap water, whereas movement in sewage water was intermediate. The salt content of the tap water and sewage water promoted virus adsorption, but evidently the organic compounds in sewage retarded adsorption. When viruses were suspended in chloride solutions of K, Na, Ca, and Mg, virus adsorption increased as the cation concentration and valence increased. The depth of virus penetration was related to the ionic strength of the solutions. Virus penetration data for NO(3), SO(4), and H(2)PO(4) salts of K, Na, and Ca indicated that other anions were more effective than Cl in promoting virus adsorption. Also, NH(4) was more effective than other cations in limiting the penetration depth of viruses. It seems that ions composed of radicals are more effective than ions composed of single atoms in promoting virus adsorption. Al was the most effective ion in limiting virus penetration, probably owing to flocculation of the viruses. Adding AlCl(3) concentrations to secondary sewage effluent to provide an Al concentration of 0.1 mM reduced the virus penetration depth to 40 cm. These studies show that the ionic composition of the suspending solutions must be considered in predicting virus penetration depths, and it may be practical to add low concentrations of a flocculating agent such as AlCl(3) to sewage water to limit virus movement through very porous soils.

Influence of long-term land application of Class B biosolids on soil bacterial diversity

AIM

To evaluate the effect of long-term annual land applications of Class B biosolids on soil bacterial diversity at University of Arizona Marana Agricultural Field Center, Tucson, Arizona.

METHODS AND RESULTS

Following the final of 20 consecutive years of application of Class B biosolids in March 2005, followed by cotton growth from April to November 2005 surface soil samples (0-30 cm) were collected from control (unamended) and biosolid-amended plots. Total bacterial community DNA was extracted, amplified using 16S rRNA primers, cloned, and sequenced. All 16S rRNA sequences were identified by 16S rRNA sequence analysis and comparison to known sequences in GenBank (NCBI BlastN and Ribosomal Database Project II, RDP). Results showed that the number of known genera (identifiable > 96%) increased in the high rate biosolid plots compared to control plots. Biosolids-amended soils had a broad phylogenetic diversity comprising more than four major phyla: Proteobacteria (32%), Acidobacteria (21%), Actinobacteria (16%), Firmicutes (7%), and Bacteroidetes (6%) which were typical to bacterial diversity found in the unamended arid southwestern soils.

CONCLUSION

Bacterial diversity was either enhanced or was not negatively impacted following 20 years of land application of Class B biosolids.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study illustrates that long-term land application of biosolids to arid southwestern desert soils has no deleterious effect on soil microbial diversity.

Viruses in recreational water-borne disease outbreaks: a review

Viruses are believed to be a significant cause of recreationally associated water-borne disease. However, they have been difficult to document because of the wide variety of illnesses that they cause and the limitations in previous detection methods. Noroviruses are believed to be the single largest cause of outbreaks, which have been documented in the published literature 45% (n = 25), followed by adenovirus (24%), echovirus (18%), hepatitis A virus (7%) and coxsackieviruses (5%). Just under half of the outbreaks occurred in swimming pools (49%), while the second largest outbreak occurred in lakes or ponds (40%). The number of reported outbreaks associated with noroviruses has increased significantly in recent years probably because of better methods for virus detection. Inadequate disinfection was related to 69% (n = 18) of swimming pool outbreaks. A lack of required reporting and nonuniform water quality and chlorination/disinfection standards continues to contribute to water-borne recreational disease outbreaks.

Occurrence of antibiotic-resistant bacteria and endotoxin associated with the land application of biosolids

The purpose of this study was to determine the prevalence of antibiotic-resistant bacteria and endotoxin in soil after land application of biosolids. Soil was collected over a 15 month period following land application of biosolids, and antibiotic resistance was ascertained using clinically relevant antibiotic concentrations. Ampicillin, cephalothin, ciprofloxacin, and tetracycline resistance were all monitored separately for any changes throughout the 15 month period. Endotoxin soil concentrations were monitored using commercially available endotoxin analysis reagents. Overall, land application of biosolids did not increase the percentage of antibiotic-resistant culturable bacteria above background soil levels. Likewise, land application of biosolids did not significantly increase the concentration of endotoxin in soil. This study determined and established a baseline understanding of the overall effect that land application of biosolids had on the land-applied field with respect to antibiotic-resistant bacterial and endotoxin soil densities.

The measurement of aerosolized endotoxin from land application of Class B biosolids in Southeast Arizona

The purpose of this study was to determine aerosolized endotoxin concentrations downwind of a biosolids land application site. Aerosol samples were collected from biosolids land application sites, tractor operation, and an aeration basin located within an open-air wastewater treatment plant. Aerosolized endotoxin above background concentrations was detected from all sites, at levels ranging from below detection up to 1800 EU m–3 of air. Biosolids loading operations resulted in the greatest concentrations of endotoxin (mean 344 EU m–3). As downwind (perpendicular to wind vector) distance increased from sources (2–200 m), levels of endotoxin decreased to near background (without biosolids application) concentrations. Overall, the detected levels of aerosolized endotoxin were within past proposed aerosolized endotoxin limits (250–2000 EU m–3) by other occupational exposure studies. Occasionally, peak concentrations were found to be above these limits. Sites in which soil was being aerosolized resulted in greater concentrations of endotoxin with or without biosolids, which suggested that the majority of endotoxin may in fact be of soil origin. This study evaluated the presence of aerosolized endotoxin from the land application of biosolids and showed that these levels were within ranges for concern suggested by other studies and that this area of research needs further investigation. Key words: biosolids, endotoxin, aerosol, bioaerosol, lipopolysaccharide.

Transport of microsporidium Encephalitozoon intestinales spores in sandy porous media

The retention and transport of microsporidium Encephalitozoon intestinales spores in two water-saturated sandy porous media was investigated in this study. The initial breakthrough of the spores in the column effluent occurred essentially simultaneously with that of a non-reactive tracer, indicating no significant velocity enhancement. A large fraction (45-73%) of the spores injected into the columns was not recovered in the effluent, indicating removal from solution through colloid retention processes of attachment and/or straining. The relative significance of attachment and straining to total retention was evaluated in additional experiments. An experiment was conducted with a sieved coarse fraction of porous media for which straining is unlikely to be of significance based on the relative diameters of the spores and porous-medium pores. The spore recovery for this experiment was similar to the recoveries obtained for microsporidia transport in the un-sieved parent porous medium. An additional experiment was conducted with a subsample of the coarse fraction that was acid-washed to reduce potential surface attachment sites. Spore recovery was complete for this experiment. These results suggest surface deposition was the primary removal mechanism in our system. This conclusion is supported by the results of an experiment wherein deionized water was flushed through a column that was previously flushed with electrolyte solution. The effluent spore concentrations were observed to increase upon injection of deionized water, indicating re-mobilization of spores upon a change in water chemistry. The measured data were successfully simulated using a mathematical model incorporating colloid filtration. The results of this study suggest that the transport of microspordia in sandy porous media is governed by established colloid-transport processes.

A national study on the residential impact of biological aerosols from the land application of biosolids

AIMS

The purpose of this study was to evaluate the community risk of infection from bioaerosols to residents living near biosolids land application sites.

METHODS AND RESULTS

Approximately 350 aerosol samples from 10 sites located throughout the USA were collected via the use of six SKC Biosamplers. Downwind aerosol samples from biosolids loading, unloading, land application and background operations were collected from all sites. All samples were analysed for the presence of HPC bacteria, total coliform bacteria, Escherichia coli, Clostridium perfringens, coliphage, enteroviruses, hepatitis A virus and norovirus. Total coliforms, E. coli, C. perfringens and coliphage were not detected with great frequency from any sites, however, biosolids loading operations resulted in the largest concentrations of these aerosolized microbial indicators. Microbial risk analyses were conducted on loading and land application operations and their subsequent residential exposures determined.

CONCLUSIONS

The greatest annual risks of infection occurred during loading operations, and resulted in a 4 x 10(-4) chance of infection from inhalation of coxsackievirus A21. Land application of biosolids resulted in risks that were <2 x 10(-4) from inhalation of coxsackievirus A21. Overall bioaerosol exposure from biosolids operations poses little community risk based on this study.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study evaluated the overall incidence of aerosolized micro-organisms from the land application of biosolids and subsequently determined that microbial risks of infection were low for residents close to biosolids application sites.

Estimation of bioaerosol risk of infection to residents adjacent to a land applied biosolids site using an empirically derived transport model

AIM

The purpose of this study was to develop an empirically derived transport model, which could be used to predict downwind concentrations of viruses and bacteria during land application of liquid biosolids and subsequently assess microbial risk associated with this practice.

METHODS AND RESULTS

To develop the model, coliphage MS-2 and Escherichia coli were aerosolized after addition to water within a biosolids spray application truck, and bioaerosols were collected at discrete downwind distances ranging from 2 to 70 m. Although coliphage were routinely detected, E. coli did not frequently survive aerosolization. Data on aerosolized coliphage was then used to generate a virus transport model. Risks of infection were calculated for various ranges of human virus concentrations that could be found in biosolids.

CONCLUSIONS

A conservative estimate at 30.5 m (assumed to be nearest adjacent residences) downwind, resulted in risks of infection of 1 : 100,000, to the more realistic 1 : 10,000,000 per exposure. Conservative annual risks were calculated to be no more than 7 : 100,000 where as a more realistic risk was no greater than 7 : 10,000,000. Overall, the viral risk to residences adjacent to land application sites appears to be low, both for one time and annual probabilities of infection.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study demonstrated a simple approach towards modelling viral pathogens aerosolized from land applied liquid biosolids, and offers insight into the associated viral risk.

Tracking the concentration of heterotrophic plate count bacteria from the source to the consumer's tap

The goal of this project was to quantify the concentration of heterotrophic plate count (HPC) bacteria within water reaching consumer's taps, and from the sources used by a major utility serving the City of Tucson, AZ. With this information, the amounts and sources of HPC bacteria consumed at the tap could be determined. Samples of water were collected on a monthly basis from two well fields, the CAVSARP recovery well field and Southern Avra Valley well field which serves as one of the groundwater sources for Tucson, AZ, and the distribution system which serves the same homes from which tap water was also tested. The average concentration of HPC in source waters within Southern Avra Valley Wells was 56 CFU/ml (range 1-1995/ml). From the CAVSARP recovery well field, corresponding values were 38 CFU/ml (1 to 502 CFU/ml). Unblended groundwater in the chlorinated distribution system averaged 22 CFU/ml (range 1-794). Blended water at the chlorinated distribution site averaged 47 CFU/ml (range 10-158). There was a major shift in the percentage of gram negative to gram-positive bacteria from the wells to the distribution system, to the tap. In the surface CAP source water, 76% of the bacteria were gram-negative compared to 27% gram-negative in the CAVSARP recovery wells. In contrast, Avra Valley wells contained 17% gram-negative bacteria. In both the Tucson groundwater distribution sites and blended distribution sites, the corresponding number of gram negative bacteria was 12%. Finally at the tap, only 0.2% of the bacteria were gram-negative. The average number of bacteria in household taps averaged 3072 HPC/ml and was equal or greater than 500 ml 68% of the time. This study shows that the number of HPC bacteria increases dramatically from the distribution system to the consumers tap. Thus, the major source of bacteria ingested by the average consumer in Tucson originates from bacteria within the household distribution system or the household tap, rather than from source waters or the distribution system. It is also clear that consumers' regularly consume more than 500 HPC/ml from drinking water taken from the household tap.

Evaluation of electrochemically generated ozone for the disinfection of water and wastewater

Effective wastewater treatment is critical to public health and well-being. This is especially true in developing countries, where disinfection of wastewater is frequently inadequate. People who live in these areas may benefit from wastewater disinfection using ozone. This study evaluated the ability of a new electrochemical process of ozone generation, which produced ozone continuously at high pressure and concentration by the electrolysis of water, to disinfect tap water and secondarily treated wastewater. Inactivation of Klebsiella terrigena, Escherichia coli, MS2 bacteriophage and poliovirus 1 was evaluated first in reverse osmosis (RO) treated water. Inactivation of K. terrigena (6-log), E. coli (6-log), MS2 (6-log) and poliovirus 1 (>3-log) was observed after 1 min of ozonation in a 1 L batch reactor. Experiments were then performed to assess the microbiological impact of disinfection using ozone on secondarily treated municipal wastewater. The effect of ozonation on wastewater was determined for total and faecal coliforms, bacteriophages and heterotrophic plate count (HPC) bacteria. Electrochemical ozone generators provided an effective, rapid and low-cost method of wastewater disinfection. Based on the results of this research, electrochemically generated ozone would be well suited to remote, small-scale, disinfection operations and may provide a feasible means of wastewater disinfection in developing countries.

Bioaerosols from the land application of biosolids in the desert southwest USA

This study evaluated bioaerosol emissions during land application of Class B biosolids in and around Tucson, Arizona, to aid in developing models of the fate and transport of bioaerosols generated from the land application of biosolids. Samples were collected for 20 min at distances between 2 m and 20 m downwind of point sources, using an SKC BioSampler impinger. A total of six samples were collected per sampling event, which consisted of a biosolid spray applicator applying liquid biosolids to a cotton field. Each application represented one exposure. Samples were collected in deionised water amended with peptone and antifoam agent. Ambient weather conditions were also monitored every 10 min following initiation of sampling. Concurrently with downwind samples, background (ambient) air samples were collected to compensate for any ambient airborne microorganisms. In addition, biosolids samples were collected for analysis of target indicator and pathogenic organisms. Soil samples were also collected and analysed. Significant numbers of heterotrophic plate count (HPC) bacteria were found in air samples collected during the biosolid application process. These could have arisen from soil particles being aerosolised during the land application process. Aerosolised soil may contribute significantly to the amount of aerosolised microorganisms. Soil particles may be able to more readily aerosolise, due to their low density, small particle size and low mass. Aerosolised HPC bacteria found during biosolids land application were similar to those found during normal tractor operation on non-biosolids applied fields. Coliforms and coliphages were not routinely detected even though they were found to be present in the biosolids at relatively high concentrations, 10(6) and 10(4)/g (dry weight) of biosolids respectively. This could be due to the die-off rate of aerosolised Gram-negative bacteria or sorption to the solid portion of the biosolids. Low numbers of aerosolised coliphages may likewise be due to sorption phenomena. We theorise that only organisms in the aqueous phase of the biosolids were available to desorb and be aerosolised. Animal viruses, which were not detected in the biosolids, were likewise not detected in the aerosol samples. Clostridium perfringens was detected in only a small percent of aerosol samples although it was detected during all weather conditions; other microorganisms were detected during more favourable environmental conditions (relative humidity >10%). Despite the fact that many of these organisms were present in the biosolids at significant concentrations, their presence in bioaerosols generated during the land application of biosolids was limited to only a small percentage of samples. Bacteria as well as viruses may sorb to biosolids, which contain a high percentage of organic matter, and desorption during land application of biosolids may not readily take place; therefore, these microorganisms may not be readily aerosolised.

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.

Rapid reduction of Staphylococcus aureus populations on stainless steel surfaces by zeolite ceramic coatings containing silver and zinc ions

This study demonstrates the anti-Staphylococcus aureus properties of stainless steel surfaces coated with zeolite containing 2.5% silver and 14% zinc ions. Stainless steel panels with and without the heavy-metal-containing coatings were inoculated with S. aureus and incubated at room temperature. Survival of S. aureus was significantly reduced by the silver/zinc coatings within 1 h. Many hospital surfaces could be constructed of stainless steel with silver/zinc zeolite coatings. Such measures may reduce rates of hospital-acquired S. aureus infection.

Giardia and Cryptosporidium removal from waste-water by a duckweed (Lemna gibba L.) covered pond

AIMS

To determine the ability of duckweed ponds used to treat domestic waste-water to remove Giardia and Cryptosporidium.

METHODS AND RESULTS

The influent and effluent of a pond covered with duckweed with a 6 day retention time was tested for Giardia cysts, Cryptosporidium oocysts, faecal coliforms and coliphage. Giardia cysts and Cryptosporidium oocysts were reduced by 98 and 89%, respectively, total coliforms by 61%, faecal coliforms by 62% and coliphage by 40%. There was a significant correlation between the removal of Giardia cysts and Cryptospordium oocysts by the pond (P < 0.001). Influent turbidity and parasite removal were also significantly correlated (Cryptosporidium and turbidity, P=0.05; Giardia and turbidity, P=0.01).

CONCLUSIONS

The larger organisms (parasites) probably settled to the bottom of the pond, while removal of smaller bacteria and coliphages in the pond was not as effective.

SIGNIFICANCE AND IMPACT OF THE STUDY

Duckweed ponds may play an important role in wetland systems for reduction of Giardia and Cryptosporidium.

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.