Potential Public Health Impacts of Deteriorating Distribution System Infrastructure

Assessment of mould remediation in a healthcare setting following extensive flooding

BACKGROUND

A new hospital building was close to completion when a large pipe carrying clean water broke, causing extensive flooding.

AIM

To determine the flood-associated fungal risk to susceptible patients who would use that building.

METHODS

Though standard flood remediation by the builders was relatively straightforward, there was no model for specialist assessment of patient risk due to the flood-associated mould growth. As levels of background airborne fungal spores can be expected to vary significantly over time, we could not use absolute levels to indicate either an excess of airborne fungal spores or successful remediation. Therefore it was decided to use weekly settle plates, exposed at the same time in flooded (test) and equivalent non-flooded (control) areas to compensate for variations in background levels. Flood-related risk was estimated by the ratio between fungal colonies on the test and control sets of settle plates, rather than absolute number.

FINDINGS

Whereas the physical flood remediation, including the use of 'anti-fungal' treatments, was completed in three weeks post flooding, fungal contamination in flooded areas took 38 weeks to return to control levels and remained so for a further six weeks of observation.

CONCLUSION

By the use of this method, we were able to assure the absence of flood-associated fungal risk to susceptible patients who would use that building. We recommend that infection prevention and control teams consider using this approach should they be faced with similar situations.

Establishment and inactivation of mono-species biofilm in a semipilot-scale water distribution system using nanocomposite of silver nanoparticles/montmorillonite loaded cationic chitosan

This study presents a novel approach in the synthesis and characterization of nanocomposites comprising cationic chitosan (CCS) blended with varying concentrations of silver nanoparticles/montmorillonite (AgNPs/MMT). AgNPs/MMT was synthesized using soluble starch as a reducing and stabilizing agent. Subsequently, nanocomposites, namely CCS/AgMMT-0, CCS/AgMMT-0.5, CCS/AgMMT-1.5, and CCS/AgMMT-2.5, were developed by blending 2.5 g of CCS with 0, 0.5, 1.5, and 2.5 g of AgNPs/MMT, respectively, and the corresponding nanocomposites were prepared using ball milling technique. Transmission electron microscopy (TEM) analysis revealed the formation of nanocomposites that exhibiting nearly spherical morphologies. Dynamic light scattering (DLS) measurements displayed average particle sizes of 1183 nm, 131 nm, 140 nm, and 188 nm for CCS/AgMMT-0, CCS/AgMMT-0.5, CCS/AgMMT-1.5, and CCS/AgMMT-2.5, respectively. The narrow polydispersity index (~0.5) indicated uniform particle size distributions across the nanocomposites, affirming monodispersity. Moreover, the zeta potential values exceeding 30 mV across all nanocomposites that confirmed their stability against agglomeration. Notably, CCS/AgMMT-2.5 nanocomposite exhibited potent antibacterial and antibiofilm properties against diverse pipeline materials. Findings showed that after 15 days of incubation, the highest populations of biofilm cells, Pseudomonas aeruginosa biofilm, developed over UPVC, MDPE, DCI, and SS, with corresponding HPCs of 4.79, 6.38, 8.81, and 7.24 CFU/cm2. The highest cell densities of Enterococcus faecalis biofilm in the identical situation were 4.19, 5.89, 8.12, and 6.9 CFU/cm2. The nanocomposite CCS/AgMMT-2.5 exhibited the largest measured zone of inhibition (ZOI) against both P. aeruginosa and E. faecalis, with measured ZOI values of 19 ± 0.65 and 17 ± 0.21 mm, respectively. Remarkably, the research indicates that the youngest biofilm exhibited the most notable rate of inactivation when exposed to a dose of 150 mg/L, in comparison to the mature biofilm. These such informative findings could offer valuable insights into the development of effective antibiofilm agents and materials applicable in diverse sectors such as water treatment facilities, medical devices, and industrial pipelines.

Cross-connections in drinking water distribution networks: Quantitative microbial risk assessment in combination with fault tree analysis and hydraulic modelling

Deficiencies in drinking water distribution networks, such as cross-connections, may lead to contamination of the drinking water and pose a serious health risk to consumers. Cross-connections and backflows are considered among the most severe public health risks in distribution networks. The aim of this paper was to provide a framework for estimating the risk of infection from cross-connection and backflow events. Campylobacter, norovirus, and Cryptosporidium were chosen as reference pathogens for this study. The theoretical framework was constructed based on the fault tree analysis methodology. National aggregated cross-connection incident data was used to calculate the probability of a contamination event occurring in Swedish networks. Three risk cases were evaluated: endemic, elevated, and extreme. Quantitative microbial risk assessment (QMRA) was used to assess daily risk of infection for average national estimates. The framework was also evaluated using local data from the Gothenburg network. The daily risk of infection from cross-connection and backflow events in Swedish networks was generally above an acceptable target level of 10^-6 for all reference pathogens and modelled cases; the exception was for the Gothenburg system where the risk was lower than 10^-7. An outbreak case study was used to validate the framework results. For the outbreak case study, contaminant transport in the network was simulated using hydraulic modelling (EPANET), and risk estimates were calculated using QMRA. The outbreak simulation predicted between 97 and 148 symptomatic infections, while the epidemiological survey conducted during the outbreak reported 179 cases of illness. The fault tree analysis framework was successfully validated using an outbreak case study, though it was shown on the example of Gothenburg that local data is still needed for well-performing systems. The framework can help inform microbial risk assessments for drinking water suppliers, especially ones with limited resources and expertise in this area.

The Impact of Pipe Material on the Diversity of Microbial Communities in Drinking Water Distribution Systems

As many cities around the world face the prospect of replacing aging drinking water distribution systems (DWDS), water utilities must make careful decisions on new pipe material (e.g., cement-lined or PVC) for these systems. These decisions are informed by cost, physical integrity, and impact on microbiological and physicochemical water quality. Indeed, pipe material can impact the development of biofilm in DWDS that can harbor pathogens and impact drinking water quality. Annular reactors (ARs) with cast iron and cement coupons fed with chloraminated water from a municipal DWDS were used to investigate the impact of pipe material on biofilm development and composition over 16 months. The ARs were plumbed as closely as possible to the water main in the basement of an academic building to simulate distribution system conditions. Biofilm communities on coupons were characterized using 16S rRNA sequencing. In the cast iron reactors, β-proteobacteria, Actinobacteria, and α-proteobacteria were similarly relatively abundant (24.1, 22.5, and 22.4%, respectively) while in the cement reactors, α-proteobacteria and Actinobacteria were more relatively abundant (36.3 and 35.2%, respectively) compared to β-proteobacteria (12.8%). Mean alpha diversity (estimated with Shannon H and Faith's Phylogenetic Difference indices) was greater in cast iron reactors (Shannon: 5.00 ± 0.41; Faith's PD: 15.40 ± 2.88) than in cement reactors (Shannon: 4.16 ± 0.78; Faith's PD: 13.00 ± 2.01). PCoA of Bray-Curtis dissimilarities indicated that communities in cast iron ARs, cement ARs, bulk distribution system water, and distribution system pipe biofilm were distinct. The mean relative abundance of Mycobacterium spp. was greater in the cement reactors (34.8 ± 18.6%) than in the cast iron reactors (21.7 ± 11.9%). In contrast, the mean relative abundance of Legionella spp. trended higher in biofilm from cast iron reactors (0.5 ± 0.7%) than biofilm in cement reactors (0.01 ± 0.01%). These results suggest that pipe material is associated with differences in the diversity, bacterial composition, and opportunistic pathogen prevalence in biofilm of DWDS.

Identifying challenges in drinking water supplies: assessment of boil water advisories in Norway (2008-2019)

The issuing of boil water advisories (BWAs) is a widely used response to microbiological contamination events in drinking water supply systems, and may therefore serve as an indicator for the access to safe drinking water. To supplement data source on the overall status of water supply systems (WSSs) in Norway, we analysed public media reports published in Norway to assess trends, causes, geographical and seasonal distribution of BWAs issued during the period 2008-2019. We identified 1,108 BWA events increasingly reported over the study period but characterised by a decreasing trend in time with respect to duration. The two main frequent causes for BWA were detection of faecal indicator bacteria (42.6%) and risk of contaminants intrusion in the distribution system (21%). We observed higher reporting rates in summer and autumn compared with winter, and higher reporting rates in Northern and Eastern Norwegian regions compared with the Central region. The results of this study could serve as supplementary information to better understand the overall status among WSSs in Norway, particularly in case of recurrent BWA's events, as well as suggest the relevance of BWAs' monitoring in identifying risk factors and planning targeted interventions.

Occurrence and diversity of waterborne fungi and associated mycotoxins in treated drinking water distribution system in South Africa: implications on water quality and public health

Despite increased public health concerns on the occurrences of potentially pathogenic/mycotoxigenic fungi in public drinking water system, dissemination of hygienically relevant fungi and their associated mycotoxins via distribution system under the dual burden of ageing infrastructure and ancillary distribution network lacking infrastructure for high-pressure water delivery systems is unknown. In this study, the diversity of fungi and occurrence of mycotoxins at 30 different points along treated piped water supply and ancillary distribution networks in Johannesburg, South Africa, were monitored for 12 months. Mycological analysis using cultural and molecular methods yielded 282 fungi belonging to phylum Ascomycota, having Aspergillus (91%), Penicillium (65%) and Trichoderma (31%) as dominant genera, with Aspergillus fumigatus, Penicillium citrinum, Purpureocillium lilacinum and Aspergillus flavus as the most prevalent species. Communal standpipe and reservoir outlets had significantly higher prevalence than other water samples. There was no strong correlation between total coliforms (r = 0.4266) and residual chlorine (r = - 0.1937), and fungal prevalence at p < 0.05. LC-MS/MS analysis detected aflatoxins B1, M1, G1 and G2 in 50, 9, 9 and 46% of water samples analysed, respectively, ranging between 0 and 3.18 ng/l. Deoxynivalenol (DON), 3-acetyl DON and 15-acetyl DON levels were between 8.4-96.1, 18.7-145.7 and 15.2-71.6 ng/l, respectively. However, the estimated average daily dose (ADD) for detected mycotoxins was below the tolerable daily intake (TDI), suggesting no toxicological risk. Presence of potentially mycotoxigenic fungi, despite the low toxicological risk, demonstrates a need for appropriate monitoring for fungi and mycotoxins in treated drinking water distribution systems for improved water quality and long-term public health assurance.