Species within the Mycobacterium avium complex (MAC), a subset of nontuberculous mycobacteria (NTM), are of major human health concern and contribute to a significant drinking water burden in the United States (US) and worldwide. The risk increases when MAC levels in environmental media are high, the hosts are susceptible, and exposures to aerosols containing MAC are frequent. MAC is typically not monitored in drinking water; currently, there are no numeric guidelines for NTM or MAC concentrations in distribution networks or building plumbing systems. To address this gap, the primary objective of this study was to identify risk-based critical MAC concentrations for identifying problematic conditions in building water. Critical concentrations were based on an annual risk benchmark of 1 in 10,000 commonly referenced in the US for drinking water-related infections using quantitative microbial risk assessment (QMRA). Critical concentrations of MAC were calculated for eight potential scenarios including inhalation and ingestion exposures for children, immune-compromised individuals, and the general population. Median critical concentrations corresponding to an annual infection risk of 10-4 are lower for the general population via the inhalation route (∼10-2 to 103 CFU/ L) compared to immunocompromised populations and children via the ingestion route (∼100 to ∼102 CFU/ L). Shower exposures were the main driver of the inhalation risk from building plumbing exposures. This study provides a risk framework for MAC exposure in the building plumbing environment for developing mitigation strategies.

Modeling Legionella exposure from building water systems is valuable to inform water management plans, but accurate risk estimates require accounting for spatiotemporal variations in concentrations. This comprehensive literature review covers existing mathematical approaches for predicting Legionella fate and transport in building water systems and proposes a framework for advanced modeling considering all mechanisms influencing its presence in water and biofilm during different life-stages (e.g., within protozoan hosts). Current models include persistence of culturable cells in a heater, growth and decay throughout simplified hot water systems, concentrations linked to water age using fitted growth rates, and a calibrated model for a highly-monitored system. The challenges of modeling influencing factors are also discussed, including water demand, hydraulics, nutrient availability, pipe materials, temperature, and chemical disinfection. By contrasting laboratory and field observations with existing models, this review highlights knowledge gaps and data needs for integrating Legionella growth and persistence into hydraulics, water quality and, ultimately, exposure models to define minimal-risk design and operational practices.

Understanding and predicting the role of waterborne environments in transmitting antimicrobial-resistant (AMR) infections are critical for public health. A population ecology-quantitative microbial risk assessment (QMRA) model is proposed to evaluate urinary tract infection (UTI) development due to recreational waterborne exposures to Escherichia coli (E. coli) and antibiotic-resistant extended-spectrum β-lactamase-producing (ESBL) E. coli. The horizontal gene transfer (HGT) mechanism of conjugation and other evolutionary factors were modeled separately in the environment and the gut. Persistence/dilution dominated HGT in the environment; however, HGT highly impacted predicted ESBL populations in the body. Predicted disability life year (DALY) risks from exposure to ESBL E. coli at concentrations consistent with US recreational water criteria were less than the 10-6 pppy benchmark value but greater than the susceptible E. coli DALY risks associated with a UTI health outcome. However, the prevailing susceptible dose-response relationship may underestimate ESBL risk if HGT rates in vivo approach those reported in vitro. A sensitivity analysis demonstrated that DALY values, E. coli/ESBL concentrations, and exposure parameters were influential on predicted risks. The model is a preliminary tool to begin the expansion of the QMRA paradigm to explore the impacts of evolutionary changes in AMR risk assessment.

Antibiotic-resistant bacteria (ARB) have become a major threat to public health and modern medicine. A simple death kinetics-based dose-response model (SD-DRM) was incorporated into a quantitative microbial risk assessment (QMRA) to assess the risks of exposure to reclaimed wastewater harboring antibiotic-resistant E. coli, Legionella pneumophila, and Mycobacterium avium for multiple exposure scenarios. The fractions of ARB and trace antibiotics present in the body were incorporated to demonstrate their impact on infection risks. Both ARB and antibiotic susceptible bacteria, ASB, are assumed to have the same dose-response in the absence of antibiotics but behave differently in the presence of residual antibiotics in the body. Annual risk of L. pneumophila infection exceeded the EPA 10-4 pppy (per person per year) benchmark at concentrations in reclaimed water greater than 103-104 CFU/L, depending on parameter variation. Enteropathogenic E. coli infection risks meet the EPA annual benchmark at concentrations around 105-106 total E. coli. The results illustrated that an increase in residual antibiotics from 0 to 40% of the minimum inhibitory concentration (MIC) reduced the risk by about 1 order of magnitude for E. coli but was more likely to result in an untreatable infection.

Agricultural irrigation using reclaimed urban wastewater (RWW) represents a sustainable practice to meet the ever-increasing water stress in modern societies. However, the occurrence of residual antibiotics and antibiotic resistant bacteria (ARB) in RWW is an important human health concern. This study applied for the first time a novel Simple-Death dose-response model to the field data of Escherichia coli and Pseudomonas spp. collected from three greenhouses for cultivation of tomatoes irrigated with RWW. The model estimates the risk of infection by enteropathogenic E. coli associated with consumption of tomatoes and the risk of eye-infection caused by Pseudomonas aeruginosa in cultivation soil through hand-to-eye contacts. The fraction of antibiotic resistant (AR)-E. coli measured in irrigation water and AR-Pseudomonas spp. in soil was incorporated in the model to estimate the survival of ARB and antibiotic susceptible bacteria in the presence of trace level of antibiotics in human body. The results showed that the risk of E. coli infection through consumption of tomatoes irrigated with RWW is within the WHO and USEPA recommended risk threshold (<10(-4)); Pseudomonas aeruginosa eye-infection risk is at or below the acceptable risk level. The presence of residual antibiotic in human body reduced the overall risk probabilities of infections but selectively enhanced the survival of ARB in comparison to their susceptible counterparts, which resulted in antibiotic untreatable infection. Therefore, the outcomes of this study call for a new risk threshold for antibiotic untreatable infections and highlight the key importance of adopting work safety measures for better human health protection.

SARS-CoV-2 wastewater surveillance (WWS) at wastewater treatment plants (WWTPs) can reveal sewered community COVID-19 prevalence. For unsewered areas using septic tank systems (STSs) or holding tanks, how to conduct WWS remains unexplored. Here, two large STSs serving Zuma Beach (Malibu, CA) were studied. Supernatant and sludge SARS-CoV-2 concentrations from the directly-sampled STSs parameterized a dynamic solid-liquid separation, mass balance-based model for estimating the infection rate of users. Pumped septage before hauling and upon WWTP disposal was also sampled and assessed. Most (96%) STS sludge samples contained SARS-CoV-2 N1 and N2 genes, with concentrations exceeding the supernatant and increasing with depth while correlating with total suspended solids (TSS). The trucked septage contained N1 and N2 genes which decayed (coefficients: 0.09-0.29 h-1) but remained detectable. Over approximately 5 months starting in December 2020, modeled COVID-19 prevalence estimations among users ranged from 8 to 18%, mirroring a larger metropolitan area for the first 2 months. The approaches herein can inform public health intervention and augment conventional WWS in that: (1) user infection rates for communal holding tanks are estimable and (2) pumped and hauled septage can be assayed to infer where disease is spreading in unsewered areas.

The effects of climate change, population growth, and future hydrologic uncertainties necessitate increased water conservation, new water resources, and a shift towards sustainable urban water supply portfolios. Diversifying water portfolios with non-traditional water sources can play a key role. Rooftop harvested rainwater (RHRW), atmospheric and condensate harvesting, stormwater, recycled wastewater and greywater, and desalinated seawater and brackish water are all currently utilized and rapidly emerging non-traditional water sources. This review explores the status and trends around these non-traditional water sources, and reviews approaches and models for prioritizing, predicting, and quantifying metrics of concern. The analysis presented here suggests that understanding the challenges of location specific scenarios, socioeconomic knowledge gaps, water supply technologies, and/or water management structure is the crucial first step in establishing a model or framework approach to provide a strategy for improvement going forward. The findings of this study also suggest that clear policy guidance and onsite maintenance is necessary for variable water quality concerns of non-traditional sources like harvested rainwater and greywater. In addition, use of stormwater or reuse of wastewater raises public health concerns due to unknown risks and pathogen levels, thus rapid monitoring technologies and transparent reporting systems can facilitate their adoption. Finally, cost structure of desalination varies significantly around the world, largely due to regulatory requirements and local policies. Further reduction of its capital cost and energy consumption is identified as a hurdle for implementation. Overall, models and process analyses highlight the strength of comparative assessments across scenarios and water supply options.

As climate change-induced variables exacerbate water scarcities, the use of seawater reverse osmosis (SWRO) membrane desalination technology for treating seawater could potentially provide a long-term drought-proof source of drinking water. This study carried out a technoeconomic assessment (TEA) for three SWRO desalination plants in the U.S. and one in Israel to set baselines for the cost and energy consumption for seawater desalination. In addition, a breakeven curve for implementing SWRO desalination was estimated in relation to the cost of water conservation measures to meet drought-induced reduction of the traditional water supply. The results show that the cost of SWRO water production scales with the plant capacity while energy intensity is not dramatically different across the plants. The higher cost in some U.S. plants is due to high capital investment, including land acquisition and permitting. Variations in plant capacity utilization have the greatest impact on the levelized cost of water (LCOW) over the plant service life, suggesting the importance of reducing fouling and maintenance-related downtime. Scenario analysis of fixed labor cost reduction through process automation indicates investments in automation and sensing technology could result in long-term savings. Breakeven analysis shows the decision to adopt SWRO is highly dependent on the local cost associated with water conservation to meet water supply reduction. Moreover, a small reduction in SWRO cost can influence a shift toward the adoption of SWRO over water conservation measures. Incorporation of future water demand, water conservation potential, and water stress data around the nation indicates SWRO desalination could be an important contributor to the future municipal drinking water portfolio in the U.S.

In September 2017, two category-5 hurricanes Irma and Maria swept through the Caribbean Sea in what is now known as the region’s most active hurricane season on record, leaving disastrous effects on infrastructure and people’s lives. In the U.S. Virgin Islands, rain cisterns are commonly used for harvesting roof-top rainwater for household water needs. High prevalence of Legionella spp. was found in the cistern water after the hurricanes. This study carried out a quantitative microbial risk assessment to estimate the health risks associated with Legionella through inhalation of aerosols from showering using water from cisterns after the hurricanes. Legionella concentrations were modeled based on the Legionella detected in post-hurricane water samples and reported total viable heterotrophic bacterial counts in cistern water. The inhalation dose was modeled using a Monte Carlo simulation of shower water aerosol concentrations according to shower water temperature, shower duration, inhalation rates, and shower flow rates. The risk of infection was calculated based on a previously established dose–response model from Legionella infection of guinea pigs. The results indicated median daily risk of 2.5 × 10−6 to 2.5 × 10−4 depending on shower temperature, and median annual risk of 9.1 × 10−4 to 1.4 × 10−2. Results were discussed and compared with household survey results for a better understanding of local perceived risk versus objective risk surrounding local water supplies.

The COVID-19 pandemic has had a profound impact on human society. The isolation of SARS-CoV-2 from patients' feces on human cell line raised concerns of possible transmission through human feces including exposure to aerosols generated by toilet flushing and through the indoor drainage system. Currently, routes of transmission, other than the close contact droplet transmission, are still not well understood. A quantitative microbial risk assessment was conducted to estimate the health risks associated with two aerosol exposure scenarios: 1) toilet flushing, and 2) faulty connection of a floor drain with the building's main sewer pipe. SARS-CoV-2 data were collected from the emerging literature. The infectivity of the virus in feces was estimated based on a range of assumption between viral genome equivalence and infectious unit. The human exposure dose was calculated using Monte Carlo simulation of viral concentrations in aerosols under each scenario and human breathing rates. The probability of COVID-19 illness was generated using the dose-response model for SARS-CoV-1, a close relative 01 SARS-CoV-2, that was responsible for the SARS outbreak in 2003. The results indicate the median risks of developing COVID-19 for a single day exposure is 1.11 x 10(-10) and 3.52 x 10(-11) for toilet flushing and faulty drain scenario, respectively. The worst case scenario predicted the high end of COVID-19 risk for the toilet flushing scenario was 5.78 x 10(-4) (at 95th percentile). The infectious viral loads in human feces are the most sensitive input parameter and contribute significantly to model uncertainty. (C) 2020 Published by Elsevier B.V.