Risk-Based Critical Concentrations of Legionella pneumophila for Indoor Residential Water Uses.

Legionella spp. is a key contributor to the United States waterborne disease burden. Despite potentially widespread exposure, human disease is relatively uncommon, except under circumstances where pathogen concentrations are high, host immunity is low, or exposure to small-diameter aerosols occurs. Water quality guidance values for Legionella are available for building managers but are generally not based on technical criteria. To address this gap, a quantitative microbial risk assessment (QMRA) was conducted using target risk values in order to calculate corresponding critical concentrations on a per-fixture and aggregate (multiple fixture exposure) basis. Showers were the driving indoor exposure risk compared to sinks and toilets. Critical concentrations depended on the dose response model (infection vs clinical severity infection, CSI), risk target used (infection risk vs disability adjusted life years [DALY] on a per-exposure or annual basis), and fixture type (conventional vs water efficient or "green"). Median critical concentrations based on exposure to a combination of toilet, faucet, and shower aerosols ranged from ∼10-2 to ∼100 CFU per L and ∼101 to ∼103 CFU per L for infection and CSI dose response models, respectively. As infection model results for critical L. pneumophila concentrations were often below a feasible detection limit for culture-based assays, the use of CSI model results for nonhealthcare water systems with a 10-6 DALY pppy target (the more conservative target) would result in an estimate of 12.3 CFU per L (arithmetic mean of samples across multiple fixtures and/or over time). Single sample critical concentrations with a per-exposure-corrected DALY target at each conventional fixture would be 1.06 × 103 CFU per L (faucets), 8.84 × 103 CFU per L (toilets), and 14.4 CFU per L (showers). Using a 10-4 annual infection risk target would give a 1.20 × 103 CFU per L mean for multiple fixtures and single sample critical concentrations of 1.02 × 105, 8.59 × 105, and 1.40 × 103 CFU per L for faucets, toilets, and showers, respectively. Annual infection risk-based target estimates are in line with most current guidance documents of less than 1000 CFU per L, while DALY-based guidance suggests lower critical concentrations might be warranted in some cases. Furthermore, approximately <10 CFU per mL L. pneumophila may be appropriate for healthcare or susceptible population settings. This analysis underscores the importance of the choice of risk target as well as sampling program considerations when choosing the most appropriate critical concentration for use in public health guidance.

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.

Perceptions in the U.S. building industry of the benefits and costs of improving indoor air quality.

How building stakeholders (e.g. owners, tenants, operators, and designers) understand impacts of Indoor Air Quality (IAQ) and associated energy costs is unknown. We surveyed 112 stakeholders across the United States to ascertain their perceptions of their current IAQ and estimates of benefits and costs of, as well as willingness to pay for, IAQ improvements. Respondents' perceived IAQ scores correlated with the use of high-efficiency filters but not with any other IAQ-improving technologies. We elicited their estimates of the impacts of a ventilation-filtration upgrade (VFU), that is, doubling the ventilation rate from 20 to 40 cfm/person (9.5 to 19 l/s/person) and upgrading from a minimum efficiency reporting value 6 to 11 filter, and compared responses to estimates derived from IAQ literature and energy modeling. Minorities of respondents thought the VFU would positively impact productivity (45%), absenteeism (23%), or health (39%). Respondents' annual VFU cost estimates (mean = $257, s.d. = $496, median = $75 per person) were much higher than ours (always <$32 per person), and the only yearly cost a plurality of respondents said they would pay for the VFU was $15 per person. Respondents holding green building credentials were not more likely to affirm the IAQ benefits of the VFU and were less likely to be willing to pay for it.

Variance in Bacillus anthracis virulence assessed through Bayesian hierarchical dose-response modelling.

AIMS: To develop a predictive dose-response model for describing the survival of animals exposed to Bacillus anthracis to support risk management options. METHODS AND RESULTS: Dose-response curves were generated from a large dose-mortality data set (>11,000 data points) consisting of guinea pigs exposed via the inhalation route to 76 different product preparations of B. anthracis. Because of the predictive nature of the Bayesian hierarchical approach (BHA), this method was used. The utility of this method in planning for a variety of scenarios from best case to worst case was demonstrated. CONCLUSIONS: A wide range of expected virulence was observed across products. Median estimates of virulence match well with previously published statistical estimates, but upper bound values of virulence are much greater than previous statistical estimates. SIGNIFICANCE AND IMPACT OF THE STUDY: This study is the first meta-analysis in open literature to estimate the dose-response relationship for B. anthracis from a very large data set, generally a rare occurrence for highly infectious pathogens. The results are also the first to suggest the extent of variability, which is contributed by product preparation and/or dissemination methods, information needed for health-based risk management decisions in response to a deliberate release. A set of possible benchmark values produced through this analysis can be tied to the risk tolerance of the decision-maker or available intelligence. Further, the substantial size of the data set led to the ability to assess the appropriateness of the assumed distributional form of the prior, a common limitation in Bayesian analysis.

Addressing uncertainty and conflicting cost estimates in revising the arsenic MCL.

The current effort to revise the arsenic drinking water standard is one of the first times that the promulgation of a Maximum Contaminant Level (MCL) for drinking water has been influenced explicitly by benefit-cost considerations. Different stakeholders have developed different estimates of the costs, benefits, and appropriate decision-making criteria for a lower standard. In this study, alternative analyses prepared by the U.S. EPA and by independent researchers are compared. The large discrepancies in the aggregate national cost estimates are shown to result largely from differences in the engineering cost estimates for arsenic treatment processes. Further research is needed to resolve these discrepancies. Alternative regulatory approaches, such as providing point-of-use treatment or exempting water systems with high household compliance costs, yield only modest improvement in the overall cost-effectiveness of lower standards but are effective at addressing serious affordability problems for the small percentage of (primarily small) water systems where these problems are predicted to occur. The U.S. EPA may wish to provide more explicit guidance to state regulators and to water utilities as to the conditions under which these options will be acceptable.