Factors of Full-Scale Drinking Water Treatment that Contribute to Risk of Opportunistic Infectious Disease

Each year, 16,000 hospitalizations and 3,000 deaths caused by non-tuberculous mycobacteria occur in the USA. Non-tuberculous mycobacterial infections are primarily transmitted by water. This work helps to explain why mycobacteria are present in the finished water produced by drinking water treatment plants, and identifies treatment plant design and operational considerations to minimize the risk of waterborne mycobacterial infection. It was found that viable microbial cell concentrations decreased significantly in the first ozone contact chamber of multi-chamber ozone contactors in a full-scale drinking water treatment plant. However, cell concentrations rose in subsequent chambers across the contactors. This increase resulted from detachment from biofilms on contactor surfaces and from biomass in sediments within a hydraulic dead zone. The biofilms downstream of the dead zone contained a significantly higher relative abundance of mycobacteria than biofilms in earlier chambers. Viable mycobacteria populations were detected in ozone contactor effluents and in biologically-active carbon (BAC) filters downstream. These findings present an argument for improved hydraulic efficiency in multi-chamber contactors, e.g., through decreasing chamber width, and underscore the importance of filter maintenance practices that avoid reinforcing the presence of mycobacteria. During BAC filter backwashing with water containing monochloramine, monochloramine concentrations at the top of filter beds were measured to be similar to concentrations previously shown to be sub-lethal for the mycobacterial species Mycobacterium avium. M. avium dislodged during filter backwashing upregulated mammalian cell entry gene mce1C substantially. M. avium’s response to disinfectant exposure during backwashing raises the possibility of an adaptive response that increases its resistance to disinfection. Its upregulation of mammalian cell entry genes has implications for its role as an intracellular pathogen, and is consistent with laboratory scale findings that sub-lethal monochloramine exposure induces mycobacterial virulence factors. Where possible, utilities should limit the use of backwash water with disinfectant to reduce selecting for disinfectant-resistant bacteria. Mycobacteria can resist residual disinfectant in distribution systems and, therefore, distribution systems represent a transmission route of mycobacteria in treated waters to consumers. Despite higher concentrations of mycobacteria reported in water disinfected with chloramine compared to chlorine, the type of disinfectant used to provide a residual disinfectant during distribution of water was not a significant predictor of infection in a case control study of patients at the University of Michigan’s academic medical center Michigan Medicine. However, the use of drinking water primarily sourced from a surface water body compared to a groundwater source was found to be significantly associated with infection. This result suggests that monitoring mycobacteria in source waters used for drinking water production may be a proactive strategy that can be implemented by drinking water treatment plants. The results presented in this dissertation suggest that specific drinking water treatment plant design and operational considerations minimize risk of waterborne infectious disease. This work should assist water system managers to improve the microbial quality of drinking water to promote health for everyone, including individuals sensitive to opportunistic bacterial infections.PHDEnvironmental EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/138669/1/kotlarz_1.pd

Using detrending to assess SARS-CoV-2 wastewater loads as a leading indicator of fluctuations in COVID-19 cases at fine temporal scales: Correlations across twenty sewersheds in North Carolina

Wastewater surveillance emerged during the COVID-19 pandemic as a novel strategy for tracking the burden of illness in communities. Previous work has shown that trends in wastewater SARS-CoV-2 viral loads correlate well with reported COVID-19 case trends over longer time periods (i.e., months). We used detrending time series to reveal shorter sub-trend patterns (i.e., weeks) to identify leads or lags in the temporal alignment of the wastewater/case relationship. Daily incident COVID-19 cases and twice-weekly wastewater SARS-CoV-2 viral loads measured at 20 North Carolina sewersheds in 2021 were detrended using smoothing ranges of ∞, 16, 8, 4 and 2 weeks, to produce detrended cases and wastewater viral loads at progressively finer time scales. For each sewershed and smoothing range, we calculated the Spearman correlation between the cases and the wastewater viral loads with offsets of -7 to +7 days. We identified a conclusive lead/lag relationship at 15 of 20 sewersheds, with detrended wastewater loads temporally leading detrended COVID-19 cases at 11 of these sites. For the 11 leading sites, the correlation between wastewater loads and cases was greatest for wastewater loads sampled at a median lead time of 6 days before the cases were reported. Distinct lead/lag relationships were the most pronounced after detrending with smoothing ranges of 4–8 weeks, suggesting that SARS-CoV-2 wastewater viral loads can track fluctuations in COVID-19 case incidence rates at fine time scales and may serve as a leading indicator in many settings. These results could help public health officials identify, and deploy timely responses in, areas where cases are increasing faster than the overall pandemic trend

A High-Throughput Approach for Identification of Nontuberculous Mycobacteria in Drinking Water Reveals Relationship between Water Age and Mycobacterium avium

Nontuberculous mycobacteria (NTM) frequently detected in drinking water (DW) include species associated with human infections, as well as species rarely linked to disease. Methods for improved the recovery of NTM DNA and high-throughput identification of NTM are needed for risk assessment of NTM infection through DW exposure. In this study, different methods of recovering bacterial DNA from DW were compared, revealing that a phenol-chloroform DNA extraction method yielded two to four times as much total DNA and eight times as much NTM DNA as two commercial DNA extraction kits. This method, combined with high-throughput, single-molecule real-time sequencing of NTM rpoB genes, allowed the identification of NTM to the species, subspecies, and (in some cases) strain levels. This approach was applied to DW samples collected from 15 households serviced by a chloraminated distribution system, with homes located in areas representing short (24 h) distribution system residence times. Multivariate statistical analysis revealed that greater water age (i.e., combined distribution system residence time and home plumbing stagnation time) was associated with a greater relative abundance of Mycobacterium avium subsp. avium, one of the most prevalent NTM causing infections in humans. DW from homes closer to the treatment plant (with a shorter water age) contained more diverse NTM species, including Mycobacterium abscessus and Mycobacterium chelonae. Overall, our approach allows NTM identification to the species and subspecies levels and can be used in future studies to assess the risk of waterborne infection by providing insight into the similarity between environmental and infection-associated NTM

Biofilms in Full-Scale Drinking Water Ozone Contactors Contribute Viable Bacteria to Ozonated Water

Concentrations of viable microbial cells were monitored using culture-based and culture-independent methods across multichamber ozone contactors in a full-scale drinking water treatment plant. Membrane-intact and culturable cell concentrations in ozone contactor effluents ranged from 1200 to 3750 cells/mL and from 200 to 3850 colony forming units/mL, respectively. Viable cell concentrations decreased significantly in the first ozone contact chamber, but rose, even as ozone exposure increased, in subsequent chambers. Our results implicate microbial detachment from biofilms on contactor surfaces, and from biomass present within lime softening sediments in a hydraulic dead zone, as a possible reason for increasing cell concentrations in water samples from sequential ozone chambers. Biofilm community structures on baffle walls upstream and downstream from the dead zone were significantly different from each other (<i>p</i> = 0.017). The biofilms downstream of the dead zone contained a significantly (<i>p</i> = 0.036) higher relative abundance of bacteria of the genera <i>Mycobacterium</i> and <i>Legionella</i> than the upstream biofilms. These results have important implications as the effluent from ozone contactors is often treated further in biologically active filters and bacteria in ozonated water continuously seed filter microbial communities

Characteristics of NTM culture-positive samples.

<p>Characteristics of NTM culture-positive samples.</p

Improvement in NTM DNA extraction from spiked sputum samples with the modified as compared to the standard lysis protocol.

<p>Log₁₀ <i>atpE</i> gene copies/mL in DNA extracted from sputum spiked with either (A) MABSC or (B) MAC using the standard (blue circles) or the modified (red squares) lysis protocols. Error bars indicate mean and SD.</p

Impact of lysis method on community structure.

<p>Bray-Curtis-based nonmetric multidimensional scaling (NMDS) plot showing pairwise comparison of samples processed with the standard (blue symbols) or modified (red symbols) lysis protocols. Solid symbols represent paired samples with greater separation.</p

Culture-Independent Identification of Nontuberculous Mycobacteria in Cystic Fibrosis Respiratory Samples - Fig 2

<p>(A) Relative abundances of NTM OTUs and (B) total bacterial load in NTM culture-positive samples. (A) The mean relative abundance of NTM OTUs in the samples processed with the standard protocol was not significantly different from that observed when these samples were processed with the modified protocol (mean 0.098% and 1.21%, respectively; p = 0.08, paired t-test). (B) Total bacterial load in NTM culture-positive samples as measured by 16S rRNA gene qPCR did not significantly differ between lysis protocols. (p = 0.91, paired t-test). Error bars indicate mean and SD.</p

Differences in alpha diversity between lysis protocols.

<p>Samples processed with the modified protocol had higher levels of (A) richness (p = 0.04, paired t-test), and higher (C) Shannon diversity (p = 0.004, paired t-test) than samples processed with the standard protocol. (B) Evenness did not differ between the lysis protocols (p = 0.06, paired t-test). Blue and red symbols represent paired samples with greater separation on NMDS. Error bars indicate mean and SD.</p