Wastewater surveillance for SARS-CoV-2 provides an approach for assessing the infection burden across a sewer service area. For these data to be useful for public health, measurement variability and the relationship to case data need to be established. We determined SARS-CoV-2 RNA concentrations in the influent of 12 wastewater treatment plants from August 2020 to January 2021. Technical replicates for N1 gene concentrations showed a relative standard deviation of 24%, suggesting it is possible to track relatively small (∼30%) changes in SARS-CoV-2 concentrations over time. COVID-19 cases were correlated significantly (ρ ≥ 0.70) to wastewater SARS-CoV-2 RNA concentrations across large and small service areas, with weaker relationships (ρ ≥ 0.59) in two communities. SARS-CoV-2 concentrations normalized to per capita slightly improved correlations to COVID-19 incidence, but normalizing to a spiked recovery control (BCoV) or a fecal marker (PMMoV or HF183) reduced correlations for a number of plants. Daily sampling demonstrated that a minimum of two samples collected per week were needed to maintain accuracy in trend analysis. The differences in the strength of SARS-CoV-2 relationships to COVID-19 incidence and the effect of normalization on these data among communities demonstrate that rigorous validation should be performed at individual sites where wastewater surveillance programs are implemented.

Microbial source tracking (MST) methods measure fecal contamination levels and identify possible sources using quantitative PCR (qPCR) that targets host-associated fecal microorganisms. To date, most established MST assays for human sources, especially bacterial markers, have shown some nonhuman host cross-reactions. Recently developed assays, such as the crAssphage CPQ_056, Lachnospiraceae Lachno3, and Bacteroides BacV6-21, have more limited information on host sensitivity and host specificity for human or sewage sources, particularly in countries other than the United States. In this study, we rigorously evaluated six sewage-associated MST assays (i.e., Bacteroides HF183, human adenovirus [HAdV], human polyomavirus [HPyV], crAssphage CPQ_056, Lachno3, and BacV6-21) to show advantages and disadvantages of their applications for MST. A total of 29 human and 3 sewage samples and 360 nonhuman fecal samples across 14 hosts collected from a subtropical region of Australia were tested for marker host specificity, host sensitivity, and concentrations. All sewage samples were positive for all six marker genes tested in this study. Bacterial markers were more prevalent than viral markers in human feces. Testing against animal hosts showed human feces (or sewage)associated marker gene specificity was HAdV (1.00) Ͼ HPyV (0.99) Ͼ crAssphage CPQ_056 (0.98) Ͼ HF183 (0.96) Ͼ Lachno3 (0.95) Ͼ BacV6-21 (0.90), with marker concentrations in some animal fecal samples being 3 to 5 orders of magnitude lower than those in sewage. When considering host specificity, sensitivity, and concentrations in source samples, the HF183, Lachno3, and crAssphage CPQ_056 tests were the most suitable assays in this study for sewage contamination tracking in subtropical waters of Australia. IMPORTANCE Large financial investments are required to remediate fecal contamination sources in waterways, and accurate results from field studies are crucial to build confidence in MST approaches. Host specificity and sensitivity are two main performance characteristics for consideration when choosing MST assays. Ongoing efforts for marker assay validation will improve interpretation of results and could shed light on patterns of occurrence in nontarget hosts that might explain the underlying drivers of cross-reaction of certain markers. For field applications, caution should be taken to choose appropriate MST marker genes and assays based on available host specificity and sensitivity data and background knowledge of the contaminating sources in the study area. Since many waterborne pathogens are viruses, employing both viral and bacterial markers in investigations could provide insight into contamination dynamics and ecological behavior in the environment. Therefore, combined usage of marker assays is recommended for more accurate and informative sewage contamination detection and fecal source resolution. KEYWORDS microbial source trackingCitation Ahmed W, Gyawali P, Feng S, McLellan SL. 2019. Host specificity and sensitivity of established and novel sewageassoc...

The human microbiome contains many organisms that could potentially be used as indicators of human fecal pollution. Here we report the development of two novel human-associated genetic marker assays that target organisms within the family Next-generation sequencing of the V6 region of the 16S rRNA gene from sewage and animal stool samples identified 40 human-associated marker candidates with a robust signal in sewage and low or no occurrence in samples from nonhuman hosts. Two were chosen for quantitative PCR (qPCR) assay development using longer sequences (the V2 to V9 regions) generated from clone libraries. Validation of these assays with these markers, designated Lachno3 and Lachno12, was performed using fecal samples ( = 55) from cat, dog, pig, cow, deer, and gull sources, and the results were compared with those of established host-associated assays (the Lachno2 marker and two human markers, the HB and HF183/BacR287). Each of the established assays cross-reacted with samples from at least one other animal species, including animals common in urban areas. The Lachno3 and Lachno12 markers were primarily human associated; however, the Lachno12 marker demonstrated low levels of cross-reactivity with samples from select cows and nonspecific amplification with samples from pigs. This limitation may not be problematic when testing urban waters. These novel markers resolved ambiguous results from previous investigations of stormwater-impacted waters, demonstrating their utility. The complexity of the microbiome in humans and animals suggests that no single organism is strictly specific to humans, and the use of multiple complementary markers in combination will provide the highest resolution and specificity for assessing fecal pollution sources. Traditional fecal indicator bacteria do not distinguish animal from human fecal pollution, which is necessary to evaluate health risks and mitigate pollution sources. Assessing water in urban areas is challenging, since the water can be impacted by sewage, which has a high likelihood of carrying human pathogens, as well as pet and urban wildlife waste. We demonstrate that the Lachno3 and Lachno12 markers are human associated and highly specific for the detection of human fecal pollution from urban sources, offering reliable identification of fecal pollution sources in urban waters.

Wastewater surveillance for SARS-CoV-2 provides an approach for assessing the infection burden across a city. For these data to be useful for public health, measurement variability and the relationship to case data need to be established. We measured SARS-CoV-2 RNA concentrations in the influent of twelve wastewater treatment plants from August 2020 to January 2021. Replicate samples demonstrated that N1 gene target concentrations varied by 21% RSD between technical replicate filters and by 14% RSD between duplicate assays. COVID-19 cases were correlated significantly (rho≥0.70) to wastewater SARS-CoV-2 RNA concentrations for seven plants, including large and small cities. SARS-CoV-2 data normalized to flow improved correlations to reported COVID-19 cases for some plants but normalizing to a spiked recovery control (BCoV) or a fecal marker (PMMoV or HF183) generally reduced correlations. High frequency sampling demonstrated that a minimum of two samples collected per week was needed to maintain accuracy in trend analysis. We found a significantly different ratio of COVID-19 cases to SARS-CoV-2 loads in one of three large communities, suggesting a higher rate of undiagnosed cases. These data demonstrate that SARS-CoV-2 wastewater surveillance can provide a useful community-wide metric to assess the course of the COVID-19 pandemic.

The identification of sewage contamination in water has primarily relied on the detection of human-associatedBacteroidesusing markers within the V2 region of the 16S rRNA gene. Despite the establishment of multiple assays that target the HF183 cluster (i.e.,Bacteroides dorei) and otherBacteroidesorganisms (e.g.,Bacteroides thetaiotaomicron), the potential for more human-associated markers in this genus has not been explored in depth. We examined theBacteroidespopulation structure in sewage and animal hosts across the V4V5 and V6 hypervariable regions. Using near-full-length cloned sequences, we identified the sequences in the V4V5 and V6 hypervariable regions that are linked to the HF183 marker in the V2 region and found these sequences were present in multiple animals. In addition, the V4V5 and V6 regions contained human fecal marker sequences for organisms that were independent of the HF183 cluster. The most abundantBacteroidesin untreated sewage was not human associated but pipe derived. Two TaqMan quantitative PCR (qPCR) assays targeting the V4V5 and V6 regions of this organism were developed. Validation studies using fecal samples from seven animal hosts (n = 76) and uncontaminated water samples (n = 30) demonstrated the high specificity of the assays for sewage. FreshwaterBacteroideswere also identified in uncontaminated water samples, demonstrating that measures of totalBacteroidesdo not reflect fecal pollution. A comparison of two previously described humanBacteroidesassays (HB and HF183/BacR287) in municipal wastewater influent and sewage-contaminated urban water samples revealed identical results, illustrating the assays target the same organism. The detection of sewage-derivedBacteroidesprovided an independent measure of sewage-impacted waters.IMPORTANCEBacteroidesare major members of the gut microbiota, and host-specific organisms within this genus have been used extensively to gain information on pollution sources. This study provides a broad view of the population structure ofBacteroideswithin sewage to contextualize the well-studied HF183 marker for a human-associatedBacteroides. The study also delineates host-specific sequence patterns across multiple hypervariable regions of the 16S rRNA gene to improve our ability to use sequence data to assess water quality. Here, we demonstrate that regions downstream of the HF183 marker are nonspecific but other potential human-associated markers are present. Furthermore, we show the most abundantBacteroidesin sewage is free living, rather than host associated, and specifically found in sewage. Quantitative PCR assays that target organisms specific to sewer pipes offer measures that are independent of the human microbiome for identifying sewage pollution in water.