Norovirus, a genera in the Caliciviridae family, is a nonenveloped virus with a positive-sense RNA genome. There are ten genogroups of Norovirus and 48 genotypes. The most common transmission route is person-to-person, followed by contaminated food or water and contact with contaminated fomites.
However, the lag between norovirus testing and reporting can be as long as a few weeks–unacceptably long for a highly transmissible virus. Furthermore, data aggregated across participating states has minimal value for informing communities, and much of norovirus transmission goes undetected by conventional surveillance systems due to asymptomatic cases and cases that do not require clinical care. Research on alternatives to traditional surveillance includes wastewater monitoring and digital epidemiology.
However, the lag between norovirus testing and reporting can be as long as a few weeks–unacceptably long for a highly transmissible virus. Furthermore, data aggregated across participating states has minimal value for informing communities, and much of norovirus transmission goes undetected by conventional surveillance systems due to asymptomatic cases and cases that do not require clinical care. Research on alternatives to traditional surveillance includes wastewater monitoring and digital epidemiology.
Wastewater monitoring for HuNoV has the potential to provide more local, early-warning information to inform public health decision-making—potentially before clinically detected outbreaks. Additionally, wastewater data can easily be made publicly available. Unlike other surveillance data, it is not as biased by human care-seeking behavior and clinical testing. However, rather than replace conventional epidemiological monitoring methods, wastewater data provides an alternative data source to triangulate with existing imperfect clinical data streams.
To assess the timeliness of norovirus wastewater testing compared with syndromic, outbreak, and search term trend data for Norovirus, a new study quantified human norovirus GII in composite influent samples from 5 wastewater treatment plants (WWTPs) using reverse transcription-digital droplet PCR and correlated wastewater levels to syndromic, outbreak, and search term trend data.
Five WWTPs in southeast Michigan provided samples based on agreements established in June 2021. WWTP personnel collected daily influent samples between 7/18/2021 and 7/14/2022, except in Tecumseh, where sample collection began on 1/12/2022.
Scientists noted, “Our results suggest that wastewater monitoring of HuNoV GII leads or concurs with other epidemiological monitoring methods, but correlations between wastewater and other data sources varied by the degree of overlap between the sewer shed and the population catchment of the other data source. For example, the cross-correlation values obtained when comparing state syndromic data to wastewater HuNoV GII values varied greatly between WWTPs.”
“Overall, our results suggest that smaller populations and closer overlap between the wastewater and syndromic or case populations results in closer temporal correlation. However, there is a limit to how small a sewershed population can be before other factors such as large signal variability and individual shedding variations become an issue, and this may vary by pathogen.”
“The best correlations between data sources were observed when the wastewater sewershed population had high overlap with those included by other monitoring methods. The increased specificity and earlier detection of HuNoV GII using wastewater compared to other data and the ability to make this data available to healthcare, public health, and the public in a timely manner suggests that wastewater measurements of HuNoV GII will enhance existing public health surveillance efforts of Norovirus.”
Journal Reference:
- Ammerman ML, Mullapudi S, Gilbert J, Figueroa K, de Paula Nogueira Cruz F, Bakker KM, et al. (2024) Norovirus GII wastewater monitoring for epidemiological surveillance. PLOS Water 3(1): e0000198. DOI: 10.1371/journal.pwat.0000198