Norovirus Outbreaks are Detectable by Wastewater Monitoring Earlier Than by Other Surveillance Methods

Fig 1. HuNoV GII wastewater levels at 5 wastewater treatment plants in 2021–2022. A. Comparison of PMMoV-normalized HuNoV GII levels from 5 WWTPs in Michigan from 2021–2022. HuNoV was quantified in influent samples using ddPCR at least weekly and PMMoV normalized values were plotted over one year. The only exception is TM, where sample collection began later, in January 2022. Lines connect all values measured for each WWTP. B. Seasonal HuNoV GII values in log10 (median, IQR) for each individual WWTP are presented using box-and-whisker plots for all 4 seasons. Note, no fall values for TM were obtained. The definition of the seasons is meteorological, beginning on the 1st day of the months of the equinoxes or solstices.

While the Centers for Disease Control and Prevention (CDC) coordinates several outbreak and clinical surveillance systems for norovirus, norovirus is strongly under-reported due to individuals not seeking care or not being tested. As a result, norovirus surveillance using case reports and syndromic detection often lags rather than leads outbreaks. Digital epidemiology sources such as search-term data may be more immediate, but can be affected by behavior and media patterns.

Wastewater monitoring can potentially provide a comprehensive and consistent data stream that can help to triangulate across these different data sets. To assess the timeliness of norovirus wastewater testing compared with syndromic, outbreak and search term trend data for norovirus, Ammerman, et al. (2024) quantified human norovirus GII in composite influent samples from five wastewater treatment plants (WWTPs) using reverse transcription-digital droplet PCR and correlated wastewater levels to syndromic, outbreak, and search term trend data. Wastewater human norovirus (HuNoV) GII RNA levels were comparable across all WWTPs after fecal content normalization using Pepper mild mottle virus (PMMoV). HuNoV GII wastewater values typically led syndromic, outbreak, and search term trend data.

The best correlations between data sources were observed when the wastewater sewershed population had high overlap with the population 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.

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.

Source: PLOS Water