Wastewater sequencing predicts COVID waves

Science published a study on May 21 showing that sequencing SARS-CoV-2 in wastewater can do more than measure how much virus is present. Researchers reported that the genetic diversity of virus fragments in sewage tracked community transmission better than standard concentration-based monitoring and, in New York data, anticipated reported COVID-19 cases and hospitalizations earlier. A companion commentary in Science said the work points to a broader role for sequence-based wastewater surveillance in public health, while also urging validation in other settings. ### What did the researchers actually measure in wastewater? Dustin T. Hill and colleagues wrote in Science that they analyzed whole-genome sequencing data from 12,290 wastewater samples collected across New York state. Instead of relying only on viral concentration — the amount of SARS-CoV-2 genetic material in a sample — they measured how genetically diverse the viral material was. The paper said wastewater contains a mix of variants circulating in a community at the time of sampling. The authors argued that this diversity signal can capture transmission more cleanly because it is less affected by some of the noise that complicates concentration-based measures, including differences in shedding and other sampling effects. ### Why does diversity matter more than just viral concentration? The Science paper said viral concentration has been the main wastewater metric used to estimate disease transmission. But the authors wrote that concentration can be distorted by differential shedding, sampling bias, persistence in sewage systems and evolutionary changes that affect how much virus infected people shed. Justin Lessler and Ariel Christensen, writing in a Science commentary accompanying the study, said standard wastewater methods also depend on normalization steps tied to fecal volume or wastewater flow rate. By contrast, they wrote, the diversity-based approach estimates prevalence from the heterogeneity of genomes recovered from a sample. ### How much earlier were the signals? The Science commentary said Hill and colleagues’ approach showed “excellent performance” in predicting COVID-19 cases and related hospitalizations 1 to 2 weeks before they had been reported. That is the clearest practical claim in the paper package: diversity-based wastewater sequencing did not just correlate with transmission, it provided earlier warning in retrospective analysis. The main paper said average weekly viral diversity had a significant correlation with average weekly new COVID-19 infections. It also said multiple diversity measures produced similar results, which the authors said supports the use of genetic diversity as a routine signal rather than a one-off metric. ### Where did the data come from? The study’s supplementary materials said New York state has tested wastewater for SARS-CoV-2 since May 2020 and implemented statewide whole-genome sequencing in 2022. The analysis included 194 wastewater treatment plant sites with at least one valid whole-genome sequence. That statewide network gave the researchers a large retrospective data set spanning multiple waves and variant shifts. The paper used those sequences to compare diversity-based estimates against more familiar indicators such as reported infections and hospitalizations. ### Are the authors saying public-health systems should change now? Justin Lessler and Ariel Christensen wrote in Science that the study shows how sequence-based approaches can improve wastewater surveillance and inform public health action. But they also said more research is needed to test whether the same relationship between diversity and prevalence holds across pathogens and across different surveillance settings. The next step, according to the paper package published on May 21, is broader validation beyond SARS-CoV-2 in New York. That work will determine whether diversity metrics move from a strong COVID-19 case study into a standard part of wastewater surveillance systems.