Understanding trends in COVID-19 transmission rates is vital both public health monitoring and policymaking decisions. However, diagnostic capacity may be limited, and test sampling is often non-random, and often COVID-19 cases are not reported when patients have mild or asymptomatic disease. What is the solution? A paper in Nature Biotechnology argues that wastewater testing may be one solution.

Understanding the full extent of the COVID-19 pandemic is an ongoing challenge for public-health officials. Any epidemiological indicator has biases and limitations. Diagnostic testing capacity may be insufficient; hospitalizations lag infections by weeks and do not report on people with mild or asymptomatic disease. Experience with other viral diseases has shown that monitoring sewage for traces of a pathogen enables effective surveillance of entire communities, providing a sensitive signal of whether the pathogen is present in the population and whether transmission is increasing or declining. Researchers around the world are now pursuing the same approach for COVID-19 with the hope that wastewater data can supplement current measures of its prevalence. The novel coronavirus, SARS-CoV-2, has already been detected in wastewater.
In this issue, Peccia et al.3 demonstrate that concentrations of SARS-CoV-2 RNA in primary sewage sludge tracked COVID-19 cases and hospital admissions during the early weeks of the outbreak in the New Haven, Connecticut, area. Departing from traditional methods of examining wastewater, they report a high-resolution dataset generated from sewage sludge rather than influent and apply statistical analysis to infer the lead time their data may provide over epidemiological indicators. Their results strengthen the evidence that wastewater monitoring could be a powerful tool in tracking the spread of COVID-19.Wastewater surveillance of COVID-19 could have many benefits. It is a cost-effective way to survey transmission dynamics of entire communities. It avoids the biases of other epidemiological indicators4. It collects data from people who lack access to healthcare. And if it were successful in revealing infection dynamics earlier than diagnostic testing, it could provide public-health officials with near-real-time information on disease prevalence (Fig. 1).

Wastewater monitoring has the advantage of being cost-effective, of capturing COVID-19 rates among patients with limited access to health care or health insurance, and results can be viewed in near real time. When combined with appropriate testing methods, wastewater could be a scientific gold mine for information on COVID-19 disease prevalence.

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