science

To track Covid-19 surges, scientists are studying sewage

To track Covid-19 surges, scientists are studying sewage

Public-health experts traditionally track the spread of an infectious disease through clinical data such as test results, hospitalizations and deaths. As Covid-19 continues to spread, scientists are turning to an alternative measure: wastewater analysis. SARS-CoV-2, the virus that causes Covid-19, can be shed in an infected person’s feces. By sampling sewage at waste-treatment plants, scientists can get a picture of how widespread Covid-19 has become in a community, and how its prevalence changes over time. The extent of Covid-19 testing has varied throughout the pandemic. Because wastewater can be sampled at regular intervals, it may provide a reliable adjunct to data from clinical tests. The method has previously been used to track other pathogens, such as the virus that causes polio, as well as use of illegal drugs. Data from wastewater analysis often tracks closely with data compiled from lab results. Wastewater testing can also offer early signs of a Covid-19 uptick. Patients can shed the virus in their feces before they develop symptoms and think to get tested, so evidence of an outbreak may first show up in the sewers. Mariana Matus, chief executive and co-founder of Biobot Analytics, says wastewater analysis is most effective at early detection within smaller populations before disease is widespread. “Its most important application as a leading indicator is in small communities, she said, such as dormitories, nursing homes and prisons. By genetically analyzing sewage samples, scientists are also able to track the rise and fall of individual Covid-19 variants. Genomic sequencing of wastewater showed the Delta variant rapidly gaining ground in the U.S. during the summer. This rise preceded an increase in the actual concentration of SARS-CoV-2 in wastewater. Dr. Matus said that suggests there is an offset of a few weeks between the rise of Delta and the rise in disease transmission. The Centers for Disease Control and Prevention said Monday that Omicron is now the dominant variant in the U.S., surpassing Delta. In the week ended Dec. 18, Omicron’s prevalence reached 73% in the U.S., up from a revised figure of 13% a week earlier. In the New York/New Jersey region, the figure topped 90%. Sewage testing is often effective in the early stages of an outbreak. “Generally, wastewater is a leading indicator when the disease prevalence is very low, said Dr. Matus. Last spring, the Delta variant was detected at Houston’s wastewater treatment plants weeks before the first clinical cases were confirmed in the city. More recently, the city had its first lab-confirmed case of the Omicron variant Dec. 9. But the variant was detected in Houston wastewater collected about 10 days earlier. Similarly, scientists from the Sewer Coronavirus Alert Network (SCAN) detected Omicron in Merced, Calif., wastewater collected Nov. 25, before the state’s first positive clinical case was identified Dec. 1. SCAN processes samples daily from 12 wastewater treatment plants in Northern California. Download.

science 2021-12-21 Livemint