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 solution: wastewater analysis. SARS-CoV-2, the virus that causes COVID-19, can be shed in the feces of an infected person. 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 spread changes over time.
The extent of COVID-19 testing has varied during the pandemic. Because wastewater can be sampled at regular intervals, it can provide a reliable adjunct to data from clinical trials.
This method has previously been used to track other pathogens, such as the virus that causes polio, as well as the use of illicit drugs. Data from wastewater analysis often tracks closely with data compiled from laboratory results.
Wastewater testing can also give early signs of a COVID-19 uptake. Patients may shed the virus in their stool before symptoms develop and even before they can think of getting tested, so the first sewer may show evidence of an outbreak.
Marianna Matus, chief executive and co-founder of Biobot Analytics, says wastewater analysis is most effective within small populations before the disease becomes 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 different COVID-19 variants.
Genomic sequencing of wastewater showed that the delta variant is increasing rapidly in the US during the summer. This increase was preceded by an increase in the actual concentration of SARS-CoV-2 in the wastewater. Dr. Matus said there is a gap of a few weeks between the rise of the delta and the rise in disease transmission.
The Centers for Disease Control and Prevention said on Monday that Omicron is now the dominant form in the US, overtaking Delta. In the week ending December 18, Omicron’s prevalence in the US reached 73%, up from the revised 13% figure from a week earlier. In the New York/New Jersey area, this figure is above 90%.
Sewage testing is often effective in the early stages of an outbreak. “Generally speaking, wastewater is a leading indicator when disease spread is very low,” Dr. Matas said.
Last spring, weeks before the first clinical cases were confirmed in the city, the Delta variant was detected at Houston’s wastewater treatment plants.
Most recently, the city had its first laboratory-confirmed case of the Omicron variant on 9 December. But the type was detected in Houston wastewater collected about 10 days ago.
Similarly, scientists at the Sewer Coronavirus Alert Network (SCAN) traced omicrons in Merced, Calif., wastewater collected on November 25, the state’s first positive clinical case identification prior to December 1. SCAN processes samples daily from 12 wastewater treatment plants in Northern. California.
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