With at-home Covid-19 tests in high demand and their efficacy in question, health departments from California to Massachusetts are turning to sewage samples to get a better idea of how much the coronavirus is spreading through communities and what might be in store for health care systems.
Experts say wastewater holds the key to better understanding the public health of cities and neighborhoods, especially in underserved areas that do not have equal access to care.
“Every time an infected person uses the toilet, they’re flushing this information down the toilet, where it’s collecting and aggregating and mixing with poop from thousands of other people,” said Newsha Ghaeli, a co-founder and the president of Biobot Analytics, a wastewater epidemiology company based in Massachusetts.
“Even if you can’t access a test, you’re still pooping,” Ghaeli said. “It doesn’t depend on you having access to health care or health insurance.”
Monitoring sewage can also measure other public health concerns, such as obesity, opioids and even polio, said Sheree Pagsuyoin, an associate professor of civil and environmental engineering at the University of Massachusetts Lowell. The pandemic has ushered in a new era of wastewater analysis, once a maligned discipline, to inform public health policy.
“It’s sort of like mapping a trend,” Pagsuyoin said, adding that there has been a “paradigm shift” as more cities turn to sewage analysis to better understand local challenges.
Recent wastewater analysis from a variety of sources across the country indicates an unprecedented surge in infections at a time when millions of people are forced to reconsider travel and holiday plans.
According to Biobot Analytic's wastewater dashboard, coronavirus levels detected in sewage samples across the country are higher now than at any previous point in the pandemic.
Recent wastewater samples in Houston, for example, show that there has been a sharp increase in the amount of the coronavirus detected in the city’s sewage. As of Dec. 20, Houston’s viral load, or the amount of virus found in samples, was at 546 percent compared to July 6, 2020, and the positivity rate was at 14 percent, according to the city Health Department’s wastewater dashboard. The viral load is up from 142 percent last week and 76 percent the previous week.
More than 700 city employees have contracted the virus, Mayor Sylvester Turner said on Twitter. As a result, Turner announced the opening of two additional megasites that will offer free testing for residents.
Dr. Amesh Adalja, a senior scholar at the Johns Hopkins Center for Health Security, said: “Wastewater is going to be a leading indicator for what’s going on in a given community.
“It will also give an indication of what’s to come, because not every Covid case comes to clinical attention — many cases are mild or asymptotic,” he added. “But the fact is that people who are infected are going to shed the virus in their stool.”
Sewage monitoring also shows case numbers surging in parts of California, Colorado, Idaho, Massachusetts, Missouri and North Carolina, as well as Canada, Spain and the United Kingdom.
A team of researchers at the University of Missouri has been working with the state Department of Health and Senior Services and the Department of Natural Resources to track the virus through wastewater.
Researchers in Missouri separate the virus from larger particles of waste and extract its genetic material. They can also amplify the genetic material and study it in greater detail through a process known as quantitative reverse transcription polymerase chain reaction. In addition to detecting the presence of the virus that causes Covid-19 in human waste, researchers are also able to identify specific variants.
New data show that the highly contagious omicron variant is spreading quickly throughout the state.
Expanded testing conducted Dec. 20 found mutations associated with the omicron variant in 32 of 57 wastewater samples collected statewide, Jeff Wenzel, who oversees the wastewater surveillance program for the state health department, told The Associated Press. Testing conducted the week before found the mutation in 15 of 63 test locations.
Pagsuyoin is part of a team in Massachusetts developing a wireless sensor that could detect SARS-CoV-2, the virus that causes Covid-19, in the air and in wastewater days before an outbreak occurs. Researchers will undertake a three-year study using data from three monitoring sites, two of them in Massachusetts and the other in the Philippines.
“People are becoming a little bit more open about using wastewater data to know where a disease is supposedly coming out,” she said. “We can use this technology to more efficiently monitor population health.”
Sewage analysis is most effective as an early warning signal between surges — particularly because people are not testing as often when rates are down — and in tracking cases when waves begin to dissipate. It can also help fill in some gaps during waves when testing is insufficient and serve as a way to compare waves, said Dr. Albert Ko, a professor of public health, epidemiology and medicine at Yale University’s School of Public Health.
“What it is useful for is looking at trends over time and comparing, let’s say, ‘Are we as bad in transmission this wave as compared to the last one?’” Ko said, although he added that variants and seasonality can “hamper interpretation” of such comparisons.
Ko said wastewater surveillance is best used as part of a broader analysis of an outbreak that takes other data points into consideration, like testing.