Miami-Dade County is tracking its sewage as a way to monitor how many people have had coronavirus, the South Florida Sun Sentinel reports.
With testing efforts often limited to people with symptoms, it has been challenging to find out how many people have or had the virus.
Because all infected people, symptomatic or not, flush the toilet, officials are hoping measuring virus levels in wastewater can show how big an outbreak is or when a new wave of cases may be coming.
"When you look at this data, you're looking at what's happening in the total population at once, rather than random people being tested," Dr. Aileen Marty, a professor of infectious diseases at Florida International University, told the newspaper. "It really represents the overall status of the population."
To monitor the wastewater, the county sends raw sewage samples to Massachusetts-based Biobot Analytics once a week.
The company calculates the number of coronavirus infections based on concentrations of the virus in the wastewater and sends the county a report. The virus monitoring program has been operating since March 25.
The highest readings were measured on April 9 and showed that up to 2% of the county's almost 2.3 million wastewater customers, or about 46,000 people, may have had the disease.
Deputy director of the Miami-Dade Water and Sewer Department Doug Yoder told the newspaper that the percentage found in the wastewater "is substantially more than cases being reported in terms of individual testing."
The 2% estimate is almost four times higher than the nearly 12,000 documented infections in the county, but below those predicted by Miami-Dade's second round of antibody testing, records show. That study, which took random blood samples from county residents, estimated that between 4.4% and 7.9% of the county's nearly 3 million people had contracted the disease.
The wastewater tracking method is still new and scientists are still learning how to determine the number of people who have actually been infected.
"There are a lot of uncertainties [about] what the shedding rate of infected patients is," Yoder said.
Dr. Mary Estes, professor of molecular virology and microbiology at Baylor College of Medicine, said monitoring wastewater is a good approach that she thinks will catch on in other cities.
"When the virus is beginning to disappear, you will no longer be able to detect it," she said.
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