Will reopening reignite pandemic? Tests of poop at Miami-Dade sewage plants may be first clue
The biggest fear for Miami-Dade County and every other Florida community now easing into reopening parks, shops and restaurants is doing too much too soon and triggering a dreaded “second wave” of COVID-19 infections.
The first warning of that might not come from rising 911 calls or hospital visits but from a surprising place — human poop piped to county sewage plants.
Since late March, Miami-Dade’s Water and Sewer Department has been sampling the flow of untreated waste and sending it to a specialty lab in Boston as possible way to broadly estimate infection rates in the population. But, perhaps more important, the sampling could potentially detect early indicators of another infectious surge.
“The analysis is still a work in progress, but we hope that in the future the data will help us better assess the spread of the disease, identify hot spots and even predict future waves of infection,” said Douglas Yoder, deputy director of Miami-Dade’s Water and Sewer Department.
It’s long been known that human waste can carry a lot of nasty pathogens that survive passage through the bowels — from bacteria like cholera and fecal coliform to assorted viruses like hepatitis and, over the last few months, the novel coronavirus. Already in cities like Paris, researchers have been able to trace the outbreak through coronavirus concentrations in the sewage and believe upticks will appear in wastewater before cases show up at hospitals and clinics.
What is less clear is what level of risk that wastewater poses for people. Obviously, most people aren’t exposed to raw sewage — although pipe ruptures have been a major concern in South Florida for more than a decade, with Fort Lauderdale experiencing a string of them in the last year alone.
Be wary of public toilets
But in a blog post about exposure risks that went viral last week, topping 16 million views at last check, Erin Bromage, a University of Massachusetts Dartmouth associate professor of biology, put the toilet on the list of things to worry about — at least in public restrooms where most toilets have no lids. The concern is that an infected person could poop, then flush that toilet and potentially send up a invisible mist of coronavirus that could linger in the air or land on surrounding surfaces — not unlike the respiratory droplets from a cough or a sneeze that can cause infections.
In the May 6 post in a blog he started to advise friends and family, Bromage emphasized the uncertainty of whether and how long virus in poop remains viable — or in high enough concentrations to infect someone. Still, he cautioned, be wary of public facilities.
“We still do not know whether a person releases infectious material in feces or just fragmented virus, but we do know that toilet flushing does aerosolize many droplets. Treat public bathrooms with extra caution (surface and air), until we know more about the risk,” he wrote.
As COVID-19 continues to spread around the globe, wastewater epidemiologists are trying to figure out how the virus behaves in water, and how much viral load would be necessary for a person to be infected when exposed to a toilet plume or swimming in a canal contaminated by raw waste. Right now, there doesn’t appear to be a reason to worry about your household toilet.
“The short answer is we don’t have enough data yet to quantify and detail those risks,” said Bromage in an interview with the Miami Herald. “But if flushing and public toilets were a major factor in the transmission of the disease we would be seeing that more often in the data.”
The duration of exposure is one key factor in spreading the virus, he said.
In order to get sick, a person needs to be exposed to an infectious dose for a certain period of time, which can range from minutes to hours depending on the circumstances. Given the speed and range of the COVID-19 pandemic, the coronavirus is considered highly contagious. Infectious dose studies with this one and other coronaviruses showed that small viral loads are enough for infection to take hold.
Using influenza data as a guide, Bromage demonstrated that about 200 virus particles per minute are released in the environment when an infected person is speaking. Assuming the virus is inhaled, it would take about five minutes of speaking face-to-face to receive the required dose, he wrote in the blog.
Scientists already know quite a bit about how the coronavirus behaves in the air. And people are breathing all the time, shedding the virus.
Watered down virus
In the water, it’s a different story, said Bromage, who teaches courses on immunology and infectious diseases. The viral load would need to be larger than in the air; the raw sewage would have to come from a high-density area with a high prevalence of coronavirus infections.
There are also environmental factors affecting the virus while it’s in the water: temperature, sunlight, exposure to UV rays, and how other microorganisms might interact with it. And people are simply not in contact with contaminated water as much.
In the ocean, “dilution would be infinite,” said the scientist, who is also a surfer. He said he’s not concerned about getting in the water doing the pandemic.
“That’s futile anxiety. It’s a theoretical risk,” he said.
Still, environmental activists are concerned with the potential risk of COVID-19 transmission given the frequent sewage spills and overflows in South Florida, especially in Fort Lauderdale.
“We know there is a serious infrastructure problem in those counties and that sewer line breaks and overflows will continue to happen,” said Jerry Phillips, Florida director at the Public Employees for Environmental Responsibility (PEER).
Hurricanes and other major storms frequently result in wastewater treatment plants having to release sewage into rivers to prevent it from backing up in homes, while leaks can also result in raw sewage in streets or lawns, he added. While drinking water is highly unlikely to carry viruses, PEER wants utilities to routinely screen it for COVID-19 following overflow events.
The group is also concerned about the higher risk of exposure for workers in wastewater treatment plants.
In Miami-Dade, Yoder said that the utility’s concern about worker safety was the reason it initially reached out to the Boston testing firm Biobot for the COVID-19 analysis.
“We wanted to see evidence that our workers could be at potentially greater risk during the pandemic because they work around wastewater all the time,” he said.
Sewage plant protection
With enough personal protective equipment and current protocols that treat wastewater as hazardous materials, as well as social-distancing measures such as workers traveling in separate vehicles, the utility has only tallied a handful of COVID-19 cases among its staff of 2,600.
In Miami-Dade, Yoder said the weekly estimates provided by Biobot are still not reliable as a tracking mechanism of COVID-19 in the community; results have varied widely, with the numbers showing large spikes in April that were not backed up by data collected by the Florida Department of Health.
But Yoder said the system is being perfected, and will be useful in predicting hot spots or new rounds of outbreaks in the future. Research in a number of other states and countries also are developing techniques that might turn poop into an important measuring stick of public health.
“There are serious concerns about a potential second wave of this pandemic, so this analysis will be very useful as an early warning indication of where outbreaks might occur,” Yoder said.
This story was originally published May 20, 2020 at 2:20 PM.
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