‘It’s truly an early warning system.’ Sewage shows COVID cases rising in Miami-Dade
Every day, more than 143 million gallons of sewage flow into Miami-Dade’s Central District Wastewater Treatment Plant on Virginia Key — the accumulation of countless toilet flushes in homes and businesses throughout Miami, Doral, Coral Gables and Miami Beach.
But it takes only a cup of all that wastewater, gathered in tiny amounts over a 24-hour period, for public health officials to get a good idea of whether COVID-19 is spreading among the nearly 830,000 residents served by the treatment plant.
Over the past six weeks, the volume of COVID-19 particles in wastewater samples taken at the Central District treatment plant has more than doubled — from about 43,000 copies per liter on March 3 to 107,745 copies per liter on March 17, according to Miami-Dade’s pandemic dashboard.
Similar increases were recorded in March at the county’s wastewater treatment plants in the north and south of the county, which serve an estimated 1.7 million additional residents.
During April, COVID-19 concentrations in the county’s wastewater have kept rising, said Roy Coley, director of the Water and Sewer Department.
“Now they’re at about 200,000 copies per liter,” he said, “which is about 20% of what it was in January but triple of what it was six weeks ago.”
County officials closely monitor other pandemic data, Coley said, including the ratio of COVID-19 tests that come back positive and the number of cases per 100,000 residents — both of which have increased in recent weeks.
But unlike the omicron wave and the delta surge before it, the rising indicators have not yet led to a significant increase in hospitalizations.
“Our numbers are going up, but hospitalizations have not,” Coley said. “Everyone is still figuring out what it means.”
An early warning system
Peter Paige, a physician and chief medical officer for Jackson Health, said wastewater surveillance data “help give us an idea of where we’re going to end up.”
Paige said people with COVID-19 can shed particles of the virus in their feces days before they develop symptoms, providing county officials with an early warning of what’s ahead.
“If you can see it four or five days before symptoms develop or a positive test, that can give you a little more time to be proactive if you’re concerned about mitigation strategies around public health to try and decrease the risk of transmission,” he said.
There’s no surprise now that cases are rising, Paige said. But there are still questions about how many people will end up in a hospital due to the disease, and whether that will stress capacity and staffing as hospitals experienced during the omicron and delta waves.
At Jackson Health System, Miami-Dade’s public hospital network, the number of inpatients with COVID-19 declined during the last six weeks. The hospital system reported 79 inpatients with the disease on March 1 and about 32 inpatients in mid-April. On Thursday, Jackson Health reported 35 inpatients with COVID-19.
But among all Miami-Dade hospitals, patient admissions have begun to tick up, with 121 county residents admitted to a local hospital with a confirmed case during the week ended April 13 — a 30% increase over the previous week, according to the Community Profile Report provided by the White House COVID-19 Team.
The number of confirmed COVID-19 cases reported in Miami-Dade also have shot up to 4,452 during the week ended April 14, about a 48% increase over the prior week.
Despite the increases in cases and hospitalizations, the Centers for Disease Control and Prevention reports that Miami-Dade has a low COVID risk level.
The immunity effect
Paige said he suspects that vaccinations, boosters and prior infections — particularly with the omicron variant — have created a baseline immunity among Miami-Dade residents and may lead to fewer people being hospitalized during the current surge.
About 83% of Miami-Dade’s eligible population age 5 and older has been fully vaccinated, meaning they have received two doses of the Pfizer or Moderna vaccines or one dose of the Johnson & Johnson vaccine, according to the Florida health department. About 33% of Miami-Dade residents have received a booster.
The health department has also reported about 1.2 million cumulative cases among Miami-Dade residents during the pandemic, though it’s not clear how many were infected with the omicron variant.
But because the current increase in cases is being driven by the omicron subvariant called BA.2, which is more contagious than omicron, Paige said immunity derived from previous infections will also play a key role in how many people end up in the hospital due to COVID-19.
“How much that is going to impact the potential increase in hospitalizations remains to be known,” he said. “We anticipate cases to increase in the hospital at some point as the numbers continue to increase. ... The other factor you always have to factor into this is hospitalizations that test positive for COVID aren’t necessarily hospitalizations because of COVID.”
Of the 35 inpatients with COVID-19 at a Jackson Health System hospital on April 21, at least 20 were diagnosed with the disease after admission for another medical reason. Though these patients are not severely ill with COVID, they must be isolated and staff must don protective gear when treating them.
“It’s still a burden on hospitals but different,” Paige said. “Hospitals still have to manage them but we’re not seeing the same severity of disease.”
During the omicron surge in December and January, many hospital workers also became infected and were forced to miss work due to required isolation periods — stretching staff thin.
‘A leading indicator’
Wastewater disease surveillance has been used for decades to track infectious agents, from polio to norovirus. But the method has taken on greater importance as the pandemic’s impact continues to shift, with omicron and its subvariant, BA.2, producing what appears to be less severe disease.
With the rise of at-home tests whose results do not get reported to the health department and the closure of mass testing sites, case counts will be less reliable. But wastewater surveillance can help fill that gap, Coley said.
“Wastewater is a leading indicator,” he said. “It’s turned into an invaluable piece of information.”
Each week, scientists and technicians at the wastewater treatment plants in north, south and central Miami-Dade collect samples of the murky water, package it and then ship it to a lab in Boston, where more scientists test the liquid for particles of COVID-19 shed in the feces of infected people.
Miami-Dade pays about $780 per test, which comes to about $10,000 a month for the three wastewater treatment plants. Test results take about three days to receive after a sample is shipped to the lab.
Miami-Dade began surveying wastewater for COVID-19 in March 2020, said Coley, the county’s Water and Sewer Department director.
“We were first in the nation,” he said.
In September 2020, the CDC launched the National Wastewater Surveillance System to help state and local governments anticipate surges and prepare a response.
But with 400 sites in 34 states, focused mainly in areas of high population, and only a dozen states routinely reporting results, the national system has gaps in monitoring.
Wider coverage would produce a more detailed snapshot of the pandemic’s peaks and valleys and potentially help governments monitor future disease outbreaks.
Mary Jo Trepka, an epidemiologist and professor at Florida International University’s Stempel College of Public Health and Social Work, said she’s been monitoring the county’s wastewater reports to anticipate when cases will rise. She said about a week after she noticed that COVID-19 particles were rising in the county’s wastewater, cases also started to rise.
‘Unlike forecasting the weather’
“That’s really nice. It’s truly an early warning system,” she said. “So with this current surge we saw evidence beginning with the sample that was made on March 17 ... and then we started to see cases increasing during the week of March 25 a week later. Now with this most recent report, we’re starting to see an increase in the hospitalizations, the week of April 7 to April 13.”
Wastewater surveillance indicated a surge about two to three weeks before the county reported an increase in the hospitalizations, Trepka said.
“For hospitals that’s important to know. ... We can always hope it doesn’t spill over to the hospitals, although it’s starting to look like it is, although slowly,” she said. “We’re not seeing a rapid increase like we did with omicron.”
But Trepka warned that long-term forecasting of COVID-19 will be much more difficult to accomplish.
Though the CDC recently launched a new Center for Forecasting and Outbreak Analytics that is supposed to function as a National Weather Service for infectious diseases, Trepka said the nature of the coronavirus itself will make it difficult to accurately predict when and where COVID-19 will surge in the future or what the impact will be on local hospitals and other healthcare providers.
“Unlike forecasting the weather, we have a lot of historical information with the weather and I don’t feel like we have good historical information with the virus because it keeps changing on us. It’s becoming a new animal on a regular basis,” she said.
With the BA.2 subvariant of omicron, cases have risen and hospitalizations are starting to rise, too, but at a much slower rate, Trepka said.
“Right now we’re seeing 636 cases a day in our county,” she said, “And to contrast that, let’s go back to what happened with omicron here. ... On Dec. 3, we were at 380 cases a day. Within three weeks, we were at 7,491 cases a day. Then we had 16,000 cases a day within about a month.”
New cases during the omicron wave rose higher and faster than previous surges, Trepka noted, but the disease itself was not as devastating in terms of severity and mortality when compared to the delta wave.
Predicting the future of COVID
So far, BA.2 does not seem to be acting the same way as omicron, but that doesn’t make it easy to predict, Trepka said.
“How the virus in our community is going to look six months from now I really don’t know,” she said. “It depends on how it’s mutating around the world and what ends up coming back here. That’s sort of the conundrum. It’s an uncertainty we have to live with.”
Learning to live with uncertainty does not mean that people cannot take steps to protect themselves, such as getting vaccinated and boosted, especially those individuals who are at higher risk of severe illness due to an immuno-compromised condition, Trepka said.
Paige, Jackson Health’s chief medical officer, said he expects that Miami-Dade like the rest of the nation will learn to live with the changing risks of COVID-19 by adapting behaviors.
“There’s still unpredictability about how much protection people are going to have. This virus is still dangerous,” Paige said. “As I look at it, this is going to be around, and at some point we have to treat it like it’s going to be around and we know about it, take all our steps and be protective as possible.
“But at some point, we have to get back to a normal state, so to speak. ... We’re in the third year of this pandemic. I understand some of the relaxation of restrictions. But we have to be smart. If we consider ourselves at higher risk, we have to be more cautious.”
This story was originally published April 22, 2022 at 12:46 PM.
