Since the COVID-19 public health emergency expired in May, free testing clinics established across Indiana have closed as Hoosiers turned to at-home nose swabs.
That's made it difficult to get an accurate read on the number of new cases. So how has Indiana continued to track the virus?
The answer lies in the toilet.
People infected with SARS-CoV-2, which causes COVID-19, can shed the virus in their stool, whether or not they show symptoms or seek medical care. More than 20 wastewater treatment plants across the state are now testing sewage in their communities to determine the pathogen’s spread.
The program is part of a Centers for Disease Control and Prevention project launched in September 2020 called the National Wastewater Surveillance System. The agency coordinated with health departments in every state to build out the nation’s capacity to track the presence of the virus in sewage.
Indiana joined the same year, initially partnering with communities that had a college or university to run smaller testing programs. Early monitoring proved the results accurately predicted upcoming surges.
The Indiana Department of Health began coordinating the program in March 2022, growing it from just four participating utilities to 21, according to Lisa Welch, the departments media relations coordinator.
Those sites provide data representing 1.92 million Hoosiers — nearly 30% of the state’s population.
Today, the number of reported COVID cases and hospital visits sit far below the peak numbers in 2022, but the state’s sewage surveillance shows the virus is far from gone. Last month, the amount of the pathogen detected in wastewater was the highest it’s been since the start of the pandemic.
“This tells us that the virus is circulating in our communities and likely causing infections, though not all that have the virus will experience symptoms or need to seek medical treatment,” Welch said.
PREPERATION AND PITFALLS
A major benefit of wastewater surveillance is that it detects the virus in an entire population, regardless of whether people have access to healthcare or COVID testing or seek care when sick. That creates a more accurate picture of the virus’s presence in a community.
It also serves as an early indicator of increasing or decreasing COVID cases, which appear in sewage well before the numbers get reported from doctor’s offices or hospitals.
A case in point: reported infections hit an all-time high on Jan. 10, 2022, when nearly 19,000 Hoosiers tested positive. That surge showed up two weeks prior in the wastewater, which contained what was then a record-setting concentration of the virus.
Drew Roudenbush, the Clark County Health Department’s environmental health supervisor, said having that early warning allows county health officials to alert hospitals that they should brace for a spike in infections.
“It gives you an idea a little prior to what the trends are going to be and what we're going to see as far as people receiving care,” he said.
But wastewater numbers have become less reliable in predicting how many people will head to a hospital for treatment. Immunity from the virus, either from a prior infection or vaccination, has led to fewer COVID-related hospitalizations, according to a study published by researchers in August.
That means even although a record number last month shed the virus in stool, it’s become far less likely they will show symptoms or need medical care.
Even if wastewater testing shows an upcoming spike in COVID, there’s little medical staff can do these days to prepare for a potential increase in patients, argued Dan Nafziger, chief medical officer and infectious disease consultant for Goshen Hospital.
Rapid response teams no longer exist, and the ongoing shortage of healthcare workers makes it hard to keep with the patients they already have, he explained.
“We don't really have good levers to do anything about it as a hospital or as a health system,” Nafziger said. “There are a limited number of things that a local or state health department is going to be able to do even when the numbers are increasing.”
The lag between when wastewater testing is reported and when it’s published on the state’s COVID dashboard also hinders its usefulness, argued Patrick Milligan, a physician specializing in infectious disease with Community Physician Network. Numbers are only updated once a week.
The trends in the wastewater data do mirror the admission rates for COVID in Community Health Network hospitals, he said. However, it doesn’t allow for enough lead time to work as a predictive tool. Milligan said his team does not rely on the numbers to prepare for a surge.
Sewage testing is just “one tool in our belt,” explained Welch with the state department of health. Hospitals should use it in conjunction with other data to create a solid game plan. The state primarily uses it to share messaging with health officials to help them make that decision, she noted.
“Each local health department, hospital and community can see the data and use it in the best ways they see fit and what is needed for their situation,” Welsh said.
'PART OF THE SOLUTION'
Today, the National Wastewater Surveillance System encompasses over 1,000 testing sites which covers 35% of the entire U.S. population, according to the CDC. The number of sites depends on the state. New York, for instance, has over 100 locations, while Kentucky has just one.
In Indiana, state health officials plan to expand wastewater surveillance by enrolling more facilities, especially those in underrepresented areas or populations, Welsh explained. Testing will also expand to include pathogens like influenza and respiratory syncytial virus (RSV), which has also surged this winter.
The CDC is currently working to better understand how wastewater surveillance can also be used to detect and respond to infectious diseases threats like antibiotic resistance and foodborne diseases, according to the agency’s website.
In Bloomington and Monroe County, public health officials in late 2022 partnered with Indiana University to already start testing for influenza as well as monkeypox, which saw a major outbreak in the U.S. in August 2022.
Lori Kelley, health administrator for the Monroe County Health Department, said the additional viral tests will help determine new trends and how to respond to them. That could include sending a mobile testing site or increasing vaccine access in areas experiencing an uptick in cases.
“That’s the key here: to have this additional data, more quickly, to help us make better informed decisions,” she said in a release from IU.
Expanding and maintaining a wastewater testing infrastructure will be important in Indiana and the U.S. as more pandemic-causing viruses are likely spread in the future, argued Nafziger with Goshen Health.
“These are things that seem to be happening every decade or so, not every century or every 1,000 years,” he said.
The CDC is now also testing wastewater collected from airplanes at six U.S. airports to catch any new viruses or COVID variants that may arrive from other countries. The airplane wastewater program is currently expanding from a pilot phase to broader implementation, according to the agency.
Indiana’s testing program is funded for several years through CDC grants, Welch explained. She said the state department of health will continue to apply for additional funding as it becomes available.
Dr. Nafziger said he hopes the state implements the program for the long haul and continues to make it more robust. After all, it’s sure to be needed as the state, nation and world to face the never-ending specter of another viral outbreak.
“From my perspective, the state of Indiana is being part of the solution by strengthening its public health infrastructure,” he said. “Having a system that's actually in place and functional will be very helpful during the next pandemic.”