Sewer Sleuths: Using Wastewater to Monitor Mpox

Wastewater surveillance provides a heads-up that a virus is circulating in the community and whether the number of infections is likely going up or down.

The first sign of a new disease reaching the United States might not be someone showing up at a doctor’s office. It might appear in a sample of sewage.

CDC’s National Wastewater Surveillance System (NWSS) started testing for COVID-19 in 2020. When mpox began to spread globally in 2022, CDC expanded wastewater surveillance to look for mpox. And now, with an outbreak of a different, more severe type of mpox causing a large outbreak in the Democratic Republic of the Congo (DRC), CDC has begun using the same tools to keep a watch for that type of mpox in the United States as well.

“Wastewater monitoring has proven to be a reliable and effective tool for detecting mpox in communities,” says CDC microbiologist Amy Kirby, the chief science officer for NWSS. “It has the potential to detect one mpox case in a community, making it a powerful tool for early detection of an outbreak.”

CDC monitors sewer systems to look for pieces of the virus that causes mpox. If someone is infected with the virus, their body sheds those pieces in urine, feces, or lesions on skin. Those virus bits flow into the sewers when the person flushes or showers.

Before the wastewater from that sewer gets treated, workers take samples to send to a laboratory. The laboratory runs tests that look for signs of the virus. If they appear, that means someone in the area served by that treatment plant has mpox.

Wastewater surveillance can’t identify specific people; instead, it gives public health officials a heads-up that the virus is circulating in the community and whether the number of infections is likely going up or down. CDC began testing wastewater for mpox in October 2022 and has expanded testing to include hundreds of monitoring sites across the United States.

The virus that causes mpox has two types, known as clades. CDC’s wastewater testing can detect either type – the one now circulating in DRC and the one that caused the global 2022 outbreak — “as quickly as a few days after waste enters the sewer,” Kirby says.

This innovative use of wastewater surveillance also includes testing for mpox at select airports across the United States through CDC’s Traveler-based Genomic Surveillance program. But at this time, there have been no reported cases of the type of mpox circulating in the DRC in the United States or anywhere outside countries in central Africa where it exists naturally.

Any outbreak signals on wastewater testing could result in enhanced surveillance for cases at the local level as well as further genetic testing to determine which type it contains.

“Unlike other types of public health reporting, wastewater monitoring doesn’t depend on people having symptoms, having access to health care, visiting a doctor when they get sick, or getting tested for an infection,” Kirby says. “This early warning helps public health experts and medical providers take action quickly to help protect the people in their communities.”

Wastewater monitoring is just one of the tools CDC is using to protect the public from further outbreaks of mpox. To learn how to protect yourself and others, visit cdc.gov/mpox.