Can Wastewater Surveillance Predict Monkeypox Cases?

Wastewater surveillance in San Diego, California has accurately predicted COVID-19 case surges. Now, investigators want to expand this program to forecast monkeypox infections.

California’s first monkeypox infection was confirmed in late May 2022. Since then, cases have risen to at least 100 in San Diego County, and over 1300 in California overall. The state declared monkeypox a public health emergency on August 1, 2022, with the United States declaring a federal public health emergency on August 4.

The country remains in a state of emergency due to the COVID-19 pandemic, only the fifth such emergency declared in over 20 years.

Thus, San Diego investigators sought to expand their wastewater surveillance initiative to screen for the monkeypox virus as well as COVID-19. “It’s the same process as SARS-CoV-2 qPCR monitoring, except that we have been testing for a different virus,” said Rob Knight, PhD, professor and director of the Center for Microbiome Innovation at the University of California San Diego. “Monkeypox is a DNA virus, so it is a bit of a surprise that our process optimized for SARS-CoV-2, which is an RNA virus, works so well.”

In early June, Knight and his team began monitoring wastewater from the Point Loma treatment plant for monkeypox virus. The plant processes wastewater from an estimated 2.2 million San Diegans.

On July 10, the investigators had their first positive indicator of monkeypox at 10565.54 viral copies per liter of wastewater, levels near the detection limit. In the month since, levels have been trending upward significantly. On August 2, the current high of 189309.81 viral copies per liter of wastewater was recorded.

The research team will have to wait and see, Knight said, whether monitoring the monkeypox viral load levels in wastewater can accurately predict a case spike. “It depends on when the virus is shed from the body relative to how bad the symptoms are that cause people to seek care,” Knight explained. “This is, in principle, different for each virus, although in practice wastewater seems to be predictive for multiple viruses.”

Additionally, the wastewater surveillance program is not currently set up to sequence monkeypox genomes, meaning emerging variants may go undetected. However, Knight said, this is not necessarily an inhibitor: “DNA viruses evolve a lot slower than RNA viruses, so we would not expect variants to emerge and spread as quickly.”

Screening wastewater for viruses works because infected persons shed virus even before exhibiting symptoms. Thus, the first-ever wastewater screening program was launched in response to COVID-19 in late 2020. US San Diego and UC San Diego Health collaborated to collect wastewater samples for auto-sampling robotic analysis. The objective was to track and predict COVID-19 outbreaks to enable students to safely return to campus.