Detection of monkeypox viral DNA in a routine wastewater monitoring program

Wastewater represents a composite biological sample from the entire contributing population. People infected with monkeypox excrete monkeypox virus DNA via skin lesions, saliva, feces and urine and these can enter the wastewater via toilets, sinks, and shower drains. To test whether monkeypox can be detected and monitored in wastewater during a period when publicly reported monkey cases in the region were increasing, we deployed digital PCR assays that target genomic DNA from the monkeypox virus in our routine, ongoing wastewater surveillance program in the Greater Bay Area of California, USA. We measured monkeypox virus DNA daily in settled solids samples from nine wastewater plants over the period of approximately 4 weeks. During that period, we detected monkeypox virus DNA in wastewater solids at nearly all the wastewater plants we routinely sample. Frequency of occurrence and concentrations were highest at plants serving San Francisco County. To confirm the presence of monkeypox DNA, we used two assays that target distinct sequences on the monkeypox genome on a subset of samples and results from both assays were in close agreement strongly suggesting true positives in the wastewater. Additionally, we show that concentrations of monkeypox DNA is 103 times higher in the solid fraction compared to the liquid fraction of wastewater on a mass-equivalent basis.