As wastewater testing continues to prove useful in estimating the spread of the coronavirus, scientists again are using sewage to track the latest public health emergency: monkeypox.
In late June — about a month after the first California case was confirmed — monkeypox DNA was detected in wastewater in San Francisco, according to the WastewaterSCAN coalition, a group of scientists who have been testing sewage for the presence of the coronavirus since 2020.
The group recently confirmed the presence of the monkeypox virus in Los Angeles County waste.
“It helps understand how widespread this is,” said Stanford civil and environmental engineering professor Alexandria Boehm, one of the lead researchers on the WastewaterSCAN team.
She said COVID-19 sewage testing has been particularly useful during “the onset phase,” or immediately after a new variant has been identified but it’s unclear the extent of its presence. Public health officials can use the information to theorize how great the spread could become.
“We’re sort of in that [phase] for monkeypox now,” Boehm said.
Monkeypox DNA was first detected in Los Angeles County wastewater July 31, about 20 days after the WastewaterSCAN group expanded its monkeypox testing beyond the Bay Area to almost 40 other facilities nationwide — including in L.A. — according to data from the group.
Samples from L.A.’s Joint Water Pollution Plant in Carson, which serves about 4 million residents and businesses, showed a small presence of the monkeypox virus July 31 and for three days during the first week in August, according to WastewaterSCAN data. The virus since has not been detected there, despite rising monkeypox cases in Los Angeles County.
By comparison, monkeypox DNA has been detected almost every day since June 27 at two wastewater facilities in San Francisco — and at much higher levels than in L.A. County.
Still, Boehm said that doesn’t mean there’s not more monkeypox in Los Angeles County; it’s just difficult to detect among the massive sample size.
Because the L.A. wastewater facility serves such a massive number of people “you have to think about the sensitivity of detecting monkeypox relative to the incident rate in the population,” Boehm said. “Just because you don’t detect monkeypox, doesn’t mean there’s nobody [in that waste watershed] with monkeypox.”
The two facilities in San Francisco serve a much smaller population, about 100,000 residents each.
While both Los Angeles and San Francisco have seen a rapid rise in monkeypox cases in recent weeks, the totals are still only a fraction of each county’s population: about 600 in San Francisco among fewer than 1 million residents and roughly 1,000 in L.A. County among 10 million residents, according to each county’s public health departments.
“We are doing [wastewater] surveillance for monkeypox, and it was only just identified,” the Los Angeles Department of Public Health said in a statement. “It took longer to identify here than in some places most likely because we have a large population relative to the number of cases. Wastewater surveillance is relatively new and somewhat investigational.”
It was not immediately clear whether the L.A. County health department plans to expand monkeypox testing in wastewater or how it would use the data. The county has been monitoring wastewater for the coronavirus for months, including at the Joint Water Pollution Plant, as well as at the Hyperion Water Reclamation Plant in Playa Del Rey and facilities near Lancaster and Malibu.
When at-home COVID-19 testing began to limit the ability to monitor case counts, L.A. County public health officials often used wastewater data to track transmission trends — one factor that played a role in a decision to not implement another indoor mask mandate.
“It’s helpful to have this additional lens into the epidemiology and dynamics of disease because it doesn’t rely on behaviors of people or testing,” Boehm said. “There’s kind of a health-equity component.”
She said wastewater data can help inform public health decisions, such as where to target information, clinics or treatment.
The scientists behind WastewaterSCAN call the data on viruses “invaluable,” having already found monkeypox in 22 California wastewater facilities, from San Diego to Sacramento, as well as at nine facilities in seven other states.
There’s not yet a national database to track monkeypox in waste, such as the CDC does for COVID-19, but Boehm said she’d like to see the testing expand. Her team also is working to test sewage for influenza A and respiratory syncytial virus (RSV), which she hopes can continue to help answer questions about viral transmission.
She said she’d like the wastewater testing, which has been found to be extremely accurate, to be used to inform care, treatment and even vaccine development of current viral outbreaks — as well as future ones.
“I’m a scientist, so I’m just curious how far we can take this,” Boehm said. “Its’ turning out to be a really interesting and sort of amazing resource for understanding public health.”
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