Wastewater can detect mpox, especially as cases increase
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Key takeaways:
- Wastewater surveillance can detect cases of mpox, especially as the number of infected grows.
- Wastewater data could improve the public health response to an outbreak.
Wastewater surveillance can detect a single mpox case in large samples representing thousands to millions of people, and its effectiveness increases as the number of cases grows, according to a study.
Carly Adams, PhD, MPH, an Epidemic Intelligence Service officer in the CDC’s National Center for Emerging and Zoonotic Infectious Diseases, and colleagues said mpox detection in wastewater, combined with clinical cases, can help guide the public health response — and the absence of mpox in wastewater can also confirm that there is not a large outbreak.
“An isolated Monkeypox virus detection likely warrants a limited public health response,” Adams and colleagues wrote. “Absence of Monkeypox virus detection in a monitored community can provide reassurance that large numbers of cases are not present.”
The CDC, which has also tracked SARS-CoV-2 in wastewater, started a routine program to track mpox in wastewater in October 2022, about 6 months after the global mpox outbreak started. New York state in 2022 also used wastewater to identify the spread of poliovirus after a reported case of vaccine-derived polio.
Elsewhere, studies in Calgary and Belgium have shown that wastewater can help identify and track the spread of more than a dozen pathogens, beyond just respiratory viruses like influenza and respiratory syncytial virus.
Adams and colleagues analyzed sample-level wastewater data from the CDC’s National Wastewater Surveillance System collected between August 2022 and May 2023, comparing it with case surveillance data collected through the National Notifiable Disease Surveillance System for the same time period.
The researchers analyzed 3,492 wastewater samples from 89 sites in 26 counties in 16 states. They detected mpox DNA in 95 samples (3%) from 17 counties (65%) and included 281 cases from 12 counties in their study.
The sensitivity of wastewater surveillance on any given day to detect a single case of mpox was 14% (95% CI, 10.7%-17.4%) when at least one person was shedding virus, 29% (95% CI, 21.9%-36.8%) when five or more people were shedding virus and 48% (95% CI, 35.2%-61.6%) when 15 or more people were shedding, according to the study.
Wastewater surveillance in a single week had a sensitivity of 32% (95% CI, 23.6%-40.7%) for detecting one or more people shedding the virus, 49% (95% CI, 33.7%-64.2%) sensitivity for detecting five or more people shedding the virus and 77% (95% CI, 50.1%-93.2%) for 15 or more people shedding the virus.
The weekly positive predictive value and negative predictive value for detecting people shedding mpox in a county were 62% and 80%, respectively.
Based on the number of mpox detections during the study period, the researchers said wastewater data, along with case data, can help determine and scale a proper public health response to a potential outbreak.
“Because wastewater surveillance is sufficiently sensitive to detect very few mpox cases, a single, isolated wastewater detection might not warrant a large public health response,” Adams and colleagues wrote. “[And] nondetection of Monkeypox virus in wastewater, in combination with no reported cases, can provide reassurance to public health officials that large numbers of cases are not present in communities.”
References:
- Adams C, et al. MMWR Morb Mortal Wkly Rep. 2024;doi:10.15585/mmwr.mm7302a3.
- CDC. National wastewater surveillance system: U.S. mpox wastewater data. https://www.cdc.gov/nwss/wastewater-surveillance/mpox-data.html. Updated Jan. 17, 2024. Accessed Jan. 18, 2024.
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