By Elizabeth V. Robilotti, MD, MPH
Assistant Attending Physician, Division of Infectious Diseases, Hospital for Special Surgery, New York, NY
SYNOPSIS: Researchers evaluated the use of wastewater surveillance to monitor the mpox outbreak in California.
SOURCE: Wolfe MK, Yu AT, Duong D, et al. Use of wastewater for mpox outbreak surveillance in California. N Engl J Med 2023;388:570-572.
In a New England Journal of Medicine correspondence and extensive supplementary appendix, Wolfe et al described the use of wastewater testing for outbreak surveillance of mpox (monkeypox) in California as part of the public health response following identification of human-to-human transmission of mpox virus (MPXV) outside of previously reported regions.1 This study evolved from an existing collaboration among the California Department of Public Health, Emory University, Stanford University, and Verily Life Sciences beginning in 2020 to use routine wastewater monitoring to monitor the COVID-19 pandemic in California.2
In this study, 407 samples were collected from nine wastewater treatment facilities from June 19 to Aug. 1, 2022, across sewershed regions serving more than 4 million people in and around San Francisco, CA. Three hundred sixty-four samples were used to construct time series data graphically presented in the primary correspondence, which enumerated positive and negative sample results over the time period by locations. Additionally, the authors reported average MPXV deoxyribonucleic acid (DNA) concentrations over time per milligram of wastewater solids from the four facilities with positive samples on 10 or more days during the study period compared to reported mpox incident cases over the same time period. A statistically significant positive correlation between MPXV DNA concentration in wastewater and reported mpox cases was identified. This persisted regardless of surveillance definition used, such as case onset date vs. case report date. The authors concluded that wastewater surveillance expanded to monitor non-enteric and non-respiratory viral pathogens was feasible and essential for expanding public health surveillance.
COMMENTARY
Wastewater surveillance is a promising approach to enhance public health surveillance for emerging pathogens in high population concentration areas. In contrast to event-based surveillance methods, wastewater surveillance offers an unbiased assessment of community viral concentration independent of any trends in cases or symptoms that come to clinical attention. This can be particularly useful in communities with unequal access to healthcare, limited availability of diagnostic testing, or where health-seeking behavior may be hampered by stigma.
Unbiased testing has specific advantages for the identification of emerging pathogens. It can identify viruses for which there is limited clinician experience and a broad differential, as in the case of mpox. Wastewater samples from the majority of sewersheds included in this study identified MPXV DNA prior to the first case report date or upon first sampling (in communities with cases already documented prior to project initiation). Although not appreciated in the MPXV DNA study, wastewater surveillance also has the potential to identify asymptomatic viral shedding on a community level prior to a sentinel event that would be captured by event-based reporting. This has been demonstrated previously with detection of poliovirus circulation within communities prior to clinical case identification.3
The advantages are obvious, but wastewater surveillance is not without limitations. Regions that were able to rapidly scale-up environmental surveillance for recent threats, such as mpox, built on preexisting programs. In this study, MPXV DNA assessment leveraged existing infrastructure for COVID surveillance. The means of sample collection, transport, storage, and analysis were already established when mpox emerged. Access to technical expertise for specimen processing and data analysis may not be routinely available across all health departments, even if the wastewater specimens can be obtained.
Robust data connecting wastewater pathogen detection to public health action remains limited.4 The authors did not connect their temporal estimates of MPXV DNA in wastewater to specific public health actions in the corresponding communities. Wastewater surveillance for infectious diseases offers promise, but pathogen-specific data on wastewater concentration and correlates of community disease transmission are needed to create effective modeling that can inform public health policy.
REFERENCES
- Wolfe MK, Yu AT, Duong D, et al. Use of wastewater for mpox outbreak surveillance in California. N Engl J Med 2023;388:570-572.
- Wolfe MK, Topol A, Knudson A, et al. High-frequency, high-throughput quantification of SARS-CoV-2 RNA in wastewater settled solids at eight publicly owned treatment works in northern California shows strong association with COVID-19 incidence. mSystems 2021;6:e0082921.
- Shulman LM, Mendelson E, Anis E, et al. Laboratory challenges in response to silent introduction and sustained transmission of wild poliovirus type 1 in Israel during 2013. J Infect Dis 2014;210(Suppl 1):S304-S314.
- Kilaru P, Hill D, Anderson K, et al. Wastewater surveillance for infectious disease: A systematic review. Am J Epidemiol 2023;192:305-322.