Wastewater surveillance for poliovirus identified ongoing transmission of poliovirus in Rockland County and adjacent New York counties during an outbreak of poliovirus in the United States (10). It also retrospectively demonstrated the presence of poliovirus in the community for several months before the paralytic polio case was identified. Genetic characterization of the detected polioviruses confirmed that almost all wastewater detections were related to the virus isolated from the paralytic polio case. However, wastewater surveillance in NYC also identified a separate importation of VDPV2 that was not genetically related to the New York state case or other outbreaks globally. This second importation was an isolated detection and was not associated with a paralytic case. No related virus has been identified in subsequent testing in NYC or the surrounding counties, indicating that no sustained transmission occurred after that importation. An additional importation of poliovirus was identified in wastewater in Utah by researchers in 2022 and confirmed as poliovirus by CDC (25). Subsequent testing from the same site and from the surrounding areas failed to detect additional poliovirus-positive samples. Other researchers have likely tested wastewater for poliovirus in the United States, but CDC was not notified to confirm a positive result (26).
No poliovirus was detected in wastewater surveillance by the pilot jurisdictions (Michigan, Illinois, and Chicago) or the retrospective testing of samples from New Jersey, Connecticut, and 47 additional counties in New York. The last poliovirus-positive samples detected in New York state and NYC, where wastewater testing has continued in the outbreak-affected areas, were collected on October 12, 2022, and February 22, 2023. As of October 2024, >2 years after the paralytic case and >1 year after the last positive wastewater detection, no further positive detections have been reported, suggesting the end of the outbreak (27,28).
The findings in this report indicate that the United States experiences periodic importations of poliovirus from other countries and is at risk for community transmission, especially in communities that are undervaccinated. However, even though this report was limited to 7 jurisdictions, the data suggest that sustained transmission after importation into the United States is likely a rare event, possibly because of high-quality water and sanitation services and generally high vaccination coverage in most of the country (29). Although the transition from oral poliovirus vaccination to inactivated polio vaccine in routine immunization in the United States might enable gastrointestinal poliovirus infection and extensive asymptomatic transmission, no evidence exists of widespread poliovirus transmission in the United States.
The first limitation of this study is that only 80% of US households are on a sewer system that can be sampled by sewershed wastewater surveillance, and this report includes data for just 7 jurisdictions (30). Further, outside of New York state, only a few counties in each jurisdiction participated, with limited sewersheds and for a limited period of time. Therefore, these data might not be representative of the United States as a whole, and poliovirus might have been present in wastewater in communities where testing did not occur. In addition, negative results should be interpreted with caution, because sensitivity and limits of detection of PCR testing for poliovirus in wastewater have not yet been defined. Every jurisdiction was responsible for their own test validation and testing methods were not validated by CDC. However, all jurisdictions reported identifying nonpolio enteroviruses. The selection of sewersheds, timing of poliovirus shedding, and the number of infected persons can all affect the ability to detect poliovirus if present. Some sewersheds included in this report had catchment areas that were larger than those recommended by the WHO (≈300,000 persons), potentially affecting the sensitivity of results (31,32). In addition, varying sewage treatment, concentration, and testing methods might affect the results. Any pretreatment of wastewater might affect the integrity of nucleic acids, giving false-negative results in downstream molecular testing.
As wastewater surveillance for other pathogens continues to expand, the appropriate role of wastewater surveillance for rare diseases like polio in nonendemic areas is still being refined. When used during an outbreak, as in New York, Connecticut, and New Jersey in 2022, wastewater surveillance is a useful tool for identifying the geographic and temporal scope of the outbreak and for identifying the communities at increased risk for poliovirus exposure. Outside of the outbreak setting, several key considerations exist for jurisdictions considering wastewater surveillance for poliovirus. Although instituting a new wastewater surveillance system is challenging, participating jurisdictions found that implementing poliovirus testing within an established wastewater surveillance infrastructure such as NWSS was generally feasible (30). However, implementing the additional precautions for poliovirus testing as described by the National Authority for Containment of Poliovirus can be burdensome, not only for health departments but also for laboratories and institutions located within the sewershed areas that are tested (32,33). Other considerations include ensuring that watershed companies and employees responsible for sample collection are not overburdened with collection processes, that the health and safety of workers are protected, and that any poliovirus detections are communicated clearly to workers and the general public (32).
When selecting sewersheds and communities for possible wastewater surveillance for poliovirus, health departments should consider the size of the sewershed catchment area and community perception of being selected for surveillance. A sewershed serving a population that is too small could lead to privacy concerns, whereas sewersheds with larger-than-recommended catchment area populations might compromise test sensitivity. Targeting specific communities for wastewater testing is controversial, and ethical considerations for testing should be taken into account, particularly when specific racial, ethnic, or religious communities might be identified by their sewershed (32,34,35). The same communities that are at risk for polio because of undervaccination might also be at increased risk for stigmatization and health inequities because of ethnic, religious, or racial makeup. Incidental identification of specific counties or communities because of wastewater surveillance could contribute to increased stigmatization (36). For those and other reasons, wastewater surveillance might not be acceptable to all communities. Health departments should consider the potential negative consequences of wastewater surveillance and collaborate with at-risk communities when deciding if and where they conduct wastewater surveillance.
Health departments implementing wastewater surveillance for poliovirus should also develop clear communication plans for both negative and positive results to ensure affected populations understand the public health implications and the appropriate action to take, if any. Communication of any poliovirus detections should clarify that poliovirus in wastewater reflects the presence of poliovirus in the community (i.e., not just in sewage material) and should emphasize the importance of vaccination to prevent paralysis. All health departments conducting wastewater surveillance for poliovirus, especially those in communities with poliovirus detections, should anticipate an increase in inquiries about polio vaccination and whether the public needs additional doses. A substantial proportion of those inquiries might come from fully vaccinated persons and persons who are not at increased risk for infection; communication plans should also clarify who is at risk and provide reassurance for those who are not.
Ultimately, the primary purpose of wastewater surveillance for poliovirus is to prevent cases of paralytic polio by identifying communities at increased risk for poliovirus exposure and ensuring high vaccination coverage in those communities. However, how wastewater detections affect public perception of risk, or whether they lead to behavior change (i.e., vaccine uptake), is unclear. In New York state during the 2022 outbreak, publicity surrounding the presence of poliovirus in wastewater did not substantively increase vaccination rates in affected undervaccinated communities (1,12). Findings from focus groups have highlighted challenges involved in addressing barriers to vaccination (12,34). Similar challenges with barriers to vaccination and perceived low risk for poliovirus infection among communities with lower vaccine coverage were noted in the United Kingdom during a 2022 response to multiple detections of VDPV2 in sewage (37). Certainly, identifying undervaccinated communities and improving routine vaccination coverage are public health priorities. This work can and should be ongoing before, or even without, a wastewater detection.
Wastewater surveillance has the potential to be a vital public health tool for monitoring disease and promoting public health action in certain situations, as seen in the COVID-19 pandemic and during the outbreak response to the 2022 paralytic polio case in New York. However, outside of the outbreak setting, considering the public health resources required for ongoing surveillance and whether the data will lead to public health action are key (38). As long as poliovirus is circulating elsewhere in the world, periodic importations into the United States are to be expected (7). Regardless of wastewater surveillance availability in jurisdictions, vaccination, the most effective public health intervention to prevent paralytic polio, is readily available in the United States. State and local health departments should identify communities with low vaccination coverage and collaborate with those communities to improve vaccination rates to prevent paralytic polio and other vaccine preventable diseases.