Wastewater surveillance could improve influenza preparedness

Already used for tracking community SARS-CoV-2 levels, wastewater surveillance could improve local preparedness and response to seasonal respiratory virus disease outbreaks, according to a study published in the Centers for Disease Control and Prevention’s Morbidity and Mortality Weekly Report.

The report states that wastewater surveillance has been used to help public health authorities track local transmissions of SARS-CoV-2, though using this process to track spread of influenza and respiratory syncytial virus (RSV) is less clear.

This system, which is independent of health care access or potential testing biases, could help supplement outbreak data. Amid the 2022-2023 respiratory disease season, influenza A and RSV was tracked in the 3 largest cities in Wisconsin.

Surveillance data for influenza A and RSV were compared with associated emergency department (ED) visits to determine if this tool could be useful and complementary for future use in Wisconsin.

Samples were collected at least once per week from approximately 40 wastewater treatment plants. After being shipped to either the Wisconsin State Laboratory of Hygiene or a University of Wisconsin-Milwaukee laboratory for processing, the refrigerated samples were analyzed.

ED visits for RSV and influenza were reported to the Electronic Surveillance System for Early Notification of Community-Based Epidemics (ESSENCE). Of the 139 EDs in Wisconsin, 129 report to ESSENCE.

Wastewater surveillance from 4 treatment plants servicing Green Bay (1), Madison (1), and Milwaukee (2) were included in the study, as was ED visit data, so long as it included patients with a Green Bay, Madison, or Milwaukee residential zip code and were reported by a Wisconsin ED from August 2022 to March 2023.

Kendall’s Tau, a nonparametric measure of correlation, was used to assess statistical agreement for the surveillance systems. The measurement, applied in previous wastewater surveillance literature, quantifies the relationship between 2 data sources with higher values indicating a stronger correlation.

In all, there were 6,271 influenza-associated ED visits and 1,518 RSV-associated ED visits during the study period. RSV peaked in early November while influenza peaked approximately 1 month later, according to wastewater surveillance and ED data in each of the 3 cities observed.

Positive correlations were observed between paired wastewater surveillance and ED in all 3 cities, for both viruses. Kendall’s Tau values for influenza were 0.50 for Green Bay, 0.52 for Madison, and 0.63 for Milwaukee, respectively. For RSV, values were 0.37 for Green Bay, 0.49 for Madison, and 0.30 for Milwaukee.

Findings from the study are consistent with other reports stating influenza and RSV can be detected by wastewater surveillance, ahead of rising cases, the report states.

The examination of the data suggests that influenza and RSV were “generally detected in wastewater before significant increases in numbers of ED visits. However, this work was unable to determine the consistency or reliability of this lead time across cities or pathogens; for example, weekly aggregated data were too sparse to accurately calculate any time-shifted correlation coefficients.”

The study authors wrote that future work could prioritize data from late summer and early fall seasons to better ascertain lead time values. This potential advanced warning because of wastewater surveillance, “might provide health care and public health systems time to scale up capacity, ensure availability of treatment (e.g., antivirals), and promote preventive measures in advance of a clinical surge,” the study concluded.

Reference:

Wastewater surveillance data as a complement to emergency department visit data for tracking incidence of influenza A and respiratory syncytial virus — Wisconsin, August 2022–March 2023. Morbidity and Mortality Weekly Report. September 15, 2023. December 5, 2023.